Optimum Design Of Base-isolated Structures And Chaos In Numerical Methods For Engineering

The performance based seismic design, base isolation, energy dissipation and structural control are the developmental direction and trend of earthquake resistant technology for engineering structures, which are related closely each other from the idea to the implemental method. These trends will cause important changes and influence on the seismic engineering. One of them, base-isolated building structures are accepted by the professionals in the earthquake engineering due to the excellent effectiveness of vibration reduction, good security, durability, economy, and adaptability. At present, the base-isolated technology with rubber bearings has been quite mature and become a very important kind of method of structural control.The present paper is divided into two parts: the optimum design of base-isolated structures and the chaos in numerical methods for engineering. In the first part, the base isolation technology being extended to the application actively in the world is taken as the major research subject, and the main works are as follows.Firstly, the state of the art of the research and application in both China and abroad is summarized and reviewed systemically, and the main problems to be solved are discussed.Secondly, the integrated optimum design of base-isolated structures based on the cost-effective criterion is implemented. Because one important issue of the extended application of base-isolated structure is the problem of investment, the integrated optimization formulation and computational method of base-isolated structure with the lead core rubber bearing (LRB) are established based on the criterion of the cost-effectiveness, in which the total cost of structure in the life circle is taken as the objective function including the initial cost and loss expectation, and the dimensions of cross section of members in the superstructure and the parameters of isolators are taken as design variables simultaneously. The optimization design of the base-isolated reinforced concrete (RC) frame structure is conducted, in which the response spectrum method and time history analysis method are used to obtain the structural response respectively. The selective dynamic rounding-off method is incorporated into sequential quadratic programming with potential constraints strategy to solve the dynamic optimum design problem of nonlinear isolated structure with discrete and continuous variables.Thirdly, the seismic response and optimum design of base-isolated RC frame structure with LRB under near-fault earthquakes are focused. Because the distinct long-duration pulse motion in the near-fault ground motions may cause the adverse influence on the seismic performance of the base isolation building, some near-fault and far-field earthquake records are selected as the input of ground motions, and the seismic responses of multi-story base-isolated frame structures are conducted using nonlinear time history analysis. It is demonstrated quantitatively from the numerical results that the near-fault pulse-like effect on the base-isolated structures is remarkable, which cannot be neglected in the structural designof base-isolated buildings. In addition, the integrated optimum design of base-isolated frame structure subjected to near-fault ground motion is carried out. It is concluded from the calculated results that through the parametric optimum design of base-isolated building subjected to the pulse-like near-fault earthquake, the optimal structure can satisfy simultaneously the structural design requirement under both the pulse-like and the general non-pulse-like near-field ground motions.Through the above-mentioned research of simultaneous optimization for the sectional dimensions of superstructure and parameters of isolators, the aseismic ability of base isolation structure is enhanced, and the total constructional cost is lowed, which provides the reference for the practical design of isolated structures. From the benefit analysis of structural seismic performance, initial cost and loss expectation, it is illustrated that by co...