The founder and the long-time leader of the research group received the highest national and international recognitions for the research work, which (as he has always stressed) is interwoven into the activities of the whole group. The highest possible recognition on the national scale has been the Zois Award, which he received in 2015. As stated in the explanation of the award “Peter Fajfar founded modern earthquake engineering in Slovenia and with his achievements made a decisive contribution to the development of this branch of science up to the top in Europe and the World.” It should be noted that this prestigious award in science was awarded to members of engineering community only four times since its long-time existence, which stresses even more the importance of the achievement. N2 method (described in more detail elsewhere in this report) was pointed out as one of the key contributions of the author and the research group as a whole. This achievement was in 2016 selected as one of the five achievements in the field of engineering, which were presented in the framework of the ARRS project Excellent in Science. The work of Peter Fajfar and the research group as a whole is highly recognized within the international earthquake engineering communities. See Section 20 “Status and international excellence of programme group members” for more detailed description. Let us here point out again that he is recognized by the leading world universities and earthquake engineering centres as the authority whose work achieves an exceptional degree of citation. The SICRIS database ranked him first in the number of standardized quotations in the last 10 years (NC10 = 3783), not only in seismic engineering and wider construction engineering, but also in the field of research activities of all technical sciences in Slovenia. The Microsoft Academic Search Database ranked him 54th out of more than 175,000 construction professionals and among the top 10 researchers in the field of earthquake engineering in the world and the first in Europe.
COBISS.SI-ID: 7951201
Member of the research group Peter Fajfar is one of four authors who wrote a book on seismic design of reinforced concrete (RC) buildings according to the European (and Slovenian) standard Eurocode 8 (EC8). All four authors have played a leading role in the development of the standard. The book, which has around 400 pages, presents the fundamentals of earthquakes and their effects at the ground level, provides guidance for the conceptual design of concrete buildings and their foundations for earthquake resistance, overviews and exemplifies linear and nonlinear seismic analysis of concrete buildings for design to EC8 and their modelling, and presents the application of the design verifications, member dimensioning and detailing rules of EC8 for concrete buildings, including their foundations. Alongside simpler examples for analysis and detailed design, the book includes a comprehensive case study of the conceptual design, analysis and detailed design of a realistic building with six stories above grade and two basements, with a complete structural system of walls and frames. The book serves as a commentary of the parts of EC8 relevant to concrete buildings and their foundations, supplementing them and explaining their proper application. It suits graduate or advanced undergraduate students, instructors running courses on seismic design and practicing engineers interested in the sound application of EC8 to concrete buildings. P. Fajfar contributed the entire chapter on the analysis, which, inter alia, presents for the first time in a comprehensive book form the practice-oriented N2 method for nonlinear structural analysis, which was developed within the research group. In addition, he participated in the preparation of the remaining chapters of the book.
COBISS.SI-ID: 6993505
This achievement has been selected to illustrate the worldwide recognition of the research group and its work. Members of the group organized four famous workshops (in 1992, 1997, 2004, and 2011), which became known simply as the Bled Workshops. These workshops produced widely cited reference books, which provided visions about the future development of earthquake engineering, as foreseen by world leading researchers in the field. There are very few scientific events which can repeatedly bring together the best and leading researchers from all over the world coming from top ranking universities including UC Berkeley, Stanford, Tokyo, and Canterbury, and thus provide a forum with a strong impact and authority for important developments in a particular scientific field. In 2011 the workshop topic was “Performance-Based Seismic Engineering – Vision for an Earthquake Resilient Society”. The participants have again produced a reference book providing answers to crucial questions in up-to-date earthquake engineering “What visible changes in the design practice have been brought about by performance-based seismic engineering? What are the critical needs for future advances? What actions should be taken to respond to those needs?” Answers were provided by regional groups from Japan and Asia, USA and North America, Europe, and the rest of the world (mainly from New Zealand and Chile). Discussion was strongly influenced by the knowledge gained during, at that time very recent, devastating earthquakes (Great East Japan – Tohoku earthquake and Christchurch and Chile) with special emphasis on the Tokushima NPP disaster. It was a great honour that Japanese researchers were willing to participate during the difficult time so soon after the disaster. The answer to the posed questions has been first of all that our research interest should go beyond the narrow technical aspects, and that the seismic resilience of society as a whole should become an essential part of the planning and design process. The participants discuss, develop and promote this, at that time a break-through, idea in the light of the state-of-the-art achievements in the field.
