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Due to soil -structure-interaction (SSI), the seismic lateral structural deformations may be substantially different from the ones traditionally calculated from the fixed-base structure on free-field approach. Additionally, the actual displacements of foundations considering soil compliance are of practical interest in some applications. In the present study, seismic elastic displacement demand of compliant coupled soil- structure (SFS) systems, is investigated through numerical time history analyses. The numerical displacement demand is validated through an analytical solution, comparison between FEM and analytical solution is provided and finally, a practical, simplified approach for displacement evaluation is proposed. The displacements are presented in terms of dimensionless parameters such as soil to structure stiffness ratio 1/σ and slenderness ratio h/B, while closed-form relationships are proposed. [ABSTRACT FROM AUTHOR]

The accuracy of a seismic risk model to predict future losses is a significant challenge as it depends on many parameters, each with important uncertainties, that are present in all components of the model. The aim of this study is to present a process that can be followed to validate the efficiency of a predictive risk model for seismic risk assessment at urban or regional scale, through comparison of estimated physical damages with those recorded at past seismic events, discussing at the same time the uncertainties involved in the different steps of this process. The proposed process is applied for the verification of the open-access uniform European Seismic Risk Model (ESRM20), considering two major past seismic events in Greece, i.e. the Athens 1999 Mw 5.9 and the Thessaloniki 1978 Mw 6.5 earthquakes, for which we possess relatively good damage reports for a representative portion of the two metropolitan agglomerations. Despite the numerous uncertainties and the unavoidable simplifications, a good comparison is found between the estimated and observed damage, especially for the city of Thessaloniki. Regarding the distribution of damage, it is anticipated that the most heavily damaged typologies for both case studies are found to be the low-to-medium-rise, non-ductile masonry buildings. The analyses also revealed the importance of the credibility of the adopted exposure model and of the adequate selection of ground motion models for seismic hazard assessment. Τhis challenging work and the positive results acquired so far aim to contribute to the efforts towards increasing the resilience of cities. [ABSTRACT FROM AUTHOR]

This paper presents the results from extensive parametric dynamic analyses of soil-structure systems that focus on the clear modification (increase or decrease) of the acceleration amplitude at the foundation with respect to the free-field, especially for squatty structures. Properties of the systems are selected such as to cover a wide range of meaningful geometries and materials for engineering practice. The results are presented in terms of weighted modification factors of the maximum foundation acceleration amplitude with reference to the corresponding maximum acceleration amplitude at free-field, for squatty and more slender structures. For the large majority of the studied systems, foundation acceleration decreases from the free-field by 10-15% on average. Nevertheless, acceleration demand at the foundation increases compared to the free-field, for 30% of squatty and for 15% of the more slender structures. Modification of the foundation acceleration amplitude is also correlated with the ratio of the predominant period of the input motion to the flexible-base system period. Finally, the findings of this study are compared with sparse available recorded data from the Seismic Hazard Harmonization in Europe database. [ABSTRACT FROM AUTHOR]

The seismic acceleration loading of structures founded on compliant soil is investigated through numerical elastic time history analyses of coupled soil-foundation-structure (SFS) systems and appropriate reduction factors of acceleration demand for free-field to evaluate acceleration demand for the SFS systems are proposed. The proposed reduction factors are the division of the acceleration demand for the coupled SFS system over the acceleration demand for the free-field, and propose an alternative method to calculate the actual acceleration loading considering interaction effects. The advantages of the proposed methodology are i) its accuracy, as the reduction factors result from coupled SFS numerical finite element analyses and consider both inertial and kinematic interaction effects and ii) its practicality, as it can be applied by the user performing no finite element numerical analysis. Additionally, the presented methodology can be applied to systems with important mass (e.g. bridge structures). The proposed acceleration reduction factors are presented in terms of dimensionless engineering parameters such as soil to structure stiffness ratio and the structure's aspect ratio. The accuracy, efficiency, and practicality of the proposed methodology are highlighted through an application to a typical bridge structure. Because structures with surface foundations are examined, inertial interaction mainly affects the acceleration demand. Therefore, the proposed reduction factors clearly demonstrate and quantify the beneficial effect of damping on buildings and bridges, as the maximum average acceleration at the top of the actual SFS system can reduce to about 55–85% of the acceleration demand for the free-field motion. [ABSTRACT FROM AUTHOR]

Seismic risk assessment and loss estimation are of major importance for decision-making with respect to the reduction of earthquake-induced losses in large urban areas. However, the methodological chain of seismic risk assessment, from seismic hazard assessment to evaluation of potential losses, encompasses numerous uncertainties, both aleatory and epistemic, associated with different sources. The present study is a comprehensive application of the Capacity Spectrum Method to the seismic risk assessment of the city of Thessaloniki, aiming to give an insight into epistemic uncertainties involved in the above methodology, owing to hazard modelling, structural capacity, fragility and damping, as well as shaking duration. To quantify and discuss the uncertainties, a logic tree approach is used. A sensitivity analysis of the computed seismic risk results is performed to determine the input parameters having the greatest impact. The analyses were carried out for the building stock of the city of Thessaloniki, Greece, for which detailed building inventory and very good knowledge of the soil conditions are available. Only physical losses due to the structural damage of the building stock were considered. Considerable scatter in the risk estimates was observed due to epistemic uncertainties. The sensitivity analyses demonstrated that the most influencing parameters when applying the Capacity Spectrum Method are the selection of the fragility curves for the buildings and the seismic hazard model adopted in the analysis. The decision-making process with respect to seismic risk assessment should therefore carefully account for uncertainties and pay attention to the most influencing parameters regardless of the methodology used. [ABSTRACT FROM AUTHOR]

