Bearing Capacity Assessment Of The Suspension Bridge And Mechanical Analysis Of Main Elements

In the 70 s and 80 s of the 19 th century,on the Yellow River upstream,in order to devolope the local economic,a number of suspension bridges were constructed across the Yellow River.The bridges span is not big,about 200 m.With the service life increasing,there is appeared a certain defects.In order to determine bearing capacity of the suspension bridge and provide reinforcement program,the key links of appeared defects need to be checked.Bended over the wheel wire rope anchor end is an old bridge using anchor end structure,nowadays a lot of domestic small local suspension and cable bridges are still use bended over the wheel wire rope anchor end structure.So it is necessary to make theoretical calculation analysis for this kind of anchor end.In order to find the most dangerous stress and destruction points for this type of fastening.At the same time,to make base for the later reinforcement programs,the common tunnel type of anchorage of suspension bridges was calculated.In order to compare and choose the best types of this two anchor joint structure,the same load value test was used.Suspension bridge under the live load action at saddle part of main cable,can occur an angle changes of main cable.At cable band of suspender the main cable also can occur angle changes.All of this angle changes will case bending stress of the main cable.So that's for its need to make calculation of bending stress for main cable of saddle and cable band.At the same time,there are clamping force between cable band and the main cable,the effection of clamping force of cable band to main cable should be considered.During a long service time of suspension bridge,bearing capacity will reduce.So the old suspension bridges bearing capacity assessment is also very important.The best way to evaluate suspension bridges bearing capacity is to make a load test.In this article take as an example suspension bridge across the Yellow River which have been constructed in West North region in eighties.In order to obtain the maximum capacity of the bridge,using the most unfavorable load forced on the bridge.At the same time all of this article calculations made on the bridge background.The main research work can be concluded as follows:(1)First of all,breaking force of suspension bridge wire rope was calculated,determine maximum allowed working load of the main cable wire rope,at the same time were calculated internal force of the suspension bridge main cable and side cable.On this basis,continue to make analysis of wire rope with anchor end and main cable with cable saddle and cable clamp analysis.(2)Then,make bearing capacity analysis of the two types anchor fastening,which is: bended over the wheel wire rope anchor fastening and straight wire rope anchor fastening.Bended over the wheel wire rope anchor fastening rigid resistance and bended over the wheel wire rope anchor fastening rotary torque were calculated.Bended over the wheel wire rope anchor fastening and straight wire rope anchor fastening 3D models were built by using PTC Creo Parametric software.Equivalent stress,total deformation,and safety factor analysis of the two types anchor fastening were calculated by using ANSYS finite element analysis software.For two types anchor fastening structure were made comparison.Straight wire rope anchor fastening under the load comparing with bended over the wheel wire rope anchor fastening structure is more safe.Repairing bended over the wheel wire rope anchor fastening pay attention to pulley pin and the top of bending wire rope structure.Suggested structure to use is: straight wire rope anchor fastening.(3)Angle changes of the saddle placed main cable wire rope impact on main cable carrying capacity were studied.Two types of structural models were built: saddle placed main cable with bending angle of 18 degrees and saddle placed main cable with bending angle of 21 degrees.Two types of saddle placed main cable 3D contact models were built by using PTC Creo Parametric software.Equivalent stress,total deformation,and safety factor analysis of the two types contact models were calculated by using ANSYS finite element analysis software.For two types saddle placed main cable structure were made comparison.Saddle placed main cable with bending angle of 21 degrees,comparing with saddle placed main cable with bending angle of 18 degrees is more dangerious.Angle changes of the saddle placed main cable has increasing equivalent stress and total deformation impact.The maximum equivalent stress of saddle placed main cable with bending angle of 18 degrees is 562.48 MPa,the maximum equivalent stress of saddle placed main cable with bending angle of 21 degrees is 683.57 MPa.The maximum total deformation of saddle placed main cable with bending angle of 18 degrees is 2.8mm,the maximum total deformation of saddle placed main cable with bending angle of 21 degrees is 3.32 mm.On this basis it can be concluded that angle changes of the saddle placed main cable has a very serious impact.