基于断裂力学的木结构螺栓节点横纹受拉承载力算法研究

Tensile load carrying capacity of bolted timber connections loaded perpendicular to grain based on fracture mechanics

在重型木结构框架和屋面桁架等木结构体系中,螺栓-钢填板连接节点往往会受到横纹方向荷载作用,破坏源于裂缝的萌生和扩展,存在突然性。以横纹受力的螺栓-钢填板连接节点为研究对象,基于断裂力学原理推导螺栓端距为零和无穷大时节点横纹受拉承载力计算式,在此基础上提出基于等效受拉面积的螺栓节点横纹受拉承载力计算式。该算法克服了现有计算式不能同时考虑节点区木构件有效高度和螺栓端距影响的局限性。基于所收集的单螺栓和多螺栓节点横纹受拉荷载实测值和相应的材料性能测试数据,比较了试验结果和预测算式,以及国内外相关规范中的计算式与计算结果的差异。结果表明,所提出的计算式具有良好的计算精度,且概念清晰,便于使用,可以为我国相关规范修订提供参考。

Bolted timber connections with steel plates in heavy timber frames and roof trusses are often subjected to loading perpendicular to grain. Failure originates from crack initiation and expansion and has brittle nature. In this paper, the bolted timber joints subjected to loading perpendicular to grain is studied based on the theory of fracture mechanics. Calculation formulas for the cracking load with zero and infinity bolt end distance are derived, based on which, a calculation formula incorporating the concept of the equivalent tensile area is proposed. The proposed formula can consider both the effective height of the beams and the end distance of the bolts, and thus is superior to the existing calculation formulas. By utilizing the test results in literature regarding bolted timber connections with single and multiple bolts and loaded perpendicular to grain, the accuracy of the proposed formula is verified. Meanwhile, the results from the proposed formula and the formulas suggested in relevant domestic and international design codes are discussed. It is found that the proposed formula has better accuracy and can provide reference for revision of design codes considering its clear concept and convenience for calculation.