Submitted on: 15 April 1998.
Revised on: 26 April 1998.
Accepted on: 16 May 1998.
STRUCTURAL ENGINEERING AND MECHANICS
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Submitted on: 26 May 2008.
Revised on: 25 June 2008.
Accepted on: 14 July 2008.
STRUCTURAL ENGINEERING AND MECHANICS
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http://reply.papertrans.cn/3/288/28768/28768-35.png
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