NOTE: This article is meant for the informational purposes to the design community and friends of Leslie Robertson. It is not to be published, reproduced, or quoted publicly without the expressed written consent of both Mr. Leslie Robertson, LERA Consultants, and Mr. Christopher M. Hewitt, Penn State University.
Les Robertson Speaks at the National Council of Structural Engineers Association Conference. A student’s perspective.
By: Christopher M. Hewitt
On October 5th, Leslie Robertson, the designer of the World Trade Center, spoke to a group of professionals from across the country and two students from Penn State University, about the design, construction, and collapse of the World Trade Center. Although his presentation did not add much as a source of debate for members of the profession, it is the first time that Mr. Robertson has spoken publicly about the incident since the buildings’ untimely demise.
When the tragic event occurred, Mr. Robertson was at dinner with some friends in Hong Kong. He received word via telephone that a plane had struck his building. Mr. Robertson expressed that at that time he was not overly concerned, figuring that a news helicopter had flown too close and struck the building. He called back to New York to find that the damage was far worse than he had hoped. While on the phone with people at his firm, the second plane struck the building. Immediately, he tried to return to New York, but planes were grounded and he was stranded in Japan. He was finally able to make it back to New York late Saturday night/Sunday morning.
In addition to not being able to sleep, Mr. Robertson has been hounded by the press since the event, having even been called at 2AM for an interview, which he sidestepped the next morning. The presentation appeared to be extremely difficult for him. Several times he stopped in the middle of his sentences, having been overcome with a surge of emotion that could only result in an outpouring of tears should he continue. Struggling with the use of the past tense intertwined with the present, he spoke about the buildings’ original design and construction.
As the trademark building of his career, the World Trade Center was Mr. Robertson’s first building over 20 stories in height. The design was started some 40 years ago. According to Mr. Robertson, it was the first building designed to withstand the load of an airplane crashing into it – a Boeing 707, the largest plane of the time. The construction maintained natural redundancy with the inclusion of an outrigger system combined with closely spaced perimeter columns – a design that came as a result of the Architect’s fear of heights. It was thought that the columns should form the mullions for the windows and should be placed at a spacing such that a person could put one hand on each column to support himself from falling out. The initial bombing a few years ago took out 2/3 of the columns on one side of the building without causing a major collapse of the structure.
The exterior column and skin splices occurred at every third level, adding yet another level of redundancy to the structure. The light and airy building was incredibly sound.
One of the major issues of concern during the design was that this building did not include the masonry infill that had been included in the skyscrapers of the past. Although thought on paper not to contribute much to the overall stiffness of a building, comparative analysis of the as-built stiffness of this and other skeletal buildings was substantially less than the masonry-infill predecessors. Regardless, the World Trade Center performed beautifully during its life.
At one point during the presentation Mr. Robertson was asked, “What he would have done differently.” His simple answer was the only possible reply: “I wish that I could have made it stand up a little bit longer.” Stunned at the thought of this tragedy and the impact that it had made on a man whom every person in the room accepted as a mentor and a master of the profession, all voices stood silent in awe. I can only infer that they were stunned as I was at the unavoidable thought: that could have been me.
Shortly after, Mr. Robertson was applauded by this group of professionals for the successful performance of the building’s structure beyond that which would be reasonably expected for the day. The design and demise of the World Trade Center has made all of us realize that even the strongest are not infallible. This attack on our country has effected every profession in the same way. The indestructible has been destructed and terror, in many forms, has swept across the country. The solution? In torment to us as engineers, I find that there isn’t one. Looking solely at one profession, the number of equations doesn’t match the number of variables and no sort of fumbling on the part of the design world will arrive at a correct solution. From time to time even the strongest among us succumb to forces that we cannot control. Steel is steel. Concrete is concrete. The raw materials cannot withstand forces beyond their strength. Even in a design constructed of sold titanium, some force of terror will be able to strike its wrath against it. The only solution seems to be to eradicate the force of terror.
In this profession, we can applaud those whose achievements represent the best that can be predicted in an unpredictable world. That is what this conference was to me. A man whom I consider a mentor confronted and defended his creation to those who would understand him. His critique was met with reverence, acceptance and applause.