http://www.nist.gov/el/disasterstudies/wtc/wtc_contracts.cfm 1

Awarded Contracts for External Experts to Support the 

NIST World Trade Center (WTC) Disaster Investigation

Contract No. Awarded to Date Awarded

SB1341-04-Z-0002 Simpson Gumpertz & Heger, Inc. 

(SGH)

10/30/2003

THERMAL-STRUCTURAL RESPONSE OF THE WORLD TRADE CENTER TOWERS WITH AND 

WITHOUT IMPACT DAMAGE TO DETERMINE PROBABLE COLLAPSE INITIATION SEQUENCES

Under solicitation number SB1341-03-R-0044, an indefinite deliverable, indefinite quantity (IDIQ) 

purchase order has been awarded to Simpson Gumpertz & Heger Inc. (SGH) of Waltham, 

Massachusetts, to determine the response of structural components and systems to the fire environment 

in the World Trade Center towers and to identify probable structural collapse mechanisms.

SGH is an engineering firm that specializes in design, investigation and retrofit of buildings and structures 

of all types. SGH has a highly skilled technical staff with expertise in building structures, materials, and 

investigation and specialized research and is well qualified to conduct the structural fire response and 

collapse analysis of the World Trade Center towers.

SGH strengths include: advanced finite element analysis capabilities; expertise in building technology, 

materials analysis and testing and engineering mechanics; sophisticated investigative capabilities utilizing 

state of the art NDE and monitoring technologies. SGH is partnering with Computer Aided Engineering 

Associates (CAEA), an engineering consulting company specializing in advanced engineering analysis 

services. CAEA specializes in thermal-stress analysis and has extensive experience in applied 

mechanics, dynamics, contact mechanics and finite element code development.

Together, SGH and CAEA bring many years of experience in nonlinear finite analysis, high-rise building 

design, material studies for thermal effects and failure investigations. 

The specific tasks that SGH will perform include:

Develop and validate thermal-structural models of floor and column component and subsystem 

models, including passive fire protection. 

Determine the transient thermal-structural response of the component and subsystem models to 

standard test fire conditions (ASTM E119 and E1529). 

Estimate the thermal environment necessary to damage or fail critical members or connections. 

Develop and validate a global thermal-structural model, including passive fire protection, 

assuming no impact damage. Conduct analysis for ASTM E119 and E1529 standard fires and for 

estimated heat flux densities and temperatures in undamaged compartments. 

Develop and validate global thermal-structural models with aircraft impact damage by modifying 

the undamaged model for each tower. Conduct thermal and structural analysis of possible fire 

growth and spread sequences in each tower. 

Conduct parametric studies to determine the effect of uncertainty in influential parameters on 

predicted outcomes and on the most probable collapse sequence. 
2 http://www.nist.gov/el/disasterstudies/wtc/wtc_contracts.cfm

The studies are based upon the approach described in the paper “Assessing the Most Probable 

Structural Collapse Sequence: Integrating Impact Damage, Fire Dynamics, Thermal-Structural Response, 

& Collapse Initiation.”

Identify candidate collapse initiation hypotheses for each tower from analyses. 

The key personnel at SGH and CAEA include: Project Manager, Mehdi Zarghamee; Structural 

Performance Review Committee, Glen Bell, Ronald Hamburger and Pedro Sifre; Computation/Modeling 

Review Committee, Said Bolourch, Atis Liepins and Peter Barrett; and Computation Manager, Frank Kan.

Mehdi S. Zarghamee, a Principal and Head of the Engineering Mechanics and Infrastructure 

Division at SGH, has 30 years of engineering experience in analysis and design of precision 

structures. He has been responsible for analysis, design, and failure investigation of complex 

structural and mechanical systems. Dr. Zarghamee earned his Ph. D. in Structural Engineering 

from the University of Illinois and his S.M. in Mathematics from the Massachusetts Institute of 

Technology.

Glen Bell, Principal and Chief Executive Officer, has been with SGH for 28 years. Mr. Bell 

specializes in structural failure investigations and has extensive experience in earthquake 

engineering, structural design and rehabilitation. He received his B.S. degree in Civil Engineering 

from Tufts University and his M.S. in Structural Engineering and Structural Mechanics from the 

University of California at Berkeley.

Ronald Hamburger, a Principal at SGH, has 28 years of experience in civil and structural 

engineering, damage and forensic investigations, engineering research, building code and 

standards development and project management. He was a member of the Building Performance 

Assessment Team that investigated the collapse of the World Trade Center Buildings in New 

York. Mr. Hamburger received his M.B.A. from Golden Gate University and his B.S. and M.S. 

from the Polytechnic Institute of New York.

Pedro Sifre, Senior Project Manager, has 16 years of experience in high-rise building design and 

optimization of lateral load resisting systems. He received his B.S. in Civil Engineering and his 

M.S. in Aeronautics and Astronautics from the Massachusetts Institute of Technology and his 

M.S. in Structural Engineering from the University of California at Berkeley.

Atis Liepins, a Senior Associate has been with SGH for 25 years. He is an expert in the 

performance of finite element analysis, structural design, and failure analysis. Mr. Liepins 

received his S.B., S.M., and C.E. in Civil Engineering from the Massachusetts Institute of 

Technology.

Said Bolourchi, Staff Consultant, has 24 years of experience. His expertise is in risk assessment 

and failure analysis and evaluations including nonlinear dynamic analysis and response spectrum 

analysis of structures. Dr. Bolourchi received his B.S. in Mechanical Engineering from Queen 

Mary College, London, and his M.S. in Mechanical Engineering and Ph.D. in Applied Mechanics 

from the Massachusetts Institute of Technology. 

Peter Barrett, Consultant, has over 20 years of experience in thermal-structural analysis 

applications using the finite element method and has been with CAEA since 1993. He has 

conducted numerous geometric and material nonlinear static and dynamic analyses to evaluate 

the strength, stability, and fatigue life of structures. 

Frank Kan, a Senior Project Manager, has been with SGH for 16 years. He has been involved in 

structural and seismic analysis, design, and investigation of buildings, bridges and special

structures. Mr. Kan received his B.Eng. in Civil Engineering and Engineering Mechanics from 

McMaster University, Ontario, and his M.S. in Civil Engineering from the Massachusetts Institute 

of Technology. As Computation Manager, Mr. Kan will be responsible for all computational 

aspects of the project as well as coordination between the SGH Computation Team and the 

CAEA Consultant Team.