Special Issue on Earthquake Ground-Motion Selection and Modification for Nonlinear Dynamic Analysis of Structures

Over the past decade, considerable progress has been made in developing tools to predict nonlinear response of structures to ground motions, an important consideration in the design and assessment of earthquake-resistant structures. With increase in computational power, nonlinear response-history analysis (RHA) is becoming a common tool in practice. This rigorous method of analysis requires a suite of records as direct input. These records should be selected and modified appropriately to make them compatible with the site-specific hazard level considered. Most of the procedures to modify ground-motion records fall into one of two categories: spectral matching and amplitude scaling. This special volume contains 17 technical papers. These papers evaluate current procedures and present new, practical procedures for ground-motion selection and modification. The first four papers of this issue focus on ground-motion modification procedures. The paper by Kunnath et al. compares and contrasts spectralmatching and amplitude-scaling methods considering realistic structural systems. How to characterize and spectrally match bidirectional ground motions to two separate target spectra is presented next by Grant. The following paper, by Kalkan and Chopra, proposes a modal-pushover-based scaling (MPS) procedure to scale ground motions. In the MPS method, the ground motions are scaled to match a target value of the inelastic deformation of the first-mode inelastic single degree-of-freedom system whose properties are determined by first-mode pushover analysis. Huang et al. compares displacement responses from amplitude scaling of ground motions based on three different methods with those from spectrally matched records. The next eight papers focus on ground-motion selection. The paper by Baker uses “conditional mean spectrum” as a new target for selecting spectrum-compatible records. Haselton et al. also considers spectral shape in selecting and scaling ground motions for use in nonlinear dynamic analysis for collapse assessment. The following paper, by Stafford et al., selects records providing the best match to the target spectrum and demonstrates a procedure to approximate the distributions of interstory or roof drifts. Without amplitude scaling, Hines et al. recommends a ground-motion selection process based on deaggregation of hazard into magnitude and distance bins. The paper by Masi et al. identifies the measure of seismic intensity that provides the best scaling of effect with respect to input and compares different approaches to selecting or generating synthetic records. Cimellaro et al. explores the influence of spectrum-matched and amplitude scaled ground motions on the development of fragility functions for structures and investigates the sensitivity of the number of accelerograms producing consistent results. The following paper by Honda and Ahmed presents a simple scheme for selecting few numbers of records representing the set of large numbers of possible ground motions generated considering the uncertainties of structural and seismic parameters. For ground-motion selection, a new intensity parameter considering the expected elongated period of the structure in the inelastic range has been proposed by Kadas et al. The next two companion papers by Dickinson and Gavin provide a quantitative measure of the variability among ground motions and develop response-spectrum-compatible models for biaxial synthetic ground motions. The next paper by Halldorsson et al. utilizes a “specific barrier model” to simulate ground motions that can be used with confidence in seismic design. In order to reduce the computational effort in the prediction of the incremental dynamic analysis (IDA) using a large set of records, Azarbakh and Dolsek introduces progressive IDA for the selection of representative ground-motion records. The last paper of this volume, by Moustafa, develops a new framework for modeling earthquake loads for seismic-resistant design of structures using the method of critical excitations. His method relies on the high uncertainty associated with the occurrence of earthquakes, their characteristics, and also on the structural safety requirements. The 17 papers presented here meet the goals of having the potential to inform and advance ground-motion selection and modification techniques for practice and pointing to new investigation avenues for future studies.