Punching shear strength analysis of corroded reinforcement concrete slab

Abstract

Reinforcement steel bars corrosion is a serious problem worldwide. Reinforcement bars corrosion is not the only root cause to all structural defects, it has also become a safety risk of great concern, as structural integrity deteriorates as a result. The bearing capacity strength of the reinforced concrete members is impaired in numerous behaviours, as reinforcement corrodes. Corrosion will result in expansion in volume of concrete, which increases internal tensile stress due to the increased frictional force cause by interlocking of aggregates. Consequently, surrounding concrete cracks and causes spalling as corrosion advanced. Moreover, internal tensile stress during corrosion tend to result in existing fine line or micro cracks to enlarge, resulting in increasing permeability of concrete and form a chain of interconnected defects. Further, reinforcement cross section is progressively lost to corrosion, causing a decreasing in members flexural strength, decreasing in yield strength of reinforcement bars and reduction in ultimate elongation rate. Furthermore, the bond between reinforcement and surrounding concrete weakens, which critically affects bonding strength, thus the load transfer mechanism will be affected. Therefore, corroded reinforcement will adversely affect the durability, bearing capacity and functionality of the structure. The flat plate slab system presents a complicated mechanism, especially in the of slab-column connection. Punching shear resistance is one of the critical design considerations. It is known that punching shear failures occur suddenly with no warning. Moreover, triggering of progressive collapse could happen in punching shear failure. Therefore, thorough theoretical and experimental studies on the punching shear resistance of reinforced concrete have been the focus in recent studies. Design parameters such as size, column rectangularity, flexural reinforcement ratio, concrete compressive strength and span-depth ratio have been studied extensively over the recent years. In 2018, calculation of punching shear failure load for slab under low reinforcement ratio using general and simplified method was presented by Susanto [T1]. In the same year, glass FRP were revealed to greatly increase punching shear resistance in a study by Ahmed [H2]. The research mainly focuses on the improvement of the punching shear behaviour when FRP were used. Another study on use of high strength concrete also produced similar conclusion [Y3]. However, there was inadequate research on other parameters such as steel corrosion rate. Sea levels are rising due to climate change, hence this parameter is of increasing importance for structures under long term corrosive environment. There will be a significant decline in the shear strength resistance in the long run. This will be a serious safety issue which will cause catastrophic consequence to buildings and human lives. Therefore, our experiments focus on changes in punching shear behaviour due to different corrosion rate.