The Research On Hysteretic Energy-based Evaluating Method Of Structures' Seismic Performance

Ruinous earthquake will cause great destruction and damage on the national economy and property, even lead to death. Therefore the seismic analysis and design of structure under strong earthquake is the significant research subject and hotspot on seismic engineering. Normal seismic design mainly considers the carrying capacity of structure. The performance target of performance-based design mostly is concerned with ultimate displacement or ductility. Ultimate displacement contributes to the destruction of buildings basically, so does cumulative damage which is caused by nonlinear hysteretic cycles. Performance-based seismic design procedure possesses several advantages, such as clear in conception and simple in computation, which can preferably represent the influence of earthquake intensity, frequency character and ground motion duration on the structural destruction. At present energy-based design procedure mainly adopt hysteretic energy to evaluate structural damage degree. The dissertation computes hysteretic energy demand and capacity of structures under severe earthquake respectively by the means of sum-up of former research fruits, systemic academic investigation and large numbers of computation. Therefore hysteretic energy-based seismic evaluating procedure is built primarily, and uses steel frame and concrete frame as example in design and check. The main contents of this dissertation are described as follows:1. On the basis of vibrational theory of single degree of freedom elastic-plastic system, a Matlab time-history analysis program is made to compute the structural energy response. 302 Northridge in USA and 339 ChiChi in Taiwan earthquake ground motion records are classified according to soil condition and duration of strong ground motion, and their mean hysteretic energy demand spectra is computed by means of nonlinear program. The result shows that force reduction factor and stiffness reduction factor have little influence on the hysteretic energy values, and peak hysteretic energy is proportional to the square of peak ground motion acceleration approximately.2. The bilinear hysteretic energy demand spectrum mathematical equations of Vidic-Fajfar and Chai-Fajar model are developed because of different velocity peak amplification factor of equivalent seismic input energy spectrum. Through the energy response result of time-history analysis, a simple formulation of hysteretic energy is proposed by means of nonlinear regression analysis, in which site character and duration of strong ground motion are considered. Former three kinds of demand spectrum are compared, and bilinear hysteretic energy demand spectrum is conservative. Especially for large structural period, bilinear hysteretic energy demand values are much larger than the time-history response values.3. The hysteretic energy capacity which corresponds to structural collapse state can be calculated from modified Park-Ang damage model and low-cycles fatigue model. The monotonic displacement ductility factor can be calculated through nonlinear static Push-over, and the cyclic displacement ductility factor can be calculated through the structural force-reduction factor too.4. The structural hysteretic energy demand can be calculated through 12 kinds of different equivalent system scheme(ESS), which can avoid of complicated and time-consuming nonlinear time-history analysis of multi degree of freedom(MDOF) system. In order to analyze equivalent effect of different ESS, the floor-shear model should be built by experiential formulae or nonlinear Push-over firstly. The energy response of MDOF and equivalent single degree of freedom (ESDOF)systems can be computed by self-compiling Matlab programs. Therefore it is convenient to acquire hysteretic energy ratios of ESS. The result indicates that site characters and normal hysteretic energy have significant influence on the hysteretic energy ratios. Consequently the hysteretic energy ratios expressed by site characters(value a/v) and normal hysteretic energy(S_E) can be calculated by means of nonlinear regression analysis of the hysteretic energy ratios produced by typical earthquake waves.5. Real multi degree of freedom structures correspond to different hysteretic models. This dissertation uses bilinear, semi-degraded trilinear and degraded trilinear hysteretic models which can represent the steel frame, brickwork and concrete structures respectively well. By means of Matlab program, corresponding hysteretic energy demand and energy ratio is calculated precisely. Compared to bilinear model, trilinear models can consider stiffness degradation which reflects the mechanical characters of reinforce concrete and brickwork structures more truly.6. Hysteretic energy-based design checking equation is built via energy equilibrium ideology to judge whether the building will collapse. The damage index of modified Park-Ang damage model quantifying structural damage can mark the structural performance target which is required by owners. Then the hysteretic energy capacity can be computed to create the elementary performance-base seismic designing and checking procedure considering hysteretic energy.7. In order to make use of former analysis in the seismic evaluation and design of real structure, steel frame and concrete frame are chosen as examples. Their hysteretic energy demand and capacity values under strong earthquake are calculated to judge whether the collapse or target performance will happen. Via second design we can obtain suitable components and reinforcing steel bar etc.