Research On Mechanical Characteristics And Improvement Of Negative Moment Zone Of Double-steel Box Composite Continuous Beam Bridge

The mechanical properties of steel-concrete composite continuous girder bridges are special,concrete slab in negative moment zone is easy to crack,and the stresses on the concrete slab in the negative moment zone under external loads are of great concern.The construction of a combined continuous girder bridge with a double steel box section is special,and the slip effect at the combined interface is not negligible,resulting in a more complex loading condition for this type of bridge.The analysis of reasonable section sizes and the detailed study of ways to improve the forces in concrete slabs in the negative moment zone for this structural form of bridge are of great importance for both design and construction.Bridge models were established for the overall stress analysis of the combined girder bridge by ABAQUS and Midas civil,and the study was carried out under four conditions: selfweight and second-stage load,maximum negative moment,maximum positive moment and lane load deflection arrangement.Transverse slip.The results of the two software simulations are basically the same and together they show that the forces at the concrete near the centre pivot point are more sensitive to changes in external loads.ABAQUS was used to carry out parametric sensitivity analysis on the concrete slab thickness,steel beam web thickness and steel beam bottom slab thickness of the cross-section.The effect of concrete slab thickness on the slip of the pegs is most obvious.The concrete slab thickness has the most significant effect on peg slip.The spanwise displacement is positively correlated with the concrete slab thickness and negatively correlated with the steel beam web thickness and bottom slab thickness.The transverse displacements of the four webs in the span of the double steel box girder and the distribution of the longitudinal concrete stresses at the pivot points in the cross-bridge direction were analysed under deflected loads and found to be asymmetrically distributed,the transverse displacements of the steel box girder webs near the location of the deflected load were most pronounced due to distortion,decreasing towards the distal steel box girder webs.As the concrete slab thickness decreases and the steel box girder web thickness increases,the transverse displacement effect of the web decreases.The longitudinal stresses in the concrete slab at the pivot point are greater on the side of the deflected load than on the distal side.Study of different force improvement measures in negative moment zones,detailed analysis of concrete slab segmental casting method and support displacement method using Midas civil.Both methods are effective in improving the concrete slab near the mid-support point.The long-term effect of the concrete will cause the tensile stress at the mid-support to increase gradually.The unsynchronised fall of the two intermediate bearings will result in a large compressive stress reserve in the concrete slab at the rear fall bearing,but the concrete stresses in the vicinity of the two intermediate bearings will differ considerably under loads such as Phase Ⅱ paving.