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 modeling, 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 storeys 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 practising 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
The damage assessment to cultural heritage assets after recent earthquakes showed the high vulnerability of some types of historical structures (e.g. palaces, churches, towers). Earthquakes also proved that strengthening interventions adopted in the last decades are often invasive, ineffective and might also increase the vulnerability. Thus, there is an urgent need for developing reliable assessment procedures and promoting effective strategies for the seismic risk mitigation of cultural heritage. The preservation of cultural heritage assets must guarantee their capacity to last over time against decay, natural hazards and extreme events, without losing their authenticity and use. The PERPETUATE project (Performance Based Approach to Earthquake protection of Cultural Heritage in European and Mediterranean Countries) had as main objective to produce European Guidelines for the evaluation and mitigation of seismic risk to cultural heritage assets, useful to support the design of strengthening interventions for the preservation of the architectural building and the contained unmovable artworks. In the frame of the PERPETUATE the members of the research program group (Bosiljkov, Žarnić, Kržan) contributed in the year 2015 exceptional number (7) papers in the special issue of the Bulletin of Earthquake Engineering, which ranks into the journals with the highest IF in earthquake engineering (COBISS 6642785, 6794849, 6643297, 6643041, 6649441, 6642529, 6643809). For illustration, the content of one of these papers is described in this section. The effect of uncertainties regarding modelling choices and knowledge of specific structural configurations on the seismic vulnerability evaluation of masonry buildings in Slovenia were studied using two case studies: a set of damaged buildings from the rural area of NW Slovenia hit by earthquakes in 1998 and 2004 and the urban buildings from the historic city centre of Ljubljana. Two modelling strategies were applied – failure mechanisms analysis by means of macro element methodology (MEM) and non-linear response analysis by means of structural element modelling (SEM). The accuracy in predicting failure modes by MEM ranged between 50-80% of the stock of building in rural area. Given the uncertainties associated with the data relative to the urban architecture stock, the MEM analysis was carried out considering different hypotheses, leading to a range of 30 to 70% damaged buildings, for 475 years return period. For single building of rural architecture already damaged during previous earthquake in 2004, where due to the extensive in-situ campaign the influence of uncertainties were minimised, direct comparison of the effectiveness of both methods were investigated. MEM assessment yields more conservative results in respect to non-linear approach with prevailing out-of-plane failures and thus may be an efficient tool for the design of local strengthening measures for heritage buildings to prevent damage in lower intensity events with higher probability of occurrence.
COBISS.SI-ID: 6649441
In the year 2015 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 the exceptional socio-economic achievement). The behaviour of precast systems predominantly depends on the performance of the specific connections between the precast elements. In European precast construction practice, the most common type of connection between beams and columns is a dowel connection, which was studied in the frame of the presented paper. Such connections are subject to the following types of potential failure mechanism: (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. Namely, none of the methods has explicitly taken into account the fact that the global failure of the dowel connection is changed/improved by the presence of stirrups from brittle to ductile. In the paper, a new procedure for the estimation of resistance against global failure is proposed. Taking into account an appropriate strut and tie model of the connections, the influence of stirrups on this resistance as well as on the type of the failure is taken into account explicitly. Comparisons between the numerically calculated strength and the experimental results demonstrated the efficiency of the proposed model.
COBISS.SI-ID: 6916705
Based on the results of the infrared thermography of 51 artificially created defects - voids and delaminations - in concrete, it was shown that it is possible to detect defects at depths that are equal or less than the defect size D using the thermal contrast method. By applying the phase contrast method, an increase of 50% in the maximum depth for a given defect size D was achieved. Delaminations containing thin air gaps were detected with the same success as much larger voids of the same cross section.
COBISS.SI-ID: 7065697
The cyclic response of a typical bridge column with I-shaped cross-section and substandard transverse reinforcement was investigated by means of experimental and numerical research. The amount of transverse reinforcement was sufficient to ensure adequate shear strength, but other requirements of the Eurocode 8/2 standard related to the confinement and buckling of the longitudinal bars were not fulfilled. Failure was brittle due to the buckling and rupture of the longitudinal bars, which caused a progressive reduction of strength. The results of the experiment showed that the requirements of Eurocode 8/2 (which are quite stringent) related to the minimum volumetric ratio and the maximum centre-to-centre distance of the stirrups along the column, as well as the maximum distance between the engaged longitudinal bars, are justified in the investigated case. It was demonstrated that improperly designed stirrup hooks can cause a significant reduction in the ductility capacity of the column. An attempt was made to strengthen the column using CFRP sheets. The strengthening was not straightforward. Two types of anchoring were investigated. The most efficient method of anchoring was based on the use of bolted steel plates. Due to the unfavorable dimension ratio of the column cross-section, the efficiency of the strengthening was limited. The results of the experiment were used in order to identify the most suitable numerical models. The methods included in Eurocode 8/3 were found to be inadequate to evaluate seismic response of the strengthened columns.
COBISS.SI-ID: 7075169