Page:Popular Science Monthly Volume 88.djvu/673

 Rocking a Three-Hundred Foot Masonry Tower with Your Hand

BY the mere pressure of your hand you can rock "Sather Campanile" — the three-hundred-and-two- foot memorial tower just completed on the campus of the University of California.

In order to minimize the danger from earthquake shocks, the architect, Professor John Galen Howard, and the engineer. Professor Charles Derlith, Jr., so built the strong steel frame of the Campanile that cross-bracing is elimi- nated at alternate stories. As a result the vibration of the tower is like that of a steel rod one end of which is thrust in the ground. In an earthquake the tower would vibrate like a tree.

According to Professor Elmer E. Hall's tests, the tower has a vibration period of i .13 seconds. By pressing against the steel frame at the top of the Campanile every 1.13 seconds he -as able to rock the tower, so that earthquake recorders (seismographs they are called) registered the vibrations. However, the amount of motion was less than the thickness of this sheet of paper.

The plan on which the tower was built is to prevent a re- enforcement of the rocking caused by an earthquake vibra- tion. For instance, a child can set a hammock swinging violently simply by pushing at the right moment, no mat- ter how hea\^- the load may be. If the pushes are not timed correctly, the swinging is retarded. It is the same with the Campanile. The plan is to prevent cumulative swaying, such as would occur if the period of the earthquake and the vibra- tion of the tower were the same, and such as would cause the structure tocollapse. Mrs. Jane K. Sather erected the memorial to her hus band

���The pressure of your hand will swing the bell-tower at Berkeley, Calif., which in height is second only to Wash- ington Monument. It was erected, as a memorial, by Mrs. Jane K. Sather at cost of two hundred and twenty-five thousand dollars

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