On the Seismic Response of Protected and Unprotected Middle-Rise Steel Frames in Far-Field and Near-Field Areas

Dora Foti

doi:10.1155/2014/393870

Abstract

Several steel moment-resisting framed buildings were seriously damaged during Northridge (1994); Kobe (1995); Kocaeli, Turkey (1999), earthquakes. Indeed, for all these cases, the earthquake source was located under the urban area and most victims were in near-field areas. In fact near-field ground motions show velocity and displacement peaks higher than far-field ones. Therefore, the importance of considering near-field ground motion effects in the seismic design of structures is clear. This study analyzes the seismic response of five-story steel moment-resisting frames subjected to Loma Prieta (1989) earthquake—Gilroy (far-field) register and Santa Cruz (near-field) register. The design of the frames verifies all the resistance and stability Eurocodes’ requirements and the first mode has been determined from previous shaking-table tests. In the frames two diagonal braces are installed in different positions. Therefore, ten cases with different periods are considered. Also, friction dampers are installed in substitution of the braces. The behaviour of the braced models under the far-field and the near-field records is analysed. The responses of the aforementioned frames equipped with friction dampers and subjected to the same ground motions are discussed. The maximum response of the examined model structures with and without passive dampers is analysed in terms of damage indices, acceleration amplification, base shear, and interstory drifts.

Highlights

Recent destructive earthquakes in Northridge (1994); Kobe (1995); Kocaeli, Turkey (1999); and Chi-Chi, Taiwan (1999) caused great impact on society due to the relevant number of collapsed buildings and victims
It must be noticed that if the station is located toward the direction of the fault rupture, the near-field ground motions are quite different from the usual far-field ones
In the present study the seismic response of five-story steel moment-resisting frames subjected to Loma Prieta (1989) earthquake, a far-field register and a near-field register, is analysed

Summary

Introduction

Recent destructive earthquakes in Northridge (1994); Kobe (1995); Kocaeli, Turkey (1999); and Chi-Chi, Taiwan (1999) caused great impact on society due to the relevant number of collapsed buildings and victims. To significantly reduce the maximum ductility demand and to avoid the failure, the strength of the upper portion of slender frames must be increased (keeping the column cross section constant along the total height of the structure) This new aspect has been emphasised in the response of frames equipped with friction dampers [14]. The passive damping systems can reduce significantly the response of the moment-resisting frame structures under near-field motions, they cannot by themselves prevent the collapse Anyway, these systems could be a solution to avoid story mechanism. In the present study the seismic response of five-story steel moment-resisting frames subjected to Loma Prieta (1989) earthquake, a far-field register and a near-field register, is analysed. The maximum response of the examined model structures with and without passive dampers is discussed in terms of damage indices, acceleration amplification, base shear, and interstory drifts

Description of the Frames

Ground Motions

Results

Conclusions