| Eight simply supported beams without web reinforcements and different ratio of longitudinal reinforcement were tested under static top loading, with the shear-span ratio being kept around 1.5.Among them, four beams were doubly reinforced and the left four beams were simply reinforced. On this basis, the overall process of failure under shear and the effect of longitudinal reinforcement ratio on cracking, failure modes, strain distribution of reinforcements and ultimate capacity of RC beams without web reinforcements were investigated. In the experiments, development of the cracks was carefully recorded. Strains on the longitudinal reinforcements and deflection of the beams were measured in detail. Furthermore, correlation between the measured strain profiles of the reinforcement and the observed cracking development of each specimen was pursued. Principal factors contributing to the cracking pattern and failure mode were figured out as a result. Secondly, comparison of the tested results between the beams with and without web reinforcements unveiled effect of the stirrups on development of cracking, final failure mode, strains on the longitudinal reinforcements and ultimate capacity. At the same time, compare the result of nonlinear finite element program VecTor2 and the result of experiment, the author evaluate the validity of the program to analysis deep simply supported beam and the rationality of the basis theory. Primary conclusions were thus drawn. ⑴With the increment of longitudinal reinforcements ratio, the failure mode of beams without web reinforcements was change from flexural failure to shear failure. The development of the flexural cracks was less sufficiency and the position of the shear cracks was moved from the load point to the support. ⑵With the increment of longitudinal reinforcements ratio, shear capacity index Vu / fcbh0 of beams increased. When the tensile reinforcements ratio was the same, the shear capacity index of simply reinforced beam was bigger than the index of doubly reinforced beam. Furthermore, the simply reinforced beam L4 has the biggest shear capacity index Vu /fcbh0 . ⑶When the longitudinal reinforcements ratio was the same, the ultimate capacity and the stiffness of beams with stirrups were bigger than the beams without stirrups. And the research also shows that the shear capacity of beams with web reinforcements was simply equal the shear capacity of beams without web reinforcements plus the capacity of stirrups was not a rational idea. ⑷As for ultimate shear capacity prediction of beams failed in shear, the tested results were lower than the results predicted by nonlinear finite element program. As for the beam failed in flexure, contrary result was gained. Furthermore the program has a bigger stiffness prediction and less deflection prediction. ⑸The cracks'number, angles, height and width could not be accurate simulated by nonlinear finite element program VT2 based on smeared crack model. Improvement of the smeared crack model should be in process.
|
PDF Full Text Request