FEMA154_PresentationRapid Visual Screening of Buildings for Potential
Seismic Hazards
PowerPoint Presentation
Slide 1 Text
FEMA
Rapid Visual Screening of Buildings for Potential
Seismic Hazards
Slide 1 Notes
This presentation describes a procedure for identifying nonstructural elements
that may
pose a hazard in the event of an earthquake. The primary focus of this
presentation is to
help the reader understand how to conduct a survey of a building to identify
nonstructural
items that are vulnerable in an earthquake and most likely to cause personal
injury, costly
property damage, or loss of function if they are damaged.
The Federal Emergency Management Agency (FEMA) provided the funding for
developing this presentation.
Slide 2 Text
Documents
(Copies of publication covers)
Slide 2 Notes
The original and current project produced two reports: the FEMA 154 Handbook and
FEMA 155, the supporting Documentation. The Handbook, on the left, provides
detailed
procedures for rapid visual screening of building for potential seismic hazards.
Detailed
methodology and background information are contained in the companion Supporting
Documentation report, shown on the right.
The FEMA 154 Handbook was the first in a series of FEMA-sponsored resource
documents intended to facilitate the mitigation of hazards posed by existing
buildings.
Other FEMA-sponsored documents provide methods for detailed evaluation of
buildings
that have been identified as potentially hazardous and for rehabilitation of
hazardous
buildings. FEMA 310 Handbook for the Seismic Evaluation of Existing Buildings- A
Prestandard, is the current edition of the handbook used for detailed seismic
evaluation
of existing buildings. FEMA 310 supersedes FEMA 178. The current handbook for
seismic rehabilitation of existing buildings is FEMA 356 Handbook for Seismic
Rehabilitation of Existing Buildings – A Prestandard. FEMA 356 supersedes FEMA
273.
Slide 3 Text
Project Participants
Principal Investigator: Christopher Rojahn
Project Director: Charles Scawthorn
Project Advisory Panel:
Thalia Anagnos
John Baals
James Cagley
Melvyn Green
Terry Hughes
Anne Kiremidjian
Joan MacQuarrie
Chris Poland
Lawrence Reaveley
Doug Smits
Ted Winstead
Slide 3 Notes
The current FEMA 154 procedures and documents were developed by a group of
nationally-recognized earthquake engineering specialists from various regions of
the
country.
The Principal Investigator was Christopher Rojahn of the Applied Technology
Council.
The overall concept and detailed procedures were developed by the Project
Director,
Charles Scawthorn. Typical of ATC projects, a senior-level “blue-ribbon” Project
Advisory Panel provided overview and guidance for the project. The Project
Advisory
Panel consisted of structural engineers, building officials, and architects from
California,
Utah, Washington, D.C. They include, Thalia Anagnos, John Baals, James Cagely,
Melvyn Green, Terry Hughes, Anne Kiremidjian, Joan MacQuarrie, Chris Poland,
Lawrence Reaveley, Doug Smits, and Ted Winstead. The affiliations of these
individuals
are provided in the FEMA 154 handbook. Also included are the names of the other
consultants that helped in publication, the FEMA staff involved in oversight
during the
development of the project, and the consultants that were involved in the
development of
the first edition.
During the development of the second edition, a survey was made available to
invite
feedback from users of the first edition. A workshop was held to invite
presentation from
users of the first edition and facilitate discussion of the methodology that
would be used
for the second edition. A list of participants from the workshop and a summary
of the
presentations and discussions are included in the FEMA 155.
Slide 4 Text
Table of Contents
1. Introduction
2. Planning and Managing Rapid Visual Screening (RVS)
3. Completing the Data Collection Form
4. Using the RVS Procedure Results
5. Example Application of Rapid Visual Screening
6. Appendices
Slide 4 Notes
This slide shows the title of the five chapters in the Table of Contents of FEMA
154:
Chapter 1 is the introduction.
Chapter 2 describes the planning and managing of the Rapid Visual Screening
(RVS).
Chapter 3 describes the procedures for completing the Data Collection Form.
Chapter 4 describes using the RVS Procedure Results.
Chapter 5 provides examples of the use of the RVS procedure.
Following the 5 chapters, there are six appendices, labeled A through G, that
include
background information on such topics as seismicity, reviewing structural
drawings, and
assessing the building characteristics from an exterior survey.
Note to Trainer:
It is recommended that all of the students receive a copy of the FEMA 154
Handbook at
the beginning of the presentation. We recommend encouraging further study of the
handbook, including the appendices, for additional insight into the rapid visual
screening
of buildings for potential seismic hazards.
Slide 5 Text
Outline of Presentation
• Description of Procedure
• Behavior of Buildings
• Building Types and Typical Damage
• Basic Scores and Score Modifiers
• Occupancy and Falling Hazards
• Implementation of Procedure
• Example Applications
Slide 5 Notes
This presentation is organized into these main topics:
• A description of the procedure
• A discussion of the earthquake behavior of buildings
• A description of standard building types and their typical seismic
performance
characteristics
• A description of the basic scores used in the RVS procedure and the score
modifiers
• A discussion of occupancy and falling hazards
• A discussion of the implementation of the procedure
• A presentation of example applications of the procedure
Note to the Trainer:
The trainer is encouraged to modify and supplement the slides and narrative in
the
original FEMA 154 presentation with slides and narrative reflecting:
• his or her own experience,
• local building construction or special situations, and
• experience of the intended participants.
The trainer may modify the material wherever it is appropriate, using standard
PowerPoint procedures. However, to keep modified and unmodified presentations
distinct and recognizable, the trainer should add a note to this slide to
indicate that
revisions were made.
Slide 6 Text
Procedure Overview
1. Pre-Field Trip
1.1 Define project, train personnel
1.2 Determine seismic hazard region, choose form
1.3 Determine seismic code dates
1.4 Determine soil type data
2. Rapid Visual Screening Field Trip
2.1 Identify building type, calculate basic score
2.2 Identify modifiers, calculate final score
2.3 Sketch, photo, and complete form
3. Post-Field Trip
3.1 Database entries and summary
Slide 6 Notes
This slides outlines that three stages of the RVS procedure and the types of
activities that
would occur during each stage. Each of these stages of the procedure is
important in the
overall implementation of the program. The Field Trip refers to the actual
visual
observation of the building to record the score.
• Prior to the Field Trip, project should be defined and the personnel
trained. The
background information should be obtained for the area being screened. This
background
information include the seismic hazard region, the dates of implementation of
seismic
building codes, and soil type data for the area.
• During the Field Trip, the screener will use the RVS procedure to identify
the
building type and the applicable score modifiers, determine the scores based on
these
observations, and record the information on the RVS form.
• Following the Field Trip, the data from the RVS screenings will be
compiled and
summarized.
Slide 7 Text
Purpose and Limitations of Procedure
Purpose
• Screen for potential seismic hazards
• Identify buildings that may be hazardous
Limitations
• Some hazardous buildings might not be identified
• Some adequate buildings might be identified as hazardous
• Accurate results dependent on experience of screener and thoroughness of
pre-
field activities
Slide 7 Notes
The procedure presented in the handbook is meant to be preliminary screening
phase of a
multi-phase program for identifying, evaluating, and rehabilitating hazardous
buildings.
As such, it is a “screening only” procedure to identify buildings where
reasonable doubts
about earthquake resistance may exist. The procedure is based on known
characteristics
of buildings.
When this procedure is used, some critical information about a building’s
seismic
resisting characteristics may not be visible, and as a result, the procedure may
not lead to
the building being characterized as potentially hazardous. More information that
can be
obtained regarding the building, such as from interior access and a review of
building
plans, can improve the likelihood of identifying potentially hazardous
characteristics.
Conversely, some building identified as hazardous using the RVS procedure may
prove
to be adequate based on subsequent evaluation. It is therefore important to
emphasize that
the results are preliminary and dependant on further evaluation. Buildings
identified as
potentially hazardous must be analyzed in more detail by a professional engineer
experienced in seismic design. The procedure for the detailed evaluation are not
described in this handbook, but can be performed using FEMA 310.
The results obtained from the RVS procedure is strongly affected by the
experience of the
screener. Also, the thoroughness of the pre-field trip activities, such as
determination of
code dates, seismicity, and soil type, can influence the results.
Slide 8 Text
Earthquakes in the United States
(Maps only)
Slide 8 Notes
This slides shows the occurrence of significant earthquakes in the United
States. It
provides insight into the variation of seismic hazard throughout the United
States.
On this map, the size and color of the circle depict the relative magnitude of
the
earthquake.
Earthquakes are not distributed uniformly, but are clustered where there are
faults in the
earth’s crust at or within the boundaries of tectonic plates. The edges of the
tectonic
plates, as depicted on the map by yellow lines, are particularly evident along
the west
coast of the continental US and along the Aleutian Islands of Alaska. It should
be noted,
however, that areas that have not experienced a significant earthquake during
this period
are not immune from future earthquakes.
This slide contains three maps that depict all areas of the United States. The
presenter is
encouraged to modify this slide as appropriate for the target audience. This
could include
removing the maps of Hawaii or Alaska so that the map of the continental US can
be
enlarged. Alternatively, a detailed map of a state, territory, or region of
interest can be
substituted.
Slide 9 Text
Seismic Hazard Map
(Map only)
Slide 9 Notes
This map of the contiguous 48 states shows three levels of seismic hazard used
for this
procedure: low, moderate, and high. The map levels are based on the current US
Geological Survey (USGS) maps of probable seismic hazard. The preparation of the
maps considers the magnitude and frequency of past earthquakes, the location of
known
faults, and the expected earthquake shaking attenuation. These maps are based on
an
earthquake with a 2 percent chance of being exceeded in 50 years, which is also
referred
to as an earthquake with an average return period of 2475 years.
These maps, used in the second edition of FEMA 154, are different than those
used in the
first edition for a couple of reasons. First, more information has been
accumulated
regarding the seismic hazards throughout the country. Second, the earthquake
probability
used in creating this map is different than that used in the first edition. In
the first edition,
the earthquake hazard was based on an earthquake with a 10 percent probability
of being
exceeded in 50 years, or a 475 average return period.
The definition of the regions of seismicity is based on two parameters, the
spectral
acceleration at short periods and the spectral acceleration at 1 second periods.
The maps
have been simplified to present the seismicity based on the highest seismicity
in each
county. In some areas, the variation is seismicity within a county could allow
the use of
lower seismicity at some locations within a county. The USGS web site, as well
as other
sources, can provide the seismicity parameters for a location based on zip code
rather
than by county. Users should be encouraged to use the USGS web site to obtain
more
accurate seismic parameters that can be used to determine the appropriate
regions of
seismicity for the buildings being studied.
Slide 10 Text
Map Areas Based on County Boundaries
(Map only)
Slide 10 Notes
The FEMA 154 handbook provides detailed regional seismicity maps. Each county is
identified as belonging to one of the three regions of seismicity based on the
expected
seismic activity. Counties shown in green are considered low seismic hazards;
those in
yellow are considered moderate seismic hazards; and those in red are considered
high
seismic hazards. The seismicity of a region is based on the best available
knowledge. Due
to uncertainties in earthquake hazard determination, it is possible that an area
designated
as high region of seismicity may not experience strong ground shaking during the
life of
a given building. Similarly, it is possible for a building in a region
considered low
seismicity to experience strong ground shaking.
The person performing the rapid visual screening determines which region of
seismicity a
given building is located in using the maps provided in FEMA 154 Second Edition,
or by
using the data from the USGS web site to determine the region of seismicity.
Note to Trainer:
This slide displays one of the detailed seismicity maps provided in FEMA 154.
The CD
that contains this presentation comes with picture files in JPEG format that
show the
detailed seismicity maps of each of the groups of states provided in FEMA 154.
These
other pictures can be inserted in place of this map to show the seismicity of
the applicable
region of the training.
