| Prefabricated concrete frame structure is a common prefabricated structure system,with good overall performance and seismic performance,which has been widely used in practical engineering.The composite beam is the horizontal member of the system.At present,for the composite beam,the design workload is large,the production efficiency is low,the production cost is high,and the steel bar collision problem is easy to appear on site.It does not play its due advantages in the actual project of prefabricated building,and sometimes the problems are even more than the cast-in-place structure.Based on this,this paper designs 8 test beams,including 6 composite beams and 2 cast-in-place contrast beams.The main research contents and conclusions are as follows:(1)Through the concentrated loading test on the specimen beam,the results show that the test beam has a typical shear failure mode,a main inclined crack appears on the inclined section,the upper mid span concrete of the beam is seriously damaged and crushed by the load,the precast stirrups and cast-in-place stirrups reach the yield state,and the beam is damaged.(2)The bearing capacity of the composite beam is calculated by using the formula in the code.The cracking resistance of the composite beam with hoop stirrups is equal to or even better than that of the cast-in-place beam.The cracking load calculation formula shows that the actual cracking load of the composite beam is stronger than the theoretical calculation;the ultimate load calculated according to the traditional shear bearing capacity formula is very close to the measured test value.Finally,some design and construction suggestions are given.(3)Based on the analysis of the test data obtained in the experiment,the load mid span deflection curve is drawn,and the load concrete strain and steel strain curve is depicted.The results show that the load deflection curves of the specimens are basically the same,and the strain of the longitudinal reinforcement is very small before the specimens reach the cracking load.The difference of longitudinal bar strain between "concave" composite beam and cast-in-place beam is large,especially after cracking.The internal force transfer effect of "convex" type composite beam hoop stirrup is the same as that of integral stirrup.From the analysis of stirrup strain data,it can be seen that the effect of this method is similar to that of the traditional mode of a whole stirrup.Although they are separated in form,the force transfer effect is equivalent to that of the traditional whole stirrup.Based on the load-strain curves of the two groups of specimens,it is found that the ring lap stirrup beam has little difference from the cast-in-place stirrup beam under the load,and can also transfer the shear capacity under the load,even 20 k N higher than the load that the cast-in-place stirrup beam can bear.(4)The finite element method is used to simulate the specimen beam,and the stress nephogram of reinforcement and concrete damage are analyzed.It can be concluded that the stress trend of composite beam is similar to that of cast-in-place beam.The stress of precast and cast-in-place side stirrups is continuous.Comparing the crack distribution and development trend observed in the test,it can be seen that the stress of composite beam is similar to that of cast-in-place beam The development trend of cloud image is basically consistent. |
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