This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the “PEER NGA” (Pacific Earthquake Engineering Research Center’s Next Generation Attenuation) project. For periods less than 1s , the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude M, closest horizontal distance to the surface projection of the fault plane R JB , and the time-averaged shear-wave velocity from the surface to 30 m VS30. The equations are applicable for M =5–8 , RJB 200 km, and VS30= 180– 1300 m / s. DOI: 10.1193/1.2830434

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Ground-motion prediction equations for the average horizontal component of PGA, PGV, and 5%-damped PSA at spectral periods between 0.01 s and 10.0 s

We present a new empirical ground motion model for PGA, PGV, PGD and 5% damped linear elastic response spectra for periods ranging from 0.01– 10 s. The model was developed as part of the PEER Next Generation Attenuation (NGA) project. We used a subset of the PEER NGA database for which we excluded recordings and earthquakes that were believed to be inappropriate for estimating free-field ground motions from shallow earthquake mainshocks in active tectonic regimes. We developed relations for both the median and standard deviation of the geometric mean horizontal component of ground motion that we consider to be valid for magnitudes ranging from 4.0 up to 7.5–8.5 (depending on fault mechanism) and distances ranging from 0 – 200 km. The model explicitly includes the effects of magnitude saturation, magnitude-dependent attenuation, style of faulting, rupture depth, hanging-wall geometry, linear and nonlinear site response, 3-D basin response, and inter-event and intra-event variability. Soil nonlinearity causes the intra-event standard deviation to depend on the amplitude of PGA on reference rock rather than on magnitude, which leads to a decrease in aleatory uncertainty at high levels of ground shaking for sites located on soil. DOI: 10.1193/1.2857546

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NGA Ground Motion Model for the Geometric Mean Horizontal Component of PGA, PGV, PGD and 5% Damped Linear Elastic Response Spectra for Periods Ranging from 0.01 to 10 s

The true performance of ground-motion prediction equations is often not fully appreciated until they are used in practice for seismic hazard analyses and applied to a wide range of scenarios and exceedance levels. This has been the case for equations published recently for the prediction of peak ground velocity (PGV), peak ground acceleration (PGA), and response spectral ordinates in Europe, the Middle East, and the Mediterranean (Akkar and Bommer 2007a,b). This paper presents an update that corrects the shortcomings identified in those equations, which are primarily, but not exclusively, related to the model for the ground-motion variability.

Strong-motion recording networks in Europe and the Middle East were first installed much later than in the United States and Japan but have grown considerably over the last four decades. The databanks of strong-motion data have grown in parallel with the accelerograph networks, and in addition to national collections there have been concerted efforts over more than two decades to develop and maintain a European database of associated metadata ( e.g. , Ambraseys et al. 2004).

As the database of strong-motion records from Europe, the Mediterranean region, and the Middle East has expanded, there have been two distinct trends in terms of developing empirical ground-motion prediction equations (GMPEs): equations derived from a large dataset covering several countries, generally of moderate-to-high seismicity; and equations derived from local databanks for application within national borders. We refer to the former as pan-European models, noting that this is for expedience since the equations are really derived for southern Europe, the Maghreb (North Africa), and the active areas of the Middle East. The history of the development of both pan-European and national equations is discussed by Bommer et al. (2010), who also review studies that consider the arguments for and against the existence of consistent regional …

Empirical Equations for the Prediction of PGA, PGV, and Spectral Accelerations in Europe, the Mediterranean Region, and the Middle East

Seismic Rehabilitation of Existing Buildings

In code-based seismic design and assessment it is often allowed the use of real records as an input for nonlinear dynamic analysis. On the other hand, international seismic guidelines, concerning this issue, have been found hardly applicable by practitioners. This is related to both the difficulty in rationally relating the ground motions to the hazard at the site and the required selection criteria, which do not favor the use of real records, but rather various types of spectrum matching signals. To overcome some of these obstacles a software tool for code-based real records selection was developed. REXEL, freely available at the website of the Italian network of earthquake engineering university labs (http://www.reluis.it/index_eng.html), allows to search for suites of waveforms, currently from the European Strong-motion Database, compatible to reference spectra being either user-defined or automatically generated according to Eurocode 8 and the recently released new Italian seismic code. The selection reflects the provisions of the considered codes and others found to be important by recent research on the topic. In the paper, record selection criteria are briefly reviewed first, and then the algorithms implemented in the software are discussed. Finally, via some examples, it is shown how REXEL can effectively be a contribution to code-based real records selection for seismic structural analysis.

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REXEL: computer aided record selection for code-based seismic structural analysis

Several sources of uncertainty affect the assessmen t of xisting buildings, including uncertainties as sociated with the material properties and the displacement capaci ty of the elements. In engineering practice, Monte Carlo simulations of the nonlinear seismic response of st ructures lead often to excessive computational cost s and therefore rarely carried out. This paper proposes a simple logic tree approach, where a moment-matchin g technique is proposed to define the optimal sampling points a d combination weights to apply to its branches. As a more refined method, a novel application to structural e ngineering of a recently proposed Point Estimate Me thod (PEM), which aims at reducing the required number of simul ations further, is tested. Both methods are applied to a historical stone masonry building, which is modelle d by an equivalent frame approach. The methods are benchmarked against the results of a Monte Carlo si mulation and other approximate methods applied in t he literature (FOSM, response surface method), which h g lights the good accuracy of such methods for est imating the performance uncertainty of the tested building. Moreover, the effect of the different sources of u ncertainty on the modelled performance of the building are discus ed, identifying the displacement capacity as a maj or source of uncertainty, whose effect can be compared in ter ms of order of magnitude to the record-to-record va riability.

