| Steel-concrete composite box girder is widely used in the design of expressway overpass bridge and ramp bridge because of its high torsional stiffness,strong stability,light weight and large span.With the improvement of bridge function,continuous composite beam bridge has strong competitiveness in many cases with its larger span capacity and smaller structure height.Based on the actual project,the development and distribution of cracks,slippage and deflection of pre-stressed steel-concrete box composite beams are obtained by scale test in the negative moment area.On this basis,the influence of web and baffle flange studs on the sliding development of composite beams is analyzed by using ABAQUS solid finite element model.In addition,the influence of pre-stressed bars on the cracking load of composite beams is obtained by analyzing the parameters of pre-stressed bars in the negative moment area of the model beam,and the applicability of the law to the original bridge is verified.Finally,Midas is used to analyze the construction stage of the original bridge and study the influence of the negative bending moment of composite beam on the compressive stress of composite beam slab under the action of pre-stress by using partial shear joint design and partial concrete design.The specific research contents of this paper are as follows:(1)The development and distribution of cracks,slippage and deflection of composite beams were studied by scale test in the negative moment area of composite beams.The results show that the crack distribution of composite beam is consistent with that of ordinary steel bar.According to the development curve of slip and deflection,the failure process of composite beam can be divided into elastic stage before concrete slab cracking,elastic stage after crack before steel beam yielding and yield stage of steel beam gradually yielding.(2)Through ABAQUS solid finite element model,the influence of web and baffle flange stud on slip development of composite beam was analyzed.The results show that the horizontal shear bearing capacity of box composite beams is provided by web flange stud,the setting of baffle flange stud cannot improve the shear connection degree of composite beams,and the elimination of baffle flange stud can relieve the force on the baffle and provide theoretical basis for reducing the stiffener of baffle.(3)Based on the analysis of the parameters of the pre-stressed bar arrangement in the negative moment area of the model beam,the influence of the pre-stressed bar on the cracking load of the composite beam is obtained,and the applicability of the rule to the prototype beam is verified.The results show that under different pre-stress levels,the cracking load is large when the resultant force point of the pre-stressed bars on the symmetry axis of the concrete slab is within the range of 0.15~0.50 times the width of the slab,and the cracking moment of prototype beam can be increased by 11% by optimizing the pre-stress arrangement.(4)Through Midas,the stress of concrete slab in the negative moment area of the original bridge is analyzed in the construction stage when partial shear connection design and partial concrete design are adopted simultaneously.The results show that:the positive moment zone of composite beam adopts the complete shear connection design,and the negative moment zone adopts the combination of partial shear connection design and partial outsourcing concrete design,which can improve the deflection of composite beam in construction stage and reduce the tensile stress of concrete slab in the negative moment zone of composite beam.The compressive stress of concrete slab in the negative moment zone of composite beams can be effectively improved by changing the semi-normal pre-stressed steel beam to pier top beam. |
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