两种不同环境下预应力混凝土梁疲劳破坏试验对比分析

Comparative Test Analysis of Fatigue Failure of Prestressed Concrete( PC) Beam in Two Different Environments

以我国目前普通铁路既有线上32 m跨度全预应力混凝土简支T梁为工程背景,通过12片1/6预应力混凝土模型梁非腐蚀环境和腐蚀环境下疲劳试验,对预应力混凝土梁疲劳破坏形态进行研究,对其破坏机理进行分析,结果表明非腐蚀环境下,恒、活载跨中弯矩在0.45Mu时为配筋合适的预应力混凝土梁疲劳破坏时的临界荷载点(Mu为跨中静载极限弯矩,临界点以疲劳寿命为200万次进行定义),超过该临界点后,需要适时加固;腐蚀环境下,梁底普通钢筋锈蚀后(预应力筋不锈蚀),疲劳损伤程度随锈蚀率增大而增大,锈蚀率越大疲劳寿命越短;锈蚀率7%为腐蚀疲劳破坏的临界点(临界点以疲劳寿命为200万次进行定义),超过腐蚀临界点以后,需要对预应力混凝土梁进行加固。两种不同环境下预应力混凝土梁疲劳破坏试验对比分析结果表明,预应力混凝土梁中非预应力筋虽然对静载承载力贡献不大,但是对疲劳抗裂作用明显,设计中应保证非预应力钢筋配置充足,包括充足的细密的箍筋、侧面纵向补充钢筋和梁底纵向抗裂钢筋、锚下螺旋钢筋等非预应力筋,以便分散裂缝宽度,提高疲劳破坏时的延性。

With reference to the engineering practices of 32m-span PC simply supported T-type beams on the existing lines and the test of a total of 12 1/6-scale PC model beams under non-corrosion and corrosion environments, an analysis of fatigue pattern and mechanism of PC beams is conducted. The results show that the mid-span moment 0.45Mu （ Mu is the limit bending moment） under the dead and live loads is the critical loading point of fatigue failure of PC beams with proper mixed-reinforcement （the critical loading point of fatigue failure is defined by the fatigue life of two million cycles ） under non- corrosion environment. Beyond the critical point, 0.45Mu, the fatigue reinforcement of beam should be properly provided. As to PC beams with corroded steel bars （the prestressed tendons are not no corrosive） , the fatigue damage becomes heavier and the fatigue life shorter with the increase of corrosion rate. And the corrosion rate 7% is the corrosion fatigue critical point （the point is defined by the fatigue life of two million cycles） and the beam should be strengthened if the corrosion rate of steel bars is over 7%. The results also indicate that although the non-presstressed steel bars may contribute little to the static load carrying capacity of PC beam, they have an obvious effect on the fatigue cracking. Thus, it shall be addressed that there shall be sufficient non-prstressed steel bars while designed, including stirrups, longitudinal reinforcement and anchor spiral reinforcement to disperse the crack width and improve the ductility in case of fatigue failure.