Study On Friction Slip For Cable And Distribution Of Longitudinal Force Of AS Method

With the rapid improvement of domestic design and construction level for the suspension bridge,a series of suspension bridges with different spans and structural systems have been built in China.At present,PPWS method is used in most of suspension bridges built in China.Yangbaoshan bridge is the first suspension bridge constructed by AS method in China.The number of single strand steel wires constructed by AS method is much larger than that by PPWS method,resulting in larger cable saddle groove than that of conventional cable saddle.The anti-slid performance of cable saddle under thick plates of wide groove road needs to be evaluated by model test.Based on Yangbaoshan bridge,the thesis discusses the slide law of cable strand under wide groove road and the influence of diaphragm thickness on the antislide performance of saddle through model test and numerical simulation.In addition,the transmission and distribution of cable strand force in the saddle are rarely mentioned in the existing research.In the thesis,the transmission and distribution characteristics of unbalanced force in the longitudinal direction of the saddle groove are discussed with the help of the cable strand saddle sliding test platform.Based on ABAQUS /Explicit calculator,the variation law of stress transfer and distribution of steel wire with friction slip is studied in the steel wire level.The main contents and conclusions are as follows:(1)By ABAQUS/Explicit calculator,the appropriate grid density and mass magnification factor are selected.Evenly selecting the measuring points along the longitudinal direction of the steel wire,the stress increment of each measuring point under different loading steps is extracted.The results show that the newly added cable force is distributed among the steel wires according to the proportion of the friction force.With the increase of the cable force,the stress increment is gradually transferred from the increasing end of the cable force to the constant end of the cable force.When the tension increment reaches the constant end,it corresponds to the slip moment of the steel wire.The slip of the steel wire will drive the redistribution of the cable force between the steel wires until all the steel wires slip,and finally the stress difference between the two ends of each steel wire tends to be constant.In addition,with the increase of the force difference between the two ends of the steel wire,the new internal force will gradually transfer to the other end after overcoming the static friction along the way,the internal force of the section where the internal force increases is basically linear distributed.When the steel wire slips,the internal force of the wire is linearly distributed along the longitudinal direction.The more the number of steel wires,the greater the friction coefficient,the larger the increment of cable force transmission per unit length,and the distribution of steel wire internal force along the longitudinal direction of saddle groove is not affected by the two,which is still linear distribution;(2)Using the test platform of cable strand saddle friction slip,the smooth steel wire is selected to arrange strain gauges along the groove.The variation law of stress increment with unbalanced force is tested.The results show that: the stress of the measuring point close to the tight side is incresing,and the increment of the measuring point close to the loose side is decreasing.The stress increment of the measuring point closer to both ends is greater;when the cable strand slips,the stress increment decreases.The results show that the longitudinal slip of the cable strand along the saddle groove occurs at the same time in the range of the cable length.The friction force needs to be overcome in the transmission process of the unbalanced force,and the stress increment gradually decreases from both ends to the middle.When the cable strand slips,the stress distribution is basically linear along the cable length;(3)Through the design of synchronous tension at both ends to the dead load,tension the saddle to make it rotate and then produce unbalanced force test,the test analysis shows that:the cable force difference on both sides of the cable strand increases linearly with the increase of unbalanced tension at the initial stage of loading,and the increase rate of the cable force difference of the lower cable strand is greater than that of the upper cable strand,which proves that the distribution of unbalanced force is positively related to the friction.With the rapid increase of unbalanced force,the distribution of unbalanced force increases.The results show that the nominal friction coefficient of 10 mm plate is generally greater than that of 5mm plate,which indicates that the thickness of plate is positively related to its anti-slid ability.The slip between cable strand and saddle groove is simulated by ABAQUS.According to the lateral deformation state of diaphragm,it is divided into two types: restraint lateral deformation and lateral freedom.ABAQUS calculation model of 34-wire with single channel is established.The calculation results confirm that the anti-slid performance of saddle groove with 10 mm plate is better than that of 5mm plate;(4)On the basis of the existing calculation program of main cable saddle friction slip,a layer is embedded in the program by subsection method,and the initial value of each section is updated cyclically.On the basis of verifying the correctness of the iterative program,multi subsection calculation is carried out.The results show that the cable force is basically linear along the longitudinal direction during the sliding process,and the friction tends to be a stable value when there are enough sections.The nominal friction coefficient at all levels calculated according to the piecewise sliding program is basically between the experimental value and the calculated value of the overall sliding,which proves that the sliding time judged by the slope of the relative displacement curve is closer to the ultimate sliding of the cable strand.The anti-slid performance of saddle for Yangbaoshan bridge is evaluated by using sectional sliding program.