Definition Of Seismic Hazard Research Articles

Seismic performance and cost comparison of RC moment resisting and dual frames using UBC 97 and IBC 2021

The transition from the Uniform Building Code (UBC-97) to the International Building Code (IBC-21) marked a major shift in the definition of seismic hazard. The term “seismic hazard” in the form of peak ground acceleration (PGA) is replaced by spectral acceleration. This paper investigates the effect of using new seismic hazards on the structural performance of reinforced concrete (RC) buildings. It also looks into the financial impact on the capital costs of new buildings. Useful insights are made to understand the structural performance and financial impact of adopting IBC 21 for structural design in contrast to UBC 97. This study was carried out from the perspective of a developing country, Pakistan. Reinforced concrete moment resisting and dual frames are used as the main structural system of a typical 7-story residential building to investigate the aforementioned effect. The frames are assumed to be located in two locations with high and low seismic hazards. The effect on structural performance is investigated via nonlinear pushover analysis. Financial impact is judged mainly through cost estimation for steel and concrete. A detailed discussion is also presented on the seismic design guidelines in both codes.

Event-based assessment of seismic resilience in Mexican school buildings

This paper presents a methodology to quantify a proposed parameter defined as expected annual seismic resilience, which takes into account all possible events that affect a site of interest by following the next steps: (1) definition of seismic hazard, (2) definition of the exposure database, (3) computation of structural and human vulnerability, (4) estimation of seismic risk, (5) definition of rehabilitation strategies and (6) estimation of repairing times and required resources in the proposed rehabilitation process. In this study, consequential physical losses and indirect cost are not considered in the resilience computation. The methodology is applied to a case study of existing school buildings, located in Mexico City given its important seismic activity. The results are presented in annual resilience maps that will allow to graphically observe the distribution of resilient structures and use this information to take better decisions in disaster prevention and response. From this research it was found that a large percentage of the studied school buildings do not achieve an acceptable annual resilience value according to the rating proposed, which is important, since the seismic design codes do not explicitly consider resilience concepts. However, with the information of expected annual seismic resilience values in Mexico City, obtained in this research, it is possible to identify those buildings that require immediate attention associated to the lower resilience values so that they may be taken into consideration in the decision-making process of disaster prevention and response.

Probabilistic Seismic Hazard Assessment for Jamaica

A probabilistic seismic hazard analysis was performed to generate seismic hazard maps for Jamaica. The analysis was then conducted using a standard logic-tree approach that allowed systematically taking into account the model-based (i.e., epistemic) uncertainty and its influence on the computed ground motion parameters. Hazard computations have been performed using a grid of sites with a space of 0.05 degrees. Two different computation methodologies have been adopted: the standard approach based on the definition of appropriate seismogenic sources and the zone-free approach, which overcomes the ambiguities related with the definition of the seismic sources solely reflecting the characteristics of the earthquake catalogue. A comprehensive and updated earthquake catalogue for Jamaica has been compiled for the years 1551-2010 and new empirical relationships amongst magnitudes MW-MS and MW-mb have been developed for the region. Uniform hazard spectra and their uncertainty have been calculated for the horizontal component of ground motion for rock site conditions and five return periods (95, 475, 975, 2,475 and 4,975 years) and spectral accelerations for 34 structural periods ranging from 0 to 3 s, and 5% of critical damping. The spectral accelerations have been calculated to allow the definition of seismic hazard in Jamaica according to the International Building Code 2012. The disaggregation analysis for Kingston Metropolitan Area suggests that the magnitude-distance pair that contributes most to the hazard corresponds to events with M 7.8 and M 7.0 in the Enriquillo Plantain Garden Fault and the Jamaican Faults at a distance of 28 km and 18 km for short and long period structures respectively corresponding to 2,475 years return period. However, for long period structures, a substantial contribution is found for a M 8.2 at a distance of 198 km in the Oriente Fault Zone.

Probabilistic Seismic Hazard Assessment at the Eastern Caribbean Islands

A probabilistic seismic hazard analysis has been performed to compute probabilistic seismic hazard maps for the eastern Caribbean region (10° N-19° N, 59° W-64° W), which includes in the north the Leeward Islands (from Anguilla to Dominica) and in the south the Windward Islands (from Martinique to Grenada), Barbados, Trinidad, and Tobago. The analysis has been conducted using a standard logic-tree approach that allowed systematically taking into account the model-based (i.e., epistemic) uncertainty and its influence on the computed ground motion param- eters. Hazard computations have been performed using a grid of sites with a space resolution of 0.025 degrees covering the territory of the considered islands. Two different computation methodologies have been adopted: the standard Cornell-McGuire approach (Cornell, 1968; McGuire, 1976) based on the definition of appropriate seismogenic zones (SZ), and the zone-free approach developed by Woo (1996), which overcomes the ambiguities related with the definition of seis- mic sources. The interplay and complexities between shallow crustal, intraplate, and interface subduction seismicity of the Caribbean region have been thoroughly investigated. By merging all available databases, a comprehensive and updated earthquake catalog for the region has been compiled. Also, a thorough investigation has been undertaken to identify the most suitable ground motion prediction equa- tions to be used in the analyses. Uniform hazard spectra have been calculated for the horizontal component of ground motion (rock and level site conditions), 4 return periods (RP) (95-, 475-, 975-, and 2475-yr), and 22 spectral accelerations (SA) with structural periods ranging from 0 to 3 s. SAs at 0.2 and 1.0 s for 2475-yr RP have been calculated to allow the definition of seismic hazard in the region of study according to the International Building Code (IBC, International Code Council (ICC), 2009).