COBISS.SI-ID: 2062695
Significance of the achievement: An incremental dynamic analysis is used in earthquake engineering to determine the relationship between the seismic intensity and damage of the facility of the building for all damage states including collapse. The basic version of the method takes into account only the impact of the randomness of ground motions, while the influence of the modelling uncertainty is neglected. This shortcoming of the basic IDA was eliminated by the proposed new method. It was demonstrated by examples, that modelling uncertainty cannot be simply neglected since their effect can significantly reduce the estimated capacity of the structure. This triggered several similar studies. The article was awarded as the most quoted article published in 2009 in Earthquake Engineering & Structural Dynamics. Description: Incremental dynamic analysis (IDA) was extended by introducing a set of structural models in addition to the set of ground motion records which is employed in IDA analysis in order to capture recordtorecord variability. The set of structural models reflects epistemic uncertainties, and is determined by utilizing the latin hypercube sampling (LHS) method. The effects of both aleatory and epistemic uncertainty on seismic response parameters are therefore considered in extended IDA analysis. It is shown that epistemic uncertainty could significantly reduce the collapse capacity of a structure. The estimated seismic risk is consequently underestimated if the impact of the epistemic uncertainty is neglected.
COBISS.SI-ID: 4362337
Significance of the achievement: Simulation of the seismic response of buildings is extremely complex, since a minor variation of input data can cause large difference in the estimated damage. To ensure earthquake safety, it is therefore very important to understand which model parameters have a key impact on predicting damage of the investigated building. The results of the study showed that the importance of the input data of the model changes with the severity of the damage. Although the masonry infills have a very strong impact on the stiffness and the strength of the building, it is more important to accurately describe the deformation capacity of the columns if the objective is prediction of the near collapse damage. This new insight into the seismic response of buildings triggered the interest of researchers throughout the world. Description: The sensitivity of the seismic response parameters to the uncertain modelling variables of the infills and frame of four infilled reinforced concrete frames was investigated using a simplified nonlinear method for the seismic performance assessment of such buildings. This method involves pushover analysis of the structural model and inelastic spectra that are appropriate for infilled reinforced concrete frames. Structural response was simulated by using nonlinear structural models that employ one-component lumped plasticity elements for the beams and columns, and compressive diagonal struts to represent the masonry infills. The results indicated that uncertainty in the characteristics of the masonry infills has the greatest impact on the response parameters corresponding to the limit states of damage limitation and significant damage, whereas the structural response at the near-collapse limit state is most sensitive to the ultimate rotation of the columns or to the cracking strength of the masonry infills. Based on the adopted methodology for the seismic performance assessment of infilled reinforced concrete frames, it is also shown, that masonry infills with reduced strength may have a beneficial effect on the near-collapse capacity, expressed in terms of the peak ground acceleration.
COBISS.SI-ID: 5776993
Significance of the achievement: Unique experimental results are presented (due to their size structural walls are relatively seldom tested; only few tests were done on shake tables; in particular tests of the coupled walls have been practically non-existent). Therefore there was a great interest of the research community in these results to be published. The in-paralel developed numerical model was later used in several benchmark studies. In two of them the research group made the best blind prediction of the shake table response of structural walls among participants of the leading institutions in the field of earthquake engineering. For these achievements the group got the prestigious NEES (Network of Earthquake Engineering Simulation) Award for the best benchmark prediction of the shaking table response of structural walls. The award has been recognized as the significant research achievement of the year 2012 by the Slovenian Research Agency. Description: A shake-table test of a 1:3 scale model of a thin, lightly reinforced concrete (RC), 5-story coupled wall, representing a typical apartment building with a high wall-to-floor area ratio, was performed. The wall consisted of two T-shaped piers, faced to each other by the webs, which were connected at each story level by the coupling beam and slab. The wall was subjected to a series of uniaxial and biaxial seismic excitations. Two different structural details providing different degrees of confinement were used at the free edges without boundary columns. The lightly confined free edges of the flanges (using hairpin transverse reinforcement) behaved satisfactorily in the case of moderate seismic demand. Due to the beam-slab interaction and the slab, which was considerably ticker than in typical buildings, the coupling beams were much stronger than expected, causing brittle shear failure of the overloaded wall piers under bidirectional excitation. The analyzed wall developed substantial strength and low ductility. The main observations of the experiment were confirmed by the results of postexperimental analytical studies performed using a three-dimensional (3D) multiple vertical-line element model, which has been incorporated into a well-known open-code program system.
