Mechanical Behavior Of Assembled Discrete Group Stud Shear Keys In Composite Beams

Supported by the National Natural Science Foundation of China(NSFC)key project "design theory and intelligent construction method of prefabricated hybrid structure bridge in mountainous area"(U20A20312)and Chongqing Natural Science Foundation Project "behavior and calculation theory research of double uncoupled structure of prefabricated composite beam"(cstc2018jcyj ax0509),aiming at the mechanical behavior and shear capacity calculation method of prefabricated discrete group stud shear key in composite beam,the push-out test of prefabricated assembled group stud shear key was carried out,and the mechanical behavior and parameter influence law of prefabricated shear key were studied.Built on the analysis of the influence of the force difference between the push-out specimen and the composite beam,the calculation method of the shear capacity of the assembled discrete group stud shear key in the composite beam is proposed.The main work and achievements are as following:1.Taking the number of post cast key groups and the number of stud rows as the test parameters,the fabricated push-out test of 3 groups of 6 specimens was drawn up and carried out.The results demonstrate that the load displacement curve and the load interface slip curve can be divided into elastic stage and elastic-plastic stage.There are obvious differences between double bond group specimens and single bond group specimens in cracking form and development,and the cracks between bond groups reduce the bearing capacity of double bond group specimens.The single nail bearing capacity of double bond group specimens is 17.1% and 12.9% lower than that of a single bond group of four rows and single bond group two row specimens,respectively.2.The numerical model of push out loading of prefabricated shear key is established,which is in good agreement with the test.It is determined that the failure modes of multi bond group and single bond group are stud shear,and the cracks of multi bond group first appear between double bond groups,and the cracks of single bond group first appear at the interface.The number of studs and bond groups is the main influencing factors of bearing capacity reduction.3.The effects of strategic group spacing,number of key groups and stud diameter on the shear capacity of prefabricated push-out are analyzed.When the bond group spacing increases from 1.43 times the height of the reserved hole to 2.86 times the height of the reserved hole,the bearing capacity increases by 35%,when the number of bond groups increases from 1 to 4,the bearing capacity of single bond group decreases by 28%,and when the stud diameter increases from 13 mm to 16 mm,the bearing capacity increases by 7%.Based on the existing stud calculation method,the shear capacity calculation formula of assembled key group considering the reduction of key group and study group is proposed.4.By comparing the mechanical behavior of shear keys in pushing out shear and in beam shear,it is found that the bearing capacity of a stud to push out test is higher than that of beam shear,and the stiffness is smaller than that of beam shear.The influence of transverse dimension of post cast hole,width of precast slab and degree of clustering on shear bond in composite beam is analyzed.When the degree of cluster increases from0.111 to 0.25,the bearing capacity of single nail decreases by 33%;when the ratio of transverse dimension of post cast hole to beam length increases from 0.0175 to 0.03,the bearing capacity of single nail decreases by 35%.Following consideration of the size effect and the reduction factor of the cluster degree,the calculation method of the shear capacity of the shear key in the fabricated composite beam is proposed,which is in good agreement with the test results.