Analysis Of Mechanical Behavior Of External Slanted Pedestrian Arch Bridge With Curved Beam

With the development of social economy,urban bridges attach more importance to bridge aesthetics and art.External slanted pedestrian arch bridge has the advantages of novel concept and beautiful shape.However,this arch bridge is rare because of complex spatial structure at home and abroad,and the insufficient understanding of its mechanical behavior restricts the development of similar bridges.Based on the Q10 design scheme of Chengdu Luhu,the static and dynamic characteristics and bearing capacity of the bridge are analyzed.The design of Luhu Q10 pedestrian bridge is accompanied by both sides of highway bridge due to the limitation of terrain.Therefore,its actual design parameters are limited by many factors and the geometric relationship is complex.The layout of arch ribs,main girders and suspension cables are alienated,so their non-linearity is strong and the stability of the structure is prominent.It is necessary to analyze the structural design parameters and explore the relevant parameters affecting the behavior of the structure under stress.In this dissertation,ANSYS is used to establish the finite element model of bar and beam,and the influence degree and law of the parameters such as the height of main girder,the form of intermediate support,the inclination angle of arch rib and the section size of arch rib on the stress and deformation behavior of this kind of bridge under various load conditions are analyzed.The results show that the structural stress and deformation can be effectively improved by increasing the stiffness of the main girder and arch rib.Increasing the stiffness of the beam or arch alone will make the member bear more live load in the beam-arch composite system.The supporting form has a greater impact on the supporting reaction.It is suggested that only one vertical and transverse constraint should be set at the middle support.It is helpful to improve the transverse bending moment of arch ribs.According to design traffic volume of German Pedestrian Overpass Design Guidelines,an equivalent crowd load model is established.The influence of main girder size,bearing form,arch rib inclination angle and arch rib cross-section size parameters on structural natural vibration characteristics,vertical peak acceleration and lateral peak acceleration is analyzed by harmonic response analysis method,and the comfort degree is evaluated.For bridges that do not meet the comfort requirement,pedestrian comfort can be guaranteed by adding dampers to increase structural damping or setting reasonable crowd traffic volume.The different forms of intermediate support have great influence on the acceleration response-frequency curve of the main girder under crowd load.The main beam height,arch rib inclination and arch rib section size change mainly by affecting the natural frequency of the structure,so as to avoid the sensitive frequency or in the reduction interval to achieve the purpose of optimizing peak acceleration under crowd load.Finally,the elastic stability of external slanted pedestrian arch bridge is analyzed,and the elastic stability safety factor and instability form are determined.At the same time,the analysis model is established to analyze the ultimate bearing capacity of the arch bridge.Two loading modes are adopted and the safety factors of the ultimate bearing capacity of the special-shaped pedestrian arch bridge under the two loading modes are determined to meet the requirements.Due to the layout of the northern span suspension and other factors,the main girder of the northern span yielded first,and then the main girder of the southern span yielded,and finally the whole bridge structure failed.The results show that the increase of yield strength can obviously improve the bearing capacity of the structure.In the design,the yield strength of the main girder can be improved,and the arch ribs can yield first,which can effectively enhance the bearing capacity.Through the analysis of the plastic strain of the whole bridge,the failure path is determined: the main girder of the northern span enters the yielding state first,then the main girder of the middle support begins to yield,and finally the main girder of the southern span enters the yielding state,which leads to the overall failure of the structure.The ultimate bearing capacity of arch ribs is analyzed when the main girder and suspension cable are assumed to be in elastic state.The results show that when the arch rib of the northern span enters the yield under 14 times the crowd load,the displacement of the main beam of the northern span will be affected nonlinearly after the arch rib enters the yield,but it has little effect on the southern arch rib and the main beam of the southern span.