预应力混凝土枕螺栓孔区纵向裂纹计算分析

Calculation and Analyses of Longitudinal Crack from Bolt-Hole Area of PC Sleeper

预留螺栓孔区纵裂是铁路预应力混凝土枕伤损的主要形式 ,使用中的轨枕发生纵裂的概率几乎是 10 0 % ,这大大缩短了轨枕的使用寿命 ,危及行车安全 .应用弹性力学理论进行了力学计算分析 ,揭示出纵裂产生的根本原因在于预压应力等产生的孔区局部拉应力过大 ,其值远远大于混凝土的抗拉强度 ,所以 ,轨枕未出厂往往就已出现微裂纹 .轨枕上道后 ,在预压应力和上拔力共同作用下 ,螺栓孔区应力分布更加不均匀 ,拉应力的数值增大 ,使纵裂更加严重 .因此 ,螺栓孔纵裂是必然的 .

Longitudinal cracks in the bolt-hole area of PC sleeper which greatly shorten its service life are the dominant failure on railway lines in China. According to considerable surveying of railway lines, cracks occur in almost all servicing sleepers and seriously endanger driving security of railway vehicles. The theory of elastic mechanics is used in calculating and analyzing crack problems. So the fundamental reason for the longitudinal cracks is explored. Furthermore, Through calculating and analyzing, some primary conclusions are drawn out.The fundamental reason leadng to longitudinal cracks is excessive local pulling stresses in the bolt-hole area, which are induced by pre-stress, are greater than the pulling strength of the concrete itself of PC sleeper, and therefore, micro-cracks have already occurred while it is still in factory without ever having been used. This fact is proved true by surveying the PC sleepers with instruments in factories. The pulling stresses increase more when PC sleepers are working on the railway lines, because at this time the pre-stress and upward pulling forces are working together. As a result it makes the crack problem more serious. Therefore, the cracks occur to almost all servicing sleepers. This fact is also proved true by surveying the PC sleepers on railway lines.