Effects of the compressive reinforcement buckling on the ductility of RC beams in bending

This paper presents a study on the structural behavior of 15 reinforced concrete beams. The beams were 3 m long and the rectangular cross section measured 0.20 × 0.30 m2. They were subjected to two concentrated forces, applied at a third of the span until the failure occurred. The beams had different amounts of longitudinal and transverse reinforcement and were divided into five series. Their strength, deformation and type of failure were analyzed. The main results are presented and discussed in terms of load-displacement, moment–curvature, ductility factor and plastic rotation capacity.In the light of the results it was concluded that beams with high tensile reinforcement ratios suffer premature failure due to the buckling of the compressive bars. These results indicate the importance of the stirrups spacing in RC beams. The influence of the tensile reinforcement ratio and the transverse reinforcement on the plastic rotation capacity and on the general beam behavior was analyzed. This experimental study made it possible to define maximum values for ρ and minimum values for Asw/s to ensure a certain structural energy dissipation capacity.

► The stirrup spacing in beams is important to avoid buckling of the compressive bars.
► The curve M − 1/r post-peak could be very different depending on ρ and Asw/s values.
► Stirrups made with special ductility steel are not relevant for beam’s ductility.
► The parameters ρ and Asw/s were related with the basic behavior factor qo.
► It is presented a relationship between θpl and Asw/s in terms of ρ.