Study On Integrity Analysis Of Fatigue Of Spatial Latticed Structure

Under wind loads, seismic loads and loads caused by mechanical vibrations, the dynamic response of long-span spatial structure may damage the structure and lead the structure to brittle fatigue failure. And then the fatigue weak area is not always on the position of stress maximum. In order to ensure structural safety in the design working life, it is necessary to carry out integrity analysis of fatigue and to evaluate the degree of fatigue damage on the structure.The FEM was introduced to analyze the transient response of the spatial latticed structure and the structural stresses of time history were obtained. The analysis of fatigue procedure was as follows: translate the stress of time history into peak stress signal, apply the rainflow counting algorithms to count the stress-strain cycle history under considerations of Goodman mean stress correction, select a suitable stress-life (strain-life) curve about the material, estimate the fatigue damage of members in one stress-strain cycle, and then accumulate the fatigue damage in the whole stress-strain cycle history by Miner linear accumulated fatigue damage theory. All the steps above were translated into APDL and performed in ANSYS. In the end the degree of fatigue damage on each part of the structure can be figured out and the fatigue weak area can be found out.The structural integrity fatigue was attributed to the fatigue property of material, the type of loading spectrum and the dynamic performance of structure. It was showed that the fatigue damage of the latticed truss under mechanical vibrations relate to directions, amplitude, frequency and difference phase of the vibrations, and the fatigue damage of the cantilever roof structure under wind loads relate to directions, amplitude and loading rapidity (it was described as parameter R) of wind.Parametric analysis of integrity fatigue on the spatial latticed structure indicates, for the structural design on carrying large variable loads, design value of strength should be decreased so that the amplitude of stress cycle turned low accordingly. At the same time the big differential of fatigue damage should be avoided. If it happened, the members of the fatigue weak area should be strengthened. Some conclusions were summarized and the problems that should be studied further were put forward in the end of the dissertation.