Research on Causes of Slip of Steel Hoops During Bridge Construction and Anti-Slip Measures
This paper theoretically analyzes the mechanical properties of steel hoops and proposes the measures to prevent slip of steel hoops during bridge construction.To address the slip caused by water ingress in steel-concrete interface as well as insufficient bolt tightening torque,the steel-concrete interface friction factors and the nut factors were tested and quantitatively analyzed.In accordance with the test results and field experience,the steel hoop anti-slip measures were proposed.It is shown that the static friction factor of the dry steel-concrete interface is 0.62,greater than the common design value of 0.3 to 0.4,indicating sound load bearing condition of the steel hoops.When the steel-concrete interface is wetted,the static friction factor is decreased,but still higher than the common design value,meaning that water ingress indeed undermines the load bearing capacity of steel hoops,but does not reach the degree to induce slip of steel hoops.The improper value of nut factor is considered the main cause of the slip of steel hoops,as the common design value of which is only 1/1.7 to 1/3.6 of the tested value,indicating potential safety risk.The angle between the bolt axis and normal of load bearing plate is a key consideration in determining the nut factor,it is suggested to get a field-measured value to ensure the agreement of the bolt pre-tension with the design value.In the design of steel hoop,the friction factor can be set at 0.45,and the nut factor set at the maximum of the allowable range.The number of bolts should be determined with a safety coefficient of 1.5 to 2.0,to effectively prevent the slip of steel hoops.
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维普
