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Investigation of the Seismic Response of a Lightly-Damped Torsionally-Coupled Building.
Boroschek, R. L.; Mahin, S. A.
National Science Foundation, Washington, DC., December 1991, 277 p.
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The earthquake behavior of lightly-damped, torsionally-coupled moment resisting steel space frames is investigated by analyzing the recorded three-dimensional response of a regular thirteen story steel frame building located in California, and by performing several elastic and inelastic computer analyses of this and similar structures. Of several earthquakes recorded in the case study building, three are considered in the report: the 1984 Morgan Hill, the 1986 Mt. Lewis and the 1989 Loma Prieta events. During these events the building responded severely, though no structural damage was observed. The recorded responses of the structure were unusual; characterized by long duration, narrow banded periodic motions, with strong amplitude modulation; by large displacements and torsional motions; by large amplification of the input ground motions; and by slow decay of the building's dynamic responses. The investigation concludes that lightly-damped regular space frame structures like the one studied are highly susceptible to strong lateral-torsional and modal coupling because of the closeness of their predominant periods and the possible severe effects of small accidental eccentricities. It is shown that even small input motions can produce large responses, if the predominant periods of the structure match those of the site. These various effects together with the large flexibility often found in steel moment resisting frames can create structures that exhibit unusually severe seismic responses.
; Earthquake damage; Dynamic response; Buildings; Steel structures; Earthquake engineering; Case studies; Loads (Forces); Structural vibration; Joints (Junctions); Vibration damping; Torsion; Seismic effects; Structural members; Displacement; Elastic analysis; California; Mathematical models; Structural analysis; Framed structures; Nonlinear systems