by A.F. Shakal and M.J. Huang
Shakal, A.F. and M.J. Huang (1986). Torsional Response of Three Instrumented Buildings During the 1984 Morgan Hill Earthquake. Proceedings of the Third U.S. National Conference on Earthquake Engineering, Volume 3, August 24-48, 1986, Charleston, South Carolina, p.1,639-1,650.
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Torsional motion was derived from the strong-motion records obtained at three high-rise buildings in San Jose shaken during the Morgan Hill earthquake of April 24, 1984. The buildings include a moment-resistant steel-frame building and two reinforced concrete buildings, all 10-13 stories in height, The steel frame building exhibited clear torsional motion, with approximately 25% of the displacement at the exterior walls at the roof level being due to torsion. One of the reinforced concrete buildings exhibited torsional motion of approximately the same percentage of lateral displacement as the steel frame building, the second exhibited much less, For the two buildings exhibiting torsional response, the torsional motion at the upper floors of the structure was significantly greater than that at, the base. The amplification ratio, roof to base, was greater than a factor of five for both buildings. Thus, the torsional motion is not simply due to compliance of the building with a torsional component of the incoming wave field, but rather represents a torsional response of the building to lateral motion at the base.