Study On Aseismic Capacity And Health Diagnosis For Cable-Suspended Structure Of Pipelines

The aseismic capacity and health diagnosis technology for cable-suspended structures of oil and gas pipelines are studied systematically by the theory analyses and the model experiments and numerical simulation analyses. Three kinds of basic damage modes of structures are briefly induced based on the experience from earthquake damage and the characteristics of structure's mechanics. The multilevel method of whole health diagnosis is put forward according to mode discrimination. A neural net model is set up and tested by experiment datum. Furthermore, the local health diagnosis methods are proposed through monitoring the cable forces. The damage modes and the damage positions and the damage degrees of structure system can be judged by using the whole health diagnosis methods in combination with the local health diagnosis methods. The main content and outcome of this paper are as following: Firstly, the model scaled to be one eighth of the actual cable-suspended structure of pipelines is designed and made. Three kinds of basic damage modes of the structure (the damage of tower frame, the breaking of a sling and the inclined cable loses its function) are briefly induced based on the experience from earthquake damage and the characteristics of structure's mechanics. The experiment studies on non-damage mode and three kinds of damage modes are completed respectively. The experiments include modal tests, vibration tests by knocking, shaking table tests by inputting white-noises and seismic waves, and tests of cable forces and vibration frequencies. The experiment results supply a demand for evaluating the aseismic capacity of structural system and putting forward health diagnosis methods of the structural system. Secondly, two finite models are built by ANSYS according to the actual structure and the model structure respectively. Under non-damage mode and three kinds of damage modes the static analyses and modal analyses are made taking cable prestress and large deformation into consideration. The earthquake response analyses are tried to be done. The experiment results basically tally with the values of numerical simulation analyses in cable forces and free frequencies of structural system. Numerical analyses also show that the actual structure is in the similitude of the model structure, and the result of model experiments provides the basis for analyzing actual engineering. Thirdly, the model experiments and numerical analyses all show that the cable-suspended structures of pipelines have a good aseismic capability and systematic stability. While inputting three dimension ground motion acceleration reaches 0.5g (is equivalent to China earthquake intensity â…¸) the element strengths in the structure are still under the limit of strength, and no element damages. Even though the structure is under three man-made damage modes, the structure system keeps stability and maintains normal function. Fourthly, the first and the second frequencies are determined as index of health diagnoses through analyzing statistical characters of structure systematic free-frequencies got by experiments and checking prominence of the experiment datum by symbol test method in different damage modes. A multi-level whole health diagnosis method is set up based on frequency parameters (frequencies and ratio of frequencies), and can be used to recognize three damage modes of the structure. Fifthly, a BP artificial neural net used for health diagnoses of cable-suspended structures of pipelines is established by the tool box in the MATLAB6.5. The net is trained by parts of modal parameters got by the experiments, and is verified by the rest of modal parameters. The results show that this net model has strong ability to distinguish three kinds of damage modes. Sixthly, the local monitoring technology methods of testing cable stresses are discussed. The experiments and analyses show that the cable forces are linear with the frequencies. The cable forces can be estimated by knock-excited methods. The structural health diagnoses can be made according to the cable forces, because the inclined cables have key function in keeping the system stability and the inclined cable forces vary in different damaged modes. Through combining the local monitoring methods with the whole health diagnosis methods, the damaged modes can be distinguished, and the degrees can be estimated, and the location can be determined.