City Square: Structural Engineering, Democracy and Architecture

Abstract

I watched the attacks on the World Trade Center towers at home in New York, on television. My office is on Broadway a block away from the site, but I was leaving home late that morning. Like most others I did not realize till the second plane hit at 9.03 a.m. that this was an attack. And it took me another half hour watching the fire in the north tower to understand that it would collapse. I know these structures well, from study, the work of a design studio conducted at Princeton in 1999, and discussions with their structural engineer, Leslie Robertson. I knew, as I think the terrorists did, that they were especially robust. I began calling my colleagues-engineers, emergency response specialists, and others in the earthquake engineering community. It was very hard to reach anyone. The city's emergency response headquarters, which I had visited in June, was destroyed with the WTC7 tower. I was able to reach my colleagues Ramon Gilsanz and Aine Brazil, and we discussed how we might mobilize volunteer engineers through the Structural Engineers Association of New York (SEAoNY), a group we had founded together in the early 1990s. Aine's firm, LZA/Thornton Tomasetti (LZA/TT), had already been hired by the city to help on the site, to advise the contractors on safety as they assisted with the search and recovery efforts. George Tamaro and his firm Mueser Rutledge were hired to consult on the below-grade structures. The Mayor's Office of Emergency Management (OEM) had assigned to the NYC Department of Design and Construction (DDC) the supervision of construction-related work on site. The DDC agreed to give SEAoNY a role, with LZA/TT, in providing teams of engineers, organized by the individual firms, to be on site with the four contractors (Amec, Bovis, Tully, and Turner/Plaza), around the clock on twelve-hour shifts. Each shift would begin with a briefing by the departing group and a detailed discussion of all the engineering issues of concern. These included the safety of existing structures, the design of crane platforms and access ways, and the demolition strategies. A second task was to inspect the surrounding buildings and determine which were safe for re-occupancy. On September 13 and 14 I proposed to