Residual Bearing Capacity Calculation and Fatigue Life Evaluation on Parallel Steel Strand Cable
To investigate the stay cables condition in the corrosive environment and under long-term fatigue loading,the study was conducted with the bridge stay cables in southwest of China,which had been in service over two decades.The residual bearing capacity calculation and fatigue life evaluation method was developed by using the mechanical property tests and finite element simulations.First,the high-magnification microscopy was used to obtain the comprehensive corrosion images of steel strand cables.According to the current standards,the corrosion levels of these strands were classified.The tensile fracture and fatigue tests were performed.The data of ultimate tensile strength and fatigue life were counted.The S-N curves were fitted for the material of strand cables.Subsequently,the stochastic traffic flow model was established to simulate the cable forces varying with time,taking into account the random characteristics of vehicle type,weight,and spacing.The simulated data were compared with the actual monitored cable force data by using the multi-parameter analysis.Finally,a reduction factor K was introduced to assess the overall bearing capacity of stay cables.The simulated cable force data were processed by using the rain flow counting method.The residual fatigue life of cable was calculated based on the cumulative damage theory.The result indicates that the ultimate tensile strengths of steel strand cables do not meet the current standard requirements.The maximum ultimate tensile strength is only 1 852.186 MPa,representing 4%decrease in the overall ultimate tensile strength of cables.The simulated cable forces show less than 5%discrepancy of extreme values,mean values,and the 95th percentile value compared with the actual measurements.The average absolute percentage error is 5.387 5%,which is below 10%,indicating the reliability of stochastic traffic flow model.The fit goodness of S-N curve of stay cable steel strand material is 0.994,which possesses the relatively high accuracy in predicting the fatigue life of stay cable.Eventually,the fatigue life of stay cable is calculated to be approximately 4.6 years.
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