Behavior of Reinforced Concrete Wide Beams

Abstract

Researchers have a concern that normal beam design procedures are not fully applicable to RC wide beams. Many studies have been conducted on RC wide beams and researchers have diverse results regarding shear strength of wide beams. Studies have shown that the shear behavior of RC wide beams varies depending on various factors such as aspect ratio (b/h), shear span to depth ratio (a’/d), longitudinal reinforcement configuration, amount and configuration of vertical stirrups, presence of temperature and shrinkage reinforcement and stirrup spacing across the width of beam. Another important subject is the behavior of RC wide beams at high longitudinal reinforcement ratios (closer to balanced reinforcement ratio). A beam designed under balanced reinforcement conditions and secured for shear is expected to fail in a ductile manner but there is a possibility of stiffer mode of failure at high longitudinal reinforcement ratios. Such stiff mode of failure can cause a beam fail in a sudden manner. It is important to mention that wide beams may be reinforced closer to balanced reinforcement ratio to meet high flexure demands. Moreover, web shear reinforcement is provided in all practical concrete beams. Therefore, there is a need to study the behavior of RC wide beams with web shear reinforcement demanded from the ultimate load which would cause flexure failure. How the shear strength (Vc + Vs) at ultimate load varies with the increasing percentage of longitudinal reinforcement ratio for a shear secured beam? Present study encompasses testing of eight full scale, simply supported RC wide beams. Beams are divided into two series being W and M. W series consists of 30 inches wide beams while M series contains 40 inches wide beams. In each series there are two different longitudinal reinforcement ratios provided. Four point banding method was adopted for testing of all beams with a/d ratio of 4.5. All beams have thickness and span of 10 inches and 11 ft respectively. Beams are designed in such a way that tensile flexure failure would occur before shear failure. After testing it was observed that ACI design procedures may be applied to wide beams for flexure design but at high reinforcement ratios such beams may fail in shear at a load less than that predicted by ACI shear equations. Sudden shear mode of failure was observed for the beams which were reinforced closer to balanced reinforcement ratios. It was also noted that changing width did not change the mode of failure of wide beams.