Study On Shear-Off Failure Of Keyed Epoxied Joints In Precast Segmental Bridges Under Impact

Assembly construction is one of the main directions of the development of bridge industrialization.Segmental prefabrication and assembly is the main assembly technology of prestressed simple supported beam bridge and continuous beam bridge,in which key tooth glue joint is the main form.Because the joints between segments are mainly concrete and reinforcement discontinuous,the joint position becomes the weak point of shear resistance,and the shear resistance of segment assembled beams becomes the focus and hotspot of research.Impact loads such as rolling stones,falling objects and rolling vehicles can not be ignored,which often lead to shear failure.However,at present,the research is limited to integral beams,and the research on dynamic response,failure mode and mechanism of segmental assembled beams under impact is still rare.For this reason,by means of monotonic increasing static load test,impact test of drop hammer and finite element simulation analysis,the impact resistance of keyed epoxied joint structure of segmental beams was been studied in this paper.The main research contents and conclusions are as follows:(1)Static load shear-off failure test and numerical study of single-keyed epoxied joints.Seven concrete members in two groups and 14 numerical model were designed,the shear failure characteristics of single-keyed epoxied joints and flat epoxied joints were analyzed.The test results show that the single-keyed epoxied joints and flat epoxied joints are brittle failures under direct shear.After the occurrence of the failure signs,the structure will instantaneously break down and lose its bearing capacity;there is a positive linear correlation between the normal stress level and the regularized shear stress.The numerical calculation results show that the normal stress level had no effect on the initial stiffness of the epoxied joints,but with the increase of the normal stress level,the shear damage of the epoxied joint is controlled,the degree of decline in stiffness is suppressed.(2)A drop weight test study on the shear failure characteristics of single-keyed epoxied joints under impact.Seven concrete members in two groups were designed,the shear-off failure characteristics of single-keyed epoxied joints and flat epoxied joints specimens under impact were analyzed.The test phenomenon shows that the complete shear-off failure process of the keyed epoxied joints under impact can be summarized as follows:(1)The upper corner of the key first appeared a diagonal crack extending toward the bottom.(2)Then there is a diagonal crack in the lower corner.(3)Finally,the concrete near the upper corner of the key is completely broken and extends downwards to develop and penetrate through the broken concrete at the lower corner to form a direct shear crack.It is very different from the short and small diagonal cracks at the keyed root when the key teeth are destroyed under static load.Especially when the impact force is large,there is no opportunity for the development of diagonal cracks in the lower corner.(3)Numerical study on the influencing factors and bearing capacity distribution of the shear-off failure characteristics of the epoxied joint under impact.16 single-keyed epoxied joints models and 2 double-keyed epoxied joint joints numerical models were designed,influence of concrete strength,impact form,impact speed and normal stress level on single-key epoxied joints shear were analyzed.The general law of bearing force distribution in keyed epoxied joints is summarized.The results show that the strength of concrete has a limited improvement on the impact resistance of single-keyed epoxied joints;It is more reasonable to judge damage by the initial momentum of the falling object.The larger the falling object momentum is,the more serious the damage will be.;The strength and rigidity of the keyed epoxied joints were improved with the increase of normal stress;The bearing capacity of the lower key in the single-keyed joints is the largest,and the bearing capacity of the upper key in the double-keyed joints is slightly larger than that of the lower key.