Study on Refined Numerical Simulation Method of Mechanical Behavior of Prefabricated Bailey Beam
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摘要: 为解决贝雷梁实体模型在有限元分析中建模困难、计算代价大的弊端,采用有限元分析软件ANSYS,基于已验证的贝雷梁实体有限元模型,提出一种针对装配式贝雷梁的杆系模型,并与《装配式公路钢桥多用途使用手册》中的贝雷梁试验进行比对,验证线性状态下贝雷梁实体模型与杆系模型的准确性。通过非线性屈曲分析,比较两种模型在非线性状态下的差异性,通过修正得出正确的杆系有限元模型,并采用修正后的杆系模型代替实体模型进行不同工况下的极限承载力研究,探明初始几何缺陷对贝雷梁受力性能的影响,提出了贝雷梁极限承载力验算中几何缺陷的参考幅值。结果表明:相同荷载作用下实体模型在线性阶段的位移值略大于杆系模型,跨中最大位移相差4%,但杆系模型和实体模型在各测点的位移值都与试验结果接近,且误差范围小于2%。杆系模型和实体模型的内力基本吻合,截面平均等效应力最大误差为2.78%;不同侧向支撑间距下两种模型在非线性阶段得到的失稳模式高度一致,极限承载力差值在2.4%以内,荷载-位移曲线基本吻合,破坏模式基本一致,且杆系模型的荷载-位移曲线与试验曲线吻合较好,由此可以证明,杆系模型可代替实体模型进行极限承载力分析;贝雷梁的侧向支撑间距对结构的破坏模式起决定性作用,贝雷梁的侧向支撑间距不小于7.5 m时,结构发生整体失稳,侧向支撑间距小于6 m时,贝雷梁发生局部失稳,失稳模式为跨中单元的上弦杆发生面外弯曲破坏,且出现了明显的局部失稳变形,弯曲变形最大部分的Mises应力达到屈服;当贝雷梁发生整体失稳时,整体几何缺陷对结构的承载力影响较大,而当结构发生局部失稳时,需要特别注意结构的局部几何缺陷;稳定承载力对整体缺陷的幅值较为敏感,而面内局部缺陷对贝雷梁的稳定承载力影响很小,面外局部几何缺陷对贝雷梁的稳定承载力影响较为显著,考虑面外初弯曲幅值为1/1 000的初始几何缺陷时,弦杆、竖杆及斜杆的面外局部缺陷使稳定承载力分别下降6.1%、1.3%和1.2%,而面内缺陷仅使其降低了1.0%、1.0%和0.5%。故在选用贝雷片时应格外注意弦杆的面外变形。Abstract: In order to solve the disadvantages of modeling difficulty and high calculation cost in the finite element analysis of the Bailey beam solid model, a bar system model for the assembled Bailey beam is proposed based on the verified Bailey beam solid finite element model using the finite element analysis software ANSYS, and the modeling details of the solid model and bar system model are briefly described. It is also compared with the Bailey beam test in the Multi-purpose Manual for Prefabricated Highway Steel Bridges to verify the accuracy of the Bailey beam solid model and the member system model in the linear state. This paper carries out nonlinear buckling analysis, compares the differences between the two models in nonlinear state, and obtains the correct finite element model of the bar system through modification, and uses the modified bar system model to replace the solid model to study the ultimate bearing capacity under different conditions. The influence of initial geometric defects on the mechanical properties of Bailey beams is explored, and the selection reference of geometric defects for checking the ultimate bearing capacity of Bailey beams is proposed. The results show that the displacement value of the solid model under the same load in the linear stage is slightly larger than that of the rod model, and the maximum displacement difference in the midspan is 4%, but the displacement values of the rod model and the solid model at each measuring point are close to the test results, and the error range is less than 2%. The internal forces of the bar model and the solid model are basically consistent, and the maximum error of the average equivalent stress of the section is 2.78%; in the nonlinear stage, the instability modes obtained by the two models under different lateral bracing spacing are highly consistent, and the difference of ultimate bearing capacity is within 2.4%. The load-displacement curve is basically consistent, the failure mode is basically consistent, and the load-displacement curve of the member system model is in good agreement with the test curve. It is proved that the member model can replace the solid model for the ultimate bearing capacity analysis. The lateral support spacing of Bailey beams plays a decisive role in the failure mode of the structure. When the lateral spacing of Bailey beams is greater than or equal to 7.5 m, the overall buckling of the structure occurs. When the lateral support spacing is less than 5 m, the Bailey beam will be local buckling. The buckling mode is that the top chord of the mid-span element is subjected to out-of-plane bending failure, and obvious local buckling deformation occurs, and the Mises stress of the largest part of bending deformation reaches yield. When the Bailey beam is globally unstable, the overall geometric defect has a great impact on the bearing capacity of the structure, and when the structure is locally unstable, it is necessary to pay special attention to the local geometric defect of the structure. The stable bearing capacity is sensitive to the amplitude of the overall defect, while the in-plane local defect has little impact on the stable bearing capacity of the bailey beam, and the out-of-plane local geometric defect has a significant impact on the stable bearing capacity of the bailey beam. When considering the initial geometric defect with the out-of-plane initial bending amplitude of 1/1 000, the out-of-plane local defect of the chord, vertical bar and diagonal bar reduces the stable bearing capacity by 6.1%, 1.3% and 1.2% respectively, while the in-plane defect only reduces it by 1.0% 1.0% and 0.5%. Therefore, special attention should be paid to the out-of-plane deformation of the chord when selecting the bailey sheet.
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