Method Of Complex Joint Region In Steel Truss-Concrete Composite Continuous Bridge Girders Calculationand Stability

Steel truss-concrete composite continuous bridge girders are widely used in bridge construction.With the increase of the span of the steel truss-concrete composite continuous bridge girders and the surge of traffic flow,stability performance of steel truss-concrete composite continuous bridge girders during and under the completion of the bridge has attracted much attention.Life-span construction and development of steel girders and concrete composite continuous bridge girders are selected as an opportunity,and its complex joint region girders segment stability were studied.Focusing on complex joint region rotation stiffness,sensitive parameters of rotational stiffness and complex joint region were analyzed.The influence of rotational stiffness in the complex joint region on the overall stability of the composite structure is revealed.The research provides theoretical basis for design and construction of steel truss-concrete composite continuous bridge girders.The main research contents are as follows:(1)In order to study the influence of the rotational stiffness of the complex joint region on the stability of steel truss-concrete composite continuous bridge girders,the solid fine stiffness analysis model of the complex joint region and the fine girders segment fine model of the spatial joint region considering the actual stiffness of the truss-concrete welded joints were constructed.The nonlinear spring element is used to simulate the actual stiffness of the truss welded joints,and the overall stability analysis model of the beam-solid composite structure considering the rotational stiffness of the truss joint region is established.(2)The linear and nonlinear buckling analysis is carried out on the girders section in the most disadvantageous joint region during the top push process of the steel truss-concrete composite continuous bridge girders and the completion state of the bridge.It is confirmed that the truss-welded joint position is the weakest part of the structure,which is prone to local instability.When the pilot-span ratio increases from 0.65 to 0.70 in the process of jacking,the safety and stability coefficient of the structure increases significantly,and the stability performance of the structure does not improve significantly when the pilot-span ratio further increases.The initial defects of the structure have a great influence on the stability of the girders segment in the joint region.The larger the amplitude of the initial defects is,the more obvious the stability bearing capacity of the structure decreases.(3)The bending moment-rotation curve of the belly bar,chord bar and flat joint around the strong axis and the weak axis respectively is given.Sensitive parameters of the actual stiffness of the joint region were analyzed,and the variation law of the initial stiffness of the joint region with the thickness of the joint plate,the axial compression ratio and the welding residual stress was revealed.The recommended value range of the axial compression ratio of the chord in the joint region was given.(4)Considering the influence of rotational stiffness in the joint region on the overall stability of continuous bridge girders with truss-concrete composite structure,the safety reserve of the whole structure of continuous bridge girders with truss-concrete composite structure is obtained,and the influence law of rotational stiffness in the joint region on the overall stability performance of continuous bridge girders with truss-concrete composite structure is revealed.The influence of different structural parameters on the overall stability of steel truss-concrete composite bridge girders is analyzed with multiple parameters,including the bending stiffness of truss bars(belly,chord,and flat),the stiffness of bridge decks(concrete strength and thickness of bridge decks)and the longitudinal slope of bridge.The parameters affecting the overall stability performance of the truss-concrete composite girders are defined,which provides a theoretical basis for the lifetime construction and design of the truss-concrete composite continuous girders.