混凝土槽形薄壁梁翘曲扭转效应分析及试验研究

The advantages of concrete thin-walled channel beams are the lower construction height, attractive appearance and better effect of soundproof. The thin-walled channel beams were designed as bridges in urban rail transit and city roads. The thin-wall channel beam is made with two web-slabs fixed connected to bottom slab. It is a spatial structural system and suffered composite actions of bending, shearing and torsion. The torsion resistance of such open concrete thin-walled members are not covered in the active design code of concrete structures, which based on the theory of spatial truss with variable angle. The existing research achievements mainly focus on tests and linear elastic analysis under symmetric vertical loading. There is almost no references dealing with the effects of torsion or warping torsion in concrete thin-walled channel beam. The mechanical mechanism, failure pattern and ultimate resistance of the concrete thin-walled channel beams under the action of torsion or composite actions of bending and warping or bending, shearing and torsion would be studied in this project. The researching methods include theory calculations, analysis of finite elements and testing investigation. The distributing rules of warping torsion and Saint Venant torsion, and the rules changing as the ration of the span with height, or constrains condition of the thin-walled channel beams under the action of torsion moment. The mechanical properties and bearing capacities of the concrete thin-walled channel beam will be studied under the composite actions of bending, shear and torsion. The test methods and procedures would be established according to the characters of concrete thin-walled channel beams. At last, the utility calculating and structural design methods are suggested for the concrete thin-walled channel beam under the action of torsion or composite actions of bending, shearing and torsion, which will give the technical references for the design of concrete thin-walled channel beams.

混凝土槽形薄壁梁具有建筑高度低、造型美观、隔音效果好的优点，在城市轨道和道路桥梁中应用较多。槽形薄壁梁是由两侧腹板与底板固结而成的空间结构体系，存在弯剪扭复合作用效应，基于变角空间桁架理论的现行设计规范抗扭计算未覆盖该类开口薄壁截面。已有的混凝土槽形薄壁梁的研究主要集中在对称竖向加载试验和弹性数值分析方面，很少考虑扭转或翘曲扭转效应的影响。本项目拟研究混凝土槽形薄壁梁扭转或弯扭、弯剪扭复合作用下的受力机理、破坏形态和承载能力。采用理论推导、有限元分析和试验研究的方法，研究受扭槽形薄壁梁中翘曲扭转和圣维南扭转的分配规律以及随跨高比、约束条件变化的规律；研究槽形薄壁梁在弯扭、剪扭、弯剪扭复合作用下的力学性能和承载力变化规律；研究模拟受扭特征的槽形薄壁梁加载和试验方法；提出混凝土槽形薄壁梁受扭或弯剪扭复合作用下的设计计算和构造方法，为混凝土槽形薄壁梁的工程设计提供依据。

本项目完成6个大比例（7m跨度）钢筋混凝土U型薄壁梁在纯扭或弯剪扭作用下的加载试验，考虑弯扭加载比例、配筋率等参数，获得U型薄壁梁裂缝发展和分布、纵筋和箍筋应变分布、破坏形态等试验数据。试验结果表明，U型薄壁构件约束扭转或约束扭转、弯剪综合作用下的破坏形态由翘曲弯矩和弯矩组合效应控制；纵筋屈服前扭转和剪切效应较小，且翘曲扭转和圣维南扭转的比例基本不变。纵筋屈服后，约束扭转减弱，圣维南扭转迅速增加至总扭矩的80%；U型薄壁梁在不同比例弯剪扭复合作用下，其破坏形态由纯扭的翘曲弯破坏，及弯扭比例1:1时翘曲弯与弯矩组合的单侧腹板弯曲破坏，到弯扭比例5:1时弯矩主导的弯曲破坏。可见，弯剪纽组合作用下U型截面薄壁板内外应力、裂缝分布和破坏形态的差异，由约束扭转效应（自由扭矩所占比例）和弯扭比例决定。基于试验结果、Vlasov薄壁弹性理论和变角空间桁架模型，研究建立了U型薄壁纯扭构件非线性分析模型，该模型非线性分析结果与试验结果吻合较好；研究提出了混凝土U型薄壁梁受扭或弯剪扭复合作用下承载力统一计算公式，计算结果与试验结果吻合较好，为混凝土槽形薄壁梁的工程设计提供了依据。.项目研究成果发表和录用学术论文7篇，其中2篇为SCI收录的国际著名期刊Structure Engineering和Structural Engineering and Mechanics，4篇为EI收录的建筑结构学报等学术期刊。培养博士研究生2人、硕士研究生5人。项目研究的部分成果2014年获得北京市科技进步贰等奖。