【作者】 程坤；

【导师】 项贻强；

【作者基本信息】 浙江大学 ， 桥梁与隧道工程， 2014， 博士

【摘要】 在役钢筋混凝土箱梁桥一般都处于弯剪扭共同作用的复合受力状态。本文结合国家自然科学基金项目“在役混凝土箱梁桥时变承载力的分析理论及试验研究(51178416)”,以独柱式钢筋混凝土连续箱梁桥为背景,从理论、试验和数值分析的角度对钢筋混凝土箱梁的复合受力特性进行探索。主要研究内容及成果如下：(1)提出了基于桁架模型的复合受力钢筋混凝土箱梁构件迭代配筋设计方法,并给出了详细的计算流程。(2)设计制作并完成了4个不同设计参数的独柱式钢筋混凝土双跨连续箱梁复合受力模型试验研究工作。研究探讨了不同边界及加载方式下箱梁的纵应力沿横向的分布规律；对比给出了不同设计参数下箱梁的裂缝扩展特征及破坏模式；讨论了不同配筋和宽跨比对箱梁强度、刚度等力学特性的影响。试验结果验证了提出的配筋设计方法的合理性。(3)基于有限元软件MSC.Marc的弹塑性+断裂混凝土模型,同时考虑支座接触效应和Rots裂缝面剪切模型,建立了试验构件的有限元模型。与试验对比结果表明,该模型可以较好的模拟试验的加载过程,构件抗弯和抗扭刚度的变化规律及开裂模式均与试验结果吻合良好。(4)对独柱式钢筋混凝土连续箱梁的横向倾覆稳定性进行了探讨。分析认为,箱梁抗倾覆安全性验算时应综合考虑跨径、截面形式、配筋等因素；设置抗拉支座可以显著提高箱梁的抗倾覆能力,但墩梁固结对于改善箱梁横向稳定性的效果并不明显。(5)基于正截面抗弯承载能力计算方法,引入剪扭钢筋混凝土构件的桁架理论,导出了复合受力混凝土箱梁的弯剪扭强度关系表达式,并提出了简化计算公式。计算结果表明,对于弯扭构件,用所提出的简化计算公式得到的弯扭强度关系曲线与试验和数值结果均吻合较好；与本文4个弯剪扭箱梁构件的试验结果相比,其计算结果整体偏于保守。(6)提出了适用于钢筋混凝土箱梁复合受力全过程分析的改进板-桁模型。该模型考虑了等效剪切厚度沿腹板的变化情况,可以进行复杂截面箱梁的复合受力全过程分析。与试验对比结果表明,该模型可以较好地预测复合受力钢筋混凝土箱梁构件的荷载-变形曲线和荷载-钢筋应变曲线等力学响应；同时,还能进一步预测给出构件各箱壁的主应力(裂缝)倾角。(7)提出了基于改进板-桁模型的复合受力钢筋混凝土箱梁裂缝评估方法及流程。结合剪力墙等平面受力钢筋混凝土构件裂缝控制问题的研究成果,通过提取非线性全过程分析过程中的主压应变、主拉应变、等效剪切厚度等参数,计算得到裂缝宽度和平均裂缝间距等特征参数。结果表明,不同加载等级下箱梁构件加载侧腹板的平均裂缝间距计算结果与试验观测统计值吻合较好；在裂缝扩展阶段,荷载-裂缝宽度的变化曲线与试验观测值基本一致。(8)提出了综合考虑粘结滑移效应及正交配筋效应的钢筋修正本构模型；并进一步引入钢筋和混凝土材料劣化模型,研究给出了基于改进板-桁模型的复合受力钢筋混凝土箱梁时变承载力的计算流程。算例结果表明,对纯扭和弯剪扭混凝土构件,考虑粘结滑移的钢筋修正本构可以更好的模拟构件裂后抗扭刚度的退化情况。L1构件在寿命期内抗扭强度将经历“提高-稳定-下降”的过程,在给定的一般大气环境和扭弯比受力条件下,100年后该构件抗扭强度会出现约15%的损失。更多还原

