球墨铸铁管道接口弯曲性能试验

Bending performance test of push-on joints of ductile iron pipelines

摘要:

为了研究球墨铸铁供水管道承插式接口在拉弯耦合作用下的力学性能及破坏模式,开展了系列管道接口的极限抗弯承载力试验。在外部无覆土、管内水压为0.2 MPa条件下,考虑接口不同拉弯耦合形式、单调和往复加载形式,并分别对DN150和DN200型管道承插式接口进行了四点弯曲加载,研究接口的力学性能变化过程及破坏形态。试验结果表明:根据承插式接口不同的初始张开量,管道接口的“弯矩-转角”曲线大致分为3个阶段(线性增长阶段、塑性发展阶段和承载力极限破坏阶段),当安装深度与承口深度比在0.67左右时,DN150和DN200型管道接口的弯曲转角变形能力最大,分别为15.9°和12.8°,对应抗弯承载力分别为7.8 kN·m和9.2 kN·m；往复加载下,安装较深的管道接口具有较高有效抗弯刚度,但在二次加载时刚度退化显著；承载力极限破坏时管道插口发生屈曲变形,管底最大残余应变为5.7×10^-4,接口椭圆度达4.2%。相关结论可为埋地球墨铸铁管线的震害、抗震验算、设计与措施等研究提供参考。

Abstract:

To study the mechanical behaviors and failure modes of the push-on joints of ductile iron water pipelines under both tension and bending, this paper conducts a series of quasi-static tests on push-on joints to assess their ultimate bending capacity. Four-point bending tests were performed on the push-on joints of DN150 and DN200 pipelines with internal water pressure of 0.2 MPa and without soil coverage. Different loading protocols including coupled tensile and bending tests and monotonous and cyclic loading tests were adopted in the experimental program to investigate the mechanical behaviors and failure modes of the push-on joints. Results show that for push-on joints with different initial openings, the “bending moment-angle” curves of pipeline joints could be roughly divided into three stages: linear growth stage, plastic deformation stage, and the stage corresponding to ultimate load-carrying capacity. When the ratio of the assembling depth to the socket depth was about 0.67, the maximum angles of DN150 and DN200 pipeline joints were 15.9° and 12.8°, and the corresponding bending capacities were 7.8 kN·m and 9.2 kN·m respectively. The pipeline joints with larger assembling depths exhibited higher effective bending stiffness under cyclic loading, but the stiffness degraded significantly under reloading cycles. Buckling deformation occurred at the pipeline joints when the joint reached its ultimate load-carrying capacity, with the maximum residual strain of the pipe bottom being 5.7×10^-4 and the ellipticity of joints being 4.2%. The relevant results can provide reference for the research of seismic damage, seismic checking calculation, design, and measures of buried ductile iron pipelines.