内衬混凝土对预应力导入效率的影响分析及优化

Analysis and optimization of effect of lining concrete on efficiency of prestressing introduction

针对内衬混凝土对波形钢腹板褶皱效应的约束会致使波形钢腹板组合梁桥支承区的预应力导入效率降低问题,提出一种“先撑后衬”施工方法,通过调整内衬混凝土的施工顺序来改善支承区预应力导入效率;同时提出一种适用于该方法的“内撑外拉”装置,保证施工过程中波形钢腹板的稳定性;推导波形钢腹板组合梁轴向刚度计算公式,并通过简支波形钢腹板组合梁算例验证该公式的准确性。在此基础上,以1座四跨波形钢腹板预应力混凝土连续刚构桥为背景,建立ANSYS实体有限元模型,分析不同施工方法、内衬混凝土长度及厚度变化对支承区预应力导入效率的影响,并给出内衬混凝土的合理施工工序、合理长度和厚度建议。研究结果表明:内衬混凝土会削弱波形钢腹板的褶皱效应,显著降低支承区预应力导入效率,同时会导致有内衬梁段与无内衬梁段间的过渡段出现应力集中现象;通过采用所提出的“先撑后衬”施工方法,可以降低支承区组合梁的轴向刚度,从而显著提高支承区预应力导入效率;支承区预应力导入效率随着内衬混凝土长度和厚度的增加而减小;在实桥设计时,建议内衬混凝土最小长度应大于支点处梁高,最大长度应小于2.15倍支点处梁高,最大厚度应不小于支点梁高的6%,最小厚度应满足构造要求。

Aimed at the problem that the restraint of the lining concrete on the crease effect of the corrugated steel webs will reduce the prestressing efficiency in the supporting area of composite girder bridges with corrugated steel webs.A"brace first and then lining"construction method,which adjusted the construction sequence of lining concrete,was proposed to improve the prestressing efficiency.An"internal brace and external tension"device was proposed for the brace first and then lining construction method to ensure the stability of the corrugated steel webs during construction.The formula for calculating the axial stiffness of composite girders with corrugated steel webs was derived,and the accuracy was verified by an example of simply supported corrugated steel web girder.Based on a four-span corrugated steel web prestressed concrete(CSW-PC)continuous rigid-frame bridge,an ANSYS solid finite element model was established to analyze the effect of different construction methods,variations of lining concrete length and thickness on the prestressing efficiency in the supporting area.And a reasonable construction procedure,length and thickness of lining concrete was suggested.The results show that the lining concrete reduces the crease effect and prestressing efficiency of the corrugated steel webs,and causes a stress concentration in the transition section between the lining and unlining girder sections.By adopting the brace first and then lining method,the axial stiffness of composite girders with corrugated steel webs is reduced and the prestressing efficiency is increased.The prestressing efficiency in the supporting area decreases with the increase of lining concrete's length and thickness.In the actual design,it is recommended that the minimum length of lining concrete should be greater than the height of the girder at the pier,the maximum length should be less than 2.15 times the height of the girder at the support,the maximum thickness should be more than 6%the height of the girder at the support,and the minimum thickness should meet the construction requirements.