E-Mail This Article February 7, 2002 Engineers at Ground Zero speak about experience Key figures involved in the cleanup at Ground Zero spoke in a panel discussion From Ground Zero, at the National Building Museum in Washington, D.C., January 28. Moderated by Charles H. Thornton, P.E., chair and managing partner of Thornton-Tomasetti Group, the panel included Daniel Cuoco, P.E., president and managing principal of LZA/Thornton-Tomasetti, George J. Tamaro, P.E., partner with Mueser Rutledge Consulting Engineers, and Ralph W. Johnson, senior vice president with Turner Construction. The event was cosponsored by the Associated General Contractors of America and the American Council of Engineering Companies. Cuoco noted the services that the structural engineers have provided at the WTC site: emergency damage assessment of buildings in the immediate collapse area

identify unstable areas

develop demolition and temporary stabilization procedures

identify safe locations for heavy equipment, design reinforcement, and grillages

develop and coordinate survey monitoring program

inspect more than 400 buildings in the area surrounding the collapse site in a 2-day period (rapid visual assessment)

detailed investigation of damaged buildings The panelists, sometimes in amazing detail, described the challenges in this extraordinary effort while showing slides of the site from September 11 through January. The following are excepts of Cuocos comments. Cuoco on the cleanup of the debris that had fallen on the Winter Garden glass roof adjacent to 3 World Financial Center: One of the things we had to do every night and every day was to remind the contractors that they couldnt remove the debris because the Winter Garden roof would fall. At the same time we were designing temporary shoring that would be able to hold that up so that they could remove this debris. And then, one day, the fire department said were going to remove this debris in two days because they felt they had a lot of people in there, possibly a fire chief. We said that if that debris was out before we put the shoring in, the Winter Gardens roof was going to fall down. They said, well, ok, we can rebuild it again. The priority was to try to found people. So in two days we were able to get the shoring design finished and I shored it and the debris on the Winter garden roof has all since been removed. Those are the types of things that we were up against. We had to put the priorities where they belong. Cuoco on obtaining the necessary steel beams to form a platform for a crane: Our first crane challenge was to get a crane between buildings 4 and 5 on the plaza, but there was really no way. This was a 300-ton crane. There was no way the plaza would support it. Then we realized there was this granite sculpture that was in there, if any of you remember between the two buildings and you walk up the steps there and it was on a thick concrete base. We did some calculations and we figured out that the thing weighed about 200 tons. And the structure had been strengthened in that local bay and the columns under it. So we realized if we could get rid of the sculpture, then we could put a crane there. We inspected the columns below, and they were in pretty good shape only needing some minor reinforcing. We needed to design a grillage that would span over the plaza and land on those four columns. So we did some calculations and designed some beams. The contractor called the steel fabricator for eight beams, and he said, well, I dont have those beams. So using the beams he had, we came up with some designs, faxed up a sketch and within two hours they had the steel on the truck on its way to the site. Its just incredible. No questions asked. Cuoco on using WTC box columns as supports for a crane: One day we got notice that there was an 800-ton crane on the way to the site, and it had to go right next to the opening on the slurry wall. We were told that we couldnt approach the slurry wall with a crane that heavy. You have to stay 30 feet away. Theres no way; otherwise youre going to put pressures within that 30-foot distance. So, we figured out that if we could bridge over the 30 feet and put a beam between the slurry wall and the 30-foot point, we would not put any load on that 30-foot distance. Of course the vertical load would go onto the slurry wall but that was insignificant. We did some calculations and there really werent big enough beams in the area to support the crane. So we looked in the debris pile and we realized that there were some really big box columns from the core that were 5-feet-by-3-feet, more than 30 feet long, really heavy, and some of them were pretty straight. We measured them, did some calculations and we were able to use them as runways for the 800-ton crane. . John E. Czarnecki, Assoc. AIA Return to news headlines