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

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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.