Determination of the bearing capacity of reinforced concrete beams with damages under loading

Abstract

Results of experimental and theoretical research of reinforced concrete beams with damaged concrete in a compressed zone under the load are considered in the paper. To compare the impact, reinforced concrete beams without damage, with damage and with damage under load were studied. In this latter case, the reduction of the compressed zone was carried out at the level of 0.3 of destructive load of control sample. Thus, the damage had been carried out in the first stage of the stress-strain test samples until cracks appeared. For modelling, the FEMAP calculation program and the NX Nastran calculation software were used. The damage was made in the middle of a compressed zone of 30x20 mm. For the theoretical modelling, the FEMAP calculation program and the NX Nastran calculation software were used. A comparison of the distribution of internal forces of experimental and theoretical samples of damaged concrete was also made. The study showed an increase in the bearing capacity when the element is damaged at load of 0.3 of the expected destructive load of control sample in comparison with damage prior loading. The loss of bearing capacity due to damage under the load in comparison with the sample without damage is 18.9%. Damage effects both crack resistance and appearance of atypical cracks. Atypical cracks appear due to change of direction of major forces during damaging. This experience showed that the permissible deviation was not exceeded without significant erasure of the calculation accuracy. However, it is possible to reduce the percentage of deviation in the readings due to complicated calculation, if necessary. There are various methods to reduce deviation, to increase the correspondence of physical and mechanical properties of materials (for example, use of non-linear diagrams instead of bilinear ones), to rise the number of finite elements, as well as combinations of these methods.