Fatigue Analysis Of In-Service Spatial Latticed Structures Under Wind Load

Under alternating load such as wind load, the stress amplitudes in the members of the spatial structure vary greatly which can cause the fatigue damage of the structure. At the same time, the structures are located in corrosive atmospheric environment. The steel corrosion affects the fatigue properties of the structure, leading to a huge loss of catastrophic damage. Therefore, fatigue analysis and redundancy assessment of in-service spatial latticed structures have the great practical significance.The member in the spatial latticed structures comes about fatigue damage easily under wind load. In this paper, based on the POD technique and inverse-distance weighting spatial interpolation method, load spectrums are obtained. The analysis of wind-induced vibration response is achieved in ANSYS, using the beam element model of the whole structure and the shell element model of the joints. The stress cycle courses at weld toes of welded joints are obtained by rain-flow counting method. According to the DNV Recommended Practice and Miner’s Rule, fatigue damage is calculated. The procedure is demonstrated to be correct via several examples. Numerical results show that the position of the first fatigue member is related to the average wind pressure and the fluctuating wind pressure, specifically, the upwind surface of the spherical shell with the largest average wind pressure and fluctuating wind pressure. Both the number of fatigue members and the fatigue damage of members increase with the raise of the average wind pressure and the fluctuating wind pressure.Structure sensitivity is used to describe the relationship between structural behavior and design parameters, redundancy is an important factor affecting structural robustness and reflects the structural safety in case of injury. In this paper, the P. C. Pandey method is referenced and applied to spatial latticed structures. A method, in which the derivation of element strain to the elastic modulus of elements is taken as the response sensitivity, is applied to assess the redundancy of structures under wind load. Through comparing with the distribution of fatigue damage in spatial latticed structures, Numerical results show that the redundancy can reflect the importance of structural member. Structural members with low redundancies are the key members of the structure.Corrosion is a widespread phenomenon in steel structures. In this paper, based on experimental data, an analysis method is proposed to calculate the mechanical properties of members with pitting corrosion. In this method, some assumptions about the pitting depth, diameter and distribution are put forward and the equivalent elastic modulus of structural members with different corrosion rates are obtained. Through the relationship between laboratory and natural atmosphere, practical method is proposed to obtain the mechanical performance of members in natural atmosphere.Finally, fatigue analysis and redundancy assessment are taken into in-service spatial latticed structures. The results show that considering corrosion, the position with the largest average wind pressure and fluctuating wind pressure still appears the first fatigue member and under the same wind load, both the number of fatigue members and the fatigue damage of members rise with the increase of atmospheric corrosion. Simultaneously, with the increase of atmospheric corrosion, redundancies of structural elements reduce, and structural members with low redundancies are still the key members of the structure.The main innovations in this paper are as follows:1. The hot spot stress method is applied to the fatigue analysis of spatial structures under wind load.2. A method is proposed to calculate the mechanical properties of members with pitting corrosion.3. Redundancy assessment and fatigue analysis are taken into in-service spatial latticed structures, the failure mode of spatial latticed structures under wind load is obtained.