Slide 11 Text
Alternate Seismicity Determination
(Illustration only)
Slide 11 Notes
As mentioned previously, the USGS has a web site that can be used to determine
the
seismic hazard parameters for a given zip code. This slide shows the results of
a query on
the USGS web site. On the input screen, the user types in the zip code or zip
codes of the
buildings in the study. In this example, the input zip code is 62960, located in
Metropolis,
Illinois. The web site then displays various information regarding the input zip
code.
The seismic hazard results are presented as acceleration values, in percent g,
for 3
different probabilities, 10 percent in 50 years, 5 percent in 50 years, and 2
percent in 50
years. As mentioned previously, for the purpose of determining the seismic
hazard region
for FEMA 154, the column corresponding to 2 percent in 50 years should be used.
For
each value of probability, there are 4 acceleration values provided, the peak
ground
acceleration (PGA), the spectral acceleration (SA) at 0.2 seconds, at 0.3
seconds, and at
1.0 seconds. For determining the region of seismicity, the spectral acceleration
values
used should be the value at 1 second and the value at 0.2 seconds. These values
are then
compared to the ranges provided in FEMA 154 to determine the region of
seismicity.
Slide 12 Text
Seismicity Region Definition
(Table only)
Slide 12 Notes
This slide presents the criteria that is used to determine the region of
seismcity. The
spectral acceleration values for short period (0.2 seconds) and for long periods
(1.0
second) are compared to the values in this table. The region of seismicity is
based on the
higher seismicity of that obtained using the short period acceleration and the
long period
acceleration. It is important to note that the values of seismicity provided by
the USGS
web site should be divided by 100 before comparing to the values in this table,
since the
values in this table are presented in g (the acceleration of gravity) whereas
the values
from the USGS web site are in percent g.
Slide 13 Text
Data Collection Form
(Illustration only)
Slide 13 Notes
The FEMA 154 handbook provides separate forms for each of the three regions of
seismicity; low, moderate, and high. The applicable region of seismicity is
indicated on
the top right-hand corner of each form. Although the layout of the three forms
is
identical, there are important differences in the numeric values on the forms.
It is
therefore important to be sure to used the correct form.
Once the region of seismicity is determined and the appropriate form is
selected, the form
is then used to record building identification and occupancy information. A copy
of the
form is used to record information on each building such as the basic building
type, the
applicable score modifiers, a calculation of the final score, and a
determination of
whether the building should receive further evaluation.
The form also includes spaces for sketches and for a photograph of the building,
places
for recording information regarding the occupancy and the presence of falling
hazards,
and a place to list comments.
Slide 14 Text
Building Types
Building Materials
• Wood
• Steel
• Concrete
• Masonry
Lateral Force Resisting System
• Shear Wall
• Moment Frame
• Braced Frame
Slide 14 Notes
Visual determination of the construction material for the building and the
lateral force
resisting system is a critical part of the procedure. The basic construction
materials
typically used are wood, steel, concrete, and masonry. The other factor that
influences the
building type is the lateral force resisting system used in the building. Three
of the more
common types of lateral force resisting system are shear walls, moment-resisting
frames,
and braced frames.
The FEMA1 154 guidelines provide information as to how to distinguish the
building
materials and the lateral force resisting system, which together determine the
building
type. The building type is the single most important factor in the procedure for
determining the earthquake resistance of a building. A wide range of possible
score is
available and accurate determination is necessary.
Occasionally, a building is an obvious combination of building types, either in
different
plan directions, or over the height of the building. When the building appears
to be a
combination of building types, the screener will need to record separate scores.
This
procedure can also be used when an inspector cannot determine that a building
more
closely resembles one type more than another.
Slide 15 Text
Score Modifiers
• Height: Mid rise (4-7 stories), High rise (>7 stories)
• Vertical irregularity
• Plan irregularity
• Pre-code
• Post benchmark
• Soil type
Slide 15 Notes
Determination of the basic building type leads to the basic score, which is then
adjusted
by the presence of these score modifiers. The number of score modifiers
presented in the
second edition is less than that presented in the first edition of the RVS
guidelines. Two
of the score modifiers are related to the height of the building. These height
factors are
mutually exclusive, that is only one or the other could be chosen if applicable.
Two of the
factors relate to irregularities. Buildings could have either or both types of
irregularities.
Two of the factors relate to the applicable building code. These factors are
also mutually
exclusive since a building could be classified as Pre-code or Post benchmark
design code
applicable to the design. The final factor relates to the type of soil on which
the building
is founded.
These factors will be described in detail later in the presentation.
Slide 16 Text
Structural Scores and Modifiers
(Illustration only)
Slide 16 Notes
This slide shows the array of structural scores and score modifiers from one of
the data
collection forms. There is a column of modifiers for each building type, headed
by the
basic score. Below are the numbers to be subtracted or added for each applicable
score
modifier. The resulting final score permits an estimate of the building’s
earthquake
vulnerability.
A high final score indicates that the seismic hazard associated with the
building is low. A
low score denotes probable poor seismic performance, and that the building
should be
reviewed in detail by a professional engineer experienced in seismic design.
Generally, a
final score of 2 is used as a criterion to differentiate between probable good
and probable
poor performance. Buildings with final scores less than two may not meet
acceptable
seismic performance and should be investigated further.
Normally, only one column of building type, basic score, and modifiers will be
used for
each building. In those instances where a building contains two structural
systems, then
both relevant columns should be scored. If the building type cannot be
determined, the
columns for possible building types should be scored. The lowest score is the
final score
to be reported.
Slide 17 Text
Final Score Calculation
(Illustration only)
Slide 17 Notes
Consider an example of the building in a region of low seismicity to demonstrate
the
method used to fill out the scoring portion of the RVS form. The building is
identified as
a steel braced-frame building, which is denoted as S2 (BR). The inspection
reveals two
score modifiers apply: the building is a mid-rise (4 to 7 stories high) and has
a vertical
irregularity. From information gathered before the inspection, the soil at this
location is
determined to be type C. The data collection form for Low Seismicity is chosen
and the
basic score in the S2 (BR) column is circled. The numbers in the S2 column are
circled
that correspond to mid rise, vertical irregularity, and soil type C. The basic
score and the
score modifiers are summed to obtain the final score, which is 4.8 + 0.4 - 2.0 -
0.4 = 2.8.
Determining professionally whether a building has adequate earthquake resistance
is not
this simple and requires an engineer experienced in seismic design to make the
final
determination. These procedures should help in inspecting buildings. The results
of this
screening will also provide a relative ranking of buildings. In many cases
buildings
scoring higher than 2, such as this one, can be eliminated from further
consideration, and
will not typically require further detailed review by a professional engineer.
Slide 18 Text
Building Dynamic Behavior
(Illustration only)
Slide 18 Notes
The next series of slides describes the general dynamic behavior of buildings.
When the ground shakes during an earthquake, the building foundation moves with
the
ground. The rest of the building resists, causing horizontal deformations
throughout the
building height. This slide shows two types of deformation; pendulum action
(bending
deformation) and shearing deformation. The deformations are greatly exaggerated.
The
deformations are shown for shaking back and forth in one horizontal direction.
Earthquakes cause shaking in three directions, two horizontal and one vertical.
This deformation can cause damage to structural and nonstructural elements.
There are
four general types of earthquake-induced damage or contents disruption:
• Structural element damage
• Nonstructural element damage due to shaking
• Nonstructural element damage due to building deformation
• Hazardous material damage or spills
These kinds of damage can cause full or partial collapse, create falling
hazards, block
exiting routes, and release hazardous materials.
Slide 19 Text
Earthquake Forces
(Illustration only)
Slide 19 Notes
During an earthquake, a building moves in a complex fashion due to the ground
motion.
For design purposes, the primary emphasis is on the horizontal motion. The
ground
motion causes structural distortion or deformation in the building over its
height, which
can leads to displacement of the floors of the building relative to their
position prior to
the ground motion and also relative to the ground. The displacements of the
buildings are
related to the acceleration of the ground, the weight of the floors, and the
stiffness of the
building.
For design purposes, the engineer calculates equivalent lateral forces that are
applied to
the building to approximate the amount of displacement that would occur to the
building
during earthquake ground shaking. The engineer then designs a structural system
that
extends over the height of the building that resists these equivalent forces and
can transfer
the forces down to the foundation.
It should be noted however, that earthquake design forces prescribed by building
codes
are much less than the forces that would be experienced by the building during
strong
ground shaking if the building’s structural system remains elastic. The building
codes
allow this design force reduction because damage and nonlinear structural
behavior
reduces the effective ground motion that the building will experience. If the
building is
designed with ductility, the ability to maintain strength after reaching its
yield point, then
the building should be able to remain stable without collapse throughout the
earthquake.
Slide 20 Text
Structural Systems
Moment Frames
(Illustration only)
Slide 20 Notes
There are several types of structural systems that are used to resist earthquake
forces. One
type of system is called the moment resisting frame. This system comprises
structural
frames with columns and beams that are rigidly connected at the joints. The
rigidity and
strength of the beams and columns resist the horizontal deformation of the frame
induced
by the lateral earthquake forces. The beams and columns resist both shear and
bending
moments. Moment frames typically have steel or concrete columns and girders.
The floor system or other structural elements act as horizontal diaphragms,
which transfer
the earthquake forces into the moment frames.
Slide 21 Text
Structural Systems
Shear Walls
(Illustration only)
Slide 21 Notes
Another type of structural system is the shear wall system. In this system,
structural walls
are specifically designed to resist lateral forces in the direction of the wall.
Lateral forces
acting on the building are transferred from the floor diaphragms into the shear
walls. The
forces on the walls cause shear forces in the walls and bending (overturning) of
the walls.
Shear walls can be composed of a variety of materials including concrete,
masonry, or
wood. The concrete walls can be cast-in-place or precast. The masonry walls can
be
reinforced concrete block or unreinforced brick. Wood walls have wood or metal
studs
and are sheathed with plywood, gypsum board, or other types of sheathing
material.
Slide 22 Text
Structural Systems
Braced Frames
Slide 22 Notes
The third typical structural system is the braced frame. In this system lateral
forces are
resisted by diagonal braces located within the frames of the building. As with
the other
structural systems, lateral forces on the building are transferred through the
floor
diaphragms into the braced frames.
Although other materials can be used for bracing elements, most braced frames
have steel
diagonal braces. The braces can be oriented in a variety of configurations and
can be
designed to resist only tension forces or resist both tension and compression.
Slide 23 Text
Ductile Behavior
(Illustration only)
Slide 23 Notes
This slide demonstrates the concept of ductile behavior. Earthquakes can
generate forces
that are considerably greater than design level forces. Therefore, it is
desirable for the
materials and systems used to resist earthquake forces to retain there strength
even after
the applied forces reach the yield limit of the material.
In this slide, two paperclips are depicted. For the paperclip on the left, the
applied force
to the end of the paper clip does not cause the paper clip to reach its yield
stress. When
the force is released, the end of the paperclip returns to its original
position. For the
paperclip on the right, a larger force is applied. The paperclip bends but does
not break.
When the force is released, the end of the paperclip moves back toward its
original
position, but does not return to its original position. The result is that there
is a permanent
deformation of the paperclip.
Slide 24 Text
Brittle Behavior
(Illustration only)
Slide 24 Notes
This slide demonstrates the concept of brittle behavior.
A force is applied to the middle of the simply supported beam shown on this
slide. As the
force on the beam increases, the stress in the beam reaches the yield limit of
the material.
At the yield limit, the material breaks and can no longer resist any load,
causing failure of
the beam.
Note to Trainer:
This slide includes animation to describe brittle behavior. When the slide is
initially
displayed, the beam will be shown with an applied vertical force at the middle.
Advance
the slide by pressing the space bar or clicking the mouse to display the
animation
sequence of the beam breaking and the applied force dropping.
Slide 25 Text
Elastic vs. Nonlinear Response
(Illustration only)
Slide 25 Notes
This slides compares the ductile and brittle behavior that were shown on the
previous two
slides by plotting the forces against the resulting deformations. Both curves
display
elastic behavior up to their yield point. Both curves as essentially straight
from the origin
to the yield point. This is referred to as the elastic range. If the applied
force is less than
the yield force, the deformation returns to the origin when the force is
removed.
