Effect of structural features and loading parameters on bond in reinforced concrete under repeated load

Abstract

Some reinforced concrete structures are subjected to repeated loads during their service lives, and the effect of repeated loads is stronger and more complex than static loads. This paper reports the results of the tests performed on cylindrical reinforced concrete specimens under uniaxial repeated loads. The effect of structural parameters (e.g., stirrup configuration, bond length, confinement method, and concrete cover) and loading parameters (e.g., amplitude, peak load, loading rate, and initial load cycles) on the bond properties of the reinforced concrete under repeated loads was studied in detail. In addition, the degradation mechanisms and failure modes of the specimens' bond stress were analyzed. It is found that the use of stirrups, increase of bond length, and concrete cover, as well as confinement can effectively curb the widening and expansion of cracks in concrete and significantly improve ductility and repeated load bearing capability. As the rigidity of confinement material increased, the enhancement effect of confinement on bond stress increases. Compared to the role of confinement (e.g., carbon fiber reinforced polymer), increasing the concrete cover can more effectively improve the bond stress. The rebar's subsequent residual bond stress declines as the number of early-stage load cycle increases.bond stress, load parameter, reinforced concrete, repeated load, structural feature | INTRODUCTIONReinforced concrete structures will bear various types of loads, among which constantly repeated loads during normal usage. These loads can include vehicle loads on bridges, elevated roads and underground railway tunnels, vibration loads on industrial structures, wind loads on ocean engineering constructions, and wave loads on harbor constructions. [1][2][3][4][5][6] The effect of repeated loads on the operational properties of concrete structures is more intense and complex than that of static loads. With an increasing number of load cycles, damage accumulates in the bond of the reinforced concrete, and slip occurs between the rebar and the concrete, leading to increased structural deflection, reduced strength, and even sudden failure. An effective, scientific evaluation of the accumulated level of a structure's damage in a repeated load environment and an understanding of the degradation mechanism of the bond stress between the rebar and concrete under repeated loading would enable prompt and effective strengthening and repair measures to slow the structural damage process.Because of the heterogenic nature of concrete materials and the complexity of repeated loads, performance tests are the most commonly employed means of investigating this problem. Rehm and Elingehausen 7 showed that rebar diameter and concrete strength had no effect on bond fatigue life; with an increasing number of load cycles, rebar slip was related to not only load cycles but also stress levels and loading rates, and the effect of load cycles on the ultimate bond stress was relatively small. Balazs 8 reported that the slip rate tended...

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Experimental study on the fatigue bond behavior of concrete beams reinforced with hybrid fiber‐reinforced polymer and steel bars

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