COBISS.SI-ID: 7937121
In this reporting period the research program group concluded the nearly 20 year’s long cycle of the participation in the EU Research Framework projects (ECOLEADER, PRECAST, SAFECAST, SAFECLADDING) studying the complex problem of the seismic response of precast buildings. The projects were initiated and led by the associations of the European precast producers (see also the exceptional socio-economic achievement). The behaviour and safety of precast systems predominantly depends on the performance of the specific connections between the precast elements. Therefore the first and key objective of the research was to understand complex mechanisms of the seismic response of typical connections. Large scale experiments were done and appropriate numerical models were developed and calibrated. Having such models (which were poorly developed or even non-existent in the past) it has been possible to study complex non-linear seismic response of precast systems and to perform risk analysis for different typologies of such buildings. Finally improved design procedures and formulas were formulated and published in pre-normative EC8 documents. All three papers have been frequently cited shortly after publication. Ad a) Dowel connections between beams and columns are typically used in European practice. Safety of buildings strongly depends on these connections. For this connection two types of potential failure mechanisms are possible: (a) local failure characterized by the simultaneous yielding of the dowel and crushing of the surrounding concrete, and (b) global failure, characterized by spalling of the concrete between the dowel and the edge of the column or the beam. The global failure has been far less investigated and existing procedures for the estimation of global strength are over-conservative because they do not consider the beneficial effect of hoops properly. In the paper, a new procedure for the estimation of the resistance against global failure based on the strut-and-tie model is proposed. Comparisons between the numerically calculated strength and the experimental results demonstrated the efficiency of the proposed model. The model has already significantly improved the design practice. Ad b) Many cladding panels fell off the structure during recent earthquakes in Italy. The hammer-head panel-to-structure connection proved to be the most poorly understood and weak connection in industrial precast buildings. Based on the results of the extensive experiments (cyclic tests, high-velocity cyclic tests and shake-table tests) the response of such connections is now understood and appropriate models have been developed. Ad c) The seismic vulnerability of twelve industrial precast building classes has been investigated by conducting nonlinear dynamic analyses on sample buildings from these building classes and taking into account selected seismic events. The results of the study can be used for seismic risk and loss estimation of precast building stock by considering the collapse of buildings and several other damage states, which were defined on the basis of the physical damage occurring to the vertical panels, horizontal panels, or masonry infills.
COBISS.SI-ID: 6916705
Significance of the achievement: Bridges are one of the most critical components of transport systems with decisive influence on the resilience of the society in the case of natural disasters. However, the literature devoted to these important engineering structures and in particular to their seismic performance is quite limited compared to that related to building structures. This book is an important contribution to the literature related to the seismic behaviour of bridges. Description: The book focuses on the use of inelastic analysis methods for the seismic assessment and design of bridges, on which substantial work has been carried out in recent years, and they have been gradually included to the modern standards. These methods have been mostly developed for the analysis of buildings. Since the seismic response of bridges is significantly different from that of buildings, researchers as well as designers face with numerous dilemmas when applying these methods to bridges. The key objective of this book is therefore twofold: 1) to present all important methods (including all the specifics in the case of bridges) belonging to the aforementioned category in a uniform and sufficient way for their understanding and implementation, and 2) to provide also a critical perspective on them by including selected case studies wherein several methods are applied to a specific bridge, and by offering some critical comments on the limitations of the individual methods and on their relative efficiency. In this respect, this book is a valuable tool for both researchers and practicing engineers dealing with seismic design and assessment of bridges, by both making accessible the methods and the analytical tools available for their implementation, and by assisting them to select the method that best suits the individual bridge projects that each engineer/researcher faces. This book includes the research performed by members of the TG11 – »Seismic design, assessment and retrofit of bridges«, which was set up in the frame of European Association for Earthquake Engineering.