The red curve shows brittle behavior when the force exceeds the yield point. At
yield,
brittle failure occurs and the element cannot support additional force.
The green curve shows ductile behavior. After reaching the yield point, the
additional
deformation occurs without an increase in the applied force. The horizontal
plateau of the
curve is referred to as plastic behavior. After plastic behavior has occurred,
when the
force is removed, the deformation reduces at a slope that is approximately the
same slope
as the elastic range, but does not return to the origin. This results in
permanent
deformation.
Slide 26 Text
Seismic Hazards and Performance Levels
Seismic Hazards
• Probabilistic (Return period or probability of exceedence)
• Deterministic
Seismic Performance Levels
• Collapse Prevention
• Life Safety
• Immediate Occupancy
• Operational
Slide 26 Notes
Seismic design of buildings considers two criteria: the seismic hazard being
considered
and the expected seismic performance level. Seismic design is a combination of
these two
factors.
Seismic hazard describes the earthquake ground shaking that is expected. This
can be
represented either as a probabilistic hazard or a deterministic hazard. A
probabilistic
hazard presents the earthquake shaking, considering all possible sources, in
terms of
average expected return period or probability of being exceeded in a given time
period.
Most building code use a probabilistic method of determining seismic hazards.
Typically,
the seismic hazard that is used is one based on an average return period of 475
years,
which corresponds to a 10 percent chance of being exceeded in 50 years. Another
method
of assigning a seismic hazard is a deterministic assessment in which the maximum
earthquake from a given source is considered.
The second part of the criteria is the seismic performance level. For a given
earthquake
hazard, the seismic design can vary depending on the anticipated performance of
the
building to the given hazard. In other FEMA documents, four discrete performance
levels
have been defined: Collapse Prevention, Life Safety, Immediate Occupancy, and
Operational. Collapse Prevention represents lesser performance since the intent
is only to
prevent global collapse of the structure. Operational performance, on the other
hand, is
intended to allow the building to remain continually operational during and
after an
earthquake. Most building codes consider Life Safety as the expected
performance.
Slide 27 Text
Building Types
Wood
• Light wood frame (W1)
• Large wood frame (W2)
Steel
• Steel moment frame (S1)
• Steel braced frame (S2)
• Light metal building (S3)
• Steel frame with concrete shear walls (S4)
• Steel frame with URM infill (S5)
Slide 27 Notes
This next series of slides presents the standard Building Types as used on the
Data
Collection Form. The building types are generally described by the primary
structural
material used in the building and by the type of lateral force resisting system.
These
building types will be described in detail in the following slides. This slide
and the next
slide provide a list of the building types that will be described.
The first material is wood. There are two wood building types: light wood frame
construction (W1) and large wood frame construction (W2). Wood buildings
represent
the largest number of buildings nationally.
The next material is steel. There are five steel buildings types: steel moment
frames (S1),
steel braced frames (S2), light metal frame buildings (S3), steel frames with
concrete
shear walls (S4), and steel frames with unreinforced masonry infill walls (S5).
Slide 28 Text
Building Types (continued)
Concrete
• Concrete moment frame (C1)
• Concrete shear wall (C2)
• Concrete frame with URM infill (C3)
• Tilt-up concrete (PC1)
• Precast concrete frame (PC2)
Masonry
• Reinforced masonry with flexible diaphragm (RM1)
• Reinforced masonry with rigid diaphragm (RM2)
• Unreinforced masonry (URM)
Slide 28 Notes
This is a continuation of the previous slide that lists the basic building
types.
The next group of building types is concrete. The concrete building types are
further
divided into those that are constructed of cast-in-place concrete and those
constructed of
precast concrete. The first three types listed are cast-in-place concrete:
concrete moment
frames (C2), concrete shear wall (S2), and concrete frame with unreinforced
masonry
infill (C3). The next two types are precast concrete: tilt-up concrete wall
buildings (PC1)
and precast concrete frame buildings (PC2).
The final building types are those constructed of masonry. These are also
further divided
into those constructed of reinforced masonry and unreinforced masonry. The two
types of
reinforced masonry are reinforced masonry wall buildings with flexible
diaphragms
(RM1), and reinforced masonry wall buildings with rigid diaphragms (RM2). The
final
type is the unreinforced masonry wall building (URM).
Slide 29 Text
Wood Light Frame (W1)
(Illustration only)
Slide 29 Notes
Wood light-frame buildings are commonly single- or multiple-family dwelling
units or
small commercial buildings of one to three stories. They typically have
repetitive vertical
wall framing of wood studs and repetitive horizontal framing of wood floor
joists and
roof rafters. They are sheathed with sawn wood siding, plywood or particle board
products, or stucco. They are sheathed on the interior with lath and plaster or
gypsum
board.
Wood light-frame buildings sheathed with stucco can sometimes be confused with
stuccoed concrete or concrete block shear-wall buildings. To distinguish between
them,
look for exposed wood stud wall framing in the lower floor or crawl space (if
access to
the building interior or review of the building plans is possible). If studs are
not visible, it
is possible to check by knocking on an exterior wall surface. A wood-framed
stucco wall
will have a somewhat hollow sound, whereas a stuccoed concrete wall will feel
and
sound very solid. Similarly, wood-frame buildings with brick veneer on the
exterior can
be confused with brick masonry buildings or reinforced masonry buildings. A
similar
procedure can be used to distinguish buildings with brick veneer over wood
framing.
Slide 30 Text
W1 Example
(Photograph only)
Slide 30 Notes
This photo shows and example of a typical older one-story wood-frame dwelling.
The
steps in the front are an indication that the first floor of the house is raised
off of the
ground creating a cripple wall that supports the first floor. On the right front
and sides of
the house there is wood siding on this cripple wall.
A common deficiency in light wood-framed buildings is inadequate strength in
these
cripple walls. Houses with wood-frame cripple walls are very vulnerable to
earthquake
shaking due to the lack of stiffness and strength of these walls, which often
have no
sheathing on the interior surface. Usually, the interior walls do not extend
into the crawl
space so the exterior cripple wall provides the only lateral strength for the
house below
the first floor.
Similar situation holds for the above-ground wood-framed walls of a basement, or
the
walls below floor level on a sloping site. These lowest level walls are often
inadequate
because they have large openings, are sheathed only on one side, the exterior,
to because
there or only exterior walls and no interior walls.
Slide 31 Text
W1 Performance
(Photograph only)
Slide 31 Notes
This slide from the 1992 Cape Mendocino earthquake demonstrates two of the
typical
failures associated with light wood-framed buildings. In this case, the house
had a weak
cripple wall that has failed, causing the first floor of the house to drop to
the ground.
Although the upper two stories appear relatively intact, serious damage can
occur with a
cripple wall failure due to broken utility connections, floor joist damage, or
damage that
blocks exiting from the house.
The other type of failure depicted is separation and failure of the roof over
the front
porch. When attached to residential wood frame housing, porch roofs are likely
to be
penalized on account of torsion and poor maintenance. Often these roofs are only
marginally attached to the structural framing and these connections may not
resist the
lateral earthquake forces. The main concern is that if the connection to the
building is
damaged, there is a loss of vertical support that can cause the porch roof to
collapse. This
could injure people below or could block the exits.
Slide 32 Text
Large Wood Frame (W2)
• 5000 square feet or more
• Few interior walls
• Beams or trusses over columns
• Plywood or wood diaphragms
• Shear walls or diagonal rod bracing
Slide 32 Notes
The other type of wood-framed building is the large frame building, designated
W2. This
type of building is most often used for large industrial or commercial
buildings.
This type of building has several features that distinguish it from the light
wood-framed
building:
• Floor area greater than 5000 square feet
• Large open spaces on the interior with few interior walls
• Heavy timber beams or trusses supported by timber columns
The walls may be sheathed with plywood, stucco, or sawn wood siding and the
roofs may
be sheathed with plywood or wood planks. There could also be diagonal bracing in
the
walls using wood or steel braces. The construction will usually be visible from
an
unfinished attic space of the building. It is always desirable to gain access to
the building
or to study the building’s drawings.
Slide 33 Text
W2 Example
(Photograph only)
Slide 33 Notes
This photograph shows an example of a large wood frame building. The two
distinguishing features are the wood siding and the curved or double-pitched
roof. The
wood siding is generally an indication that the building is constructed with
wood framing.
The curved or double-pitched roof indicates roof trusses that are spanning
between the
two side walls of the building. This type of roof truss is provided to allow for
a large
open space on the interior of the building. The other indicators are the windows
and doors
on the side of the building that suggest that the main part of the building has
a tall story
height.
The configuration of most of these buildings is rectangular with roof trusses
spanning
across the short direction. The main vulnerability of the vertical shear-
resisting elements
is in the short direction, which may have a large percentage of openings on the
end walls
compared to the long direction.
Slide 34 Text
Steel Moment Frame (S1)
(Illustration only)
Slide 34 Notes
Steel rectangular moment-resisting frame buildings, often called moment frames,
have
vertical columns and horizontal girders of steel H-shaped sections. The floors,
whatever
their detail, deliver the weight of the building contents to the beams and
girders. The
floors are often constructed with a concrete slab, but can be constructed with
wood frame
floors or metal deck roofs. The girders and columns support the total weight of
the
building. The girders and columns are rigidly connected together into
rectangular frames,
usually by welding the top and bottom of the girders to the columns. The
vertical web of
the girder is attached with a bolted or welded connection to transfer the
vertical shear
from the girder to the column. Horizontal earthquake forces are resisted by the
strength
and ductility of the column/girder joints and the bending strength of the
columns and
girders.
Slide 35 Text
S1 Example
(Photograph only)
Slide 35 Notes
This photo shows an example of a steel moment frame building. This example is
rather
unusual in that the steel girders and columns on the exterior of the building
are visible.
Typically, the steel members are encased in fireproofing material and thus are
not visible.
Because of the fireproofing, the steel columns typically have architectural
finishes around
them to improve the appearance. The steel beams and girders are usually hidden
from
view by suspended ceilings.
Interior columns in two- to five-story steel-frame buildings are often 10 inches
to 14
inches square inside a gypsum board enclosure. In contract, interior columns in
concrete-
framed buildings are almost always larger than this. Tapping on the interior
column
surface can indicate if it is solid concrete or a gypsum board-enclosed steel
column. If
access to the building is possible, raise a suspended ceiling tile and look for
the H-shaped
steel framing members and corrugated flooring spans above. These members will
likely
be coated with sprayed-on fireproofing.
Slide 36 Text
S1 Performance
(Photograph only)
Slide 36 Notes
Prior to the 1994 Northridge earthquake, steel moment frame buildings were
considered
to provide superior seismic resistance. Following that earthquake, engineers
discovered
buildings that experienced earthquake damage to the welded flange connections.
There
were several different types of damage associated with the brittle and premature
fracture
of the bottom flange of the girder to column connections as shown in this slide.
After extensive research, engineers concluded that a variety of factors
contributed to the
failures, including poor weld quality, weld material that did not have
sufficient
toughness, and joint details that created excessive stresses on the welds. The
reports and
recommendations that were developed from this research are available from FEMA
in
several volumes: FEMA 350, 351, 352, and 353. The results of these studies were
considered in developing the basic scores for steel moment frame buildings in
the second
edition of FEMA 154.
Slide 37 Text
Steel Braced Frame (S2)
(Illustration only)
Slide 37 Notes
braces as the primary lateral force resisting elements. This slide shows some of
the
typical configurations of bracing that can be used:
Single diagonal – where each braced bay has a single diagonal brace that is
designed to
resist both tension and compression forces
Double diagonal – where a braced bay has diagonal braces in two opposite
directions and
each brace may be designed to resist tension forces only or both tension and
compression
Chevron - where a braced bay has two diagonal braces that meet at the top of
the bay at
the center of the girder. The opposite configuration would be where the braces
meet at the
center at the bottom of the bay and is called a V brace
Eccentric braces – where the diagonal braces are intentionally oriented so that
the brace
does not meet at the girder-to-column joint. This creates a section of the
girder that is
allowed to bend and deform as the frame resists lateral forces. This section of
beam is
specifically designed to remain locally stable and ductile while resisting the
earthquake
forces.
