Structural System And Composite Grider Behavior Of Multi-SpanSuspension Bridges

The composite structures and multi-span suspension bridges are developing rapidly during recent years.This dissitation mainly focuses on the stiffness system and composite girder behavior of multi-span suspension bridges,which are investigated from the overall behavior to the key local speciality.The main results and achievement of the research are summarized as follows:(1)The theoretical models for longitudinal stiffness and vertical stiffness of multi-span suspension bridges were derived.The longitudinal stiffness formulae werederived based on the energy principle,and the elastic elongation of the cable wasconsidered which was proved to be non-negligible,especially for long-span bridges.The vertical stiffness formulae were derived according to two key parameters including the increment of the cable sag and the force transfer efficiency between adjacent spans.The proposed models were verified by previous researches and a series of finite element models(FEM)with good accuracy.The main cable stiffness and the mid-tower stiffness were found to be the key factors for the longitudinal stiffness of the bridge.The deflection under live load decreased when the dead load of cables and girders increased because the increasing dead load improved the gravity stiffness of the bridge.(2)Based on the derived theory for the stiffness system,an accurate and efficient program for the nonlinear analysis of multi-span suspension bridges(MULTI-SBPD)was developed.The proposed program was applied to different conditions of suspension bridges and was verified with good accuracy and efficiency.The program would be a stable and efficient platform for engineering design and relevant researches of suspension bridge.(3)Two three-span composite girders by overhanging the specimens to simulate the behavior of suspension bridgeswere tested.A new-kind of uplift-restricted and slip-permitted T-shape(URSP-T)shear connector was proposed to decrease the tensile stress of the concrete slab in composite girders when subjected to hogging moment.The T-shape shear connectors were installed at half side of the specimen to compare with the traditional steel studs which were installed at the other half.The test indicated that the T-shape shear connector could decrease the tensile stress of the concrete slab.The displacement of the bridge girder was mainlydue to the cable deflectionwhile the girder rigidity influenced little,especially for large-span suspension bridges.(4)The theorical model for composite girderd subjected to hogging moment was derived.The slippage effect was considered in the model.Based on the theorical model,the T-shape(URSP-T)shear connector was proved to have the ability to decrease the tensile strain of concrete slab when the girder was subjected to hogging moment.The shear force-slippage curve for the T-shape(URSP-T)shear connector was proposed.The finite element models for the tested specimens were eatablished by using the proposed connector curve,which was verified with good accuracy by comparing with the test results.(5)The design suggestions for suspension bridges which use composite girders was proposed based on the bridge program and the test results of composite girders.The behavior of composite girders and that of steel girders were compared with each other.Proper value for the key parameters were proposed for further design.