On the Need for Reliable Seismic Input Assessment for Optimized Design and Retrofit of Seismically Isolated Civil and Industrial Structures, Equipment, and Cultural Heritage

Based on the experience of recent violent earthquakes, the limits of the methods that are currently used for the definition of seismic hazard are becoming more and more evident to several seismic engineers. Considerable improvement is felt necessary not only for the seismic classification of the territory (for which the probabilistic seismic hazard assessment—PSHA—is generally adopted at present), but also for the evaluation of local amplification. With regard to the first item, among others, a better knowledge of fault extension and near-fault effects is judged essential. The aforesaid improvements are particularly important for the design of seismically isolated structures, which relies on displacement. Thus, such a design requires an accurate definition of the maximum value of displacement corresponding to the isolation period, and a reliable evaluation of the earthquake energy content at the low frequencies that are typical of the isolated structures, for the site and ground of interest. These evaluations shall include possible near-fault effects even in the vertical direction; for the construction of high-risk plants and components and retrofit of some cultural heritage, they shall be performed for earthquakes characterized by very long return periods. The design displacement shall not be underestimated, but neither be excessively overestimated, at least when using rubber bearings in the seismic isolation (SI) system. In fact, by decreasing transverse deformation of such SI systems below a certain value, their horizontal stiffness increases. Thus, should a structure (e.g. a civil defence centre, a masterpiece, etc.) protected in the aforesaid way be designed to withstand an unnecessarily too large earthquake, the behaviour of its SI system will be inadequate (i.e. it will be too stiff) during much more frequent events, which may really strike the structure during its life. Furthermore, since SI can be used only when the room available to the structure laterally is sufficient to create a structural gap compatible with the design displacement, overestimating this displacement may lead to unnecessarily renouncing of the use of such a very efficient method, especially in the case of retrofits of existing buildings. Finally, for long structures (e.g. several bridges or viaducts and even some buildings) an accurate evaluation of the possibly different ground displacements along the structure is required (this also applies to conventionally built structures). In order to overcome the limits of PSHA, this method shall be complemented by the development and application of deterministic models. In particular, the lack of displacement records requires the use of modelling, once they are calibrated against more commonly available velocity or acceleration records. The aforesaid remarks are now particularly important in the P.R. China and Italy, to ensure safe reconstruction after the Wenchuan earthquake of May 12, 2008 and the Abruzzo earthquake of April 6, 2009: in fact, wide use of SI and other anti-seismic systems has been planned in the areas struck by both events.

On non-parametric techniques for area-characteristic seismic hazard parameters

SUMMARY Usual techniques for estimating the seismic hazard, within a specific geographical area, are focused in the theory of extremes of Gumbel. Such kind of techniques suppose the existence of a parametric type of stochastic model for the process of occurrence of earthquakes. In this work, we will see that the use of non-parametric curve estimation techniques represent an interesting alternative to this procedure. From the definition of seismic hazard, we construct a nonparametric estimate of this function and other related parameters of interest, such as the modal annual magnitude, the yearly expected number of earthquakes, the mean return period and the maximum magnitude. Applications to earthquakes data of Southern Spain are made.

Comment on "How Can Seismic Hazard in the New Madrid Seismic Zone Be Similar to That in California?" by Arthur Frankel

Frankel (2004) argued that seismic hazard, defined as the maximum shaking predicted for sufficiently low probabilities of recurrence, or equivalently over sufficiently long time intervals, is comparable for sites in the New Madrid zone to that for sites in California. Many aspects of this argument are debatable, because it relies on assumptions about the size, recurrence, and shaking from future earthquakes, none of which is well known (Newman et al. , 2001), and then makes inferences about the extreme and hence uncertain “tails” of the probability distribution presumed to characterize future ground motion (Wang and Ormsbee, 2005). Even more seriously, as discussed here, it relies on a definition of seismic hazard that is of little use in formulating public policy such as building codes because it considers the maximum shaking at a geographic point over 500 or 2,500 years (10% or 2% probability in 50 years) rather than over the much shorter (50-100 year) life of typical structures. Estimating seismic hazard involves both making assumptions about future earthquakes and choosing a definition of hazard. The latter is even more arbitrary and at least as significant as the former. Hence, even if the probabilities of future earthquake occurrence and ground motion were well known—which is far from the case—different …