Jacobsen’s Pioneering Research

1. “Dynamic Behavior of Models of Timber Walls,” Lydik S. Jacobsen. This research was on the relative merits of diagonal and horizontal sheathing under dynamic loading. Wall panels nine feet square made of 2 x 4 studs with 1 x 6 sheathing were placed upright on the shaking table, guyed, loaded to simulate building conditions, and force vibrated.

2. “Motion of Soil Subjected to a Simple Harmonic Ground Motion,” Lydick S. Jacobsen. This research started in 1928 and consisted of a wooden box 2.5 x 3.5 x 16 feet secured to the shaking table. The unbalanced flywheel was used to drive the table. Soil tests were made with a Monterey sand with varying moisture content, length of the box, depth of sand, and frequency and amplitude of motion.

3. “Water Pressure in a Tank Caused by a Simulated Earthquake,” Leander M. Hoskins and Lydik S. Jacobsen. Here a tank 8 feet long by 1.5 by 2 feet, used alternatively with two equal compartments or one compartment, was placed on rollers on top of the shaking table. The tank was connected to the table and one end through a dynamometer with stiffness of either 10,500 lb/inch, 6400 lb/inch, or 2200 lb/inch. Water depths tested were 6, 9, 12, 15, and 18 inches. The shaking table periods used were nominal ¼, ½,  and 1 second. The pendulum bumper was used to excite vibration. This work, done mainly in 1932, had its recordings done by various means including motion pictures of the open ended glass stand pipes with colored water.

4. “Dynamic Shear Model of a 17-Story Building Tower,” Lydik S. Jacobsen. Professor Jacobsen in 1930 and 1931 constructed and tested a dynamic model of a proposed 17-story building. This model was a mechanical one with springs for the stiffness of the columns and walls and steel plates for the lumped masses of each floor. This model had no vertical freedom and represented a shear-type distortion wherein the floors remained level. Experiments were conducted for both a conventional first story and one having considerable flexibility—the “flexible first story” concept. The model was placed on the shaking table and it was then either force vibrated, subjected to free vibration following a pendulum impact, or given a chaotic motion. Motion pictures recorded the research. Nothing was published regarding this ground-breaking research.

5. “Dynamic Model of the Alexander Building, San Francisco,” Lydik S. Jacobsen, John A. Blume, and Harry L. Hesselmeyer. This dynamic model was based upon data derived by reconciling the computed natural periods of vibration of an existing 15-story building with the measured natural periods. “The Reconciliation of the Computed and Observed Period of Vibration of a 15-Story Building” by John A. Blume and Harry L. Hesselmeyer, June 1934, was one report generated as part of this work. This building had a significant amount of flexural freedom as well as some foundation freedom so the model was constructed accordingly. This meant the design of a mechanical model with 5 or 6 degrees of freedom per story. Five degrees of freedom was decided upon and these were obtained with horizontal coiled springs for horizontal story translation and twist, and vertical “springs” consisting of calibrated thin gauge plates spanning aluminum cylinders and supporting each floor above on ball bearings riding on plates. These bearings permitted biaxial horizontal translational motion. Vertical translation at the center of the mass was prevented by cantilever supporting arms. The model was designed by Jacobsen and Blume and built by Blume. Dr. Blume later explained, “Our problem involved the solution of fifteen simultaneous equations, one for each story of the building, over and over and over again with different constants. By trial and error, which today we’d call iteration, we were closing in on the true parameters of the structure. In other words, we were developing its characteristics—stiffness, vibration modes, and how the various materials—the steel frame, the concrete fireproofing, the brick masonry walls—how these things all work together to form a dynamic unit. This type of work had never been done before in all the history of earthquake engineering.” After much testing and modifi cation of recording devices assisted by two graduate students, E. P. Hollis and R. S. Ayre, the shaking table tests were completed in March 1937 with publication of “Experimentally Determined Dynamic Shears in a 16-Story model” by Jacobsen and Ayre in the bulletin of the Seismological Society of America.

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