混凝土箱梁桥的横隔梁拉压杆模型及配筋设计

STRUT-AND-TIE MODELS FOR DIAPHRAGMS OF CONCRETE BOX-GIRDER BRIDGES AND REINFORCEMENT DESIGN

对混凝土箱梁墩顶横隔梁的拉压杆模型构形及其配筋设计方法进行了研究。首先讨论横隔梁力学边界条件的合理简化,提出了等效计算图式。根据深梁典型拉压杆模型并结合荷载传递路径的分析,给出了实心及开洞两种横隔梁的拉压杆模型。进一步研究揭示了该区域拉压杆模型构形有以下特点:对于高宽比为0.5―1.2的双支承横隔梁,高宽比及支承间距决定了模型中水平方向拉压杆间力臂长度及斜压杆倾角;对于高宽比为1.2―2的双支承横隔梁,模型可由双支承典型深梁及小高宽比双支承横隔梁模型组合而成,且构形不再受支承间距的影响;此外,洞口大小及位置会改变荷载传递路径,从而也影响到模型中斜压杆的倾角。以该文提出的横隔梁拉压杆模型为基础,并结合美国AASHTO公路桥梁设计规范,给出了墩顶横隔梁配筋设计方法。设计示例表明该方法具有良好的实用性,可供工程设计参考。

The strut-and-tie model（STM） approach for the reinforcement design of diaphragms in concrete box-girder bridges is studied in this paper.To begin with,an equivalent model for diaphragm is established by simplifying the boundary conditions.Based on the typical STM for a deep beam and on the load path method,the STM for a solid diaphragm and the diaphragm with opening are proposed.Further study about the STM for the diaphragms reveals that： as for the double-bearing diaphragm with depth-to-width ratios between 0.5―1.2,the lever arm between the horizontal tie and strut,the angle of inclined struts are dominated by the depth-to-width ratio and the spacing of bearings;as for the double-bearing diaphragm with the depth-to-width ratio between 1.2―2,the models can be assembled by a kind of prototype models for deep beams and diaphragm models with low depth-to-width ratios,which are no longer influenced by the spacing of bearings.Moreover,the variation of size and location of opening may disturb the load paths,and impact the inclined strut angles for the above models.Applying the proposed STM approach,the reinforcement design of diaphragms can be accomplished by virtue of the AASHTO LRFD specification.Finally,a worked example demonstrates that the proposed method can be a good practical tool.