Low-Cycle Fatigue Tests of Hollow Concrete Spheres with Implications for the Survivability of Deep-Underground Rock Openings.

摘要

There has been conflicting evidence about the significance of low-cycle fatigue damage inflicted on deep-underground rock openings subjected to ground shock from sequential, multiple bursts of nuclear weapons. Few tests have been made. This investigation comprises tests and data analyses to further examine the question. Nine hollow concrete spheres, reinforced with steel-wire fibers, were instrumented and tested under cyclic, hydrostatic loads in a pressure vessel. Strain gages were mounted on the inner surface and inside the wall to detect the onset of in-plane cracking and to monitor the progressive degradation of the test specimens. Cylinders cast at the same time as the spheres were tested to define the material properties. Fatigue curves were prepared from the cyclic test data and a power law equation was fitted. From the strain-gage data, pressure/strain plots and cyclic histories were constructed. The growth of strain with cycles was analyzed. A methodology was then developed for designing a failure mode to meet a survivability goal or to assess the survivability of a design. The failure mode resistance was assumed to undergo degradation under repeated loads according to the fatigue equation, The methodology differs from standard methods of designing under random fatigue in that (1) it is structured for 1 to 100 load applications and (2) it reduces to the correct solution for the 1-load case. Sample problems illustrate the procedure. It was concluded that low-cycle fatigue needs to be considered in the survivability analysis of rock openings subjected to multiple attack. (Author)