(4)Cable clamp clamping force and bending stress on the main cables impact were researched.First of all build the finite element model of the span center main cable with the cable clip.Cable clamp here in a horizontal position and assuming that no clamping force;then build the first cable clip with main cable next to cable saddle model.Take the maximum clamping force of 10 MPa,take the main cable dip of 18 degrees,and build the calculation model.Finally,build the span center placed cable clamp model with the clamping force of 10 MPa.Differentiate finite element method for calculating the main cables and the cable clip such as equivalent stress and total deformation analysis.Results show that the cable clamp which has a clamping force and the main cable which has dip caused by the cable clamp bending stress on the main cables stress and deformation has affect.The maximum equivalent stress of the main cable under the constant load placed on bridge span center is on main cable and cable clamp contact point and it's equal to 41.75 MPa.The maximum equivalent stress of the cable clamp is equal to 37.79 MPa.The maximum equivalent stress of the suspender is equal to 35.19 MPa.The maximum allowable stress of the suspender is equal to 117.10 MPa,satisfied usage request.The main cable maximum equivalent stress on the cable clamp with dip of 18 degrees and with clamping force of 10 MPa is equal to 41.93 MPa.The maximum equivalent stress of the cable clamp is equal to 36.68 MPa.The maximum equivalent stress of the main cable placed on bridge span center and with clamping force of 10 MPa is equal to 45.02 MPa.The maximum equivalent stress of the cable clamp is equal to 37.99 ? 38 MPa.From above three results of comparison can be obtained.Cable clamp placed on the bridge span center and with clamping force of 10 MPa compering with cable clamp without clamping force,the maximum equivalent stress of the main cable and cable clamp is bigger;cable clamp with dip of 18 degrees and with clamping force compering with cable clamp placed on the bridge span center also with clamping force,the maximum equivalent stress of the main cable and cable clamp is smaller.(5)Determine the suspension bridge carrying capacity by the load test,in a total of five loading conditions: Condition 1 is a 10 th level vehicle load,the full bridge loading,the main point is to determine the main cables ultimate bearing capacity,the main cable wire rope cable force was tested,the strain of suspender and the bridge deck vertical deflection;Condition 2 is a 10 th level vehicle load placed on the span center of the bridge.Condition 3 is a 10 th level vehicle load placed on L/4 of the bridge span.Conditions 2 and 3 were tested the suspender strain,the bridge deck vertical deflection;in Condition 4 was tested the maximum bending moment of the bridge deck waybeam in span center section,in Condition 5 was tested the maximum bending moment of the bridge deck crossbeams in span center section.Conditions 2 and 3 were tested waybeam,crossbeams strain and bridge deck strain.The finite element software was used to calculate the corresponding conditions equivalent stress and total deformation,made comparison of the test value and the finite element analysis value.In order to tests and analysis determine the suspension bridge carrying capacity.The results show that the bridge after reinforcement,able to bear the original design 10 th level vehicle load.A strain calibration coefficient of the bridge deck,with measure points placed on bridge span center,is from 0.39 to 0.62;the strain calibration coefficient of the bridge deck,with measure points placed on the bridge deck's edge,is from 0.21 to 0.39.Bearing capacity of the bridge deck is satisfied 10 th level vehicle load.In Condition 1 deflection calibration coefficient of the bridge is 0.94~0.96,calibration coefficient near inflection point is too large;in Condition 2 deflection calibration coefficient of the bridge is 0.84~0.92;in Condition 3 deflection calibration coefficient of the bridge is 0.71~0.97.Span center deflection of the bridge under load Condition 1 is 0.568 m,at this time suspension bridge span center vector height changes value is less than [?f/l_p]=1/150 the bridge stiffness and satisfied usage request.