Residual crack extension resistance of post-fire wedge-splitting normal strength concrete specimen based on the cohesive force function

摘要

A comparative study on determining the crack extension resistance curves (K_R-curves) for the complete fracture process associated with two functions of the cohesive stress distribution, i.e. Peterson's softening curve and CEB-FIP Model, 1990 softening curve using an analytical method and the weight function approach is presented in this paper. Fifty wedge-splitting normal strength concrete specimens were prepared to sustain ten different elevated temperatures up to 600 ℃. The stress intensity factor curves (K-curves) were calculated from the load-displacement curves obtained on these post-fire specimens. At each temperature, the residual fracture toughness K_R(△a) increased with the crack extension length △a, whereas the K_R-curves became lower and flatter with the increasing heating temperatures T_m. It was found that the K_R-curve calculated from the weight function method coincided well with the one from the analytical method, whereas different softening curves had observable effects on the K_R-curves. The stability of the K_R-curve and the influence of temperatures on the crack tip opening displacement-crack extension curves (CTOD-△a curves) were also analyzed.