Research On Seismic Shear Capacity Of Concrete Beam With High-strength Stirrups

Our country is promoting the application of high-strength rebars in civil engineering.However,there are several problems on the mechanical and seismic behaviors of concrete structures reinforced with high-strength rebars.All kinds of members in the structures under earthquake often encounter the calculation of seismic shear capacity.Yet there is not an accurate conclusion of the upper limit of the actual achieved strength of high-strength stirrups.Moreover,researchers are also focusing on the seismic shear behaviors differences of the beams with normal strength stirrups and the beams with high-strength stirrups and whether the seismic shear behaviors of the beams with high-strength stirrups satisfy the requirement.On the other hand,in seismic design,brittle shear failure of members should be avoided and members don't fail until they obtain certain deformation capacity.There is not much research on seismic shear capacity based on deformation limit in our country.Aiming at seismic shear behaviors of beams with high-strength stirrups,the main contents are as follows:(1)Eight concrete frame beams with CRB600 H high-strength stirrups were conducted under low cycle reversed loading.The specimens were tested by cantilever loading device.The test results indicate that the failure patterns of specimens are shear failure after the longitudinal reinforcement yielding and their ultimate draft ratio is from 1/80 to 1/37.At the peak load,CRB600 H stirrups reach their yield strength.Moreover,other things being equal,increasing the stirrup characteristic value of specimens can improve their deformation capacity and dissipation capacity and slow down the stiffness degradation.Changing the stirrup arrangements of specimens and increasing the number of stirrup legs can improve their dissipation capacity,other things being equal.(2)Seismic shear behaviors of the beams with normal strength stirrups conducted by other researcher and those of the beams with CRB600 H stirrups were compared.The results indicate that if increasing the stirrup characteristic value of the beams with CRB600 H stirrups,their seismic shear capacity and deformation capacity are the same as those of the beams with normal strength stirrups.(3)Comparison of several formulas for the seismic shear capacity,including the code GB50010-2010,CECS356,EC8 and ACI318-14,was presented.The results indicate that the prediction of GB50010-2010 is higher than that of other codes and its additional safety reserve is relatively low.On the other hand,the ratio of the test values to the values calculated by GB50010-2010 is the smallest and the average ratio is less than 1.0.Considering the complexity and the large scatter of calculating seismic shear capacity,the formulas of seismic shear capacity in GB50010-2010 is not suitable for concrete beams with high-strength stirrups.(4)A total of 77 specimens with high-strength stirrups failing in shear or flexural-shear under cyclic loading were collected and stress magnitude of high-strength stirrups at the peak load was studied.The results indicate that the upper limit of the actual achieved strength of high-strength stirrups at the peak load is 618 MPa with 50% guaranteed rate and its standard value and design value are 459 MPa with 50% guaranteed rate and 400 MPa,respectively.Based on a total of 94 beams with high-strength stirrups failing in shear or flexural-shear under cyclic loading,considering the upper limit of the actual achieved strength of stirrups and deformation limit,a new equation for seismic shear capacity of beams with high-strength stirrups was proposed.In this thesis,the innovations are as follows:(1)The upper limit of the actual achieved strength of high-strength stirrups at the peak load was investigated.The specimens with the high-strength stirrups failed in shear or flexural-shear under cyclic loading.(2)Considering the deformation limit,a new method of determining the equation for seismic shear capacity of beams with high-strength stirrups was provided.