Advances in model making and testing, which should revolutionize the technique of bridge building and the construction of arch-containing structures, are now in the Engineering School. The work is done chiefly by graduate students and research fellows, among whom L. H. Johnson and D. E. Stearns are prominent, and is under the direction of Albert Haertlein, associate professor of Civil Engineering.

The work of constructing the models out of celluloid strips is facilitated by an invention of Professor George Beggs of Princeton. When the models of arches, frameworks, etc., are completed from carefully cut celluloid units they are subjected in certain parts to strains and vibrations which produce motions in other parts.

"Show Effects of Bridge Traffic"

"These resultant motions", says Professor Haertlein, "are carefully measured, and show, for example, how much one end of a steel bridge will move when traffic is rumbling over the other extremity, thus giving the engineers an idea of the strength and practicability of the contemplated structure.

"Such an apparatus, which can be carried around in convenient sets, will often be the deciding factor in the choice of one kind of structure instead of another, as the strength of the arch or framework in proportion to its weight can be found out by constructing such models," he continued.

Great Improvement

Previous to this the making of models for a bridge or skyscraper had to wait until the plans were completed, and was in itself a long and laborious process. Such a model was not easily tested for stresses and strains. The researchers have compared results of the model tests with the results of theoretical calculations and so far have found them to compare favorably.