Current Issue

SHEAR BAND CONDITIONS REQUIRED TO DEVELOP THE EQUATION FOR THE ULTIMATE BEARING CAPACITY OF A STRIP FOUNDATION 

Tse-Shan Hsu

President, Institute of Mitigation for Earthquake Shear Banding Disasters

Professor, Feng-Chia University, Taiwan

Zong-Lin Wu, Yu-Chien Wu

Directors, Institute of Mitigation for Earthquake Shear Banding Disasters, Taiwan

Da-Jie Lin, Tsai-Fu Chuang

Associate Professors, Feng-Chia University, Taiwan

Yi-Min Huang

Assistant Professor, Feng-Chia University, Taiwan

Abstract

Evaluation of the ultimate bearing capacity of a strip foundation requires the incorporation of the shear bands. However, when the applied force reaches the ultimate load, the shear bands that should be induced from localizations of deformations do not appear when expected. In view of this, in this paper, the following four conclusions are drawn based on the characteristics of the solutions of the static equilibrium equation under stable and unstable conditions. (1) Using the plastic strain hardening model or the perfectly plastic model, the elastic-plastic solution is obtained under stable conditions, so shear bands cannot be induced and the structural symmetry is maintained. (2) Using the plastic strain softening model, the elastic-plastic solution is obtained under unstable conditions and with the prescribed displacements, so shear bands are induced and the structural symmetry is lost. (3) In the development of the traditional equation for the ultimate bearing capacity of a strip foundation, the perfectly plastic model, which cannot induce shear bands, is adopted when the incorporation of shear bands is required, so the ultimate bearing capacity that meets the needs of the actual situation cannot be obtained by applying the developed equation. (4) In the case of using the perfectly plastic model, when the foundation load reaches the ultimate load, the plastic strain zone expands in an unduly symmetric manner, and the estimated ultimate bearing capacity of the strip foundation is therefore unduly high. Based on the above four conclusions, it is suggested that future evaluation of the ultimate bearing capacity of strip foundations must adopt the plastic strain softening model. Only in this way will the evaluated ultimate bearing capacity of the strip foundation meet the safety requirements.

Keywords: strain softening, perfectly plastic, ultimate bearing capacity, foundation, stable conditions, unstable conditions, symmetry.

Attachments:

1243-Final.pdf

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