Recent strong seismic events have highlighted the high vulnerability of port facilities resulting in significant physical damages and important socio-economic losses. The most widespread source of seismic damage to port structures is often not related to the ground shaking itself but to the induced phenomena principally associated to the liquefaction of loose, saturated soils that often prevails at coastal areas. In this context, this study aims at the investigation of the influence of soil liquefaction on the seismic performance and vulnerability of typical port gravity quay walls. Different gravity quay wall configurations are examined with varying base width/height ratios. Two-dimensional incremental dynamic analysis is conducted for the soil-quay wall system, under effective stresses using OpenSees software, considering a representative set of fifteen real ground motion records as input ground motion at the bedrock. Two numerical approaches are applied to investigate the effect of liquefaction on its seismic performance and vulnerability assessment: the first one without considering liquefaction, while the second considers the effects of liquefaction. The damage measure is defined in terms of the normalized seaward displacement. Fragility and vulnerability curves are finally derived in terms of different intensity measures and compared with available literature curves. Results show the important role of liquefaction in increasing the seismic vulnerability of the typical port quay wall. [ABSTRACT FROM AUTHOR]

The paper presents the application of the seismic assessment procedure developed in the PERPETUATE project on a single monument, the Neoclassical School in the Medieval City of Rhodes. The PERPETUATE methodology for the estimation of seismic risk of cultural heritage assets is based on the principles of performance-based assessment ( PBA), using nonlinear static procedures. The outcome of the PBA methodology is the maximum seismic intensity measure compatible to different performance levels. The focus of the paper is on the application of the methodology, considering the effects of both soil-foundation-structure interaction ( SFSI) and masonry foundation flexibility on the building response, before and after rehabilitation design measures. It is found that SFSI and foundation flexibility produce larger displacements and reduce the maximum ground acceleration that the building can sustain by over 50 %. However, despite the detrimental effects of SFSI on the acceleration capacity, SFSI and foundation flexibility may have a favorable effect on the structure safety, as they modify the collapse mechanism. The results of seismic analyses showed that the building, in its current state, does not sustain the demands for the Life Safety and Collapse Prevention performance levels. Stiffening the roof of the structure and providing sufficient anchorage to the structure, along with systematic grouting of the masonry walls, are the principal rehabilitation decisions considered herein. Mitigation measures were evaluated, considering SFSI and the analyses revealed the adequacy of the proposed retrofitting measure, which combines vertical (wall) and horizontal (roof) stiffening. [ABSTRACT FROM AUTHOR]

In this paper we propose reduction factors accounting for the decrease of stiffness of monumental masonry foundations due to aging, weathering, or other deteriorating effects. The proposed reduced stiffness values can be readily used in finite element structural analysis software in the framework of performance-based assessment, representing linear elastic springs at the foundation level. These springs account for foundation-soil system flexibility and soil-foundation interaction (SFI) at low-frequency vibrations. Accordingly, we propose a procedure to reduce monumental masonry foundation-wall stiffness from the rigid-footing assumption, with respect to the relative stiffness between the foundation and the soil. The proposed procedure is applied to the historical structure Arsenal De Milly in the Medieval City of Rhodes, where period elongation and ductility increase are highlighted, because of SFI and foundation flexibility. [ABSTRACT FROM AUTHOR]

Vulnerability assessment of masonry historical monuments relies on the accurate assessment of their real structural and foundation conditions, which is always a very difficult and challenging task to determine. Ambient noise measurements are among the non-destructive field techniques, which can provide useful information regarding the structural integrity, the dynamic response characteristics of the structure and the dynamic properties of the foundation soil. The performance-based design approach developed in the research project PERPETUATE for the vulnerability assessment of monuments uses all this information in a cost efficient way. Moreover, validation of the whole methodology has been made on several monuments in the Medieval City of Rhodes. To illustrate the use of ambient noise measurements in the frame of PERPETUATE methodology, we performed a number of ambient vibrations measurements on three selected monuments in the Medieval City of Rhodes (Greece) and the surrounding soil. The aim was to identify the dynamic characteristics of the selected structures and the dynamic properties of foundation-soil where these structures are founded. The Frequency Domain Decomposition technique is adopted for ambient modal identification using ARTeMIS software and the continuous wavelet transformation for calculating the wavelet energy to compare it with the pathology pattern of a typical masonry wall. The dynamic properties of the foundation soil, in terms of shear-wave velocity, were also explored using the Spatial Autocorrelation Coefficient method. The goal of the ambient noise measurement performed herein is to better simulate the complex masonry structures in view of estimating their vulnerability using the PERPETUATE methodology and support rehabilitation decisions. The improvement of the initial numerical model using the results of the ambient vibrations measurements illustrates the usefulness of the approach and provides some helpful practical guidelines. [ABSTRACT FROM AUTHOR]

