The first part of this paper is an overview of various methodologies for seismic-geotechnical hazard zonation that conform to the recommendations of International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE, 1999). The purpose of this review is to illustrate the variety of methodologies currently in use for preparation of seismic hazard maps and to evaluate basic principles of zonation for different purposes and at different scales. In the second part of the paper, input data for seismic microzonation are discussed. Promulgated seismic regulations are a prerequisite for delineation of seismic hazard zones. Guidelines and recommendations for seismic microzonation should be incorporated into seismic regulations. There are two principal approaches to earthquake loss mitigation; one relates to land use management, and the other deals with the design and construction of individual buildings. Both approaches must be considered as components of urban planning and building design, and the application and use of these approaches should be required and enforced by municipal authorities.
Keywords: seismic hazard, seismic microzonation, landslide, liquefaction, land use management
The paper describes some recent applications of the measurements of ambient vibrations (microseismic noise) in Croatia. They include free-field measurements, as well as those done within buildings. Data obtained in the field at the studied localities are consistent with the properties of shallow geological structures known to exist there. In Zagreb, Horizontal-to-Vertical Spectral Ratios (HVSR) indicate thick alluvial cover (over 100 m) that gradually gets thinner towards the slopes of the Medvednica Mt. A similar situation – on a smaller scale – is also encountered in Ston, where HVSR profiles reveal several tens of meters thick sedimentary cover over the bedrock which gets exposed at the Bartolomija hill. Analyses of records from Ston and Dubrovnik suggest that soil-building resonance must be seriously considered. Measurements in the buildings were analysed by a newly developed software package FREDA – a suite of Matlab routines. Based on tests on synthetic and real data it is concluded that spectral methods are in general more robust and less dependent on parameters of the algorithm employed, than time-domain analyses. Spectral algorithms are also better in resolving higher modes. Applications to real buildings proved that analyses of shaking induced by ambient vibrations in most cases lead to well constrained, reliable, and time independent estimates of frequencies and damping of the buildings’ vibrational modes for small excitation levels.
Keywords: ambient vibrations, microtremors, HVSR, soil-building resonance
In 1998 and 2004, two strong earthquakes shook the NW region of Slovenia. On the basis of a detailed inventory, the damages to structures were classified into five damage grades, defined in accordance with the European Macroseismic Scale (EMS). After both earthquakes, extensive geological and geophysical investigations were carried out, including geological mapping, the excavation of 60 pits, drilling of 20 boreholes down to depths of 20 m, seismic measurements, geo-electrical measurements and seismic microtremor investigations. Since 1990, local seismic effects in Slovenia have been addressed through consecutive rules covering static calculations for the structures being built; the first of these rules was the old Slovenian regulation (Uradni list SFRJ 31/81), and the other two were the last Eurocode 8 (EU8-94 and EU8-SIST EN 1998-1:2005) regulations.
In this report, we describe studies on how local ground conditions increase seismic effects on structures. On the basis of mentioned data in previous paragraph, we attempted to establish how reliably this influence can be defined. A forecast of local seismic effects was compared with actually established damage to structures. A statistical analysis was conducted in 27 selected areas (settlements) with similar geological conditions.
Through a comparison of ground-type impact assessments performed using geological mapping and drilling, geo-physical measurements and measurements of microtremors with actually established damage to structures, it was found that forecasts were more reliable if they were made with proper consideration of all relevant factors together. However, despite implementing forecasts using this type of multidisciplinary approach, the forecasts for some areas can be completely incorrect in terms of seismic effects. The best forecast was found to be produced using the last EU8 (EU8-SIST EN 1998-1:2005), while the old Slovenian (Uradni list SFRJ 31/81) and first EU8 (EU8-94) regulations produce less reliable results.
Keywords: earthquakes in NW Slovenia, European Macroseismic Scale, Eurocode 8, ground types, earthquake damage assessment, forecast of local seismic effects
The 2002 Molise earthquake, which was defined by seismologists as a normal event in the geodynamics of the Italian peninsula but had an international resonance due to the collapse of a primary school, triggered a series of research initiatives in earthquake engineering and significant modifications to building codes in Italy. The modifications were completed at the beginning of 2008 with the release of a new comprehensive building code for Italy. This document was mainly inspired by Eurocode, but it contains some changes and improvements.
In this paper, comments are made on three specific parts of the new code: definition of seismic action, analysis of liquefaction and analysis of slope stability. For the first part, seismic action is defined based on a recent careful study of the seismic hazard in Italy. For liquefaction analysis, some developments are given, keeping the same structure used in Eurocode. Finally, for slope stability, improvements are introduced to avoid overestimation of pseudostatic forces in conventional analyses.
Keywords: geotechnical characterization, liquefaction, local seismic response, slope stability, seismic code
One of the challenging tasks for Croatian accession to the European Union is the completion of the National Annex to Eurocode 8 (EC 8) that calls for the development of national seismic hazard maps. These maps need to be developed for several return periods (probabilities of exceedance) and should consider both bedrock and soil conditions. The latter is especially challenging as it calls for site characterization at a microzonation level, i.e., site characterization based upon VS,30, SPT blowcounts, and undrained shear strength, information available only in the departments of Public Works of major cities. In this paper, the authors discuss several shortcomings associated with the EC 8 ground type definitions and propose their revision. The authors also present the ongoing work for preparation of the Croatian National Annex to EC 8 and explain the rationale for the improvement of EC 8 ground type definitions.
