短語詞組短語bottom m chord 底弦bottom m chord stress 下弦桿應(yīng)力bottom oblique chord 下斜弦梁side frame bottom oblique chord 側(cè)架下斜弦桿bottom chord stress 下弦桿應(yīng)力top -bottom chord 上下弦桿curved bottom chord 曲線形下弦桿bottom chord bar 下弦桿side frame bottom chord 側(cè)架下弦桿 返回 bottom chord