Effects of triangular reinforcing on flexural and deformation behaviour of concrete beams

An investigation was conducted to evaluate structural performance of rectangular beams that had been reinforced with the triangular cage (TRC) of steel layout or triangular reinforcing. In the experiment, flexural behaviour of TRC beams was compared with that of conventional beams reinforced with the rectangular cage (RRC) of steel layout i.e. rectangular reinforcing. A set of 16 rectangular concrete beams of size 110 × 130 × 2000 mm were cast, comprising eight (8) TRC beams and eight (8) RRC beams. The main variables in the investigation were:- different concrete strengths of 30 and 60 MPa, triangular or rectangular stirrups spaced at 100 mm or 200 mm, along with varied steel areas of the bottom (tension) and top (compression) reinforcements. Experimental results showed that the load carrying capacity values of TRC beams were similar to those of RRC beams. Interestingly, TRC beams consistently gave 14% to 49% lower deflections, relative to those of their counterpart RRC beams. It was found that the limit state theory accurately predicts the deformation behaviours of TRC beams as it similarly does for RRC beams, but it tends to underestimate the load carrying capacity of the former. Use of TRC steel layout contributed up to 10.5% cost saving.