There are other configurations of braces that can be used and many different
types of
structural steel elements can be used for the braces. Typical bracing members
are steel
square tubes or pairs of steel angles.
Slide 38 Text
S2 Example
(Photograph only)
Slide 38 Notes
This picture shows a steel braced frame building without all of the exterior
cladding.
Note that the steel beams and diagonal braces are covered with fire proofing.
These
double diagonal braces are designed to take both tension and compression forces.
It
should also be noted that on the right side of the picture where the cladding is
in place,
the diagonal braces are not visible. The diagonal braces are often hidden behind
architectural finishes, making it difficult to identify the building as a braced
frame
structure. If possible, the building plans should be reviewed to determine the
presence of
bracing. It may also be possible to observe the bracing near stair wells or in
other utility
spaces.
In some newer construction, particularly in California, architects have
intentionally
allowed the bracing to be visible. This is often done in buildings that have
been
seismically rehabilitated. The intent is often to provide some level of
reassurance to the
occupants that the building has lateral strength.
Slide 39 Text
S2 Performance
(Photograph only)
Slide 39 Notes
Steel braced frames can experience a number of different types of earthquake
damage.
The damage is generally located in the brace and usually near the connections at
the ends
of the brace. Damage at the middle of the brace can also occur as the brace
buckles due to
compression forces on the brace. As the brace buckles, the ends of the brace
rotate
causing considerable stresses near the ends of the brace or connections. This
picture
shows damage to the brace near the connection where the steel tube has
fractured. The
thickness of the wall of the tube affects its ability to undergo repeated
cycling of forces.
Newer building codes have stricter requirements for the bracing members to avoid
this
type of brittle behavior of the braces.
Slide 40 Text
Light Metal Building (S3)
(Illustration only)
Slide 40 Notes
A unique type of steel building is the light metal building. These structures
are usually
single-story, utilitarian buildings with different lateral force resisting
systems in each
direction. Steel moment frames with sloping roof beams, usually exposed, are
placed
across the width of the building. Tension-only diagonal braces are placed along
the length
of the building. The roof sheathing is usually steel or aluminum corrugated
panels.
Corrugated fiberglass panels are used as skylights. Walls are usually steel or
aluminum
corrugated panels with steel rod x-bracing between columns. The roof will often
have
diagonal bracing between beams to act as a diaphragm to transfer forces into the
vertical
braces.
Slide 41 Text
S3 Example
(Photograph only)
Slide 41 Notes
This pictures shows an interior of a typical light metal building. Along the
exterior wall
are a pair of diagonal rod braces that resist lateral forces in the longitudinal
direction. At
the ends of the diagonal rods are the columns that form the transverse moment
frames. A
light metal building may be susceptible to the torsion that will develop with
unevenness
in the longitudinal stiffness in the long walls. Every x-braced bay must be
well-designed
and in good condition. A typical problem is slack in the diagonal braces.
Light metal buildings score relatively high because total collapse is unlikely,
and seldom
is there a life-safety threat. One problem that can develop is when these
buildings are
used for storage. Heavy, stacked contents can shift laterally during an
earthquake and
impose additional lateral forces on the building that were not considered.
Slide 42 Text
S3 Performance
(Photograph only)
Slide 42 Notes
This slide show the interior of a damaged light metal building. Seismic forces
caused one
of the diagonal rod x-braces to fracture and the other to stretch. When the
building
returned to its original position, the length of the stretched brace exceeded
the original
distance between its connections. Once these braces were broken, the excessive
deflection in the structure caused the wall sheathing to separate.
Inadequate connection to the foundation can allow the column base to move.
Slide 43 Text
Steel Frame with Concrete Shear Walls (S4)
(Illustration only)
Slide 43 Notes
This building has a rectangular steel frame of columns and girders to carry the
building
weight and some of the horizontal earthquake forces. Concrete shear walls are
added to
carry the remaining earthquake forces and additional gravity loads.
These shear walls are often the walls of the elevator and service core of the
building and
as such often contain large doorways, which decrease their effectiveness. If the
concrete
core is asymmetrically placed in the building plan, as shown here, it leads to
torsional
deformation – torsion about a vertical axis – which can be damaging at specific
locations
in the outer walls. The addition of reinforced concrete also introduces
concrete’s
vulnerabilities (which are detailed in the appropriate concrete buildings
section):
• Shear cracking can occur around the openings in the shear walls
• Wall construction joints can be weak horizontal planes, resulting in a
shear failure
at below expected capacity
• Insufficient attention to reinforcing details can lead to problems
Slide 44 Text
S4 Example
(Photograph only)
Slide 44 Notes
This example shows a steel frame building with reinforced concrete shear walls.
As with
many buildings of this type, the reinforced concrete walls are not easily
observable from
an exterior survey. The shear walls are often located on the interior of the
building and
are usually covered with architectural finishes. Thus, from the exterior, this
building type
can resemble a steel moment frame or steel braced frame building. A review of
the
structural drawings and/or interior survey can be helpful in distinguishing this
building
type.
Slide 45 Text
S4 Performance
(Photograph only)
Slide 45 Notes
In steel frame buildings with concrete shear walls, the concrete walls are stiff
relative to
the steel frame so the concrete walls will typically resist most of the lateral
earthquake
loads. After the forces on the concrete walls causes the shear walls to reach
their yield
strength, the walls will soften and the steel frame may start resisting more of
the
earthquake forces.
This slide shows a typical are of damage in steel frame buildings with concrete
shear
walls. As shown two slides before, the shear walls are often located at
elevators and
stairwells. The concrete walls often have door openings that reduce the cross-
sectional
area of the wall and can concentrate the damage in the wall sections adjacent to
the
openings.
Slide 46 Text
Steel Frame with URM Infill (S5)
(Illustration only)
Slide 46 Notes
The next building type has a steel frame that is infilled with unreinforced
masonry.
Usually, the masonry is multiple wythes of brick, although concrete block
masonry can
also be used. This type of construction is generally older buildings built in
the first half of
the 20th century. The masonry is usually only provided on the exterior walls and
these
walls provide the primary lateral force resistance for the building.
This slide shows a schematic diagram of the typical construction of steel frame
buildings
with URM infill. The steel floor frame members supports either a wood frame
floor or a
concrete floor. The steel beams along the exterior of the building are not
constructed in
line with exterior columns. This is done so that some of the wythes of brick can
be
directly supported on the beam, which runs continuous along the exterior face of
the
building. The exterior wythe of masonry is generally supported on a ledger plate
that may
be attached to the steel beam. The ledger plate is usually provided at each
floor so it
supports the gravity load of one story of masonry. The masonry may partially or
fully
encase the columns. When fully encased, the masonry is usually intended to
provide fire
protection for the steel.
Slide 47 Text
S5 Example
(Photograph only)
Slide 47 Notes
This slide shows an example of a steel frame building with masonry infill. This
building
has an exterior wythe of masonry composed of sandstone. Behind the sandstone are
layers of brick masonry used as backing for the sandstone. Although the
sandstone is
used primarily for aesthetic purposes, the thickness and stiffness of the
sandstone can
attract a considerable amount of the lateral seismic force.
The age of the building is a good indicator of the possibility that it is
constructed as a
steel frame with URM infill. These buildings are generally mid-rise to high-rise
buildings
constructed in the early 1900’s. Buildings that are newer that have masonry on
the
exterior walls may have concrete shear walls, steel braced frames, or steel
moment
frames. An indication of the presence of a steel moment frame building would be
if the
exterior masonry has horizontal joints that are filled with caulk instead of
mortar. The
caulking would be an indication that the design is allowing the building to move
horizontally without the masonry being allowed to resist the lateral forces,
which would
indicate that the building type is not steel frame with URM infill.
Slide 48 Text
S5 Performance
(Photographs only)
Slide 48 Notes
This slide contains two pictures of the same building that was damaged in the
Loma
Prieta earthquake. The picture on the left was taken shortly after the
earthquake. The
picture on the right was taken later after the masonry on the end of the
building was
removed for repairs and strengthening.
In the picture on the right, there is evidence of diagonal X-shaped cracking in
several pier
sections of the wall. These diagonal X cracks are due to shear forces being
resisted by the
wall in each direction. The picture on the left also shows damage along the
corner of the
building due to differential movement of the two sides of the building. Also
seen in this
picture is section of the wall in which the exterior wythe of brick has fallen
off the
building. The outer wythe of masonry is usually the most vulnerable to damage
since it is
typically not integrally connected to the inner wythes of brick and may only be
anchored
by widely spaced steel ties. These ties can often be deteriorated due to
corrosion or the
bond of the ties to the masonry may be deficient due to deterioration of the
mortar as a
result of long-term moisture exposure.
Slide 49 Text
Concrete Moment Frame (C1)
(Illustration only)
Slide 49 Notes
In reinforced concrete construction, steel reinforcing bars are embedded in the
concrete during construction. The resulting material can be effectively use in
structural framing to resist tension, compression, and shear forces.
There are five reinforced concrete building types: concrete moment-resisting
frames (as illustrated in this slide), concrete shear wall buildings, concrete
frames with unreinforced masonry infill walls (as indicated by the infill wall
shown above), concrete tilt-up wall buildings, and precast concrete frame
buildings. The concrete moment frame building has curtain walls outside of the
plane of the concrete frame instead of infill walls within the concrete frame.
The concrete moment frame has vertical columns and horizontal girders cast
together to form rectangular concrete frames, as shown here.
In addition to the illustrated floor slabs, the slab may itself include the
spanning function of girders; in these buildings the capitals at the column-to-
slab connection will be visible above the suspended ceiling.
Slide 50 Text
C1 Example
(Photograph only)
Slide 50 Notes
This building has exterior concrete frames that are visible without being
enclosed. The frames have glass windows within the frames that do not provide
any stiffness as would a masonry infill wall. The concern with this type of
construction is that the glass curtain walls be built to allow the concrete
frame to deform without causing the windows to be damaged.
Slide 51 Text
C1 Performance
(Photograph only)
Slide 51 Notes
Extensive earthquake-induced deformations of the reinforced concrete columns are
visible in this nonductile concrete moment-frame building. Most concrete moment
frame buildings in the low seismicity areas and most of those built before the
1976 Uniform Building Code in the high seismicity areas have nonductile frames.
They have a limited capacity to resist large earthquake forces, and when
deformed the nonductile concrete moment frames have been badly damaged and lost
their strength.
Nonductile behavior results from the following detailed characteristics: wide
spacing between, girders that are stronger than the columns, ties in the columns
and girders, main bar splices in the same location, insufficient shear
reinforcement, insufficient tie anchorage, lack of continuous beam reinforcement
through joints with columns, and inadequate reinforcing in joints.
The relative flexibility of the structure, compared with a shear wall structure,
creates the opportunity for nonstructural damage and pounding against adjacent
buildings.
Slide 52 Text
Concrete Shear Wall (C2)
(Illustration only)
Slide 52 Notes
In the concrete shear wall building, cast-in-place reinforced concrete walls
support the building weight and also resist earthquake forces. There are also
interior concrete beams and columns that support the building weight, but do not
contribute significantly in resisting earthquake forces.
Slide 53 Text
C2 Example
(Photograph only)
Slide 53 Notes
This is a typical older concrete shear wall building. Although it has a regular
window pattern, the visible wall of this building does not show the rectangular
grid pattern of large windows, slender piers, and shallow spandrels that is
typical of a frame building.
This is the front wall of the building that is featured in the first example
towards the end of this presentation. Note the setback above the fourth floor
that is later considered as a vertical irregularity.
