Aseismic Optimization of Nonlinear Joint Elements in Boiler Plant Structures Based on Substucture Synthesis Method

摘要

This paper deals with an optimum design method for joint elements in boiler plant structures which are excited by earthquakes. Characteristics of joint elements which connect the boiler and its supporting structure are assumed to be viscoelastic, elasto-plastic, or a combination of both. Considering the expansion of this study to an active or semiactive aseismic structural control of joint elements, the structures are modeled with the aid of a block diagram. In order to improve the efficiency of calculation, a substructure synthesis method is introduced. Time-domain optimization is carried out using a nonlinear programming technique. To prevent seismic damage of pipes and ducts, limitations for relative displacements between the boiler and its supporting structure is introduced as inequality constraints. Elastoplasticity and viscoelasticity of joint elements are simulated by a combination of a spring, a Coulomb friction and a dashpot. These joint element characteristics are optimized to minimize seismic time response of the structures. This method is applied to actual boiler plant structures and has been proven effective and practical for aseismic designs of boiler plant structures.