混凝土箱梁和T梁交接处剪应力传递与应力分布

The transfer of shear stresses from web-flange junction to flange and the distribution of normal stresses in box beams and T beams on concrete will be investigated. The typical sectional characteristics at which without shear forces or bending moments and the mechanical properties of box beams and T beams will be studied during the beam tests. The beam tests consists of one two-span continuous box beam, one simply supported box beam, six T beams with different web widths and six T beams with different flange heights. At every section, the strain gauges are attached on the top and bottom surfaces of the flanges and special gauges are embedded in the flanges as well. Based on concrete stress-strain relationship, the stresses at the section may be calculated. As per the Bernoulli-Euler theory, the transfer of shear stresses from junction to flange can be determined, and the influence of which on the bending stresses in tensile and compression will be studied meanwhile. Using the Timoshenko theory to consider the shear deformation of the web, a modified finite element method with an additive displacement shape function for flange will be proposed, and some important parameters will be studied as well. A formula to calculate the stresses in box beams and T beams of concrete will be given, which is based on the experimental and analytical results.

本项目主要研究混凝土箱梁、T梁腹板-翼板交接处剪应力传递及对翼板中正应力分布的影响。通过对混凝土简支箱梁、连续箱梁、不同厚度和不同宽度简支T梁进行试验，考察梁在纯弯曲段、反弯点和支座处梁截面的变形特征和整个梁的受力力学性能；在翼板上、下对称布置应变片同时，利用特制装置对混凝土内部的应变也进行测定；根据测定的混凝土箱梁和T梁截面应变，利用混凝土应力－应变关系计算截面的应力，比照Bernoulli-Euler梁理论，确定箱梁、T梁交接处腹板剪应力在翼板中沿宽度方向和厚度方向的传递规律，考察它们对受拉和受压弯曲应力的影响；利用Timoshenko梁单元考虑腹板的剪切变形，根据测定的截面变形修正箱梁、T梁翼板的位移形函数，建立合理的有限元分析方法，并对重要参数进行分析；综合试验和有限元分析结果，提出便于工程应用的箱梁、T梁截面应力计算公式。

箱形梁和T型梁具有结构合理、造价经济和抗弯抗扭刚度强等特点，然而其剪力滞效应问题极其突出。在20世纪70年代左右，桥梁设计中未合理考虑剪力滞引起的应力集中，造成多座梁桥破坏，这引起的各国学者对剪力滞问题的重视。.本项目开展了不同翼缘板宽度T梁及箱梁的模型试验，测量截面上（包括混凝土内部）沿宽度方向的应变分布规律，研究剪力滞效应产生的机理；测量了受力过程中各典型截面上沿宽度和厚度方向的应变情况，研究弯矩和剪力对截面上应力分布的影响。通过研究，主要得到以下结论：.(1) 简支T梁发生竖向弯曲变形时，全梁范围内均产生不同程度的正剪力滞效应，其中，剪力是产生剪力滞效应的主要因素。对于主要由剪力引起的剪力滞效应，翼板腹板宽度比的增大会对其产生削弱；而对于由弯矩引起的剪力滞效应，翼板腹板宽度比的改变对于其影响不大。集中力对于作用点附近一定范围内的应变分布起决定性作用，这作用随着距离作用点愈远则愈弱。随着荷载等级的增加，剪力滞效应一般愈来愈弱，最终趋于平缓。配筋的存在可缓和剪力滞效应。.(2) T梁在中间支座截面剪力滞效应最明显；纯剪处和边支座处截面剪力滞现象并不明显；一般情况下T梁翼板上表面比下表面剪力滞效应显著；随着弯矩增大典型截面剪力滞效应愈加显著。.(3) 剪力是引起剪力滞效应的主要原因而弯矩与剪力滞效应关系不大，剪力滞效应随截面荷载增大无明显变化，剪力滞效应在翼板厚度范围内未呈现明显规律，顶板混凝土内部剪力滞效应与表面和钢筋剪力滞效应强度情况相似。.通过本项目的研究，利用Timoshenko梁单元考虑腹板的剪切变形，根据测定的截面变形修正箱梁、T梁翼板的位移形函数，对重要参数进行分析；综合试验结果，提出便于工程应用的箱梁、T梁截面应力计算公式。