关键词: 横隔板, 箱梁, 顶板, 刚度, 泊松效应

Abstract: Generally a diaphragm is set between the rof of the pier and the mid-span in order to enhance the rigidity refers to the bend-resistance of the box-beam structure in the same direction with the bridge and the twist-resistance cross wise．However，near the diaphragm section，the diference of strength function is obvious comparing to the convention section，which is usually be ignored during the design process．Taking the rof-board crack near the pier of a bridge for example，the diaphragm 's influences on the mechanics function of the roof-board are analyzed specifically．The results show that the strength situation is obviously different between the rof-board around the diaphragm and those section far away from it．

Key words: diaphragm , box·beam, robboard, rigidity, Poisson effect