考虑不同失效模式的索杆结构构件面积缺损限值研究

Study on Area-Loss Limit of Cable-Strut Structures Considering Different Failure Modes

索杆结构长期服役过程中的锈蚀会造成构件截面损失,导致结构内力的重新分配,影响结构的安全性能。文中基于可靠度理论与结构极限状态分别建立了构件强度失效、钢索松弛失效及节点变形失效3种失效模式,并得到了不同失效模式临界状态下的可靠度限值控制不等式;通过力学推导,给出了以缺损面积为变量的杆件内力与节点位移变化公式,依据该公式可计算出可靠度限值控制不等式中的影响系数矩阵;引入钢材的锈蚀模型并结合非线性规划,提出了一种确定索杆结构构件面积缺损限值的方法。对一Levy型索穹顶的构件面积缺损限值进行了算例分析,并与规范限值进行对比。结果表明:索杆结构中的多数构件在强度失效与变形失效模式下的面积缺损限值高于耐久性限值,但松弛失效模式下的构件面积缺损限值小于耐久性限值,如按该限值要求对结构进行设计及维护将有可能发生钢索松弛失效;而安全性限值对于钢索构件较为严格,对于钢杆构件则与耐久性限值相同。因此,需综合考虑3种失效模式与规范限值,并按最严格的结果进行控制。

Corrosion of cable-strut structures during long-term service life will cause cross-sectional area loss of steel members,which will lead to redistribution of internal force and affect safety performance of the structure.This paper established three failure modes including member strength failure mode,cable relaxation failure mode and node deformation failure mode based on the reliability theory and structural limit state,and further obtained reliability limit control inequalities under critical states of different failure modes.Through mechanical derivation,it derived the formula for the members’internal force variation as well as nodal displacement variation of cable-strut structure due to variation of cross-sectional area.Based on the formula,the influence coefficient matrix in the reliability limit control inequality can be calculated.By introducing the corrosion model of steel and combining it with nonlinear programming,it proposed the method to determine the members’area-loss limit of cable-strut structure.The numerical example of a Levy cable dome was carried out and the calculated area-loss limits were compared with the current limit in specification.The result shows that the calculated area-loss limit of most members in the cable-strut structure under the strength failure mode and deformation failure mode is higher than the durability specification limit,but the area-loss limit under the relaxation failure model is smaller than the durability limit.If the structure is designed and maintained according to this limit value,the cable relaxation failure may occur.The safety specification limit is strict for steel cable members,but it is the same as durability specification limit for steel bar members.Therefore,the area-loss limit under three failure modes and specification limits should be considered comprehensively and the final limit should be controlled according to the most stringent results.