Horizontal impact loads on vertical structures In my opinion, vertical exterior columns become beams when subjected to horizontal impact loads (e.g. airliners). If the columns are supported horizontally by weak structural systems such as structural joists, they will fail miserably as vertical beams, thus allowing the source of the horizontal load to penetrate the outer structural perimeter.

Rather than dealing with protection against the penetrated interior of the building, we need to concentrate on preventing significant penetration. This can only be accomplished by providing significant structural horizontal supports of heavy reinforced concrete or structural steel. Thus, we can limit the penetration to a maximum height of one floor, or approximately 10 to 12 feet. In this manner we can protect high-rise buildings from the penetration of horizontal loads such as generated by large airplanes.

Lawrence Fischer, P.E.
Orlando, Fla.

Three cheers for the PDH Series! Huge kudos to Structural Engineer for starting a no cost Professional Development Series.What a great way for organizations like [the Portland Cement Association] to keep engineers up to date with current codes and product information.

Your magazine is providing a great service both to busy professionals and trade associations. I hope to see many more of these in future issues.

Lori Brown, P.E., S.E.
Brier, Wash.

This Professional Development Series is something that has been needed and (in my humble opinion) is well received.

Keep up the good work. Thanks.

George Harper Weaver, Jr., P.E.
via e-mail

I just found the Professional Development Series in Structural Engineer magazine and feel that it is a good way to learn for my P.E. renewal.

Thanks for your help.

John Li
via e-mail

Positive PR needed

The reinforced concrete mat under Chicago’s new Trump Tower skyscraper was described in a recent Chicago Tribune article. Reference was made to the architects but nowhere in the two page article is the structural engineer mentioned—the one who designed this tall building! I do not fault the reporter for this omission, but the blame belongs to us—structural engineers—for not informing and educating the public better of what we are doing. We need better public relations to tell people that these big buildings could not be built without us, the structural engineers.

George A. Kennedy
Chicago, Ill.