STRENGTH OF WELDED JOINTS IN CLASS A500C REINFORCING BARS UNDER LOW-CYCLE REPEATED LOADS

Abstract

For more than 25 years now, A500C class reinforcement has been the most widely used in reinforced concrete structures. The introduction of class A500C reinforcement has been accompanied by extensive research into its mechanical properties, bond with concrete, weldability and behavior under repeated loading. In particular, data have been obtained on the state diagram, the fulfilment of standardized mechanical properties such as yield strength, tensile strength, elongation at break, the bond with concrete of crescent-shaped reinforcing bars, thermal weldability, and the strength of butt and cross-shaped welded joints. At the same time, the strength of both the class A500S reinforcement itself and its welded joints under lowcycle and repeated loading remains poorly understood.This paper presents the results of experimental research on the most widely used types of welded joints for class A500C reinforcing bars – the C1-Ko type butt joint and the K1-Kт type cross joint under low-cycle repeated loading. The research carried out included tests on samples of 20A500С reinforcing bars made from St3Gps steel and 25A500S reinforcing bars made from 25G2S steel in their as- manufactured condition, their butt welds C1Ko for tensile strength and cross-shaped joints K1-Kт with 10A500С and 12A500С reinforcing bars for rationalization by welding under monotonically increasing and low-cycle repeated loading. The maximum cycle stresses were taken as 0,8𝜎𝑦, which amounted to 400N/mm², and the minimum cycle stresses as 80 N/mm². The stress range and cycle asymmetry coefficient were, respectively, ∆𝜎=320N/mm² and ��=0.2. The number of loading cycles was set at 50, after which the specimens were subjected to a monotonically increasing load until failure. It has been established that failure of the C1-Ko welded joint under monotonically increasing and ow-cycle repeated loading occurs within the heataffected zone. In tests under monotonically increasing loading, the tensile strength of the C1-Ko welded joint for 20A500C reinforcing bars was 0,88–0,92, and for 25A500C reinforcement made of 25G2S steel – 0.89–0.90 times the strength of the reinforcement in its as- manufactured condition. The test results showed that repeated loading did not have a lasting effect on the strength of C1-Ko butt welds in 20A500C and 25A500C reinforcing bars. The reduction in strength compared with a monotonically increasing load did not exceed 12%, and was within the test accuracy limits, amounting to 0,87–0,90 of the tensile strength of the reinforcement in its manufactured state. Failure of the K1-Kт welded joint under a monotonically increasing load occurred in the base metal, whereas under low-cycle repeated loading, failure occurred either in the base metal or in the heat-affected zone. The reduction in strength due to welding of class A500S reinforcement bars – 20A500С and 25A500С – in a K1-Kт type welded joint with reinforcement bars of, respectively, 10A500С and 12A500С, under a monotonically increasing load did not exceed 1–2% and was within the test accuracy limits, which, on the whole. The test results showed that low-cycle repeated loading did not have a lasting effect on strength of C1-Ko and K1-Kт welded joints made from 20A500C and 25A500C reinforcing bars; the reduction in strength, compared with tests using amonotonically increasing load, did not exceed 12% and was within the test accuracy limits, as was the case with tests on reinforcement in its manufactured state.