Estimation of Fatigue Life of Steel Masts using Finite Element Modelling

Abstract

Estimation of Fatigue Life of Steel Masts using Finite Element Modelling Fatigue is an important design consideration for tall steel structures. Accurate prediction of fatigue endurance is essential to design the elements subjected to wind and earthquake induced fatigue. The design guidelines given in codes of practices are applicable only to simple shapes and laboratory experimental verification is costly. Therefore, simulation using finite element software is becoming popular. An attempt is made to couple Abaqus finite element analysis software and fe-safe software to estimate the fatigue life of a structure. First, the accuracy of the techniques and idealizations used in simulation are validated by simulating experiments available in the literature. Standard Uni-Axial fatigue experiments which were conducted at several strain amplitudes showed a closer relationship to simulation results. Moreover sensitivity of fatigue life to surface finish and stress strain dataset importing method in fe-safe software were evaluated. It was found that the surface finish is a highly sensitive parameter and it should be estimated accurately. Elastic plastic block method gave good results while elastic block method with neuter’s rule results were poor. This indicates the importance of using elastic plastic block method for low cycle fatigue especially when stress redistribution is high. Simulation result of multi-axial fatigue experiment showed similar results to results obtained from physical experiments. The verified technique was the applied to estimate the fatigue life of a 64 m tall steel mast with an opening located at the top of a 285 m tall concrete tower. The sensitivity of the plate thickness and shape of the opening of the mast were studied. It was found that small increase in plate thickness rapidly increases the fatigue endurance. This shows the importance of using stiffeners in fatigue prone areas. Comparison of the shape of the opening showed that square shape would have higher endurance than a circular shape of same opening area. However only monolithic sections were studied here and effects on welds and bolted connections are beyond the scope of this research