Spring 2007

 Effect of Shear and Compression Reinforcement on the Ductility of RC Members

Md. Shah Aziz Akand

 

Ductility is one of the most significant properties of structural members subjected to earthquake vibration. In fact, it is the single most important factor considered in the earthquake resistant design and detailing of RC structures. The importance of shear and compression reinforcements in the detailing of RC structures has long been emphasized in several building codes including the BNBC. However, the recommendations of earthquake detailing are little known and seldom considered in the structural design of RC structures in Bangladesh.

This thesis demonstrates results of numerical and experimental works performed at The University of Asia Pacific (UAP) on the effect of confining reinforcement and compression bars on the ductility of concrete cylinders and RC beams in particular. The tests on standard (612) concrete cylinders show that their ultimate strains are more than doubled if confined by hoop-steels at the spacing of 4. The bending tests are performed on simply supported beams (6 span with 68 sections) under third-point loading with and without compression reinforcements with lateral confinements at 8, 4 and 2 spacing. The tests show the beneficial effects of lateral confinement and compression rods on the ductility of the beams. The results also demonstrate that lateral reinforcements increase the crushing strains of concrete considerably while the compression reinforcements ensure that there is no significant loss of member strengths even after the crushing of concrete. In fact, the considerable ductility of reinforcements ensures that the beams do not collapse or lose strength significantly even when the midspan deflections exceed 4. On the other hand, the distress and loss of strength of beams without compression reinforcements and with lateral confinements at 8 spacing is also significant.

The experimental load versus midspan deflection data are compared with numerical results and show satisfactory in general, although the numerical simulations could not satisfactorily model the structural behavior at concrete spalling and after the crushing of concrete, particularly in the absence of compression bars.