Keywords: site response, ground types, Eurocode 8
This paper describes how a geotechnical database may be generated from the information system (IS) of a geotechnical consulting company established in compliance with the ISO 9001, ISO 17025 QMS standards and Eurocode 7. The application of these principles is illustrated using a geotechnical consulting company Geokon of Zagreb, Croatia as an example. An overview of Geokon’s geotechnical data management system is presented by describing the procedures for data input, maintenance, use, expansion and upgrade. Included in this paper are relevant flow charts and a hierarchy of both geotechnical databases and other databases.
Keywords: data management, document flow, geotechnical database, ISO 9001, ISO 17025, Eurocode 7
Assessing and reducing the seismic risks associated with historical structures require an appropriate knowledge of structural behaviour and characteristics, as suggested by recent national and international guidelines concerning cultural heritage. However, historical structures are characterised by a high level of uncertainty, which affects material properties and structural schemes and is related to deterioration processes or previous interventions and structural modifications. The level of knowledge can be increased by experimentally evaluating a structure's dynamic properties, and the resultant data can be used to refine and update numerical models that are representative of the real structural behaviour. Moreover, the periodic monitoring of relevant parameters can help identify eventual deterioration phenomena. Thus, dynamic tests, in conjunction with model updating, are becoming reliable tools for non-destructively assessing historical structures. In this article, a brief discussion of the basic principles of dynamic identification under operational conditions is presented. Two tests with historical structures are then presented, and the main results are reported. The high performance of operational modal analysis techniques and the interesting opportunities these techniques provide for the structural assessment of historical structures are discussed.
Keywords: heritage structures, ambient vibration tests, operational modal analysis
This paper concerns the structural identification of historical masonry buildings with reference to a case study, which is discussed in detail. The building is located in Southern Italy (Lecce). It has an ancient vaulted roof that is complex and commonly found in old masonry structures. This study takes advantage of extensive historical and structural investigations of the building. Preliminary activities have been conducted to obtain information about the current state of the structure including the geometry, morphology, structural details, material properties, prior interventions, and existing damage. This process was supported by an historical investigation into the conceptual background and construction methods used to build the structure. After the historical investigation, a series of experiments, including dynamic tests, were conducted on a number of the vaults to determine their dynamic response characteristics under operational conditions. A numerical model was also determined. In this paper, the primary dynamic test results and modelling assumptions are reported. Comparisons between numerical and experimental results are discussed.
Keywords: heritage structures, ambient vibration tests, Operational Modal Analysis
A field load testing is an effective method for understanding the behavior and fundamental characteristics of cable-stayed bridges. This paper presents results of the behavior of the reconstructed cable-stayed bridge over river Danube in Novi Sad under test load. The bridge was built between 1976 and 1981 and in 1999 was heavily damaged by two Tomahawk missiles. In 2003 process of the reconstruction began and at the end of 2005 Faculty of Civil Engineering, University of Belgrade was invited to test reconstructed bridge structure. The results of static load testing presented herein include displacements, rotations and strains of the 351 m long main girder. Vibrations of the bridge were obtained by impact load produced by heavy truck passing the bridge and the time history response of vertical accelerations was recorded. The frequency content of the signals was determined using Fourier transformation and five flexural natural periods were extracted. The geological structure and engineering properties of the soil are also given. A finite element model of the bridge was made and a good agreement is achieved between the experimental and analytical results. These results have shown that the bridge is in the elastic state under the code-specified serviceability load, which indicates that the bridge has adequate load-carrying capacity and can be put safely into service.
Keywords: cable-stayed bridge, experimental analysis, numerical analysis
This study analyzes catastrophic losses due to earthquakes in the Balkan region. Analysis is based on the following data on earthquakes, collected from the OFDA/CRED International Disaster Database (Université Catholique de Louvain, Brussels, Belgium) for 1900 to 2010: numbers of fatalities, size of the affected population and costs of material damages. Catastrophic losses were caused by 62 earthquakes in countries within the region: Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Serbia, Romania, Bulgaria, Macedonia and Greece. The analysis shows that a significant number of people in the Balkan region were killed (4,974) or were affected (2,033,723) by the earthquakes and that many countries suffered significant material damages (10,410.16 million USD) during the analyzed period. The main disadvantage of using publicly available sources is the lack of consistent data on earthquake damages. A brief review of the most catastrophic earthquakes recorded in databases through the last 110 years is given, based on the data from publicly available databases.
Keywords: Balkan region, catastrophic earthquakes, natural disasters databases
The paper presents the results of determining vertical displacements of the Earth’s crust at the territory of Croatia, Slovenia, and Bosnia and Herzegovina on the basis of the data obtained in the process of establishing geometric levelling networks of the highest order of accuracy. These are the networks of the Austrian precise levelling, I. levelling of high accuracy and II. levelling of high accuracy that was established successively within the period of about 100 years (1874-1973). In accordance with the hypotheses made and the selected methodology for defining the displacements, a concrete numeric quantification of displacements has been obtained, the size and the direction of Earth's crust displacements have been determined and their characteristics and empirical parameters of behaviour indicated. It is shown that bench mark displacements are of significant amount as related to the measurement accuracy of height differences in levelling networks and that long-wave and short-wave component of their variation can be noticed in correlation with the positional distribution of bench marks. The displacements have been modelled by means of so called grid models created by the combination of the regression modelling and the minimal curvature surface modelling. Thus, on the basis of modelled vertical displacement values the speed of uniform vertical crustal movements has been determined. In spite of the fact that a very simple methodology of displacement and movement determination has been used, that is based on the absolute heights of identical bench marks positioned in various epochs – networks, the obtained results present an adequate starting point for the selection and application of more sophisticated methodologies in determining and modelling of displacements in the forthcoming research, i.e. the starting point that enables interdisciplinary explanation of geodynamic processes leading to the changes in the shape and geometry of the Earth’s crust at the observed area.
Keywords: recent crust movements, vertical movements, bench marks, levelling networks, grid model