Respecting the design

In the January 2008 issue of Structural Engineer, James Bihr’s letter ["Perpetuating a misconception?" page 10] takes issue with a previous article in the magazine ["Reducing the risk" by Steven M. Baldridge, P.E., S.E.; Francis K. Humay, Ph.D., S.E; and S.K. Ghosh, Ph.D.; November 2007, page 24] that he says perpetuates the idea that the collapse of the World Trade Center Towers was a tragic act of violence as opposed to a result of structural shortcomings in their design. His claim is that the weakness of the design was that it utilized closely spaced exterior columns, essentially acting as a bearing wall, and that it essentially had no coherent structural frame and no redundancy. This, he feels, made it lacking in resistance to progressive collapse. He closes by describing the design as uncharacteristically weak for a major structure.

On the day it collapsed, I felt terrible for the unnamed engineer who designed it—Leslie Robertson as it later turned out. It is every structural engineer’s worst nightmare to have a failure or collapse in a building he or she designed, let alone a collapse of this magnitude played out on the stage of the entire world.

As I reflected on it and studied pictures that were subsequently published of the building during construction, during the attack and fire, during the collapse, and of the rubble, I came to have great respect for Mr. Robertson’s ingenious design. The waffle grid panels of columns and beams were massive steel box sections that most likely absorbed much of the impact of the jetliners, and in all likelihood prevented the planes from causing more extensive initial impact damage to the interior structure. Furthermore, the massive moment-frame grid formed by this structure on the facade most likely allowed the upper floors to span across the wide gash the planes cut across the better part of the faces of the buildings. The unique design of these buildings—particularly the perimeter structural grid—provided the ultimate redundancy that allowed these buildings to stand for a remarkably long time following an unprecedented impact, allowing an incredible number of people to evacuate.

We should all be grateful that the terrorists did not target more conventional buildings. I fear that had they hit more conventional buildings with more widely spaced columns, the collapse would have been nearly instantaneous and many more lives would have been lost. I suspect the initial damage to the interior would have been greater. Also, I suspect that a building with wider-spaced columns would have been unable to bridge over an impacted area with the magnitude of the impact at the WTC towers.

Greg Thein, P.E.
Strongsville, Ohio


Field experience required

Having started my career doing surveying and inspection for bridge construction prior to obtaining my engineering education, I find Richard G. Weingardt, P.E.’s comments in the December 2007 issue ["The need for adequate field experience," page 50] on the mark. One of the biggest efforts I have in training any new engineering intern is providing them with a clear understanding of the details of what they are designing, going from the metaphor of what they see on the computer screen to the metaphor of what the screen becomes in a set construction documents to the metaphor of shop drawings to the actual building itself. Thank you for pointing out what is becoming a larger and larger problem in our profession.

Robert W. Crossno, P.E.


I read Richard G. Weingardt, P.E.’s article about adequate field experience in the December 2007 issue with interest. I agree with both him and Ralph Peck. However, I believe that if I had stayed in college and obtained a doctorate degree in engineering, and perhaps a law degree, things would have been different. As a retired consulting civil engineer with both field and office experience, having written many articles, two books, and received a prestigious award for excellence in heavy construction engineering, I have learned that my 50 years of experience does not equate to having a Ph.D. behind your name.

During my college days, after being discharged from the Navy, I worked summers for U.S. Forest Roads, first as a slide rule artist for a topographic surveyor, as a chainman, a rod-man, an instrument person, and then as a party chief for P-lines for new forest roads. After graduation, I went to Alaska for U.S. Public Works and lived in tents for two seasons while doing a survey for paving several highways and later for slope-staking and laying out bridges for construction of a new Seward-Anchorage highway.

Upon dissatisfaction with government work, I found employment with a small structural engineering firm in Oakland, Calif., where I learned the skills of a draftsman. After a year’s time I could turn out a drawing a day of trusses for industrial buildings. Impatient for more demanding work, I hired out at International Engineering Company in San Francisco where I did design work on dams, was sent to Guatemala to do field engineering for construction of a seaport, and on to Great Salt Lake to head up site investigations for a railroad crossing. After being passed over as project engineer, I hired out to J.H. Pomeroy Co., in Los Angeles as chief civil engineer. Pomeroy had design and build work in Kuwait, Iran, Afghanistan, Singapore, and Chile in addition to the United States. We were required to go to the job site after completing the design and make things work.

After tiring of traveling, I jumped the train, found some office space, and began doing what I enjoyed most, consulting to others for design and construction, mostly marine works. I had 20 years of experience, was registered, could survey, do design work and drafting, specify materials and equipment, perform estimating, write reports, as well as supervise. I specialized in the installation of submarine pipelines, cofferdams, and falsework for bridges and piers. I did not hire any outside help and continued on successfully for 30 years as H.V. Anderson, Engineer.

Engineering of this sort is long gone. Work was like taking an examination every day and passing it with a 100-percent grade. You had to know what you were doing, and my only hope is that this generation of engineers finds the degree of satisfaction in their work that I did … field experience can be a great asset in furthering one’s career, especially if you do not have a Ph.D.

Harold V. Anderson
Novato, Calif.