中文摘要：

在迄今所修建的混凝土箱梁桥中，不论是其施工阶段或运营阶段。箱梁上均存在较为普遍的开裂现象，造成这一现象的原因之一可能是现有箱梁温度应力的计算方法一般沿用的是工字型截面梁的计算方法，即没有考虑箱梁顶板的横向变形所导致的影响。本文基于“等效荷载法”采用能量变分法原理对等截面矩形箱梁的温度应力进行了详细的分析和理论推导，并编制了相关计算程序，其算例分析结果与ANSYS计算结果吻合较好，表明了本文方法的正确性。同时分析结果表明，箱梁在梯度温度作用下，按常规方法计算出的纵向拉应力要小于采用本文方法的计算结果，两者相差最大可达28．2％，且在顶板下缘其横向拉应力与纵向拉应力相当，因此在设计中不考虑其横向效应是偏于不安全的，应予以充分重视。

英文摘要：

The advantage of s bridges under of box girder. application of concrete box girder for long-span bridge has tructure behavior. However the cracks in the deck still exi thermal action at construction or service stage due to the ig Based on energy-variatlonal principle and the compensati increased at present due to the st in many prestressed concrete no on rance of the transverse effect method, a detailed thermal stress analysis of the simply supported and cantilever box girder with constant depth is conducted and the calculation formula for thermal stress is derived in this paper. Then a computer code developed by the authors is employed to calculate the thermal stress of box girder. The results agree well with the resuits obtained from the commercial finite element software ANSYS, which indicate that the proposed method and the computer code are accurate and reliable. The results also indicate： the longitudinal tensil stress calculated by the traditional method is 28. 2M less than that calculated by the proposed method and the transverse effect of box girder under thermal action should not be ignored. And some other conclusions are obtained which provide design consults for box girder determined under thermal action.