Experimental study of isolated building under triaxial ground excitations

Unilateral, bilateral, and triaxial shaking table tests are conducted to study the seismic response of a three-story base-isolated steel structure. The lateral force distribution formulas specified in the Uniform Building Code are evaluated experimentally. A method to calculate the lateral force distribution is proposed and experimentally verified. Seismic responses of the test model to the unilateral, bilateral, and triaxial ground excitations are compared. The effects of vertical ground acceleration on the maximum acceleration of the superstructure and the maximum displacement of the isolation system are investigated. The maximum displacements of the isolation system under bilateral and triaxial ground motions are compared with those determined from the 1.0 + 0.3 direction combination rule. In addition to the plan-symmetric condition, both one-way and two-way eccentricities are introduced into the isolation system. The increase of the peak story acceleration may be significant, compared with those obtained from unilateral and bilateral ground shakings. The experimental results from the plan-eccentric condition also are compared with the conclusions of other analytical studies.