EFFECTS OF MAIN AND SHEAR REINFORCEMENTS ON SHEAR CAPACITY OF REINFORCED CONCRETE SLENDER BEAMS

Abstract

Reinforced concrete sections can either fail in flexure or by shear. If failure is going to occur at all, it is preferable for it to be flexural failure which is ductile in nature, unlike shear failure which is brittle with little or no warning of the impending failure. However, the current design equations give an overestimated value of the shear capacity of the reinforced concrete, therefore most of the building collapse in the country is by shear failure which is sudden and catastrophic in nature. Hence, the focus of this research is to investigate the effects of main and shear reinforcements on shear capacity of reinforced concrete slender beams. The total numbers of the beams cast were twelve in which we have the un-reinforced concrete slender beams to be two having no reinforcement, the reinforced concrete slender beams without shear reinforcement also to be two with 2Y8 and 2Y12 as the reinforcements provided. The total numbers of reinforced concrete slender beams with shear reinforcement were eight with 2Y8 and 2Y12 as the main reinforcements provided while the shear reinforcement provided is Y6 at various spacing of 50 mm, 100 mm, 150 mm and 200 mm. The beams were loaded with point loads at the centre, with shear span/depth ratio of 3.8. The estimated moment of resistance for the un-reinforced slender beam is 0.86 kNm while its estimated ultimate load and shear capacity are 4.60 kN and 2.30 kN respectively. The estimated moment of resistance for reinforced concrete slender beams without shear reinforcement BWSR1 and BWSR2 are 3.9 kNm and 7.2 kNm respectively, the estimated ultimate loads are 20.80 kN and 38.40 kN, while the estimated shear capacities are 9.93 kN and 13.67 kN respectively. Also, the estimated moment of resistance for reinforced concrete slender beams with shear reinforcement BSR1, BSR2, BSR3, BSR4 and BSR5, BSR6, BSR7, BSR8 grouped together are 9.83kNm and 14.17kNm respectively while their estimated ultimate loads are 52.43kN and 75.57 kN. The estimated shear capacity(𝑉𝐸𝑆𝐹) for beams BUR, BWSR1, BWSR2, BSR1, BSR2, BSR3, BSR4, BSR5, BSR6, BSR7 and BSR8 are 2.30 kN, 9.93 kN, 13.67 kN, 23.33 kN, 27.64 kN, 36.26 kN, 62.13 kN, 25.27 kN, 29.52 kN, 50.55 kN and 63.47 kN respectively while the actual shear capacity(𝑉𝐴𝑈𝑆𝐹)for beams BUR, BWSR1, BWSR2, BSR1, BSR2, BSR3, BSR4, BSR5, BSR6, BSR7 and BSR8 are 2.25 kN, 6.00 kN, 11.00 kN, 12.50 kN, 15.50 kN, 17.50 kN, 21.00 kN, 18.50 kN, 21.50 kN, 24.00 kN and 27.50 kN respectively. These values of shear capacities show the estimated shear capacity was greater than the actual shear capacities by 2.17% to 56.67%. Above results show that the formulae for predicting moment of resistance and ultimate load for rectangular slender beams are satisfactory, while that for the prediction of shear capacity is not satisfactory and needed to be modified, in order to model what will give better results.