跨座式单轨钢混组合后浇带合理分析方法

Reasonable Analysis Method of Steel-concrete Post-pouring Area of Straddle Monorail

研究目的:以全国首例跨座式单轨简支转连续梁桥为例,其负弯矩区后浇带为“混凝土梁上覆钢板”的断面形式,后浇带纵筋采用绑扎长度短于规范的“帮条钢筋”。上述构造明显有别于常规结构,为明确其受力性能,本文对多种相关的有限元模拟理论开展不同参数下的比较,重点研究结构承载力和抗裂性能,并给出合理的分析方法。研究结论:(1)相比弥散裂缝和断裂力学模型,离散裂缝模型为钢混组合后浇带开裂模拟的最合理方法;(2)相比含钢筋的实体混凝土单元或钢筋采用桁架元但未设钢混界面的模型,在桁架元基础上增设植入式界面单元的模型为“帮条钢筋”模拟的最合理方法;(3)后浇带主筋应力随其直径增大而减小,但强度安全系数则先增大后减小,故直径并非越大越好;(4)采用本文的建模方法和裂缝公式,可直接指导该类结构的设计并减少建模分析工作量。

Research purposes: A straddle monorail project is the first project using the continuous beam turned from simply supported beam in China. The post-pouring area is the combined cross-section form of "concrete beam with overlying steel plate", and its longitudinal rebars are connected by a kind of "auxiliary short rebar" whose binding length is lower than that required by the specification. The structure above is obviously different from the conventional structure. To clarify the mechanical behavior of this area, the numerical simulations of various related FEM theories were carried out under different parameters. Its bearing capacity and crack resistance were emphatically studied, and reasonable analysis methods were given.Research conclusions:(1) Comparing to the dispersive crack and fracture mechanics model, the discrete crack model is the most reasonable method.(2) Comparing to the model using the rebar-concrete solid element or the simple truss element, the model with implantable interface element is the most reasonable method.(3) The rebar stress decreases with the increase of diameter, but its stress safety factor increases first and then decreases, hence a larger diameter is not necessarily better.(4) The modeling method and crack formula proposed in this paper can guide the design of this kind of structure and reduce the workload of FEM analysis.