The present study focuses on the dynamic system identification of the Suleiman Mosque minaret in the medieval city of Rhodes, Greece. Suleiman Mosque was built in 1522 at the site of the destroyed Christian Church of the Apostles. First, we performed sets of ambient vibration measurements at the minaret of the monument. Based on these data, we calculated the eigenproperties of the minaret. Next, we modeled the monument in three dimensions, using the finite element method. Six numerical models were considered. Model Ι is the simplest one (isolated, fixed base minaret). Model VI is the most complicated one (simulation of the whole mosque also considering soil–structure interaction and foundation flexibility). The calculated predominant periods and mode shapes of Models I–VI are validated against the microtremor field measurements, recorded on the minaret's two floors and ground level. We elaborate on the reliability of finite element models for earthquake response evaluation, considering soil–structure interaction and foundation flexibility on the mode shape eigenfrequencies. Additionally, we discuss the seismic response of the minaret compared to the whole monument. We observed no significant difference in the first two modes of response, implying that the minaret's dynamic behavior is slightly affected by the entire mosque's presence. [ABSTRACT FROM AUTHOR]

A multi-purpose and multi-scale tool for the seismic vulnerability and risk classification of critical buildings, such as schools, is proposed for pre- and post-event decision-making to mitigate the risk and reduce losses. The herein proposed "RiskSchools" system, is capable of performing the seismic risk assessment and grading of school buildings at various scales (district, municipality, region etc.), using (a) a pre-seismic rapid visual screening and grading of the school buildings in different vulnerability-risk classes and (b) a seismic risk assessment of the school buildings population, applying probabilistic or scenario-based methods for the seismic hazard and analytical methods for the vulnerability and risk assessment, also leading to a grading of the buildings' risk. The results of the two approaches are compared and combined through a flexible and adaptable expert elicitation scheme to provide a final classification of the seismic risk of the school buildings in the scale of interest and a prioritization scheme with respect to the need for seismic upgrade and retrofitting. The RiskSchools system consists of a powerful, state-of-the-art, user-friendly, and easy-to-use smartphone application for the compilation of the inventory and the rapid visual screening, and a project-dedicated multi-purpose webGIS platform for the seismic vulnerability and risk classification of school buildings at any scale. Although it is initially developed and applied to the school building stock of the Region of Central Macedonia in Greece, it has been specifically designed to be easily applied to other regions of Greece and worldwide and adapted to other critical buildings, like health care and hospital buildings. The ultimate scope of the RiskSchools System is to allow for the optimal design of decision-making procedures in support of disaster management to enhance critical buildings resilience. [ABSTRACT FROM AUTHOR]

As part of the development of a European Seismic Risk Model 2020 (ESRM20), the spatial and temporal evolution of seismic design across Europe has been studied in order to better classify reinforced concrete buildings (which represent more than 30% of the approximately 145 million residential, commercial and industrial buildings in Europe) and map them to vulnerability models based on simulated seismic design. This paper summarises the model that has been developed to assign the years when different seismic design levels (low code, moderate code and high code) were introduced in a number of European countries and the associated lateral forces that were specified spatially within each country for the low and moderate codes for typical reinforced concrete mid-rise buildings. This process has led to an improved understanding of how design regulations evolved across Europe and how this has impacted the vulnerability of the European residential building stock. The model estimates that ~ 60% of the reinforced concrete buildings in Europe have been seismically designed, and of those buildings ~ 60% have been designed to low code, ~ 25% to moderate code and 15% to high code. This seismic design model aims at being a dynamic source of information that will be continuously updated with additional feedback from local experts and datasets. To this end, all of the data has been made openly available as shapefiles on a GitLab repository. [ABSTRACT FROM AUTHOR]

The assessment of historical elements at risk from earthquake loading presents a number of differences from the seismic evaluation of modern structures, for design or retrofitting purposes, which is covered by existing building codes, and for the development of fragility curves, procedures for which have been extensively developed in the past decade. This article briefly discusses: the hazard framework for historical assets, including a consideration of the appropriate return period to be used for such elements at risk; the intensity measures that could be used to describe earthquake shaking for the analysis of historical assets; and available approaches for their assessment. We then discuss various unique aspects of historical assets that mean the characterisation of earthquake loading must be different from that for modern structures. For example, historical buildings are often composed of heterogeneous materials (e.g., old masonry) and they are sometimes located where strong local site effects occur due to: steep topography (e.g., hilltops), basin effects or foundations built on the remains of previous structures. Standard seismic hazard assessment undertaken for modern structures and the majority of sites is generally not appropriate. Within the PERPETUATE project performance-based assessments, using nonlinear static and dynamic analyses for the evaluation of structural response of historical assets, were undertaken. The steps outlined in this article are important for input to these assessments. [ABSTRACT FROM AUTHOR]