Application of a Point Estimate Method for incorporating the epistemic uncertainty in the seismic assessment of a masonry building

With the introduction of higher seismic design forces in the Swiss loading standard of 2003 most unreinforced masonry (URM) buildings fail to satisfy the seismic design check. For this reason, in new construction projects, a number of URM walls are nowadays replaced by reinforced concrete (RC) walls. The lateral bracing system of the resulting structure consists therefore of URM walls and some RC walls which are coupled by RC slabs and masonry spandrels. The same situation characterises a number of seismically retrofitted URM building across Europe in which RC walls are added to the original structure to improve its seismic behaviour. Within the framework of the FP7-SERIES project, a four-storey RC-URM wall structure was tested on the shake table at the EUCENTRE TREES Laboratory (Laboratory for Training and Research in Earthquake Engineering and Engineering Seismology) in Pavia (Italy). The test was conducted at half-scale and is part of a larger research initiative on mixed RC-URM wall systems initiated at EPFL (Ecole Polytechnique Federale de Lausanne, Switzerland). The key objective of the testing campaign was to gain insight into the dynamic behaviour of mixed RC-URM wall structures and to provide input for the definition of a performance-based design approach of such mixed structural system. Multiple shaking at increasing intensity was used to test the dynamic behaviour of the examined building. During the final shaking several of the URM walls lost their axial load bearing capacity, however, the structure did not collapse as it was subjected to uni-directional loading only and the axial load was transferred to the RC walls and the URM walls that were loaded out-of-plane. Random noise vibration tests were performed to monitor the elongation of the natural periods induced by the damage progression. The paper presents details on the structural system and the selected ground motion, the test set-up and the instrumentation. Additionally, initial results of the shake table test are presented with a first interpretation of the observed structural behaviour.

Shake Table Testing of a Half-Scaled RC-URM Wall Structure

Reinforced concrete (RC) U-shaped core walls are commonly used in buildings to provide lateral resistance for wind and earthquake actions. While there is an abundance of these structural elements within the building stocks of both low-to-moderate and high seismic regions, there have been few experimental studies focusing on the seismic resistance of RC walls with a U-shaped cross-section. Building codes in some Latin American countries, such as Colombia, currently allow very thin RC walls with a single layer of reinforcement to be constructed. This type of construction is similar to practices in Australia, prior to the revised Concrete Structures building code coming into effect in 2019. Large-scale tests of two thin RC U-shaped walls with a single layer of vertical reinforcement were conducted in the Earthquake Engineering Structural Dynamics Laboratory at Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland. This paper presents some of the test setups and loading protocols used to test the walls, as well as the initial results, including local and global failure modes.

Experimental Tests of Thin RC U-shaped Walls with a Single Layer of Reinforcement

In performance-based seismic design the global displacement capacity of structures is predicted on the basis of local engineering demand parameters and mechanical models that link local and global deformation quantities. Although unreinforced masonry (URM) is one of the most used construction materials for residential structures all over the world, the displacement capacity of in-plane loaded URM walls is still mainly estimated from empirical drift capacity models rather than mechanical relationships between local and global deformation capacities. In this article, we present an analytical model which links the top displacement of an URM wall to the applied in-plane shear load. In order to verify the model, we compare the predicted results to global and local deformation quantities from own URM wall tests. Comparison of global deformation quantities shows that we are able to predict the initial stiffness of the walls with the simple assumption of a no-tension material and a linear-elastic material in compression. For walls developing a diagonal shear failure or hybrid failure, the predicted force-displacement curve starts diverging from the experimental envelope with the formation of the first diagonal cracks. With comparison of local deformation quantities, e.g. curvature profiles and shear strain profiles, we show that this is due to the formation of a significant diagonal shear crack.

http://www.eaee.org/Media/Default/2ECCES/2ecces_eaee/773.pdf

Review and improvement of simple mechanical models for predicting the force-displacement response of URM walls subjected to in-plane loading

Experimental tests on the inelastic behavior of RC bridge piers have shown that, due to tension shift effects, the curvature profile above the base section of the structural member differs from the one that would develop according to a force-based or a classical displacement-based beam formulation with plane section hypothesis. Due to the inclined cracks in concrete members, it was found that the curvature distribution evolves in a bilinear shape along the member height during the inelastic phase of the response, and that the length of plastification increases with increasing ductility demands. Recently, it was shown that axially equilibrated displacement-based elements can more effectively predict the local-level response of RC members. The process of imposing the equilibrium of the axial forces along the element length allows the beam element to improve the simulation of both curvature and strain profiles. The finite element was originally implemented in the authors’ structural analysis software SAGRES, which was developed for nonlinear static analysis and is not freely available to the engineering community. This paper presents the validation of the implemented axially equilibrated displacement-based element in the open source finite element software OpenSees and provides some application examples of both nonlinear static and dynamic analyses. The results are compared against classical approaches (force-based and displacement-based), pinpointing the advantages of the axially equilibrated displacement-based beam element.

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Katrin Beyer

Papers

Application of a Point Estimate Method for incorporating the epistemic uncertainty in the seismic assessment of a masonry building

Shake Table Testing of a Half-Scaled RC-URM Wall Structure

Experimental Tests of Thin RC U-shaped Walls with a Single Layer of Reinforcement

Review and improvement of simple mechanical models for predicting the force-displacement response of URM walls subjected to in-plane loading

Axially Equilibrated Displacement-based Beam Element: Implementation in OpenSees and Application to Dynamic Analysis of Structures