FLEXURE-SHEAR INTERACTION FOR RC BEAM

Abstract

The relative flexure capacity Mu/Mfl can be predicted by the several types of analytical models of flexure-shear interaction. Where Mu represents the bending moment in the beam due to the shear while Mfl represents the bending moment in pure flexure. The interaction of flexure and shear is primely depend upon the reinforcement ratio (ρ) and the shear span to the effective depth ratio. When it is drawn the curve with the help of these two values then at some point the lowest value of interaction is obtained which shows the valley in the interaction diagram. At this point, the shear span to the effective depth ratio is known as the critical shear span to effective depth ratio. The two models have been studied. One is for the normal grade of concrete and another one is for the high strength of concrete. The high strength of concrete is around 60 to 75 MPa. The flexure-shear interaction diagram is plotted because many of the beams do not use their full flexural capacity and fail in shear so to check the how much flexural capacity is used by beam interaction diagram is plot. The main aim of the study is to compare the analytical model of flexure-shear interaction diagram with the experimental results and to check the type of failure in the beam whether it is shear failure or bending failure. The effect of fire is also concerned with the flexure shear interaction model. The standard fire is used to check the behavior of beam for 1 hour and 3 hours. As the temperature increases, the mechanical properties of the concrete and steel decreases like stiffness, ductility, modulus of elasticity and the strength. The strength of the concrete decreases with increase in the temperature due to the deterioration and hydration of the concrete. The rate of decrease of strength of concrete is more as compare to the steel. The strength of steel is mainly affected by the temperature of above 500 °C. To study the flexure-shear interaction model, it is divided into the two actions known as beam action and arch action. From the graph, it can be said that before the shear span to effective depth ratio (a/d) 2.5, the arch action is dominant while above 2.5 ratio beam action is dominant. The lowest point of the graph is known as the critical relative flexure capacity of the beam and it is occurred at the critical shear span to effective depth ratio (a/d). The effect of fire changes the flexure capacity of the beam because it depends upon the strength of concrete and strength of steel. v The beam is used around 50-60 % of its flexural capacity which is very low as compare to the shear so beam fail in shear before reaching its full flexure capacity.