Slide 54 Text
C2 Performance
(Photograph only)
Slide 54 Notes
Shear cracking and distress can occur in the piers between adjacent windows and
boundaries during seismic events, as shown here. Cracking can also occur due to
flexural or bending stress in tall or narrow walls. In this example there are
diagonal cracks due to shear stresses and cracks that are more horizontal at the
ends of the walls due to bending. The cracks have been repaired by epoxy
injection, which is visible along the cracks.
Shear walls can fail in other ways:
• Shear failures can occur at horizontal construction joints in walls.
• Shear cracks can occur in the spandrel beams between walls, also referred
to as coupling beams.
Slide 55 Text
Concrete Frame with URM Infill (C3)
(Illustration only)
Slide 55 Notes
Older concrete frame buildings may have unreinforced masonry walls infilling the
frame. The infill walls provide the primary lateral force resistance for the
building because the walls are very stiff relative to the concrete frame. The
concrete frames in older buildings do not have the ductile detailing to allow
the frames to undergo large deformations that can occur during strong ground
shaking.
Typically, the unreinforced masonry used as infill walls is clay brick masonry,
but other types of masonry can also be used, such as hollow clay tile, and
unreinforced concrete blocks. The infill walls are usually located along the
perimeter of the building, but there can be infill walls around stairwells.
Slide 56 Text
C3 Example
(Photograph only)
Slide 55 Notes
This an example of a concrete frame with URM infill exterior walls. The concrete
frame and infill walls are visible and form a regular grid pattern. The infill
walls and concrete frames can often be seen on the sides and back of the
building. On the front of the building, an exterior façade may hide the concrete
frame.
As seen in this example, some of the infill panels may be solid infill, while
others may have a variety of openings for windows. The behavior of the building
can be influenced by the openings in the infill walls.
Slide 57 Text
C3 Performance
(Photograph only)
Slide 57 Notes
This slides shows an example of a concrete frame with URM infill that was
damaged in the 1964 Alaska earthquake. The URM piers between the window openings
developed large X-cracks due to shear stresses in the wall. The lack of
reinforcement in the walls caused the cracks to open up wide and pieces of the
masonry to spall off.
The other effect that can be seen is the greater amount of damage at the lower
two floors of the building compared to the upper floors. This demonstrates that
the shear stresses accumulate down to the base of the building.
Slide 58 Text
Tilt-up Concrete (PC1)
(Illustration only)
Slide 58 Notes
The concrete tilt-up wall is often used for large one- or two-story industrial
or warehouse buildings. The reinforced concrete walls, which are cast as panels
on the building floor and then titled up into place, resist both gravity loads
(vertical) and earthquake forces (in their own plane). In the slide, three
panels are laid out on the surrounding ground, to pictorially open up the
building.
Pilasters are thicker sections of the wall at the panel intersections and are
often used to support roof girders. The walls of these buildings generally have
panels of regular width. Unlike shear wall buildings, formwork marks will not
show on the wall surface. These buildings usually have wood- or steel-frame
elevated floor and roofs.
Slide 59 Text
PC1 Example
(Photograph only)
Slide 59 Notes
The concrete tilt-up is used for one- and two-story office and industrial
buildings. This slide shows exposed aggregate-textured finishes on the wall, and
regular width wall panels separated by pilaster columns. Newer tilt-up
construction does not have the concrete pilasters at the joint between adjacent
panels. In newer construction, there is no positive attachment of the wall
panels to each other except for rebar embedded in the walls at the roof level
that are connected together, usually by welding. The space between the panels is
usually filled with sealant on the outside surface to keep out the weather.
Slide 60 Text
PC1 Typical Failure
(Illustration only)
Slide 60 Notes
The typical vulnerability of tilt-up buildings is in the connection of the roof
to the exterior wall panels. In older tilt-up construction, the roof joists and
sheathing are attached to a ledger that is bolted to the inside of the wall
panel as shown here. During an earthquake, the inertia forces of the wall and
roof cause the roof joists and sheathing to pull on the ledger. This results in
cross-grain bending stresses in the ledger, which the wood cannot reliably
resist. This causes premature failure of the wood ledgers.
Slide 61 Text
PC1 Performance
(Photograph only)
Slide 61 Notes
This example shows the consequence of the cross-grain bending failure of the
ledger. Once the ledger has failed, it can no longer support the weight of the
exterior bay of the roof. As can be seen on the right, failure of the ledger can
then cause the roof to collapse. The roof provides lateral stability for the
concrete tilt-up walls. As seen in the foreground, when the roof starts to
collapse, the tilt-up wall panels can loose their stability and fall.
Slide 62 Text
Precast Concrete Frame (PC2)
(Illustration only)
Slide 62 Notes
Precast concrete frame buildings have precast concrete roof and floor beams,
girders, and columns that are positioned to form rectangular vertical frames.
Typically, the building is tied together by steel inserts in adjoining elements,
which are welded together where they meet at joints. Slab topping concrete is
often placed over precast floor-spanning members, which also assists in tying
the elements together. A post-tensioned floor slab may be cast over the precast
frame.
Slide 63 Text
PC2 Example
(Photograph only)
Slide 63 Notes
The prominent joints between separate elements are usually visible when viewing
the building exterior. On the left is a cast-in-place concrete shear wall that
provides lateral force resistance for the building
Slide 64 Text
PC2 Performance
(Photograph only)
Slide 64 Notes
Precast concrete buildings are vulnerable to poor design details associated with
the precast elements.
1. Poorly designed connections between prefabricated elements can fail, as has
occurred here. Inadequate connections are difficult to identify without the
building plans.
2. Accumulated stresses can result from shrinkage and creep and due to stresses
incurred during transportation. It is possible to identify the resulting cracks.
3. Loss of vertical support can occur from inadequate bearing area and
insufficient connection between floor elements and columns.
4. Corrosion of metal connectors between prefabricated elements will cause
visible rust stains.
In this example from the 1994 Northridge earthquake, failure of the precast
connections occurred prematurely, prior to the shear wall experiencing any
significant damage.
Slide 65 Text
Reinforced Masonry with Flexible Diaphragm (RM1)
(Illustration only)
Slide 65 Notes
A common type of construction for low rise buildings is the use of masonry
bearing walls. Various types of masonry can be used including brick masonry and
concrete block masonry. Reinforced masonry bearing walls refers to walls where
steel reinforcing bars are placed within the walls both horizontally and
vertically and these walls are used to support elevated floors and the roof.
Reinforced masonry wall buildings can support either flexible floor and roof
diaphragms or rigid floor or roof diaphragms.
The first type of reinforced masonry building (RM1) refers to a reinforced
masonry bearing wall building that supports a flexible diaphragm. In older
construction, the roof can be constructed with a timber truss, as shown above
(No. 1). In newer reinforced masonry construction, the roof can be constructed
with steel joists (No. 2) and a metal deck or wood roof or with glulam beams
(No. 3) and a plywood roof, as shown above. The roof framing can be supported on
ledgers on the side of the masonry walls or can be supported on the top of the
wall.
The reinforced masonry wall, if designed and built correctly, has good
ductility. The walls support the weight of the building and are effective in
resisting earthquake forces acting in the direction of the wall. The strength
and behavior of the walls is similar to that of reinforced concrete walls. When
inspecting masonry buildings, a metal detector can be useful for quickly
confirming the presence of horizontal and vertical reinforcing in the walls.
Slide 66 Text
RM1 Example
(Photograph only)
Slide 66 Notes
Reinforced masonry wall bearing wall buildings may be a single wythe of concrete
blocks, as shown here, or hollow fired bricks. Horizontal and vertical rods are
placed in the block voids and grout is placed in the voids to bond the blocks to
the reinforcement.
Concrete block masonry can have a variety of exterior finishes from smooth to
rough to decorative patterns, such as vertical grooves as shown here. Concrete
blocks are typically 8 inches thick by 8 inches high, by 16 inches long. Running
bond refers to the pattern created when the blocks are staggered on alternate
courses.
Stack bond refers to the pattern created when the blocks are stacked on top of
each other. Stack bond walls will usually have horizontal “ladder” reinforcing,
but may have vertical reinforcing. Without the vertical reinforcing, the
building is not to be considered of reinforced masonry.
Slide 67 Text
Reinforced Brick Masonry
(Illustration only)
Slide 67 Notes
Reinforced masonry building walls often use a double wythe or two thicknesses of
solid bricks with a void between them as shown here. Sometimes the interior
walls use concrete block.
For reinforced masonry of brick or block, horizontal and vertical steel
reinforcing rods are placed in the voids within or between the masonry wythes.
Grout is then placed to tie together the masonry and the reinforcement.
Slide 68 Text
Reinforced Brick Example
(Photograph only)
Slide 68 Notes
With brick, reinforced walls may be distinguished from unreinforced by
inspecting the pattern of bricks. In reinforced walls, the long side of the
bricks in all courses will be visible. In contrast, unreinforced walls will
usually have courses of header bricks, where the bricks are laid with the short
end flush with the wall face.
This slide shows an example of a reinforced brick wall. Along the edge of the
opening, two wythes of brick are visible separated with a vertical joint that is
filled with grout. The pattern of the bricks, the two-wythe thickness of the
wall and the vertical joint between indicate that the wall is reinforced between
the wythes.
Slide 69 Text
RM1 Performance
(Photograph only)
Slide 69 Notes
Properly reinforced masonry walls will have the strength and ductility similar
to that of reinforced concrete walls. Many reinforced masonry wall buildings are
low rise so that the behavior of the wall in resisting in-plane forces is
primarily shear behavior. Earthquake damage to reinforced masonry buildings can
be separation of the roof or floor diaphragm from the wall, similar to tilt-up
wall buildings; in-plane diagonal or X-cracking, and cracking at wall corners,
either outside corners as shown here, or re-entrant corners.
Slide 70 Text
Reinforced Masonry with Stiff Diaphragm (RM2)
(Illustration only)
Slide 70 Notes
Buildings with reinforced masonry bearing walls can also be constructed with
stiff floor and roof diaphragms. This building type is referred to as RM2. The
construction of the masonry walls in this building type is similar to that of
the RM1 building type. The primary difference between the building types is the
construction of the roof and floor diaphragms. The roof and floors are
constructed with either cast-in-place concrete or precast concrete, as shown in
this figure. A cast-in-place topping slab is usually installed over the precast
concrete planks.
Slide 71 Text
RM2 Example
(Photograph only)
Slide 71 Notes
This picture shows an example of a building with reinforced masonry bearing
walls and stiff concrete floor diaphragms. Buildings with reinforced masonry
bearing walls that are more than two stories typically have stiff concrete
floors. The presence of the masonry bearing walls is usually visible from the
exterior since reinforced masonry walls typically do not have a façade. An
interior inspection may be necessary to confirm the floor framing type. Often,
the pattern of the precast floor planks can be seen at the ceiling.
Slide 72 Text
RM2 Performance
(Photograph only)
Slide 72 Notes
The performance of reinforced masonry bearing wall buildings is similar to that
of reinforced concrete shear wall buildings. The reinforced masonry walls can be
long solid walls, which are referred to as shear walls. Multiple regular
openings in the walls can form short sections of walls between openings,
referred to as wall piers. The sections of walls above and below the openings
are referred to as spandrels.
Shear walls generally experience damage due to shear-type behavior, which
results in diagonal cracking in the wall. Wall piers and spandrels can be
damaged by either flexural behavior or shear behavior. The type of behavior is
affected by the aspect ratio of the element, the ratio of the height to the
length. In this example, a reinforced masonry bearing wall building has
experienced diagonal shear cracking in a short aspect ratio wall pier,
indicating primarily shear behavior of the wall pier. A tall pier with a high
aspect ratio will more likely have horizontal cracks, indicating flexural
behavior.
Slide 73 Text
Unreinforced Masonry (URM)
(Illustration only)
Slide 73 Notes
Unreinforced masonry, often referred to as “URM”, includes both unreinforced
brick bearing wall and unreinforced concrete block bearing wall buildings. There
is little or no embedded steel reinforcement in the masonry. Walls that do not
bear vertical loads are considered as buildings with infill walls. The
unreinforced masonry structural walls support the building weight and resists
limited earthquake forces in their own plane.
