Experimental Study On Steel-concrete Connection Segment In Large-span Hybrid Cable-stayed Bridge

With the development of economy and technique in China, more and more cable-stayed bridges come into application in the past ten years, whose span ranges from a few hundred meters to thousand meters and structural types is various. Due to its superior performance, steel-concrete hybrid beams become the common girder type of large-span cable-stayed bridges. Design of large-span cable-stayed bridges with concrete girder focus on stress performance of steel-concrete connection segment as well as load-transferring performance. Based on the Jiujiang Yangtze River Bridge, this paper systematically studies stress performance of steel-concrete connection segment of lager-span composite beam cable-stayed bridges from three aspects of integral stress performance, transfer mechanism of connection segment as well as stress performance of transition segment and static and fatigue performances of local PBL shear connectors by large-scale model test, finite element numerical simulation and theoretical research. The main research content is as follows:(1) In order to master stress performance of combination segment integrally and guide the development of mode test, this paper establishes full-scale solid-shell finite element meticulous calculation models of connection segment and calculates stress state of steel beams, concrete beams and combination connectors under the most unfavorable positive bending moment working condition and the most unfavorable axial force working condition. As a result, stress performance of connection segment is mastered integrally. Research results indicate that stress state of connection segment is reasonable with stress of components in elastic phase while force transmission between stud connectors and perfobond strip is reliable to ensure the transferring performance of connection segment.(2) Model specimen is designed with a scale ratio of 1:2; load and boundary conditions are setting according to actual internal force state; test research is developed for the purpose of stress performance of connection segment. Research results indicate that stress and strain of components is in the elastic phase under each working condition and working performance is great. Furthermore, carrying capacity requirements of steel-concrete composite beam in Jiujiang Yangtze River Bridge is satisfied with certain safety margin. In addition, the stress state is reasonable of this form of connection segment, which is suitable for use in the large-span concrete girders.(3) In order to study the transferring mechanism and failure state of different forms of connection segments, two model specimens, whose configuration type is changed from the most unfavorable cell box in actual bridge, are manufactured with a scale ratio of 1:2. According to the test and calculation result, the paper investigates force transferring route, analysis the mode, ratio and area of force transferring and studies homogeneity and effectiveness of stress dispersion.(4) Through the model load test with a scale ratio of 1:2, this paper studies stress distribution law, failure mode and carrying capacity of stiffness transition segment of steel girder with different configuration forms. Research results indicate that the end parts is the weakest part under force, which enter plastic phase prior to the other parts. Diaphragms setting around the end part of transition segment not only decrease the stress concentration evidently, but restrict out-plane deformation of bottom plate around.(5) In order to study the stress performance of connection segment, this paper conducts the experimental research on static and dynamic load performance of PBL shear connectors, which consists of 7 static load specimens including 4 PBL specimens with perforated reinforcement as well as 3 PBL specimens without perforated reinforcement and 10 fatigue tests specimens used for fatigue load amplitude. The research result indicates: the average value of ultimate carrying capacity of PBL specimens with perforated reinforcement is better than PBL specimens without perforated reinforcement, load pattern has great influence on load-slip curve after reaching its ultimate carrying capacity; fatigue failure characteristics of PBL specimens with perforated reinforcement is concrete tenon failure while perforated reinforcement was sheared break. Meanwhile, load-fatigue life curve equation with failure probability of 50% and 2.3% is acquired by fitting method through fatigue tests.