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Structural Engineering Reconnaissance 
at Ground Zero 
Presented by Michel Bruneau, Andrei Reinhorn and Andrew Whittaker, 
Department of Civil, Structural and Environmental Engineering, University at Buffalo

--photo by M. Bruneau

Many buildings around the World Trade Center, such as 3 Financial Center (above), experienced heavy impact loads from falling debris. 

Three MCEER researchers, Michel Bruneau, Andrei Reinhorn and Andrew Whittaker, all from the Department of Civil, Structural and Environmental Engineering (CSEE) at the University at Buffalo (UB), gave a joint seminar on Structural Engineering Reconnaissance at Ground Zero at UB on October 11, 2001. The three visited the area surrounding the World Trade Center (WTC) in lower Manhattan to survey building damage as part of a National Science Foundation-sponsored research effort (see related article on page 2). About 70 to 80 people attended the seminar, which was co-organized by ASCE, MCEER and UB. 

Mr. Dean Gustavson, president elect of the ASCE Buffalo Section (BS 1992, CSEE graduate, UB), opened the seminar. He led the audience in a brief moment of silence to commemorate the victims of the attacks on the WTC and the Pentagon. Dr. Gary Dargush, CSEE, UB, and vice president of the ASCE Buffalo Section, then introduced the speakers. 

Dr. Michel Bruneau began the presentation by describing how earthquake engineering evolved from blast engineering around the middle of last century. Now, in light of the collapse of the WTC towers, blast engineering could possibly benefit from new developments in earthquake engineering. He gave an overview of the damage at the World Trade Center site, which was very localized, unlike the widespread damage that typically occurs after a major earthquake. The buildings around the WTC experienced heavy impact loads from falling, and sometimes flaming, debris in the aftermath of the crash. He pointed out the challenging work facing the recovery teams, such as removing debris from the site and stability concerns for the foundation retaining walls. An important challenge is to safely remove debris from surrounding buildings, some of which came to rest at considerable heights in the buildings. He emphasized that the data that the site team collected will be primarily shared with graduate students who will assist faculty members in the forensic analysis of the structural aspects of the WTC collapse and damage to adjacent buildings. 

-photo by M. Bruneau

A large portion of the facade from World Trade Center Tower 2 fell on the facade of the 130 Liberty Plaza building, removing 17 stories of the perimeter column from the structural system. 

Dr. Bruneau then handed the podium to Dr. Andrei Reinhorn, who provided an introduction and background overview of the WTC structures, which arguably were among the tallest structures in the world and state-of-the-art engineering landmarks. He described the collapse of the towers, followed by a detailed presentation of their structural characteristics, explaining the lateral and gravity structural systems and their extremely light and efficient construction. He emphasized the inclusion of viscoelastic dampers in their construction to reduce wind-induced vibrations. He mentioned, in particular, the type of floor system used in the towers and its connection to the structural system. 

Next, Dr. Andrew Whittaker presented the observations of the visiting team at 130 Liberty Plaza, Bankers Trust, a 42-story building to the north of the WTC towers. This building was hit by falling debris, including life vests and seats from American Airlines flight 767 upon impact to WTC tower 1. During the collapse of WTC tower 2, the building was showered with heavy debris. The most severe impact was from a very large portion of the façade of tower 2, which fell on the façade of the Liberty Plaza building, effectively removing a perimeter column from the structural system from the 23rd story of the building down to the 6th story, where it came to rest. Prof. Whittaker presented the structural aspects of this damaged part of the building, both of the lateral and gravity structural systems as well as the floor systems. He emphasized that despite considerable localized damage and loss of structural components, the building did not collapse, apparently due to significant reserve capacity for overloading ­ a positive note on which he ended the presentation. 

After the presentations, Dr. Dargush opened the floor to questions from the audience. Discussions regarding the prospects of salvaging the Liberty Square Building; the plan for recovery regarding the stability of the landfill and adjacent buildings; the ability of structures such as the WTC towers to withstand large lateral loads from colliding airplanes; and the role of fireproofing capabilities of construction materials followed. 

Submitted by Benedikt Halldorsson, UB-EERI Secretary, University at Buffalo

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