A Study on the Ultimate Strength of Thin Cylindrical Tubes under Static or Quasi-static Loading.

本课题旨在从理论和实验两方面确定预制短圆柱管在压缩载荷作用下的承载能力。试验在10个预制管道上进行，其中8个用于压缩试验，2个用于残余应力测量。此外，测量了所有试件的初始不平直度（OOS）和不圆度（OOR）。从实验中观察到：(1)初始OOS和OOR均低于ECCS和API的规定公差。(2)实测残余应力形状与参考文献相似，最大残余压应力约为屈服应力的20%。(3)相同半径/厚度比的试件在最大荷载前观察到的平均应力-应变曲线形状相似，但在峰值荷载后观察到的平均应力-应变曲线有所不同，即越长试件下降部分越陡峭。(4)采用日本现行公路桥规范中规定的圆柱管基本强度公式可以较好地预测实测极限强度。应用动态松弛法（DR法）进行了理论研究。编制了圆柱壳弹塑性大位移分析的计算机程序。研究得出以下结论：(1)通过刚度矩阵的最大和最小特征值确定迭代参数，可以减少迭代次数。(2)具有初始缺陷的圆柱壳的极限强度一般落在日本公路桥规范基本强度公式和ECCS预测的强度之间。

This project is to determine theoretically and experimentally the load carrying capacity of short fabricated cylindrical tubes under compressive loading. The tests were carried out on 10 fabricated pipes in which 8 were for compression tests and 2 were for residual stress measurements. In addition, initial out-of-straightness(OOS) and out-of-roundness(OOR) were measured for all the specimens. From the experiment, the following were observed: (1)Initial OOS and OOR are well below the specified tolerances of ECCS and API. (2) Measured residual stresses are similar in shape to those in a reference and the maximum compressive residual stress was about 20% of the yield stress. (3)Observed average stress-strain curves of test specimens with the same radius/thickness ratio are similar in shape up to the maximum load, but become different after the peak load, i.e., steeper descending part was observed for longer specimen. (4)Observed ultimate strength may be well predicted by the basic strength formular of cylindrical tubes specified in the current Japanese highway bridge specification. Theoretical study was also conducted by applying the Dynamic Relaxation Method (DR method). A computer program has been developed to make an elastic-plastic large displacement analysis of cylindrical shells. The following are obtained from the study: (1)It is possible to reduce the number of iterations by determining iteration parameters from the maximum and minimum eigenvalues of the stiffness matrix. (2)The computed ultimate strengths of cylindrical shells with initial imperfections fall generally between the strengths predicted by the basic strength formulas of the Japanese highway bridge specifications and ECCS.