Many unreinforced masonry brick bearing wall buildings in the United States are
more than 100 years old. The masonry walls are constructed with multiple wythes,
or thicknesses, of standard bricks. There are usually two wythes of brick at the
parapet, and a wythe is added below each roof or floor level. Often there are
shallow arches over the door and window openings. The framing for the floors and
roof, whether of wood, steel, or concrete is supported by the walls. This
building type is usually four stories or less, has thick walls with visible
header bricks, which are discussed in the next slide, and relatively small
openings for doors and windows.
Slide 74 Text
URM Bearing Walls
(Photograph only)
Slide 74 Notes
An unreinforced brick bearing wall can often be recognized by a row of header
bricks laid about every sixth row or course. These are bricks laid with the
short end flush with the wall face, as shown here. The header course ties two
wythes together for limited increase in stability. There is no path for vertical
reinforcement if there are header courses.
Unreinforced masonry infill walls, filling in between steel or concrete frame
members, are not load bearing. They may or may not have header courses. In some
locations, the use of header bricks was not common practice.
Unreinforced brick veneer has no header course.
In summary, rows of header bricks imply unreinforced masonry. The absence of
header bricks implies three possibilities: a reinforced walls with steel bars,
concrete grout, and individual ties at about 16 inches on center each way; a
veneer over a concrete steel, or wood frame or concrete or masonry wall; or,
rarely, in some locations, a URM bearing wall.
Slide 75 Text
URM Example
(Photograph only)
Slide 75 Notes
This slide shows an example of an unreinforced masonry bearing wall building.
There are several features visible that help distinguish this as a URM building.
The architectural style is indicative of its age. The shallow arches over the
door and window openings is indicative of older brick masonry construction,
which is more likely to be unreinforced. Close examination of the exterior wall
shows a regular pattern of header bricks, although this wall does not have
distinct header course as is more typical. The small size of the window openings
is another indication that the walls are unreinforced masonry bearing walls.
Slide 76 Text
URM Performance
(Photograph only)
Slide 76 Notes
In an unreinforced masonry building, the exterior walls are commonly extended
upwards above the roof line to form a parapet – a nonstructural and vulnerable
feature.
In an earthquake, these parapets often break off, creating a hazard below. If
they do not break off, they add weight, and increase the earthquake forces
acting on the wall at the roof line. This can cause the wall to detach from the
roof, as shown here, if there are poor horizontal restraints at the floor or
roof, and lead to collapse, as shown here. The floor to wall connections of
older URM construction typically very weak compared to the horizontal earthquake
forces due to the inherent weakness of the masonry wall, the weakness of the
connection to the floor framing, and the wide spacing between such connections.
Other vulnerabilities of URM buildings, up to 3 or 4 stories in height, include
low shear strength of the lime mortar used in older buildings and out-of-plane
bending of the walls that are tall and thin relative to their height.
Slide 77 Text
Unreinforced Concrete Block
(Photograph only)
Slide 77 Notes
In URM buildings of concrete block bearing walls, the walls are constructed with
a single wythe of concrete blocks. These walls both support the building weight
and resist limited earthquake forces in their own plane and out-of-plane.
One- and two-story concrete block masonry buildings are usually unreinforced in
the low and moderate seismicity areas, as are some older buildings in high
seismicity areas.
Unreinforced concrete block walls often can be distinguished from reinforced
concrete block walls by inspecting them closely. If diagonal stair-step cracks
are seen in the wall, or if the hollow of the inside of the blocks can be seen
where the walls are penetrated by pipes or ducts, the wall is probably
unreinforced. Sometimes, tapping on a concrete block wall will reveal by the
sound whether it is unreinforced, with none of the hollows filled, or
reinforced, where all the hollows are filled with grout and some contain steel
reinforcing. Walls where the vertical mortar joints line up are seldom
unreinforced. A metal detector can be used to determine if reinforcing is
present in the walls.
Slide 78 Text
Determining Building Type
• Pre-screening data
• Exterior survey
• Interior survey: Unfinished basement, Parking garage, Mechanical equipment
rooms, Suspended ceilings
Slide 78 Notes
Determining the building type is one of the important tasks in the RVS
methodology. The Basic Score assigned to the building is based solely on the
building type and the region of seismicity.
Ideally, the building type should be determined based on the pre-screening data,
such as building department records. When the pre-screening data is not
available or not definitive, the building type needs to be determined during the
RVS survey. Some building types can be identified by an exterior survey of the
building. When the exterior survey is inconclusive and the interior of the
building is accessible, the interior of the building should be surveyed to help
determine the building type. Useful interior spaces to go to determine the
building type include:
• Unfinished basement areas
• Parking garages located within the building, either in the basement or in
elevated floors
• Mechanical equipment rooms
• If possible, suspended ceilings can be moved to allow for observation of
the framing
Slide 79 Text
Multiple or Unknown Building Types
Procedure
• Eliminate building types
• Use interior inspection and drawing review, if possible
• Evaluate all probable building types
• Record lowest score
Slide 79 Notes
For many buildings, it may not be possible to determine an applicable building
type. Some buildings may be constructed with multiple building types. This can
occur either when a building is constructed on top of another structure or when
a building has a different structural system in each direction. Other buildings
may have exterior cladding or other architectural features that hide the
structural system. Others have additions in a different building type.
The following procedure is recommended when a building has an unknown building
type:
• Using visual observations, eliminate as many building types as possible
• Conduct and interior survey and/or review structural or architectural
drawings for the building, if available
• From the remaining building types, evaluate the RVS score for each
probable building type
• Record the lowest score from each of the probable building types
When a building has multiple building types, each building type should be scored
separately and the lowest score is recorded.
Slide 80 Text
Recording Building Type and Score
(Illustration only)
Slide 80 Notes
We now turn our attention to building scores and performance modifiers.
When the seismicity of the building site has been identified and the correct
data collection form selected, the building information can be recorded. The
inspector has determined the building type or possible types for the building,
and can circle its identifier and abbreviation:
S1
(MRF)
For example, on the form. Below the building type abbreviation is the basic
score for the building, which also should be circled.
Slide 81 Text
Basic Structural Hazard Scores
(Illustration only)
Slide 81 Notes
This table shows the building type basic scores by seismicity. Several patterns
are evident. Some building types have consistently higher scores; wood frame
buildings, for example. Most buildings score higher in low seismicity areas, as
expected. The variation in score between low and high seismicity is different
for different building types.
Unreinforced masonry (URM), as well as steel frame with unreinforced masonry
infill (S5), and concrete frame with unreinforced masonry infill (C3), cannot
pass the screening test in high seismicity areas when only the basic score is
considered.
Slide 82 Text
Score Modifiers
(Illustration only)
Slide 82 Notes
After determining the building type, the next step is to determine if its basic
score might be modified. The score modifiers are listed here and their location
on the form is indicated. These modifiers have varying values depending on the
building type. The score modifiers are added or subtracted to the basic score.
The modifiers are listed below and are described in the next series of slides.
Their identification is crucial if the building is scoring low.
Mid rise buildings – those that are four to seven stories high
• High rise buildings – those that are greater than seven stories high
• Buildings with vertical irregularities
• Buildings with plan irregularities
• Pre-code Buildings – those designed and constructed before the adoption
and enforcement of seismic building codes
• Post-benchmark buildings – those designed and constructed using modern
seismic building codes
There are also three modifiers that relate to the soil at the building site. If
the soil at the site corresponds to either type C, D, or E, then the appropriate
modifier for that soil type is applied.
Slide 83 Text
Mid Rise Example
(Photograph only)
Slide 83 Notes
This picture shows an example of a mid rise building. This building is six
stories high. The building type is concrete shear wall, C2, as can be seen by
the shear wall at the end of the building.
Depending on the type of building, the height can influence the seismic
behavior. The modifiers for mid rise building are typically positive numbers,
which increase the building score.
For some building types, there is no applicable modifier for mid rise
construction. This generally indicates that buildings of that type are not
generally constructed taller than 4 stories. Examples are wood light frame,
light metal buildings, and tilt-up concrete buildings.
Slide 84 Text
High Rise Example
(Photograph only)
Slide 84 Notes
This slide shows an example of a high rise building, which is defined as one
greater than 7 stories. This building is at least 10 stories tall. High-rise
buildings may be less vulnerable to earthquake damage than low-rise or mid-rise
buildings. Only full or partial-height stories above ground are counted in
determining the number of stories. Penthouses are generally not counted as a
story.
Similar to mid rise buildings, the modifiers for high rise are generally
positive numbers, which increase the building’s score. The value of the modifier
also varies depending on the building type. There are several building types for
which the high rise modifier is not applicable. This again indicates that these
building types are generally not constructed more than seven stories tall.
Slide 85 Text
Vertical Irregularity
(Illustration only)
Slide 85 Notes
The next modifier is vertical irregularity. Vertical irregularities in all
building types refers to irregular shapes or features, such as discontinuous
columns, setbacks, and large openings that can make a building vulnerable to
earthquake shaking. The intent is to describe a condition where the irregularity
produces a negative effect on the performance of a building by concentrating the
damage at the location of the irregularity. There are four types of vertical
irregularities depicted in this slide:
• Setbacks
• Hillside
• Short columns
• Soft story
The score modifiers for vertical irregularity is always negative, which reduces
the building’s score. The slides that follow provide examples of each of these
vertical irregularities.
Slide 86 Text
Setback Example
(Photograph only)
Slide 86 Notes
This photo shows an example of a building with multiple setbacks.
Setbacks can be a detriment to seismic performance since damage can be
concentrated at the floor where the setbacks occur.
The following are some considerations for applying the vertical irregularity
modifier for a building with a setback:
• The presence of a penthouse on the roof of a building should not
necessarily be considered a setback since the penthouse is typically small
compared to the typical floor and may not be considered as an integral part of
the lateral force resisting system of the building
• Setbacks in the lateral force resisting system can occur even though the
dimensions of the building do not change from floor to floor, as when the amount
of shear wall decreases substantially on higher floors or the number of braced
frame or moment frame bays change. These conditions often require review of the
building plans to identify.
Slide 87 Text
Hillside Example
(Photograph only)
Slide 87 Notes
This picture shows an example of a building on a hillside lot. Because of the
slope of the ground, part of the lower level to the right of the slide is
founded below grade, but the rest of the lower level is above grade. As a result
of this configuration, there is a difference in stiffness between the portion of
the building founded below grade and the portion that is above grade. In most
buildings with this configuration, there are more openings in the walls in the
portion that is above grade, which makes these areas more vulnerable to damage.
In the 1994 Northridge earthquake, there were many hillside houses that
experienced considerable damage due to the hillside configuration. Some of these
houses collapsed due to the lack of strength of the lower level walls along the
slope of the hill and slid down the hill.
Slide 88 Text
Soft Story Example
(Photograph only)
Slide 88 Notes
Quite often, buildings have a larger number of openings in the lowest story
compared to the upper story. This can be for garage doors, shops, or for other
architectural reasons. As a result, the exterior walls of the building are
discontinuous and do not extend continuously over the entire height of the
building. In a building that relies on the stiffness of the exterior walls for
resistance to lateral forces, the discontinuity causes one story of the building
to be soft relative to the other stories. Damage is often concentrated at these
soft stories, particularly when the soft story occurs at the base of the
building. However, soft stories can also occur at other stories if there are
abrupt changes in stiffness.
This slide shows an example of damage to s soft story apartment building in the
marina district of San Francisco caused by the 1989 Loma Prieta earthquake. The
garage doors at the first story, along with the open entrance area, caused the
first story to have much less stiffness and strength than the upper floors of
the building. This caused the damage to be concentrated at this story. Not the
there is no visible damage to the upper stories of the building.
Often, a steel moment frame (S1) or concrete moment frame (C1) building will
have less curtain wall enclosure at the ground floor than at the upper floors.
As there curtain walls are not structural elements and do not affect the frame
stiffness, the soft story modifier should not apply.
