Effects Of Multiple Earthquakes Research Articles

A Case Study on the Effect of Multiple Earthquakes on Mid-rise RC Buildings with Mass and Stiffness Irregularity in Height

A Case Study on the Effect of Multiple Earthquakes on Mid-rise RC Buildings with Mass and Stiffness Irregularity in Height

Experimental study on full-scale steel moment-resisting frames with nonstructural walls subjected to multiple earthquakes

A cyclic loading test of a steel moment-resisting frame (SMRF) with nonstructural components was conducted to evaluate the seismic performance of steel buildings subjected to multiple earthquakes. The specimen is a single-floor, one-span substructure of the intermediate story of typical current middle- or low-rise steel building in Japan. Two specimens were tested. The structural systems of these two specimens were the same, but the nonstructural components attached to the steel frame were different. The light gauge steel (LGS) partition wall and the autoclaved lightweight concrete (ALC) exterior wall were used as the nonstructural components of each specimen. One typical set of loading history that corresponds to one earthquake was created based on the response analysis results, and multiple sets of loadings with various levels were loaded to consider the effect of multiple earthquakes. Based on the observed visible damages, it was found that the structural component performed well under multiple earthquakes with a maximum story drift angle less than 1/50, while for the nonstructural component, the ALC wall performed better than the LGS wall. From the obtained load–deformation relationship, it was found that the strength of the structural component and the strength contribution of the LGS wall gradually decreased when subjected to multiple earthquakes, while the strength contribution of the ALC wall fluctuates within a close range. Moreover, the elastic stiffness of the structural component subjected to multiple earthquakes was almost constant, while the stiffness contribution of the nonstructural components decreased.

Fragility assessment of existing low-rise steel moment-resisting frames with masonry infills under mainshock-aftershock earthquake sequences

This paper presents the fragility assessment of non-seismically designed steel moment frames with masonry infills. The assessment considered the effects of multiple earthquakes on the damage accumulation of steel frames, which is an essential part of modern performance-based earthquake engineering. Effects of aftershocks are particularly important when examining damaged buildings and making post-quake decisions, such as tagging and retrofit strategy. The procedure proposed in the present work includes two phase assessment, which is based on incremental dynamic analyses of two refined numerical models of the case-study steel frame, i.e. with and without masonry infills, and utilises mainshock-aftershock sequences of natural earthquake records. The first phase focuses on the undamaged structure subjected to single and multiple earthquakes; the effects of masonry infills on the seismic vulnerability of the steel frame were also considered. In the second phase, aftershock fragility curves were derived to investigate the seismic vulnerability of infilled steel frames with post-mainshock damage caused by mainshocks. Comparative analyses were conducted among the mainshock-damaged structures considering three post-mainshock damage levels, including no damage. The impact of aftershocks was then discussed for each mainshock-damage level in terms of the breakpoint that marks the onset of exceeding post-mainshock damage level, as well as the probability of exceeding of superior damage level due to more significant aftershocks. The evaluation of the efficiency of commonly used intensity measures of aftershocks was also carried out as part of the second phase of assessment.

Changes in Permeability Caused by Two Consecutive Earthquakes—Insights From the Responses of a Well‐Aquifer System to Seismic Waves

AbstractEarthquake‐induced aquifer permeability changes have been observed both in the laboratory and the field. However, the effects of multiple earthquakes on aquifer systems have rarely been differentiated. In this study, we analyze the piezometric response to earthquake pairs that occurred on the same day. The results show that events with higher seismic energy may result in a rise in piezometric level, and the seismic waves enhanced the permeability of the aquifer by different magnitudes. Stress/strain history from consecutive earthquakes may be retained, and permeability increased much more following the second earthquake than the first one. The method proposed in this study is useful in evaluating the permeability enhancement induced by consecutive earthquakes. The stress/strain memory of aquifers also has important implications for understanding aftershocks.

Post‐repair effect of column jackets on aftershock fragilities of damaged RC bridges subjected to successive earthquakes

SummaryIn light of recent earthquakes, structures damaged during an initial seismic event (mainshock) may be more vulnerable to severe damage and collapse during a subsequent event (aftershock). In this paper, a framework for the development of aftershock fragilities is presented; these aftershock fragilities define the likelihood that a bridge damaged during an initial event will exhibit a given damage state following one or more subsequent events. The framework is capable of (i) quantifying the cumulative damage of unrepaired bridges subjected to mainshock–aftershock sequences (effect of multiple earthquakes) and (ii) evaluating the effectiveness of column repair schemes such as steel and fiber‐reinforced‐polymer jackets (post‐repair effect of jackets). To achieve this aim, the numerical model of repaired columns is validated using existing experimental results. A non‐seismically designed bridge is chosen as a case study and is modeled for three numerical bridge models: a damaged (but unrepaired) bridge model, and two bridge models with columns repaired with steel and fiber‐reinforced polymer jackets. A series of back‐to‐back dynamic analyses under successive earthquakes are performed for each level of existing damage. Using simulated results, failure probabilities of components for multiple limit states are computed for each bridge model and then are used to evaluate the relative vulnerability of components associated with cumulative damage and column repair. Copyright © 2016 John Wiley & Sons, Ltd.

