Ground Motion Selection And Modification Methods For Performing Nonlinear Dynamic Analysis Of Buildings

The ground motion input is one important part of structural dynamic analysis. The important issue for performing nonlinear dynamic analysis is to reflect the influence of ground motions for structural response and damage effectively. With the rapid development of the theory of performance-based seismic design, structural dynamic analysis software and computational facilities, nonlinear dynamic analysis is becoming more common in seismic analysis and design of numerous vital projects. Selecting the suitable ground motions is the basis of evaluate the anti-seismic performance. So far a lot of valuable results and regulations had been developed in many codes for seismic design of buildings; however, due to the stochastic of ground motions and the complexity of structure damage excited by ground motion, no consensus has been formed for selection and scaling ground motions. Thoroughly study on the methods of selection and scaling ground motions have significance value for performance-based seismic design and structural performance evaluation.In this study, the effectiveness of ground motion parameters, scaling methods, sample size of ground motions, selection methods for scenario earthquake and conditional mean spectrum are developed base on the real earthquake ground motions.The detail contents of research and conclusions are as follows:1. Study on the effectiveness of ground motion parameters. Forty-four ground motion parameters have been summarized, including amplitude type, frequency type, duration type and combined parameters. The three hundred elastic-plastic single-degree-of-freedom (SDOF) systems with different natural vibration periods and ductility factors are created as the structural model. The correlation between different parameters and the correlation between elastic-plastic displacements and ground motion parameters have been analyzed to classify these parameters and seek for the suitable parameter which has an important impact on structural seismic response. The study shows that:the peak ground acceleration (PGA) type parameters are suited to represent the seismic influence for short period structures; the peak ground velocity (PGV) type parameters are suited to represent the seismic influence for medium period structures; the peak ground displacement (PGD) type parameters are suited to represent the seismic influence for long period structures; spectral acceleration at the first mode period of vibration of the structure(Sa(T1)) are suited to short, medium and long period structure, which are regard as the ideal parameter to describe seismic action.2. Study on scaling methods of ground motions. Six reinforced concrete structure models with different height are created for nonlinear dynamic analysis. The correlation between structures’ nonlinear dynamic response and spectral acceleration at different periods had been analyzed to quantitative research the period range which play main role in structural seismic response. Comparative analysis of single-period scaling method, multi-periods method and spectrum-matching method are done to research the applicability of each scaling methods. The study shows that:The analysis of correlation between structures’ nonlinear dynamic response and spectral acceleration at different periods could quantitative seek the period range which play main role in structural seismic response. The short period structure’s responses are controlled by spectral acceleration at the first mode period of vibration of the structure. The medium and long period structures’ responses are controlled by spectral acceleration at one period range0.2T1～2T1. For the short period structure or low level earthquake intensity, the single-period method would have a good effect. For the medium and long period structure or high level earthquake intensity, the structure would be enter in the nonlinear stage, the effect of higher modes and vibration period extended should be fully considered, so the multi-periods method and spectrum-matching method are the better choices.3. Study on the sample size of ground motion based on reliability. By analyzing the statistical characteristics of the structural seismic response subject to large samples of ground motions, the difference between maximum and average value of structural seismic response is investigated and the probability distribution models of structural response are analyzed. Method for determining the sample size of ground motion is proposed based on reliability. The effect of ground motion adjustment methods on the sample size demand is analyzed, providing the basis for estimates of structural response by using small sample of ground motions. The studies show that:1) maximum value method increases the uncertainty in the estimation of structural response, and the results are too conservative. Mean value method is more appropriate to estimate the structural response when using small sample of ground motions.2) as seen through hypothesis testing, extreme value distribution is the most acceptable probability distribution model of seismic response, lognormal assumption is acceptable and normal distribution assumption is completely rejected.3) reliability-based method to determine the sample size of ground motions is proposed, which can give a quantitative judgment on confidence level and margin of error to the estimated structural response.4) multi-periods adjustment method, spectral-matching method as well as synthetic ground motion can effectively reduce the demand of ground motion sample size.4. Study on the scenario earthquake based ground motion selection method. Firstly, the demand spectrum is determined to characterize the seismic intensity level of the scenario earthquake. And this demand spectrum is set as the target spectrum to select and adjust ground motion records. Then the validity of the demand spectrum is investigate in terms of the seismic parameters (magnitude, distance, fault type) and local site conditions, providing a quantitative reference to ground motions selection. The studies shows that, magnitude, distance, fault type and site conditions should be fully considered when selecting ground motions based on the demand spectrum of the scenario earthquake. The restriction on distance can be appropriately relaxed when the number of record is not sufficient. The ground motion selection and adjustment method is proposed by effectively considering the variability of response spectra and spectral shape, ensuring that the adjusted ground motion records consistent with the demand spectrum in the statistical sense, and overcoming the limitations of Greedy Algorithm.5. Study on conditional mean spectrum based ground motion selection method. The impact of standard deviation factor ε on spectral shape and structural nonlinear dynamic response has been investigated. Then the concept and algorithmic method of conditional mean spectrum are introduced in detail. Five different ground motion selection methods are compared to research the effective of conditional mean spectrum. The study shows that:1) The standard deviation factor ε has close ties to the spectral shape and has an important impact on structural nonlinear dynamic response.2) The conditional mean spectrum overcome the conservative of uniform hazard spectrum. Structural responses from ground motions matching the conditional mean spectrum have lower bias from record scaling and smaller dispersion.