Research On The Mechanical Behavior And Curvature Optimization Of Long-span Circular Steel Box Girder Footbridge

This paper studies the mechanical behavior of the long-span annular steel box girder footbridge.Based on the summarization of the mechanical properties and the calculation theory of the annular steel box girder bridge,the Midas Fea finite element program is used to accurately simulate the steel box structure using the plate element.Each of the detailed constructions starts from the calculation and analysis of a large-span circular pedestrian bridge project,and discusses and analyzes the relevant factors affecting the mechanical characteristics of the annular pedestrian bridge,including the arrangement of different spans and the continuous and unclosed structure of the ring.The annular continuous closed structure(ie,with or without expansion joints),box beam section height,web thickness,stiffener setting,overall temperature change,curvature change,etc.,have a certain space for optimization of the span of the original bridge of the steel box beam footbridge.And should be arranged in accordance with the principle of continuous beam span arrangement;after the closed structure of the non-closed structure of the annular steel box bridge,the natural vibration frequency can be increased,which can effectively change the state of structural mechanics,so that the structural force is more reasonable;When the section height changes from 1.2m to 2.2m,the increase in the section height makes the structural strength of the annular steel box girder bridge With increasing average,the stress and displacement of the structure itself are greatly reduced.When the thickness of the web changes within the range of 14mm~22mm,the mechanical properties of the annular steel box girder bridge are less affected,and it is found that the thickness of the web is not as thick as possible;For the analysis of the original bridge,it was found that the equivalent stress values of the bulkheads and longitudinal ribs in some local locations(near the bearings)reached 170.27 MPa,which is a result not seen in previous literature,but similar structures in the past Checking the strength of diaphragms and stiffeners is neglected in the calculation.Through further analysis,it is found that when the stiffener height changes in the range of 50mm~140mm,the mechanical state of the annular steel box footbridge has no obvious change,and it is stiffened.The increase in the height of the ribs will increase the stress of the structure itself;when the spacing between the stiffeners changes from 200 mm to 800 mm,the spacing between the stiffeners increases,and the structural rigidity increases so that the deflection of each span decreases,but the increase or decrease of the spacing may make the structure itself The stress increases;the temperature changes have a significant effect on the mechanical properties of the unclosed and closed structures of the annular steel box girder bridge.The increase in temperature increases the stress of the structure itself.The axial displacement of the structure is also greatly increased,but it has no influence on the deflection of each structure;when the radius of curvature changes within the range of 33.759 m to 58.759 m,the increase of the radius of curvature causes the structural strength and stiffness to be greatly reduced,making the structure itself Stress and displacement increase dramatically.In addition,the influence of diaphragms and stiffeners on the natural vibration frequency of the annular steel box girder bridge structure is studied in this paper.The arrangement of diaphragms and stiffeners is beneficial to improve the natural frequency of the annular steel box bridge footbridge,and it is effective.Controlling the displacement of the annular steel box footbridge under natural vibration and other conclusions.Based on the above conclusions,a reasonable span setting method for a large-span circular steel box girder footbridge and a reasonable structural design and design concept are proposed: The effect of the expansion joint on the structural mechanical state of this type of annular steel box girder bridge is significant,similar to the side span.In a circular footbridge with a large span,an expansion joint may not be provided,and an annular closed structure may be provided;the thickness of the web of the steel box girder is not as large as possible,and the thickness of the web should be controlled within a design range of 14 mm to 18 mm;When designing box girder structures,the strength of the diaphragms and stiffeners should be checked,especially the strength of the diaphragms and stiffeners at the bearings.For the engineering example in this paper,the layout of the span of the steel box girder bridge under the actual position of the site is optimized,which makes the bridge have better mechanical properties.All of these large-span annular steel box bridge footbridge design ideas have important guiding significance for the design of similar structures.