Georgios Baltzopoulos

SPO2FRAG: software for seismic fragility assessment based on static pushover

SPO2FRAG (Static PushOver to FRAGility) is introduced, a MATLAB®-coded software tool for estimating structure-specific seismic fragility curves of buildings, using the results of static pushover analysis. The SPO2FRAG tool (available online at http://wpage.unina.it/iuniervo/doc_en/SPO2FRAG.htm) eschews the need for computationally demanding dynamic analyses by simulating the results of incremental dynamic analysis via the SPO2IDA algorithm and an equivalent single-degree-of-freedom approximation of the structure. Subsequently, fragility functions may be calculated for multiple limit states, using the intensity-measure-based analytical approach. The damage thresholds may also be random variables and uncertainty in estimation of the fragility parameters may be explicitly accounted for. The research background underlying the various modules comprising SPO2FRAG is presented together with an operational description of how the various functions are integrated within the software’s graphical user interface. Two illustrative SPO2FRAG applications are also offered, using a steel and a reinforced concrete moment resisting frame. Finally, the software’s output is compared with the results of incremental dynamic analysis as validation of SPO2FRAG’s effectiveness.

ACCOUNTING FOR NEAR-SOURCE EFFECTS IN THE DISPLACEMENT COEFFICIENT METHOD FOR SEISMIC STRUCTURAL ASSESSMENT

Non-linear static procedures are well-established analytical tools for performance- based seismic design and assessment. On the other hand, near-source (NS) ground motions are emerging as relevant to structural engineering because they may be characterized by seismic demand larger and systematically different than that typically induced by so-called ordinary records. This is the result of phenomena such as rupture forward directivity (FD), which may lead to the appearance of distinct velocity pulses in the ground motion velocity time-history. Lately, effort was put towards the framework necessary for taking FD into ac- count in probabilistic seismic hazard analysis (PSHA). The objective of the present study is to discuss the extension of non-linear static procedures, such as the displacement coefficient method (DCM), with respect to the inelastic demand associated with FD. In this context, the DCM is implemented to estimate NS seismic demand by making use of the results of NS-PSHA, developed for single-fault-case scenarios. A predictive model for NS-FD inelastic displace- ment ratios, previously developed by the authors, is employed. An illustrative application of the DCM, with explicit inclusion of NS-pulse-like effects, is given for a plane R/C frame de- signed under modern code provisions.

NESS1: A Worldwide Collection of Strong‐Motion Data to Investigate Near‐Source Effects

The availability of high-quality waveforms recorded in epicentral areas of moderate-to-strong earthquakes is a key factor for investigating ground-motion characteristics close to the seismic source. In this study, near-source strong-motion waveforms (named NESS1) were collected from worldwide public archives with the aim of building a flat file of high-quality metadata and intensity measures (IMs) of engineering interest. Particular attention was paid to the retrieval of reliable information about event sources, such as geometries and rupture mechanisms that are necessary to model near-source effects for engineering seismology and earthquake engineering applications. The accelerometric records are manually and uniformly processed, and the associated information is fully traceable. NESS1 consists of about 800 three-component waveforms relative to 700 accelerometric stations, caused by 74 events with moment magnitude larger than 5.5 and hypocentral depth shallower than 40 km, with Joyner–Boore distance up to 140 km. Ground-motion data were selected to have a maximum sourceto-site distance within one fault length, defined through seismological scaling relations. About 40 records exhibit peak acceleration or peak velocity exceeding 1g or 120 cm=s, and they represent some of the largest ground motion ever recorded. Evidence of near-source effects was recognized in the NESS1 dataset, such as velocity pulses, large vertical ground motions, directional and hanging-wall amplifications and fling step. In particular, around 30% of the records was found to exhibit pulse-like characteristics that are possibly due to forward rupture directivity. Electronic Supplement: Table listing the main features of the selected events, including the references of fault geometry parameters and Figures showing further metadata and intensity measures distributions of the NESS1 flat file.

SPO2FRAG V1.0: SOFTWARE FOR PUSHOVER-BASED DERIVATION OF SEISMIC FRAGILITY CURVES

Abstract. This article presents SPO2FRAG V1.0, the first (beta) version of the Static PushOver to FRAGility software. The SPO2FRAG software is an interactive and user-friendly tool that can be used for approximate, computer-aided calculation of building seismic fragility functions, based on static pushover analysis. It is coded in MATLAB® environment and is currently under development at the Department of Structures for Engineering and Architecture of the University of Naples Federico II. At the core of the SPO2FRAG tool lies the SPO2IDA algorithm, which permits analytical predictions for incremental dynamic analysis summary fractiles at the single-degree-of-freedom system level. By effectively interfacing SPO2IDA with a series of operations, intended to link the results of static pushover analysis with the variability that typically characterizes non-linear dynamic structural response, SPO2FRAG provides an expedient solution to the computationally demanding task of analytically evaluating seismic building fragility, which would otherwise require a large number of non-linear dynamic analyses.

NEAR -SOURCE PULSE-LIKE SEISMIC DEMAND FOR MULTI- LINEAR BACKBONE OSCILLATORS

Nonlinear static procedures, which relate the seismic demand of a structure to that of an equivalent single-degree-of-freedom (SDOF) oscillator, are well-established tools in the performance based earthquake engineering framework and have gradually found their way into modern codes for seismic design and assessment. Initially, such procedures made recourse to inelastic spectra derived for simple elastic-plastic or bilinear oscillators, but the request for demand estimates, which delve deeper into the inelastic range, shifted the trend towards inves- tigating the seismic demand of oscillators with more complex backbone curves. Meanwhile, the engineering relevance of near-source (NS) pulse-like ground motions has been receiving increased attention, since it has been recognized that such ground motions can induce a distinctive type of inelastic demand. Pulse-like NS ground motions are usually the result of rupture directivity, where seismic waves generated at different points along the rupture front arrive at a site at the same time, leading to a double-sided velocity pulse, which delivers most of the seismic energy. Recent research has led to a methodology being proposed for incorpo- rating this NS effect in the implementation of nonlinear static procedures. Both of the aforementioned lines of earthquake engineering research motivate the present study, which investigates the ductility demands imposed by pulse-like NS ground motions on SDOF oscillators who feature pinching hysteretic behavior with trilinear backbone curves. This in- vestigation uses incremental dynamic analysis (IDA) considering a suite of one hundred and thirty pulse-like-identified ground motions. Median, as well as 16% and 84% fractile, IDA curves are calculated, on which an analytical model is fitted. Least-squares estimates are ob- tained for the model parameters, which importantly include pulse period Tp. The resulting equa- tions effectively constitute an R-μ-T/Tp relation for pulse-like NS motions. A potential application of this result is briefly demonstrated in an illustrative example of NS seismic de- mand estimation.