COBISS.SI-ID: 5829729
Significance of the achievement: An integrated diagnostic approach of cultural heritage buildings is presented, on the example of the Pišece castle, the church of St. John the Baptist in Žiče and stone building in the Posočje region. The approach enables the planning of rehabilitation and strengthening measures by minimizing interventions in the structural and architectural elements of these buildings. It is based on a combination of in-situ tests and a numerical analysis of the response of buildings to various loads, including seismic load. In-situ tests, which are a combination of non-destructive (NDT), minor-destructive (MDT) and destructive (DT) tests, provide realistic data on the properties of materials and structural elements and their morphology. These data are later used in the numerical analysis, which explicitly explains the causes of detected damages. The proposed approach has attracted many researchers, as evidenced by the number of citations. The further development of the approach, by combining higher number of NDTs, led to the use of imaging techniques in the field of cultural heritage buildings. Description: In the scientific review paper, we collected and analysed the results of extensive in-situ tests and the results of numerical analyses of cultural heritage buildings (Pišece Castle, the Church of the Carthusian Monastery in Žiče, a stone house in the Posočje region), which differ in age, structural system and wall morphology. For the diagnosis of the structural performance, various NDT/MDT/DT tests were used, and the seismic resistance of each building was analysed numerically by means of SEM and FEM approach. In the paper effectiveness of different methods in detecting a particular problem/anomaly is discussed. Single test method is never enough. It is always necessary to select a combination of different NDT/MDT/DT tests. If DT is not allowed, the combination of different NDT tests should be combined at least with the coring (mechanical properties of mortar and brick) and video-boroscopy, through which we can evaluate the wall morphology. The costs of in-situ investigations will always be repaid, if not in the state of preparation of the project documentation, then certainly in the phase of the execution on the building site.
COBISS.SI-ID: 4963681
Significance of the achievement: Plasters with wall paintings (usually frescoes) are subject to damage by earthquakes with smaller intensities, in which the structure of the building itself is not damaged. As a rule, the part of the plaster with a wall painting is separated from the wall or from a rough plaster. It should be pointed out that the wall paintings value is often significantly higher than the value of the structural elements. Restoration of wall paintings detached from the substrate is performed with non-structural grout injection. The paper reviews the Slovene conservation practice in this field for the first time, since 1950 to the present. Comparison with the European practice of non-structural grout injection is also given. It shows that Slovenian conservators still prefer to use custom-mixed injection grouts with hydrated lime as the primary binder, whereas in today's international conservation practice commercial grouts or custom-mixed injection grouts with hydraulic lime as the primary binder are predominantly used. An innovative approach to the development of new non-structural grouts based on hydrated lime is also proposed. It is based on three levels of tests. Into the first level we include many different compositions and with a simple drying shrinkage test we eliminate those that are inadequate. In the second level, we evaluate the majority of the properties in fresh state, and in the hardened state only the drying shrinkage in the mortar cups that simulate mortar inside the walls. For further tests in the third level, we choose one or two grouts with the best properties. In the third level, the combination of a large number of tests accurately evaluates the inject-ability of the grout in fresh state and relevant physical and mechanical properties in hardened state. Description: The aim of this study is to optimize the composition of a custom-mixed injection grout with hydrated lime as the binder. The workability of fresh mixture and the physical, mechanical and rheological properties of the hardened grout were improved by two measures: by reducing the amount of water using the PCE superplasticizer and by replacing part of the binder with inert limestone filler that has an optimum particle size distribution. In this way we wanted to achieve the maximum possible volume stability and strength of the grout in hardened state. The results of the tests showed that non-structural grout consisting of 1 volume part of hydrated lime CL 90-S and 3 volume parts of inert limestone filler, with 0.5 % of the PCE superplasticizer, fulfilled most of the established requirements, so that it is thus potentially suitable for re-attachment interventions on plasters with wall paintings.
COBISS.SI-ID: 7486561