考虑剪力滞效应的Π型梁预应力张拉顺序研究

Study on Prestress Tensioning Sequence ofΠ-shaped Beam Considering Shear Lag Effect

Π型梁在按照常规预应力张拉顺序进行张拉时会因剪力滞效应突出而发生结构破坏,为避免该情况发生,从控制剪力滞效应的角度出发对Π型梁的预应力张拉顺序进行了研究。首先,利用解析法和有限元方法分析了Π型梁端梁和横隔板对剪力滞效应的影响,当考虑端梁和横隔板后,Π型梁最大剪力滞系数由1.23缩小到1.05,最小剪力滞系数由0.7增大至0.87。其次,分析了张拉过程中剪力滞系数的大小、变化趋势以及影响范围,确定了剪力滞效应纵桥向影响区域约为1倍的梁宽,减小桥面板和主肋轴向正应力差以及增大端梁和横隔板的刚度均可有效削弱剪力滞效应。最后,根据以上结论对预应力张拉顺序进行了调整,最终确定采用“首先张拉端梁和靠近端梁的3个横隔板的预应力筋,然后张拉一半主肋预应力筋,再张拉桥面板预应力筋,最后张拉另一半主肋预应力筋”的预应力张拉方案并进行计算。结果表明:端梁和横隔板的组合应力由最大的8.5 MPa拉应力转为压应力;桥面板主应力由最大的4.6 MPa降低为2.4 MPa,使得端梁、横隔板及桥面板在整个预应力张拉过程中的受力及变形均能满足设计及规范要求,避免了预应力张拉过程中可能出现的结构损伤或破坏,为类似桥梁施工控制提供了借鉴。

In order to avoid structural failure due to the prominent shear lag effect when theΠ-shaped beam is tensioned according to the conventional prestress tensioning sequence,the prestress tensioning order of theΠ-shaped beam is studied from the perspective of controlling the shear lag effect.First,the influence of end beams and diaphragms on the shear lag effect ofΠ-beam end beams and diaphragms is analyzed by analytical method and finite element method,and the maximum shear lag coefficient ofΠ-beam decreases from 1.23 to 1.05,and the minimum shear lag coefficient increases from 0.7 to 0.87 after considering the end beams and diaphragms.Second,the size,change trend and influence range of shear lag coefficient during tensioning are analyzed,and the beam width of the longitudinal bridge affected area of the longitudinal bridge under shear lag effect is determined to be about one time,and reducing the axial positive stress difference between the bridge deck and the main rib and increasing the stiffness of the end beam and the transverse partition can effectively weaken the shear hysteresis effect.Finally,according to the above conclusions,the prestress tensioning sequence is adjusted,and the prestress tensioning scheme of“firstly tension the end beam and the 3 transverse diaphragms near the end beam,secondly tension half of the main rib prestressed ribs,then tension the bridge deck prestressed ribs,and finally tension the other half of the main rib prestressed ribs”is finally determined and calculated.The result shows that(1)after adopting this scheme,the combined stress of the end beam and the diaphragm is converted from the maximum tensile stress of 8.5 MPa to compressive stress;(2)the main stress of the bridge deck is reduced from the maximum 4.6 MPa to 2.4 MPa,so that the force and deformation of the end beam,diaphragm and bridge deck in the whole prestress tensioning process can meet the design and specification requirements,avoid the structural damage or destruction that may occur during the prestress tensioning process,and provide reference for similar bridge construction control.