Hey Dr. Laman,

How is everything in State College?  As you can image, things here in NYC have been quite hectic lately, especially for the structural engineering community, in light of the events of September 11.

Soon after the tragedy, a general call went out for structural engineers to assist in the recovery efforts. 5 of the 7 structural engineers from HLW volunteered to help.  SEAoNY (Structural Engineers Association of New York) was instrumental in organizing the volunteers, who come from many firms. Ken Roko (remember him?) and I were lucky enough to be able to help.  We were taken to the site and organized into teams of 4, each team given responsibility for 1/4 of the site.  The SEAoNY volunteer teams, at the coordination of Thornton-Tomasetti (the acting city structural engineer in case of disaster or emergency), were sent out to aid in any way possible. When we got into it, little did we think we would be at Ground Zero. Instead, we thought we might be used to inspect surrounding buildings for structural integrity.  Upon our arrival, we realized that we would be used to give immediate guidance to the contractors and rescue workers in the
midst of the chaos.

The size and scope of the devastation is not to be believed. The newspaper photos and TV images simply do not show the scale or extent of the damage. The media coverage also had no way of showing the amazing cooperation shown
by all parties involved in the search and rescue efforts.  Imagine firefighters, police, ironworkers, engineers, contractors, the national guard, FEMA disaster teams, and a myriad of other skilled people working together.  You can hear about the valiant efforts of the volunteers and rescue workers a thousand times from the media, but until you see actually see it in action, I don't think you can fully appreciate it.  It was incredibly inspiring and a testament to the human spirit.

As you probably know by now, in addition to the two towers, 7 WTC and the Marriott Hotel were completely destroyed down to the ground.  The three low-rise buildings (4, 5, and 6 WTC) are completely burned out and are close to collapse.  The south pedestrian bridge was lying on West Street.  West of the WTC, the facades of the World Financial Center buildings sustained heavy damage to their facades.  The American Express building sustained severe structural damage to a corner column, though it was deemed stable.  The Winter Garden also sustained heavy damage to a portion of the roof.  To the south, the old Banker's Trust Building also sustained heavy structural damage to it's north facade, though it too was deemed stable.  The small low-rise buildings to the south, amazingly, were still standing though most
of the facades were heavily damaged.  To the east of the WTC are the two buildings that have caused the most concern and spontaneous evacuations of rescue personnel; 1 Liberty  Plaza and the Millennium Hotel.  1 Liberty (originally the US Steel Building) and the Millennium were both suspected of being unstable and near to collapse.  Both buildings were completely inspected inside and out and their alignment was measured with surveying equipment as early as Wednesday afternoon and then twice again on Thursday. Neither building sustained any direct impact from the Towers nor was there
any fire damage.  Both buildings were surveyed and found to be in near perfect alignment (all three times).  They are probably two of the safest buildings at Ground Zero.  This gives you an idea of the amount of mis-information floating around in such a situation (very frustrating for a structural engineer).

Our first night on the site was on the Thursday following the tragedy.  It was the first day of organized structural engineering presence on the site. Myself, as well as two other engineers from HLW were responsible for the
area of the remaining plaza between WTC 4 and 5, at the edge of the crater. Pieces of the Trade Centers' exterior column sections were hanging from the still burning remains of WTC 4 and 5.  Twice during the night, the alarm was sounded to get out, for fear of more collapse.  Both times were false alarms.  The general area of the plaza was relatively sound, aside from a bay where the supporting steel beams had failed plastically and a few locations where falling steel had speared though the slab.  The plaza level is at ground level, below which there are about 5 sub-basements, including a mall, parking, and train stations.  All of these sub-basements were intact to the point of the crater.  There was a huge rush to move in heavy equipment, so we had to establish loading limits for the remaining plaza and install steel framing on stub columns to support a heavy crane.  It was true engineering on the fly, and very stressful, as any decisions we made could
have immediate impact on the life safety of the rescue workers.  All the while, there was a risk of these exterior column sections (3 stories high, 3 columns each) falling off of 4 and 5.  When not busy engineering, we manned buckets in the recovery effort.

By the Friday following the disaster, SEAoNY had reached out to all of the member firms and secured approximately 140 volunteer engineers to work in teams for as long as needed. We had been working 12 hour shifts of 3-4 engineers every other day at the site, but have since scaled back to 2 shifts of 2 per week.  I have to say that I am quite impressed by the outreach that the structural community has lent to the recovery effort. There are structural teams here from all over the country.

The next few days and nights following the 13th, we were moved to the western side of the site, near the WFC buildings and the Winter Garden.  Our main responsibility was to establish where cranes should be located.  There was much concern for the "bathtub", the slurry wall some 70-90 deep, which surrounds the Trade Center complex.  We had to position the cranes some distance from this wall in order to keep soil pressure off of the wall, which now had little on the other side to resist the soil pressure.  The most challenging part of this task was to move in a 800 ton crane with a 300
foot boom.  This monster arrived on 30 some trucks and took 2 days to fully assemble.  We utilized the giant box girder columns of the destroyed towers to build a bridge and footings for the crane.  The intent was to reach the stair tower of the north tower.  The crane has been working for the last few days and has led to the recovery of many victims.

In the coming weeks and perhaps months, we will be aiding in the recovery efforts. It is quite exhausting and at times dangerous, not to mention the fact that you end up inhaling large quantities of smoke and concrete dust (and who knows what else), but honestly, I can't imagine a better way to utilize what I've learned, so I am more than happy to help.  Thanks for giving me some of that knowledge.

I've enclosed a few photos...

Take care,
Tim

Timothy Schenck
Structural Engineer
HLW International, LLP
115 5th Avenue
New York, NY 10003
212.353.4600
212.353.4666 Fax