Study On Mechanical Properties Of Twisted Steel Slings With Different Deflection Angles

In the middle and bottom arch Bridges,the sling is the bearing component connecting the arch rib and deck structure,and its safety performance directly affects the service condition of the whole bridge.Through the analysis of a large number of other scholars’ research literature and bridge collapse cases,it is found that the upper and lower ends of the sling will have different axial deflection angles under long-term load,and this phenomenon is especially prominent in the bridge deck system of floating structure system.At present,domestic and foreign scholars mainly focus on the corrosion and fatigue damage of the sling,but the phenomenon of different axial deflection angles of the upper and lower ends of the sling is rarely studied.Therefore,this paper carried out a systematic study on this phenomenon and analyzed the influence law of different axial deflection angles on the static load and fatigue performance of steel strand slings.The specific research content and results are as follows:(1)By analyzing the deck structure of the arch bridge and the connection form of the sling,the influencing factors of the deflection Angle of the sling axis of the arch bridge are summarized.The finite element analysis of two mid-bearing arch Bridges with span of 200 m and 300 m is carried out to study the extreme value of deflection of the sling axis under different load conditions.It is found that under the action of dead load and temperature,the deflection Angle of the sling axis of the arch bridge is smaller,which is below 4mrad.Under the action of moving load,the deflection Angle of the sling axis of the arch bridge is relatively large,and the maximum deflection Angle is more than10 mrad.The shaft deflection of short and sub-short slings is the most serious.With the increase of span,the limit deflection Angle of slings also increases.(2)The basic unit of the sling,class 1860 seven-wire strand,was selected to carry out the static tension test under four axis deflection angles(0,10,20,30mrad).It was found that the ultimate tensile strength of the strand linearly decreased with the increase of the axis deflection Angle.When the shaft deflection Angle reaches 30 mrad,the ultimate tensile strength of the strand decreases by 25.4%.1,3,7,12,19 and 27 strands of steel strand slings were established by finite element software,and the tension simulation of axial deflection Angle of slings was carried out.It is found that the axial deflection Angle will cause the unevenness of the steel strand force,which will lead to the stress concentration phenomenon at the anchorage end of the steel strand sling,and seriously weaken the mechanical properties of the steel strand.(3)The salt spray corrosion box was used to carry out the three-level ordinary corrosion and tensile stress corrosion on the galvanized steel strand,and it was found that within 0-360 h,the zinc protective layer of the steel strand was mainly destroyed.The corrosion rate of the steel strand would be greatly accelerated under the action of tension,so that the surface of the steel strand was more likely to produce defects.The results show that the ultimate strength of the corroded steel strand decreases gradually with the increase of the corrosion degree and the axial deflection Angle,and the relationship is basically linear.The stress analysis of the semi-spheroidal pit at different positions on the strand model shows that the pit will cause stress mutation,and the closer the pit is to the anchor end,the greater is the influence of axial deflection Angle on the stress of the pit.(4)Goodman equation is used to modify the S-N curve of the current class1860 steel strand,and the S-N curve of the strand under different axial deflection angles is derived.A complete axial deflection Angle fatigue test scheme was designed,and four angles(0,10,20,30mrad)were carried out on the steel strand.The results show that the fatigue life of steel strand slings decreases with the increase of shaft deflection Angle,and the larger the shaft deflection Angle,the faster the decline rate.When the shaft deflection Angle exceeds 20 mrad,the fatigue life of steel strand slings will be greatly weakened.When the shaft deflection Angle is 30 mrad,the fatigue life of the steel strand is reduced by 15.25%.It can be seen that the shaft deflection Angle has a significant impact on the fatigue life of the steel strand and weakens the service life of the sling.(5)Finite element simulation of axial deflection Angle fatigue life of steel strand sling and steel strand hemispherical etch pit model was carried out by using Design-life.It is found that the fatigue life of the steel strand sling is affected by the axial deflection Angle more with the number of strands.The influence of shaft deflection Angle on the life of anchorage end pits is greater than that of other positions.When the shaft deflection Angle exceeds a certain threshold,the fatigue mechanism of steel strand slings will change.The axial deflection Angle will weaken the mechanical properties of the steel strand sling,affect the normal operation of the sling,and even lead to safety accidents.Therefore,it is necessary to correct and reinforce the suspension cables when axis deflection occurs in the middle and underpass arch Bridges.