Stochastic Approach to Study the Influence of Rate of Loading on Strength of Concrete

摘要

Although any reliability analysis depends on the entering load and resistance distribution functions, the actual materials behavior has been neglected in many reliability assessments. Strength of concrete is widely scattered because of the heterogeneity of this composite material. So far no generally accepted theory to describe the stochastic nature of concrete properties is available. Beside this, hardly anything is known on the influence of rate of loading on the variability of strength of concrete. In this paper, a stochastic theory for fracture of concrete materials is presented. This theory is based on physically relevant probability models. It is possible to describe the fracture process not only under monotonically increasing load, but also under time-dependent loading conditions such as sustained load and repeated load. Moreover, this theory provides a realistic basis for a mathematical formulation of the variability of porous materials. Theoretical predictions are compared with earlier published data. Experiments have been carried out to verify the theoretical approach described in this report. Special emphasis is placed on the influence of rate of loading on the mean strength and the corresponding variability. The rate of loading has been changed by three orders of magnitude and for most series six different rates have been chosen within this range. Specimens of high strength mortar, low strength mortar, lightweight and normal concrete have been tested under compressive and bending load. The distribution function has been evaluated from about 30 individual tests for each chosen condition of loading some experiments to investigate the influence of temperature have been carried out.