Fracture mechanics based design of reinforced concrete beams-An analytical study

Abstract

For a developing country like India, construction sector will be a governing factor in deciding the growth of the nation marching towards 2040. Growing infrastructure demands utilization of huge quantities of concrete. Concrete being quasi-brittle in nature is weak in tension which has got a tendency to crack when exposed to external loading. Steel is used as a reinforcement to enhance concrete tensile strength. Traditional and conventional methodologies of design of concrete structures are based on limit states of collapse and serviceability. The existing design principles from various standards across the world overestimates the steel for increasing grades of concrete which indeed will escalate the cost of construction. Its high time that these conventional design principles needed to be revised. Fracture mechanics is one such methods which can be a deciding factor for the design of concrete structures. This can be achieved using concrete mix characteristic length and structural ductility index. The present study deals with the design of reinforced concrete beam as per existing Indian standards for both gravity and earthquake loads and compare the same with fracture mechanics-based design approach. Size independent fracture energy, tensile strength of concrete, modulus of elasticity of concrete, for various grades of concrete are used as material parameters. These parameters are obtained from the experimental investigations on concrete available in the literature. A standard prediction model is proposed based on the strong physical principles associated with the concept of fracture mechanics. It was observed that there is a 10% to 30% reduction in steel requirement for concrete flexural members using fracture mechanics-based design compared to existing Indian standard IS 456:2000 for gravity loads.