Researching of reinforced concrete beams with damaged tensile rebar under the loading

Abstract

There are defects in all reinforced concrete structures: initial (obtained during production) and operational (which arise during exploitation of the element). Operational defects arise under the influence of the environment, aggressive influences and mechanical factors. All of these damages occur under the influence of the load - starting from the weight of the structure and the above lying elements and to the design work in the exploitation stages. All defects, which arise at the action of any level of load, lead to change in the stress-strain state. Particular attention deserves investigation of damages of the tensile reinforcement in bending reinforced concrete elements. Therefore, the purpose of this article is to determine the impact on the strength of reinforced concrete bending elements damages of tensile rebar obtained under the action of the loading. To achieve researching purpose, six researching reinforced concrete beams were designed, which were divided into two series: four samples of first series and two samples of the second. All samples were identical geometric dimensions. Difference between samples consists in the diameter of the tensile rebar: the samples of the 1st series are reinforced with one rod 20 mm in diameter, class А500С, and samples of the second series - with one rod in diameter of 16 mm in the class А500С. The corrosion of the reinforcement was simulated by drilling a hole in the middle of the sample with a diameter of 5.6 mm. This diameter of the hole corresponds to the corrosion of the cross-section of the rebar with a diameter of 20 mm to a diameter of 16 mm. Damages was carried out at the initial load level of 0.7 from the bearing capacity of the control samples. Exhaustion of the bearing capacity of control samples was achieved due to the achievement of the limiting deformations with the compressed concrete zone, and for samples of the second series also the onset of yield in the tensile rebar. Damaged samples of the 2nd series were destroyed due to the rupture of tensile reinforcement and the fracture of the sample into two parts. At that time, the limiting deformations in the compressed concrete zone were not achieved. According to the results of the research, it was found that with a decrease in the cross-sectional area of the reinforcement by 35%, due to damage to the stretched armature with an aperture of 5.6 mm in diameter, under the action of the load, the bearing capacity of damaged specimens decreased by 11%. Whereas samples with an equivalent diameter of the rebar to the diameter of the damaged sample showed a carrying capacity less than 37%, which approximately corresponds to a decrease in the cross-sectional area of the stretched reinforcement.