【Abstract】 In-service reinforced concrete (RC) box-girder bridges are generally subjected to the combined actions of bending, shear and torsion. According to the National Natural Science Foundation of China (51178416), the main objective of this study is to explore the mechanical characteristics of RC box girder subjected to bending, shear and torsion. Details of this study are mainly summarized as follows:(1) Based on the truss model, an iterative reinforcement design approach of RC box girder subjected to combined actions was presented. The detailed calculation flowchart was given.(2) Experimental study of four RC continuous box girders with single-column support was conducted by considering different design parameters, in which the proposed reinforcement design approach was used. The elastic mechanical properties of test model under different condition boundaries and loading cases were analyzed. The crack patterns and failure modes of four test models were observed and compared. Also, the effect of different design parameters on the strength and rigidity of box girders were discussed. Finally, the proposed reinforcement design approach was verified by the test results.(3) Based on the elastic-plastic and fracture concrete model in the software of MSC. Marc, finite element (FE) models of the test models were developed, in which the bearing contact simulation and Rots shear crack model were considered. The results show that the whole loading process can be effectively simulated using the presented FE model. The crack patterns and the degradation curve of flexural (torsional) rigidity are in good agreement with the test results.(4) The transverse stability of RC box-girder bridge using single-column support was discussed. Theoretical analysis result shows that the factors of span, cross section and reinforcement arrangement should be considered when checking the transverse stability of RC box-girder bridge with single-column support. Parameter analysis by FE method shows that tensile bearing can obviously improve the stability performance. However, the supporting way of fixed pier and girder has little effect on overturning-resistance performance.(5) Based on the calculation method of flexural bearing capacity, the formula of bending-shear-torsion strength interaction of RC box girder was derived by introducing the truss model and shear-torsion strength interaction curve of RC member. The applicability of the proposed formula was discussed. Then a simplified formula was fitted and given by considering the parameters of height-width ratio, top slab width, reinforcement ratio in top and bottom slabs, concrete strength, and stirrup ratio. The results show that, for coupled bending and torsion member, the proposed simplified formula can be well verified when comprising with literature and FE results. Comparing with model tests of RC box girder subjected to combined bending, shear, and torsion, the predicted interaction curves are conservative.(6) A modified plate-truss model used for the nonlinear whole-process analysis of RC box girder subjected to bending, shear and torsion was proposed. In the proposed model, the truss theory was satisfied in the top and bottom slabs of box girder, the flange slabs were assumed to be non-crack compressive slabs with varying thickness, and the webs were considered to be several truss elements with different equivalent shearing thickness. The result shows that the torque-twist curves, bending moment-curvature curves, and even the load-reinforcement strain curves can be well predicted by the proposed model. The angles of principal stress in different walls of box girder are also well agreement with the test results.(7) Based on the modified plate-truss model, a crack estimation approach of RC box girder subjected to bending, shear and torsion was presented. After introducing the achievements of crack estimation for plane-stress RC member (e.g. shear wall), the parameters of principal strain and equivalent shear thickness were extracted in the whole-process nonlinear analysis. The concrete average crack spacing and width of RC box girder were then analyzed. Comparing with previous model tests of RC box girder, the results show that the predicted average crack spacing for the web of the loading side is in good agreement with the observed value. The load-crack width curves in crack propagation stage by the proposed method conform well to the test results.(8) Based on the modified plate-truss model, the time-varying ultimate capacity of RC box girder subjected to bending, shear and torsion were studied. An average constitutional relationship of steel bar was developed by considering both the bonding-slipping effect and corrosion ratio of steel bars. The calculation flowchart of time-varying bearing capacity was given by the introducing material degradation models in general environment. It is concluded that the predicted mechanical behavior conforms well to the test result for pure torsional and coupled torsional RC members. The torsional strength will decrease by15%after100years in the assumed environment and loading conditions.更多还原