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THE MAJOR CAUSE OF BRIDGE COLLAPSES ACROSS ROCK RIVERBEDS: SHEAR BANDING
THE MAJOR CAUSE OF BRIDGE COLLAPSES ACROSS ROCK RIVERBEDS: SHEAR BANDING
Tse-Shan Hsu
Professor, Department of Civil Engineering, Feng-Chia University
President, Institute of Mitigation for Earthquake Shear Banding Disasters
Taiwan, R.O.C.
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Po Yen Chuang
Ph.D Program in Civil and Hydraulic Engineering
Feng-Chia University, Taiwan, R.O.C.
Kuan-Tang Shen
Secretary-General, Institute of Mitigation for Earthquake Shear Banding Disasters
Taiwan, R.O.C.
Fu-Kuo Huang
Associate Professor, Department of Water Resources and Environmental Engineering Tamkang University, Taiwan,R.O.C.
Abstract
Current performance design codes require that bridges be designed that they will not collapse within their design life. However, in the past twenty five years, a large number of bridges have collapsed in Taiwan, with their actual service life far shorter than their design life. This study explores the major cause of the collapse of many these bridges. The results of the study reveal the following. (1) Because riverbeds can be divided into high shear strength rock riverbeds and low shear strength soil riverbeds, the main cause of bridge collapse on a high shear strength rock riverbed is the shear band effect inducing local brittle fracture of the rock, and the main cause on a low shear strength soil riverbed is scouring, but current bridge design specifications only fortify against the scouring of low shear strength soil riverbeds. (2) Since Taiwan is mountainous, most of the collapsed bridges cross high shear strength rock riverbeds in mountainous areas and, therefore, the major cause of collapse of bridges in Taiwan is that their design does not consider the shear band effect. (3) Because shear banding will induce local deep grooving of the high shear strength rock riverbed, foundations embedded in the shear band will induce the softening of the overall bridge stiffness during continuous exposure, and subsequently collapse after complete exposure. Therefore, it is suggested that the bridge design code must account for the shear band effect to ensure the stability of bridges crossing low shear strength rock riverbeds.
Keywords: bridges, collapse, scouring, soil riverbed, shear banding, rock riverbed
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