锚下控制应力对PC小箱梁裂缝发展的影响及控制方法研究

Study on Influence of Control Stress under Anchor on Crack Propagation of PC Small Box Girder and Control Method

锚下控制应力变化引起的PC小箱梁裂缝的产生及发展贯穿于PC小箱梁的施工及运营阶段,这大大制约了PC小箱梁的正常承载能力及安全性能。为改变这一局面,通过综合采用现场试验测试和数值分析的方法,对锚下控制应力引起的PC小箱梁裂缝产生及发展的成因机理及控制方法开展了研究。通过对施工张拉阶段锚下控制应力变化情况进行监测,分析了完全张拉、超张拉及张拉结束后等不同阶段PC小箱梁锚下控制应力的变化规律。采用数值模拟的方法,综合考虑PC小箱梁的成桥状态以及单梁状态,其中单梁同时考虑竖向温度梯度可能对结构产生的影响,分析了不同阶段锚下控制应力变化下PC小箱梁竖向位移、应力与裂缝产生的内在联系。将数值分析结果与现场实测数据进行了对比。从而分别从设计、施工及运营等方面对PC小箱梁桥开裂的主要成因进行了探讨。结果表明:PC小箱梁在施工阶段,预应力损失及超张拉等因素会对箱梁开裂产生一定程度的影响;根据分析结果针对性提出的PC小箱梁裂缝控制措施,可减少预应力损失以及超张拉等因素可能产生的影响,从而提升其预应力施工及运营质量控制水平。这都将进一步减少锚下控制应力变化对PC小箱梁结构安全性的影响,从而整体提升PC小箱梁裂缝控制水平。

The generation and propagation of cracks in PC small box girder caused by the change of control stress under anchor run through the construction and operation stage of PC small box girder,which greatly restricts the normal bearing capacity and safety performance of PC small box girder.In order to change this situation,by comprehensive use of field test and numerical analysis,the mechanism and control method of crack generation and propagation of PC small box girder caused by control stress under anchor are studied.By monitoring the control stress changing under anchor in the construction tensioning stage,the change rules of the control stress under the anchor of PC small box girder in different stages such as full tension,over tension and after tension are analyzed.By using numerical simulation method and comprehensively considering the bridge completion state and the single girder state of PC small box girder(also considering the influence of vertical temperature gradient on the structure for single girder),the internal relationship among the vertical displacement,stress and crack of PC small box girder under the control stress change under the anchor at different stages is analyzed.The numerical analysis result is compared with the field measured data,and the main cause of cracking of PC small box girder bridge is discussed from the aspects of design,construction and operation.The result shows that(1) the prestress loss and over tension will have some influence on the cracking of PC small box girder during the construction stage;(2) according to the analysis result,the crack control measures for PC small box girder can reduce the possible influence of prestress loss and overstretching,so as to improve the quality control level of prestressed construction and operation.All of these will further reduce the influence of the change of control stress under anchor on the structural safety of PC small box girder,so as to improve the crack control level of PC small box girder as a whole.