Analysis And Study On Thestiffness Of Reginal Confined Concrete Beams With Different Stirrup Forms

Regional confined concrete(RCC)beams,confined in the compression area of the beam top,was significantly improved in ductility and the maximum concrete compression strain compared with normal confined concrete(NCC).No longer impacted by the relative height of compression zone,the over-reinforced beam,bearing capacity and ductility of which have a certain increase,won't have brittle behavior.,Under the same carrying capacity,he height of the beam is greatly decreased,so the storey height of building can be reduced,achieved the goal of saving material.By applying structural experiment and finite element method,this paper analyzes the stiffness of 10 beams with different stirrup forms,among which there are 4 RCC beams with "?" confining stirrups,another 4 RCC beams with small square stirrups and 2 NCC beams.Firstly,due to the confined body won't crack within the whole loading period by considering the confine affection of RCC and the concrete elastic modulus have improved to some extent,the paper presents the formula of short-terms stiffness of RCC beam.Secondly,the rationality of the theory formula is validated by comparing with the result of the experiment.Finally,nonlinear finite element analysis of the beams has been made to simulate the whole process of the experiment.The experiment result shows that: the rigidity of the beam with "?" confining stirrups is effectively improved,especially for bending members;however,the confined body has little effect on shearing rigidity for the beams with small square stirrups.In order to ensure the increase of bearing capacity,ductility and rigidity,measures must be taken to enhance shear resistance of the beam with small square stirrups.The finite element analysis results show that: load-displacement curves of the finite element model show good agreement with that of the experiment,demonstrated that the parameters of the finite element model are reasonable.Similar to the experiment,the rigidity is slightly improved for the RCC beam with "?" confining stirrups under shear load,while the improvement of rigidity is obvious.The small square stirrups on the shear zone have little influence on shear capacity.However,to take full advantage of the small square stirrups in RCC structure in practical engineering,the small square stirrups and the normal stirrups together can be put in the reinforcement cage to bear shearing load.