Slide 89 Text
Short Columns Example
(Photograph only)
Slide 89 Notes
The short column modifier is applied to concrete or masonry buildings that have
many columns that are considerably shorter than the floor-to-floor height of the
building. Often this feature is caused by architectural elements that impede the
lateral movement of the structural framing. This occurs, as shown here, by a
partial height exterior infill masonry wall restraining the lower portion of the
columns. The short column failure pictured here occurred during the 1994
Northridge earthquake. When earthquake forces are applied to buildings with
short columns, they are much more likely to fail in shear, with x-cracks, rather
than failing in bending with hinges at top and bottom of the column. The shear
x-crack failure is more brittle than the hinging bending failure and will more
likely cause the column to lose its vertical load-carrying capacity. Concrete
columns, particularly in older concrete construction, do not have sufficient
horizontal confinement reinforcing to allow the columns to respond in a ductile
manner to shear forces.
Slide 90 Text
Plan Irregularity
(Illustration only)
Slide 90 Notes
Building that have irregular plan with shapes such as L, T, U, or open-courtyard
shapes tend to have less earthquake resistance than those with simple
rectangular plan shapes. Each of the wings tries to move independently during
ground shaking. The damage tends to be concentrated at inside corners, referred
to as re-entrant corners, when the design seldom considers the earthquake
demand. All building types are susceptible.
In this slide, several typical examples of plan irregularities are shown. The
arrows point to the location of the re-entrant corner or other locations where
the damage is likely to be concentrated.
Slide 91 Text
Plan Irregularity Example
(Photograph only)
Slide 91 Notes
This shows an example of a building with plan irregularities. This residential
building has multiple wings off the main section. The re-entrant corners created
by the wings presents areas of vulnerabilities.
When the wing motions are phased so that they alternately move towards each
other and apart, the stresses in the inside corner are high.
Slide 92 Text
Pre-Code
• Constructed prior to initial adoption and enforcement of seismic codes
• Applies to Moderate and High seismic zones
• Default year is 1941 (Exception: 1973 for PC1)
Slide 92 Notes
The design criteria for buildings against earthquake forces has changed
considerably over the last century. Buildings constructed before the adoption
and enforcement of seismic design requirements are less likely to contain the
necessary strength and detailing required to resist significant earthquake
shaking. The Pre-Code modifier should be used when the design and construction
of the building precedes the year in which significant seismic design provisions
were first considered. For most building types, 1941 is the default year for
assessing the need for the Pre-Code modifier. For tilt-up buildings (PC1), the
default year is 1973.
This modifier only applies to buildings in moderate and high seismic zones due
to the method used to calculate the basic structural hazard scores.
Slide 93 Text
Post Benchmark Years
(Table)
Slide 93 Notes
The adoption and enforcement of the seismic requirements of the building codes
varies amongst localities. Codes include seismic requirements if later that the
dates tabulated here for the BOCA National Building Code, the SBCC Southern
Building Code, and the ICBO Uniform Building Code (UBC). The BOCA National
Building Code is used in the northeastern US, the SBBC Southern Building Code is
generally used in the southeastern US, and the UBC is generally in use in the
western US.
Find out whether the local building department has adopted current significant
seismic requirements into its building code. If so, the year these seismic
requirements were adopted and enforced is the benchmark year for the
jurisdiction. If the inspected building was designed and built prior to that
year, it was probably not built in accordance with a seismic code. Generally
speaking, significant seismic requirements were introduced into the UBC in the
mid-1970’s and into the other model codes at later dates.
This table shows the benchmark years for half of the building types. For steel
moment frame buildings, the local building department should be contacted to
determine when the seismic design provisions incorporated seismic details. There
is no benchmark year for light metal buildings (S3), or steel frame buildings
with URM infill (S5).
Slide 94 Text
Post Benchmark (Continued)
(Table)
Slide 94 Notes
This is a continuation of the previous slide showing the benchmark years for the
remaining building types. There is no benchmark year for concrete frames with
URM infill (C3), or precast concrete frames (PC2), so there is no need to search
for it at the local jurisdiction building department. With the exception of
buildings designed using the UBC, there is no benchmark year for tilt-up
buildings (PC1), reinforced masonry buildings (RM1), or unreinforced masonry
buildings, URM.
Note that the benchmark year for the BOCA and SBBC codes for most building types
is much later than the UBC for the same building types. This is due to the BOCA
and SBCC codes late adoption of modern seismic design requirements.
Slide 95 Text
Soil Type
• Type A - hard rock
• Type B - rock
• Type C - Soft rock and very dense soil
• Type D - Stiff soil
• Type E - Soft soil
• Type F - Poor soil
Slide 95 Notes
The inspection should include an assessment of the site conditions. There are
screening procedures to identify less desirable sites. The ground shaking
intensity at the building site will be influenced by the type of soil. Deeper
soft soils increase both the strength and the duration of earthquake shaking and
increase vulnerability. Some soft soils may also be prone to liquefaction,
settlement, or subsidence.
Six soil types are defined:
• Type A is defined as hard rock, which is generally only found in the
eastern and midwestern US
• Type B is defined as rock
• Type C is soft rock or very dense soil
• Type D is stiff soil
• Type E is soft soil
• Type F is poor soil
Soft soils are found in marshlands and along the margins of bays or lakes. They
may also be deposits under former bays or lakes. City, county, state, or US
Geological Survey geologists can assist in identifying areas with soft soils.
Types C, D, and E soils require performance modifiers. If there is no basis for
classifying the soil type, a soil type E should be assumed. However, for one-
story or two-story buildings with a roof height equal to or less than 25 feet, a
class D soil type may be assumed when site conditions are not known. There is
no score modifier for Type F soil, which is used to describe conditions such as
liquefiable soils, highly organic clays or very deep deposits of clay. Buildings
on these soil types cannot be effectively screened using the RVS procedure since
the behavior of the building is significantly dependant on the behavior of the
soil. A geotechnical engineer is required to confirm the presence of Type F
soil.
Slide 96 Text
Soil Type Map
(Illustration only)
Slide 96 Notes
This map of the San Francisco Bay Area illustrates the variation of soil types.
There are four different types of soil shown here described previously. The
green areas depict rock type soils, type B. The yellow areas depict dense soil,
type C. The light orange areas depict stiff soil, type D. The dark areas depict
soft soils, type E.
Areas of soft soil have experienced more damaging ground shaking. In the Loma
Prieta earthquake, for example, buildings in the soft soils area of the Marina
district and South of Market district of San Francisco experienced more damage
than buildings in other areas. Buildings and other structures in west Oakland
also experienced significant damage. This is the location of the Cypress Freeway
structure that collapsed, causing many fatalities.
Slide 97 Text
Occupancy
• Assembly
• Commercial
• Emergency Services
• Government
• Historic
• Industrial
• Office
• Residential
• School
Number of Occupants
• 0 - 10
• 11 - 100
• 101 - 1000
• >1000
Slide 97 Notes
We now address the issues of building occupancy.
The occupancy uses listed on the form are Assembly, Commercial, Emergency
Services, Government, Historic, Industrial, Office, Residential, and School.
Residential includes hotels and motels as well as houses and apartments. Places
of public assembly are those where 300 or more people might be gathered in one
room, such as theaters, performance halls, and churches. Emergency Services
includes police and fire stations and hospitals. Circle the building use or uses
that fits best.
The occupancy load choice is 0-10, 11-100, and 100+. Circle the range that best
describes the in-use occupancy of the building. The occupancy load may be used
by the jurisdiction to set priorities for hazard mitigation plans.
Slide 98 Text
Nonstructural Falling Hazards
• Unreinforced Chimneys
• Parapets
• Cladding or veneer
• Other: Appendages, Equipment
Slide 98 Notes
Nonstructural elements are defined as those parts of the building that are not
part of the structural frames, walls, floors, or roof. Exterior nonstructural
elements include chimneys, parapets, cornices, veneers, and overhangs. Interior
nonstructural elements include suspended ceilings, equipment, large storage
racks, and bookcases. These elements may be hazardous if not adequately anchored
to the building. Check the box for Nonstructural Falling Hazard if the hazard is
significant.
Previous slides have shown veneers, parapets, and chimneys that are falling
hazards. The following four slides show additional typical exterior falling
hazards.
Slide 99 Text
Performance of Chimneys
(Photographs only)
Slide 99 Notes
Exterior brick chimneys are one of the most common sources of nonstructural
earthquake damage for several reasons. Chimneys extend above the top of the
building, creating a tall thin cantilever, which is vulnerable to flexural
behavior. Chimneys that are a part of wood frame buildings are generally not
well connected to the building. Chimneys are also generally constructed of
unreinforced masonry, which is brittle and has only marginal strength to resist
lateral forces.
In this slide, two damaged chimneys are shown. In the picture on the left, the
unreinforced masonry chimney has been severely damaged, reducing the chimney to
a pile of brick. In the picture on the right, the chimney has experienced
flexural behavior just above the roof. The arrow points to a reinforcing bar in
the chimney that provided some marginal flexural strength for the chimney, but
was not sufficient to prevent damage.
Note that even slight damage to a chimney can create a significant hazard.
Cracking of the chimney provides an opportunity for hot combustion air to escape
through the crack and ignite the building framing. Chimneys that have been
subjected to an earthquake should not be used until they have been inspected to
verify that the flue has not been damaged.
Slide 100 Text
Performance of Parapets
(Photograph only)
Slide 100 Notes
Parapets are vertical extensions of the exterior wall above the roof creating a
cantilevered element above the roof of the building. Parapets constructed of
unreinforced masonry are particularly vulnerable to flexural failure due to the
lack of bending strength of the unreinforced masonry.
The building in this slide had a large section of the unreinforced masonry
parapet fail by falling away from the building. This creates a potential life
safety hazard since this occurred above the entrance to the building. In most
cases, the parapet fails by falling away from the building since the flexural
failure occurs below the roof level and the roof provides restraint to inward
movement of the parapet.
Slide 101 Text
Performance of Cladding
(Photograph only)
Slide 101 Notes
Brick veneer can be a falling hazard for wood framed, as well as steel or
concrete frame, buildings. This wood framed building has brick veneer that was
only marginally connected to the framing and is susceptible to out-of-plane
failure. The exterior brick veneer is also at least as stiff in plane as the
wood frame sheathing but does not have the strength to resist earthquake forces.
When the building deformed in plane, the brick veneer cracked badly and became a
falling hazard.
This brick can also be used to identify the building type. All the brick is in
running bond; no end brick courses are seen. Running bond brick walls are used
as veneer in all of the concrete, steel, and wood building types, and in
reinforced and unreinforced masonry wall buildings. They are sometimes used in
concrete or steel infill wall buildings. In this building, close inspection
reveals that no inner brick wythe is present to make it a reinforced masonry
bearing wall building, and that wood framing is present to identify it as a wood
frame building.
Slide 102 Text
Appendages
(Photograph only)
Slide 102 Notes
There are several other types of exterior elements that can present falling
hazards, such as exterior equipment and nonstructural appendages. Appendages are
architectural features attached to the exterior of the building. In this
example, the building has a tower attached to the roof of the building and it
appears that the appendage is constructed of masonry. Appendages, such as this,
are particularly vulnerable to earthquake damage for the reasons similar to
those mentioned previously for parapets: they cantilever above the roof level
and can be constructed of unreinforced masonry.
Damaged appendages create a falling hazard within the building and to the areas
outside of the building.
Slide 103 Text
Other Falling Hazards
• Architectural: Interior ornamentation, Heavy partitions,
• Building services: Mechanical equipment, Electrical equipment
• Contents: Racks and shelving
Slide 103 Notes
In addition to the common falling hazards described previously, there are a
variety of other types of falling hazards that can exist. The Data Collection
Form includes a check box for other falling hazards and a space to describe the
falling hazard. Falling hazards are typically nonstructural elements, those
elements that are not part of the structural system for the building. Types of
other falling hazards include:
• Architectural elements, such as interior ornamentation and heavy
partitions
• Building services elements, such as mechanical or electrical equipment
• Building contents, such as tall storage racks and shelving
Slide 104 Text
Rapid Visual Screening Implementation
(Illustration only)
Slide 104 Notes
This slides presents the stages of the implementation of the rapid visual
screening procedure. These stages are described below and discussed further in
the slides to follow:
• Develop a budget and cost estimate for the implementation of the rapid
visual screening.
