| Prefabricated construction and composition structure are two major trends of the world bridge development,and the prefabricated steel and concrete composite beam has become immediate areas of research focus.Shear connectors,as an important component of composite beams,directly affect the overall work performance of composite beams,and the complete research system is still lacking,due to the complex structure and the numerous influencing factors.However,the existing research results are mainly applied for to the case when the shear connectors is perpendicular to steel beam flange,but not suitable for the other arrangements of shear stud.Moreover,some issues need to be further studied following as the connector mechanical mechanism under passive constrained cases,the transmission mechanism of group connectors force,and the connectors theoretical algorithm under longitudinal shear force and vertical pulling force in composite beam.Therefore,the force transfer mechanism and computation method of shear connectors are studied based on the shear connectors in prefabricated steel and concrete composite beam,the main contents of the dissertation are as followsTwenty-four shear studs,divided into eight groups,are tested to study the shear mechanism of the two types of shear studs names as HS specimen(short for " the prefabricated horizontal layout shear studs")and VS specimen(short for " the conventional vertical layout shear studs").Tests show that compared with VS specimens,for the HS specimens under push-out load,the apparent cracks appear relatively late,the ultimate bearing capacity is bigger,the load-slip curves yield platform is longer,and the specimen could still bear some of the push-out load after the shear studs are damaged.Based on the test results of shear studs,the load-slip constitutive relation curve is derived.Then,the shear stiffness characteristic coefficient analysis method of the shear studs during elastic stage and elastic-plastic stage is proposed.Based on the test results of this study and those seventy-two test results collected from other researches,the exiting design and calculation methods of shear stud are evaluated for the two failure mode as the damage of shear stud and the destroy of local concrete.And the design calculation method suitable for specific situation is suggested.The parameters such as the diameter,the plate transverse spacing,the concrete strength,as well as the contact interface characteristics which affect the shear performance of shear stud specimens are analyzed.The analysis results show that the stud diameter and contact interface characteristics are the most significant effects on the bearing capacity of specimen.According to the analysis of residual bearing capacity of the specimens under different contact interface characteristics,it is found that the interface friction has larger contribution on the bearing capacity of HS specimens.For the effect of constrained and interfacial friction of the concrete between two vertical steel plates in HS specimens,the correction formula of the bearing capacity of shear stud in HS specimen is proposed.Five groups of pull-out specimens are tested to study the shear force distribution regularity of the shear stud along the longitudinal direction in prefabricated composite components.It is found that the distribution of steel plate strain of combined interface along the longitudinal studs row obey the Lorentz distribution during elastic stage,and obey the linear distribution during elastic-plastic stage.Thus,the shear force distribution formula for the elastic stage and the elastic-plastic stage is derived.Furthermore,analysis shows that the load distribution inhomogeneity caused by studs group effect presents nonlinear distribution characteristics which is obvious under initial loading,and then increases gradually until stays stability in later loading period.Through the static cyclical loading tests of ten HS specimens which are divided into 6 groups,the influence of the crest and applied cycles of cyclic loads on the shear stiffness and slip behavior of the HS specimens are studied.The results show that,under the cyclical service loads,the HS specimens behave elastically,and the load-slip relation is mainly in the form of repeated skew lines.However,when the crest of the cyclical loads exceeds the elastic capacity,both the ultimate and residual slip increase in a nonlinear way with the crest of cyclical loads.Under the cyclic loading with the constant crest,the regression rate of stiffness of the specimens are gradually reduced with the increase of the loading cycles.Based on the statistical analysis of the testing data,the relation between regression rate of stiffness and the cyclic loads,including the applied cycles and the loading level,are established.The mechanical behaviors of shear studs both in the prefabricated steel-concrete composite beam and in conventional ones are analyzed and compared,using the numerical simulation method.The difference of the shear performance of studs between the two types of beams is theoretically investigated according to the classical material mechanics.For the fabricated steel-concrete composite beam which is simply supported,the differential equations calculating the pull-up force of transverse studs are established using the elastic theory of composite beams,and solved by the Cramer’s criteria. |
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