MA-5106 Structural Analysis 06-17-13
ProTerra Design Group, LLC Ph:(413)320-4918
1 Short Street, Suite 3 Fax:(413)320-4917
Northampton, MA 01060 E: info@proterra-design.com
June 17, 2013
Mr. Tim Burks
Site Acquisition Manager
SAI Communications Consultant for AT&T Mobility
500 Enterprise Drive, Suite 3A
Rocky Hill, CT 06067
RE: Structural Analysis Opinion of Church Steeple for AT&T New Build
AT&T Site #: MA-5106 Northampton Helen Hills Hills Chapel
115 & 123 Elm Street
Northampton, MA 01060
SUMMARY:
In our opinion, the existing steeple structure will support the proposed addition of panel
antennas to the louvered steeple section and remote radio units (RRUs) below without
modification.
Mr. Burks:
ProTerra Design Group (ProTerra) was retained to perform a site inspection at the above-referenced
location. The purpose of this inspection was to assess the structural capacity of the existing church
steeple in order to determine whether it is capable of supporting AT&T’s proposed equipment. The
following information was used to perform this evaluation:
Proposed equipment upgrade specifications in the form of an RFDS dated June 10, 2013.
Original Building Plan set entitled “Chapel for Smith College; Northampton, Mass.” Prepared by
William & Geoffrey Platt revised through May 14, 1954.
Fire Protection Upgrade Plan set entitled “Smith College; Northampton, Mass.; Fire Protection
System for Helen Hills Hills Chapel Gill Hall and Parsons Annex” prepared by Leoh Pernice &
Associates dated April 12, 1993.
HVAC Upgrade Plan set entitled “Ground Floor HVAC Renovations; Helen Hills Chapel, Smith
College; Northampton, Massachusetts” prepared by Lindgren & Sharples, PC dated November
10, 2008.
On February 11, May 15, and May 22, 2013, representatives of ProTerra visited this site to survey the as-
built conditions of the existing structure. The 136’ tall steeple was found to be constructed of a steel
frame secured to reinforced concrete footings. The steel frame supported a wooden skin with wooden
architectural elements. Horizontal steel framing members supported wooden floors. The attached SK-1
sheet illustrates the steel construction of the steeple as mapped by ProTerra during site visits. All
ProTerra Design Group, LLC Ph:(413)320-4918
1 Short Street, Suite 3 Fax:(413)320-4917
Northampton, MA 01060 E: info@proterra-design.com
steeple components including wood skin, wood floors, and steel frame were observed in good condition
with no visible water damage, rot, or rusting.
AT&T proposes to add six panel antennas and nine RRUs in three sectors of two panel antennas and
three RRUs each at the steeple’s bell level. Two surge suppressors will be located adjacent to the RRUs.
The panel antennas will be fed via coaxial jumpers from the RRUs. The RRUs will be fed via DC power
and fiber trunk cables through the steeple interior by equipment cabinets inside a proposed basement
equipment room.
ProTerra recommends pipe-mounting the panel antennas on steel frames behind the existing louvered
panels. A steel frame constructed as shown on the latest Construction Drawings prepared by ProTerra
will support each sector’s panel antennas. The frame will be secured to the steel steeple framing vertical
members. RRUs and surge suppressors will be supported on a similar frame immediately below the
panel antennas. The existing wooden louvers will be replaced with RF transparent louvers.
This structural analysis of gravity loads was conducted with the aid of the International Existing Building
Code (IEBC) 2009 for Alterations Level 2 and historic buildings for the installation of the proposed AT&T
equipment. In our opinion, the alterations proposed on the bell level will not result in an increased
design live load from wind over the original steeple’s design and construction. As a full analysis of the
steeple section is beyond the scope of this project, we have subsequently limited our evaluation to the
existing gravity carrying load bearing elements near AT&T’s proposed equipment.
Based upon calculations and analysis performed in conjunction with William O. Bishop, PE (structural
engineer), ProTerra finds the following:
The proposed AT&T panel antennas & radio equipment weighing approximately 2200 lbs. will
increase gravity loads by less than 5% at the window level. Since loads and stress are
proportional, the increase in stress from the equipment is also less than 5%. In our opinion, the
additional loads and stresses will not adversely reduce the structure’s ability to resist the design
loads imparted upon it.
The calculations provided for gravity loads show that the combined stress in the steel frame
members is below 60% of capacity. As a narrow flexible structure, wind loads likely control the
design over seismic loads. The small increase in gravity loads from the additional equipment
could improve the structure’s resistance for overturning.
In our opinion, the addition of the equipment in the steeple will not result in any increase in
steeple area or exposure to the wind that would appear to lessen the lateral resistance of the
structure over the existing conditions.
ProTerra Design Group, LLC Ph:(413)320-4918
1 Short Street, Suite 3 Fax:(413)320-4917
Northampton, MA 01060 E: info@proterra-design.com
Existing church showing from the southwest. AT&T’s antennas are to be located at bell level behind the
louvers as indicated.
Steeple interior at bell level looking up
ProTerra Design Group, LLC Ph:(413)320-4918
1 Short Street, Suite 3 Fax:(413)320-4917
Northampton, MA 01060 E: info@proterra-design.com
Steeple interior looking down at bell level
Steeple interior at bell level
ProTerra Design Group, LLC Ph:(413)320-4918
1 Short Street, Suite 3 Fax:(413)320-4917
Northampton, MA 01060 E: info@proterra-design.com
Steeple interior at bell level
Wooden louvers to be replaced as noted