• Pre-plan the field survey and identify the area or areas to be screened.
• Choose and train the personnel that will conduct the rapid visual
screening.
• Select the appropriate Data Collection Forms for the area and review the
forms.
• Acquire and review the pre-field data for the buildings in the area to be
surveyed.
• Review existing construction drawings for the buildings.
• Screen the buildings using the Data Collection Form, including sketching
the plan and elevation of the building.
• If the interior of the building is accessible, survey the interior of the
building to verify the building type and the presence of irregularities
• Photograph the building.
• Check the field data and record the building data into a record keeping
system.
Slide 105 Text
Pre-Screening Tasks
• Determine seismicity region
• Determine key seismic code adoption dates
• Determine cut-off score
• Acquire pre-field building data
• Determine soil information
Slide 105 Notes
This slide describes several of the key tasks to be completed in the screening
procedure prior to the field survey. These tasks are important in accurate
determination of building type.
• Determine the seismicity region
• Determine key seismic code adoption dates
• Determine cut-off score
• Acquire pre-field building data
• Determine soil information
Slide 106 Text
Pre-Field Data Collection Sources
• Assessor’s files
• Building department files
• Sanborn maps
• Municipal databases
• Previous studies
Slide 106 Notes
Sources of building data before the field inspection include:
• Assessor’s files, which contain information on age, square footage, number
of stories, and construction type. However, the construction type may not be
consistent with this presentation building type, and the date may not be when
designed or built, but when first eligible for taxation.
• Building department files, although drawings of the oldest buildings may
be discarded.
• Sanborn Maps are valuable in the older cities in the United States. They
were well-kept for years.
• Municipal databases may have been prepared for specific building types,
such as documenting unreinforced masonry buildings.
• Previous studies of specific buildings may be available from various
sources, such as historic buildings documentation.
Slide 107 Text
Field Survey Tools
• Binoculars for high-rise buildings
• Camera, preferably instant or digital
• Clipboard for holding Data Collection Forms
• Copy of the FEMA 154 Handbook
• The Quick Reference Guide
• Pen or pencil
• Straight edge (optional for drawing sketches)
• Tape or stapler, for affixing instant photos
Slide 107 Notes
The field screening of building using the RVS procedure should ideally be
accomplished with a team of two persons. One member of the team should be
experienced in seismic design or evaluation.
The field survey should take 15 to 30 minutes per building. If interior access
is available, the time may be increased to be between 30 to 60 minutes.
Only a few tools are necessary to carry out the RVS screening. These are:
• Binoculars, if high rise buildings are being surveyed, to allow for
observation of upper floors
• A camera, preferably an instant camera or digital camera
• A clipboard for holding the data collection forms
• A copy of the FEMA 154 handbook
• A copy of the Quick Reference Guide
• A pen or pencil for completing the form
• A straight edge for use in drawing sketches of the building
• A stapler or tape for affixing an instant photo to the Data Collection
Form
Slide 108 Text
Data Collection Form
(Illustration only)
Slide 108 Notes
Implementation of the field inspection involves completely filling out the Data
Collection Form. It is important that all of the sections of the form shown
above are completed.
The building identification information includes building address, name, year
built, number of stories, square footage, and use. Much of this information can
be obtained from the pre-field data collection sources. Note that in some cases,
multiple addresses are associated with a single building. Each of the addresses
should be recorded.
• A building sketch should ideally include a typical floor plan and an
elevation. If possible, the sketch should be drawn to scale.
• A photograph of the building exterior can be taken using an instant photo
or a digital photo.
• The presence of all nonstructural falling hazards should be checked.
• The soil type at the site should be circled.
• The occupancy type and count should be circled.
• The appropriate building type, or types, should be circled.
• Any score modifiers should be circled.
• The final score for each of the appropriate building types should be
calculated.
• Any comments regarding the building should be recorded, such as noting
features that potentially improve or detract from the expected performance of
the building.
• The final step is to indicate whether a detailed evaluation of the
building is required.
Slide 109 Text
Use of RVS Results
• Designing seismic hazard mitigation programs
• Ranking seismic rehabilitation needs
• Developing building inventories: Earthquake damage and loss impact
assessments, Planning post-earthquake building safety evaluations
• Developing seismic vulnerability information: Insurance rating, Building
ownership transfers, Triggering seismic rehabilitation requirements during
building remodel permitting
Slide 109 Notes
The results of the RVS survey should be recorded into a database and this data
can be used for a number of purposes such as:
• Designing seismic hazard mitigation programs
• Ranking seismic rehabilitation needs
• Developing building inventories for earthquake damage and loss assessments
or for planning post-earthquake building safety evaluations
• Developing seismic vulnerability information for use in insurance ratings,
building ownership transfers, or triggering seismic rehabilitation requirements
during building remodel permitting
Slide 110 Text
HAZUS Data Collection Tool
(Illustration only)
Slide 110 Notes
One use of the RVS survey mentioned on the previous slide was in developing
earthquake damage and loss estimation methods. A tool for regional earthquake
damage and loss estimation is the HAZUS computer program. HAZUS stands for
Hazards U.S. The HAZUS program uses building data, along with seismicity, soil
type, and occupancy data, to estimate building damage from various earthquake
characterizations.
As part of the HAZUS program, there is a separate program that can be used for
collecting building data called InCAST. The InCAST tool creates a database
containing information on building identification, site hazards, and general and
detailed building characteristics. This slide shows two screen shots from the
program that show some of the data that can be recorded for the general building
data, to the upper left, and some of the information that can be recorded for
the detailed building data. The InCAST program is not a substitute for the RVS
survey. Since some of the information needed for InCAST is similar to that
needed for RVS, it can be beneficial to collect the data for each at the same
time.
Slide 111 Text
Example 1
(Photograph only)
Slide 111 Notes
Here is a photograph of the first example building. Assume that we know that it
is located in Oakland, California. From the FEMA 154 maps, we determine that
this is a high seismic region, we select the data collection form marked High to
collect our data. Prior to the field visit, we collect other information,
including the dates of adoption of key seismic codes, the cut-off score to be
used in the screening, and the soil type. The pre-field data indicates that the
building is located in an area considered to be Soil Type D, and that the
occupancy is government, with 101 to 1000 occupants.
Slide 112 Text
Example 1 (Continued)
(Photograph only)
Slide 112 Notes
The exterior is fairly continuous except for the window openings. There is not a
distinct beam and column grid to the walls. The walls are of concrete and show
the grain surface and width of the boards used to form the concrete. From these
characteristics, we determine that its building type is C2, Concrete Shear Wall.
Slide 113 Text
Example 1 (Continued)
(Photograph only)
Slide 113 Notes
Next, we determine if any modifiers apply.
The building is four stories tall and is therefore considered to be mid-rise.
We remember from the previous slide, or a walk around to the right to the front
of the building) that the building has a significant setback in its façade that
should be considered a vertical irregularity.
We also observe that there is a significant wing at the back of the building, as
shown here, that gives the building a T-shaped plan. This should be considered a
Plan Irregularity.
As mentioned in an early slide, the soil type determined from the pre-field data
is type D.
Further inspection indicates that no other modifiers apply. As we make our
observations, we fill in the building identification data at the top of the data
collection form, draw a plan view in the area at the top left of the form, and
attach a photo to the right side of the form.
Slide 114 Text
Example 1 Scoring
(Illustration only)
Slide 114 Notes
This shows the structural scores and modifiers from the investigation. We have
begun by circling the building type, C2, SW and its basic score, 2.8. We have
circled the applicable modifiers, which are Mid Rise, Vertical Irregularity, and
Plan Irregularity. From information obtained during the pre-field trip data
collection, we know that this building was built after the adoption of seismic
building codes but before the benchmark year for concrete shear wall buildings.
Thus, neither the Pre-Code not the Post-Benchmark modifiers are applicable. We
also circle the soil type modifier for Soil Type D, -0.5, based on soil
information obtained for the site. We have summed the column to arrive at a
final score: 2.8 + 0.4 – 1.0 -0.5 -0.5 = 1.2.
A score of 2.0 or less identifies the building as a potential seismic hazard. A
further investigation by a professional engineer with seismic design experience
would be necessary to determine if the building is, in fact, hazardous.
Slide 115 Text
Example 1 - Completed Form
(Illustration only)
Slide 115 Notes
Here is the completed data collection form for the building. In addition to the
structural scores and modifiers, the building identification information has
been entered at the top of the form; a plan sketch has been drawn on the left;
an instant photo has been placed at the right; the occupancy and falling hazard
information has been entered in the middle of the form; comments are entered at
the bottom. Based on the final score, the need for a detailed evaluation has
been entered at the lower right.
Slide 116 Text
Example 2
(Photograph only)
Slide 116 Notes
This is a picture of the building for our second example. We treat this as an
example for comparing the result of constructing this building in Washington, DC
(low seismicity), Charleston, South Carolina (moderate seismicity), or Los
Angeles, California (high seismicity). We also demonstrate the use of interior
access to aid in determining the building type.
Inspection of this slide indicates that the Building Type is a steel or concrete
moment-resisting frame, or a steel braced frame. From the pre-field data
collection, we determine that the building is constructed on soft soil, soil
type E.
Slide 117 Text
Example 2 - Interior
(Photograph only)
Slide 117 Notes
Since the exterior review of the building was inconclusive regarding the
building type, we inspect the interior of the building. One of the interior
spaces of the building does not have interior finishes due to tenant remodeling.
Other observable interior locations, where structural elements used to assist in
identifying the Building Types, are unfinished basement areas and mechanical
spaces.
The interior inspection reveals fire-proofing covering steel framing. The column
in the center of the picture also shows a deeper beam to the right of the column
compared to the beam on the left and a stiffener plate between the flanges of
the column where the bottom flange of the beam is connected. This indicates that
the column and beam to the right are part of a steel moment-resisting frame.
Slide 118 Text
Example 2 - Exterior
(Photograph only)
Slide 118 Notes
From the previous slide, we identified the building type as a steel moment
frame, S1. The next step is to determine the presence of modifiers.
The building is five stories tall, which makes it a mid-rise building.
The building is L-shaped in plan and also has a circular section, as shown here.
This represents a plan irregularity.
From the construction date determined in the pre-field data and the building
code adoption dates, we determine this a steel moment frame building meets the
post-benchmark year.
Slide 119 Text
Example 2 - Scoring
(Table only)
Slide 119 Notes
This column summarizes and compares the scores for the building for each
seismicity regions. Note that the values for the modifiers, as well as the basic
score, is different for the various seismicity areas.
If the building is located in a low seismicity area, the basic score for the
building is 4.6. Applying the modifiers results in a final score of 2.4.
If the building is located in a moderate seismicity area, the basis score for
the building is 3.6. Applying the modifiers results in a final score of 3.3.
If the building is located in a high seismicity area, the basic score for the
building is 3.8. Applying the modifiers results in a final score of 2.7.
In all cases, the building score exceeds the cut-off score of 2.0 and would not
require further evaluation.
Slide 120 Text
FEMA 154 Second Edition Training Acknowledgement
• Developed by Wiss, Janney, Elstner Associates, Inc.: Subcontractor to URS
Corporation, a contractor to FEMA under the Hazard Mitigation Technical
Assistance Program (HMTAP); Reviewed by Applied Technology Council
• Funding by FEMA
Slide 120 Notes
The final slide in this presentation credits those responsible for the
development of the training material. This training presentation and narrative
were developed by Wiss, Janney, Elstner Associates, Inc. as a subcontractor to
URS Corporation. URS Corporation was funded by FEMA for this project under the
Hazard Mitigation Technical Assistance Program (HMTAP).