Discussion on “Effects of multiple earthquakes on inelastic structural response”

A discussion on the paper by Di Sarno (2013) is presented. The paper is focused on the inelastic response of degrading single-degree-of-freedom systems and a two-story two-bay reinforced concrete frame subjected to 5 seismic sequences recorded during the 2011 Tohoku earthquakes. While the subject to the paper is timely and the author point out some important issues about the problem, this discussion offers some comments about the nonlinear response of structures under seismic sequences (or multiple earthquakes) in order to enrich our current state of knowledge.

Effects of multiple earthquakes on inelastic structural response

The basic approach for seismic design of structures utilizes a single loading scenario and a single performance criterion; usually life-safety. In recent years, social and economic considerations have necessitated that more than one performance criterion is used, and also more than one level of earthquake intensity. This multiple load-and-limit state seismic design is the current best practice. There are a few locations around the world that warrant an alternative approach. These locations are affected by more than one earthquake within a relatively short period of time due to their special seismo-tectonic setting. Few existing studies simply assume that the first earthquake will impose the maximum damage. An opportunity has presented itself to study the effect of multiple strong earthquakes on structures as a consequence to the exceptionally rich set of records obtained from the earthquake sequence of Tohoku (Japan), starting on March 2011. In this technical note, five stations are selected to represent a set of sites subjected to multiple earthquakes of varying magnitudes and source-to-site distances. From the tens of records captured at these five sites, three are selected for each site to represent scenarios of leading and trailing strong-ground motion. A leading set is where the first earthquake has the largest peak ground acceleration (PGA) in the sequence of three, while a trailing set has the second or third records as its highest PGA signal. A short list of earthquake response parameters is selected, and the records are treated in two different manners. Inelastic constant ductility spectra for acceleration response are examined, alongside force reduction factor spectra. The final part of the technical note is a reinforced concrete (RC) frame analysis subjected to the same set of ground motions used for the response spectra. The inelastic response and force reduction factor spectra, alongside the inelastic response of the RC frame, not only confirm that multiple earthquakes deserve extensive and urgent studies, but also give indications of the levels of lack of conservatism in the safety of conventionally-designed structures when subjected to multiple earthquakes.

Structural pounding between adjacent buildings subjected to strong ground motions. Part II: The effect of multiple earthquakes

SUMMARYThe effect of collision between adjacent reinforced concrete building frames under multiple earthquakes is investigated in this paper. The four planar frames and the nine different pairs of adjacent reinforced concrete structures of the first companion paper are also examined here, under five real seismic sequences. Such a sequence of earthquakes results in a significant damage accumulation in a structure because any rehabilitation action between any two successive seismic motions cannot be practically materialised because of lack of time. Various parameters are investigated, such as the maximum horizontal displacement of top floor, ductility of columns, permanent displacements and so on. Furthermore, four different separation gaps between the building frames are considered to determine their influence on the behaviour of these frames. It is concluded that in most of the cases, the seismic sequences appear to be detrimental in comparison with the single seismic events. Copyright © 2013 John Wiley & Sons, Ltd.

연속지진하중에 의한 철근콘크리트 교량 교각의 응답해석

In this paper, the effect of cumulative damage for reinforced concrete bridge piers subjected to both single and multiple earthquakes is investigated. For this purpose, selected are three set of accelerograms one of which represents the real successive input ground motions, recorded at the same station with three months time interval. The analytical predictions indicate that piers are in general subjected to a large number of inelastic cycles and increased ductility demand due to multiple earthquakes, and hence more damage in terms of stiffness degradation is expected to occur. In addition, displacement ductility demand demonstrates that inelastic seismic response of piers can significantly be affected by the applied input ground motion characteristics. Also evaluated is the effect of multiple earthquakes on the response with shear. Comparative studies between the cases with and without shear indicate that stiffness degradation and hence reduction in energy dissipation capacity of piers are pronounced due to the multiple earthquakes combined with shear. It is thus concluded that the effect of multiple earthquakes should be taken into account for the stability assessment of reinforced concrete bridge piers.