Calculation of the strength of reinforced concrete columns under repeated longitudinal impact

Abstract

This paper reports the results of experiments with reinforced concrete column models subjected to repeated longitudinal impact loading using a pile driver. The strength of the column models is analyzed by comparing experimental data with results of mathematical modeling.The collapse of concrete-frame buildings under seismic impacts is characterized by failure of the concrete column body with a loss of stability of the longitudinal reinforcement, i.e., buckling of reinforcement bars in various directions, leading to the collapse of the structure or the entire building. Figure 1 shows the failure of the middle reinforced concrete column of the ground floor of the service center building resulting from the magnitude 7.9 earthquake on October 4, 1994 at the Goryachie Klyuchi village (the Iturup island). One can see the crushed top of the concrete column and the buckling of the main reinforcing bar due to the insufficient transverse reinforcement.Seismic calculations for concrete frame structures can be based on the results obtained for models of individual members. It should be taken into account that, during seismic impacts, the frame members are subjected to multiple shock loading. In the present work, the failure of models of concrete and reinforced concrete columns under longitudinal impact was analyzed using computational and experimental methods. The experimental studies of repeated shock loading were performed on a pile driver. Mathematical modeling, combined with the laboratory experiments, provided a more complete analysis and valid physical interpretation of test results.A mathematical model for calculating deformation and failure in porous high-strength ceramics under highvelocity impact and explosion conditions is proposed in [1,2]. Failure is treated as the formation, growth, and coalescence of microdefects under the action of stresses during loading. The model proposed in [2-4] has been used in failure calculations of brittle materials under multiple shock loading aimed at studying the particle crushing mechanisms in producing submicron-size powders of high-melting compounds in a pneumatic circulating device. In [5], this model was employed to calculate the dynamic strength of concrete.1. Experimental Studies. Reinforced concrete columns of dimensions 10 × 10 × 100 cm were made of B35 concrete and reinforced by a frame. A-III type longitudinal reinforcement of diameter 10 mm and Bp-I type transverse reinforcement of diameter 5 mm with a step 15 cm were used. The structures were installed vertically on a steel platform. The drop weight acted on the top surface through a steel distributing sheet 2 cm thick. In the experiments, the mass of the drop weight was varied from 225 to 500 kg. The weight drop height was varied from 35 to 70 cm. The measuring system was located inside a steel plate which was placed on the column head and impacted by the weight. The measurements were made by a 32-channel receiving-measuring complex in real time. The time-and-frequency parameters of the columns were determined on a p...