303 Third St,
Cambridge, MA
Brian Tufts
Structures Option
Advisor: Dr. Ali Memari
4/14/08
Architecture Overview
• Urban setting near M.I.T.
• Must appeal to affluence
• Technology area
• Contrast of materials
• Terra-cotta
• Metal paneling
• Creates it’s own world with U
footprint and green space
centrally located
• 3 levels of parking below grade
• Retail on the ground level
• Apartments start on the ground
floor
Building Programming
• Total Building Area:
830,000 SF
• Residential Area:
595,000 SF
• Retail Area: 8,000 SF
• Parking: 215,000 SF
• North Building Area:
327,000 SF
• North Building:
• 292 Units
•
•
•
•
41 Studio 650 SF EA
136 1 Bed 850 SF EA
103 2 Bed 1200 SF EA
12 3 Bed 1550 SF EA
Overview of Building Systems
• Structural
• Composite steel framing
• 3 ¼ LWC on 3” 16 ga composite
metal floor deck
• Electrical
• 2 primary power distribution boards
• (2) 300 kVA transformers provide
120/208V to panels
• Backup power via 750 kW generator
• Mechanical
• 2 cooling towers each for north and
south building
totaling ~150,000 CFM per building
• 5 water cooled AC units service
lobby and fitness areas
• 14 rooftop air conditioning units
service corridors
• 4 boilers totaling 23,300 MBH
Thesis Objectives
• Evaluate an alternative floor framing system using openweb steel joists
• Compare seismic performance
• Reduce lateral framing
• Reduce gravity columns
• Check vibration performance
• Explore fireproofing issues
• Compare cost savings
• Mechanical Breadth – Building Envelope Efficiency
• Check envelope performance with Massachusetts Energy
Code
• Propose 2 pane window to increase envelope
performance
• Compare cost of two systems and energy performance
Massachusetts State Building Code
Sixth Edition
Based on Building Officials and Code Administrators
National Building Code – BOCA 1993
 Key differences from ASCE 7

◦ Wind – The reference wind velocity for each wind load zone
is the “fastest-mile” wind velocity, in miles per hour, at 30
feet about the ground
 Pv = 90 mph for Cambridge, MA
 Reference wind pressure for Exposure C = 31 psf
 Resulting story shear is less conservative than BOCA
◦ Seismic - Equivalent Lateral Frame Method – BOCA
 R = 5.0 for Concentrically Braced Frames
 R = 4.5 for Ordinary Moment Frames
 Effective peak acceleration: Av = Aa = 0.12g for all of
Massachusetts
 Ct = 0.20
Typical Composite Steel Framing
• Beam Spacing: 12.5’ (Typ) with 18’-1” span
• Girders typically span 25’
Typical Bay Framing
Typical Bay – Composite Steel
Typical Bay – Steel Joists
Lateral Frames Along Line E
Composite Steel
Steel Joists
Lateral System & Gravity Column
Comparison
Cost: $3500/Ton for steel and erection in Boston, MA
Typical Bay Comparison
Ceiling Sections
Fireproofing
Vibration
• Analyzed the typical bay for
walking excitation and a
future office occupancy
• Typical joist is 12K1
• Typical girder is VLH24
• Δj = 0.186 in
• Δg = 0.266 in
• fn = 5.263 Hz
• a0/g = 0.003 < 0.005
Depth Study Summary
• Open-web steel joists would save initial costs in column
steel and lateral framing members.
• Steel joists are also cheaper to frame than composite
steel framing.
• Vibration is not an issue for this application of steel joists
as the typical bay is more than adequate for walking
excitation.
• If the 12’ floor-floor height is adequate, alternate
fireproofing detail would alleviate issues related to the
application of cementitious fireproofing.
• Open-web steel joists are a viable alternate framing
system for 303 Third Street.
Mechanical Breadth Study –
Building Envelope
Typical Wall Sections
Wall U-Values
Calculated using the ASHRAE
Handbook of Fundamentals
Energy Compliance Check
Specified walls and ¼” clear float glass fail energy compliance
check by 30%
Proposed Two Pane Window
• Increase building
envelope
efficiency by 14%
•Cost roughly
$45/SF including
framing and
installation,
compared to
$35/SF for single
pane windows
Image courtesy of http://www.energystar.gov
Conclusions
• Open-web steel joists are a viable alternative floor framing system
• Two pane glass may be necessary to meet minimum energy code
and result in a 14% increase in envelope performance for 303 Third
Street
• Increased envelope performance will help obtain LEED points
under the Optimize Energy Performance section of the LEED
Reference Guide
• A decrease in window area and an increase in wall insulation will
increase envelope performance, but has architectural and
apartment rent ability implications.
Thanks
• McNamara/Salvia Inc. Consulting Engineers - Boston, MA
• Mark Aho, P.E.
• John Matuszewski, P.E.
• Adam McCarthy, P.E.
• Robert McNamara, P.E., S.E.
• Joseph Salvia, P.E.
• William Waterston, AIA - Wiss, Janney, Elstner Associates, Inc. –
Cambridge, MA
• Hank Klein - Extell Development Company –Boston, MA
• Andrew Copelotti - Equity Residential –Boston, MA
• Mark Pasciuto - Bovis Lend Lease LMB, Inc.– Boston, MA
• Woth Ngan - Bovis Lend Lease LMB, Inc.– Boston, MA
• Martin Turnbull – AHA Consulting Engineers – Lexington, MA
•The AE Department
•Friends and Family who supported me while preparing this thesis
Questions?