Estimating Maximum Rotation of Beam of R.C. Moment‐resisting Frames Using Equivalent Pulses of Near-fault Motions

Abstract

Seismic events all over the world have shown that ground motions in vicinity of causative faults (within a distance of 15 km from the fault) may be categorized as large-velocity pulse and large-displacement fault which have the potential to cause considerable structural damage. Consequently, the main cause of long-period pulse formation is the cumulative effect of shear wave propagation along the fault rupture according to seismological investigations. Near-fault ground motions are severely affected by fault mechanism, rupture propagating direction relative to site and finally the permanent deformation of ground these parameters will cause two significant effects called directivity and fling step which should be taken into account in estimating the ground motions in vicinity of causative faults. The forward-directivity depends on rupture mechanism and slip direction relative to the site and is characterized by a large pulse occurring at the initiation of the record and oriented in a perpendicular direction relative to the fault plane but in contrast, the fling-step is affected by tectonic deformation in the fault and commonly generates permanent static displacement which happens parallel to the strike of the fault for strike-slip events, and normal-to-fault direction for dip-slip earthquakes. Because of the unique characteristics of the near-fault ground motions and their potential to cause severe damage to structures designed to comply with the criteria mostly based on far-field earthquakes, it is necessary to characterize and parameterize these special types of ground motions by simple and reliable mathematical models having input parameters which have clear physical meaning and scale to the earthquake magnitude. One of the newest models is the one proposed by Hoseini Vaez (Hoseini Vaez & el, 2013). The main objective of this study is to investigate capable of predicting the response of MDOF systems by model proposed by Hoseini Vaez. Generic frame models with 3 different heights and three levels of design ductility have been used to evaluate their response to 11 actual near-fault ground motions and the corresponding pulses calibrated to them. It has been found that the equivalent mathematical model being evaluated in this work is capable of estimating, fairly accurately, the height-wise distribution of inter-story drifts and maximum rotation of beams for the regular plane moment resisting frames used in this work.

Keywords

• near-fault ground motions
• simplified equivalent pulses
• forward directivity
• elastic and inelastic response