Influence of loading rate on concrete cone failure

Abstract

In the present paper the rate sensitive model, which is based on the energy activation theory of bond rupture, and its implementation into the M2-O microplane model for concrete are discussed. It is first demonstrated that the new model realistically predicts the influence of the loading rate on the uniaxial compressive behaviour of concrete. The new rate sensitive microplane model is then applied in a 3D finite element study of the pull-out of the headed stud anchors from a concrete block. In the study the influence of the loading rate on the pull-out capacity and on the size effect are investigated. The anchors are loaded with relatively high loading rates. The results of the study show that with the increase of the loading rate the nominal pull-out resistance increases. Moreover, it has been found that the size effect on the concrete cone capacity is stronger when the loading rate is higher. The result of numerical study implies that it must exist a problem dependent critical loading rate for which the size effect is minimal. INTRODUCTIONIt is well known that the loading rate influence significantly structural response. The material response depends on the loading rate through influence two different effects: (1) through the rate dependency of the growing microcracks and (2) through the creep of the bulk material between the cracks. Depending on the material, it dominates the first or the second effect. For quasibrittle materials, such as a concrete, which exhibit cracking and damage phenomena the first effect dominates for very high loading rates (impact loading). This is especially thru for the case of recently observed phenomena (Bažant et al. [1]) for which a sudden increase of the loading rate in softening leads to reversal of softening into hardening. However, for lower loading rates the second effect is more important.In the literature can be found a number of theoretical and experimental studies that deal with the problem of the rate effect for different materials (for literature review see Bažant et al. [1]). In most of these studies various stress-displacement relations, similar to the spring-dashpot models of viscoelasticity, were used. However, as pointed out by Bažant et al.[1] these models performs well only for one order of magnitude of the loading rate. Here is for the rate dependency of the crack propagation adopted a model, which is applicable over many orders of magnitude of the loading rate. The model is based on the rate process theory (Krausz and Krausz [2]) of bond ruptures. It is coupled with the M2-O microplane model for concrete (Ožbolt et al. [3]), which has been shown to be capable to realistically simulate failure of concrete structures for complex threedimensional stress-strain states (Ožbolt [4]).Experience, a large number of experiments as well as numerical studies for anchors of different sizes confirm that fastenings are capable to transfer a tension force into a concrete member without using reinforcement (Eligehausen et al. [5]). Provided the steel strength of the a...

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