مهندسی عمران شریف (Mar 1396)
POUNDING RESPONSE OF THREE ADJACENT BUILDINGS UNDER NEAR-FAULT STRONG GROUND MOTION AND ITS EFFECT ON SEISMIC BEHAVIOR OF INTERIOR AND EXTERIOR BUILDINGS
Abstract
In this investigation, a simple model of building in series, including 3-, 2-, and 3-story adjacent buildings, excited by the horizontal and vertical components of fault-normal pulse and fault-parallel displacement with different magnitudes and time lags, is considered. Each story of the buildings consists of a rigid beam connected to two axially rigid mass-less columns by nonlinear rotational springs and linear rotational dashpots. To determine the pounding force, the non-linear viscoelastic model was chosen. The ground motion was described by fault-normal pulse and fault-parallel permanent displacement, and their amplitudes and duration were selected consistent with the variables that described near-fault motions. An important physical characteristic of the selected pulse and displacement is large initial velocity associated with onset of these motions, and it is proportional to the stress drop on the fault. It is assumed that the buildings are near the fault, and that the longitudinal axis of the buildings (x-axis) coincides with the radial direction (r-axis) of the propagation of waves from the earthquake source, so the absolute displacements of the bases of columns are different due to the wave passage. The system of equations of motion was solved by the fourth-order Runge-Kutta method due to its self-starting feature and the long-range stability. For the considered model, the results indicate: (1) impact force can lead to increasing the maximum storey shear force. This amplification can be seen predominantly in exterior or end buildings which experience one-sided impacts, compared with interior building which experiences two-sided impacts; (2) by increasing initial gap size, the maximum impact force will not decrease necessarily. Depending on the period of buildings, initial gap size, and material nonlinearity, the maximum impact force can occur between the left and middle buildings or between the middle and right buildings; (3) for linear material under fault-normal pulse with magnitudes 5, 6, and 7, the expected maximum impact force and the minimum distance required to avoid pounding would be equal to 10, 58, 100 MN, and 10, 30, 50 cm, respectively; (4) for nonlinear material, the corresponding values would be equal to 10, 40, 45 MN, and 10, 20, 30 cm, respectively.
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