Extensive construction of buildings with structural system made of reinforced concrete walls had been started in the early 60s of the last century, as a continuation of the rebuild of Europe after the World War II. This was especially true in the Western Balkan region. In some way these buildings replaced multistorey masonry buildings, enabled significantly higher number of floors and a larger number of apartments. A specific construction technology with the so-called tunnel formwork was applied, which enabled rapid construction progress in terms of the height of the building. Seismic resistant structure of the buildings consisted mainly of reinforced concrete slabs and walls, whereby the reinforcement detailing was performed according to the old technical codes and the ancient state of the art of the building’s construction. Regarding the structural system, the way of the construction and structural detailing of these buildings, they can be classified as a recent historical heritage. A high-rise building in Sarajevo, with 20 residential floors, about 55 years old, with a load-bearing system made of reinforced concrete walls and slabs, almost without any beams, was analyzed. According to the modern state of the praxis, the building does not meet the requirements of contemporary seismic codes, and this especially applies to the reinforcement design and detailing. Taking into account seismic vulnerability classification of the European Macroseismic Scale the building could suffer substantial damages when exposed to the stronger earthquake motions. We tried to capture the specific design of the existing reinforced concrete walls applying more sophisticated structural models, including confined and unconfined concrete. The mechanical properties of the built-in building materials in existing slabs and walls were obtained experimentally. The results of the nonlinear analysis show a relatively satisfactory global response of the structure, but with possible damages due to the rather poor reinforcement quantity in the walls. Just to mention that some of the main structural walls possess only few longitudinal reinforcement bars in the corners. An improvement of the structural system, in order to achieve a ductile response with the dissipation of the energy introduced by the earthquake, as proposed by the latest seismic codes and recommendations, has been discussed as well.

"In everyday engineering calculations, walls in masonry structures are typically analyzed as isolated from the rest of the structure. The corresponding gravitational load is determined, and the horizontal load is applied to the wall, assuming that floors are rigid within their plane and transfer horizontal loads according to the stiffness of the walls at the building's base. The wall's bearing capacity is verified on a model isolated from the structure, considering the effects of bending moments, normal forces, and shear forces. Spatial models that include other structural elements along with the walls are rarely created. This study focuses on slender walls, where height exceeds length, which are common in our architectural tradition. Reinforced concrete ring beams are regularly constructed at the top of such walls, transitioning into lintels or beams supporting the ceiling. The study aims to investigate whether these elements, along with the ceiling as a whole, influence wall behavior during earthquakes. Experiments and post-earthquake damage reports suggest that walls behave differently depending on the level of normal force stress. Wall behavior varies based on its position in the structure, load intensity, connections, and material and geometric characteristics. Less-loaded walls, typically on upper floors, tend to fail through full-wall rotation, with or without edge crushing. Sliding occurs with lower normal forces and high shear stresses, while diagonal fractures emerge at certain stress levels. This study develops a numerical model to explore the interaction between short walls and ceilings, especially in rocking and toe crushing, aiming to answer whether walls should be considered isolated or part of spatial frame systems."

Determination of dynamic properties of structures is the first step in assessing seismic response, and they can be measured in several ways. Controlling or knowing the input excitation usually applied by impact hammer or vibration shaker, typical for experimental modal analysis (EMA) that has been around for the past few decades, is for majority of structures difficult or practically impossible. Ambient vibration testing (AVT) or operational modal analysis (OMA), on the other hand, is the output-only modal analysis. It does not require knowledge of the input excitation, which is practically induced by wind, traffic or similar random source. In this paper, an investigation of ambient vibrations and numerical modelling of the building of the Institute for Materials and Structures (IMK) of the Faculty of Civil Engineering in Sarajevo was carried out. The main goal was to determine the dynamic characteristics of the IMK building using the DIGITEX SENTRY system and Artemis modal software. In addition to testing the IMK building, testing of simpler systems such as a wooden simple beam and a steel cantilever was also conducted. For each experiment, a modal analysis was performed in the Tower 8 software package. The numerical model of the building was more flexible than measured in the experiments, and the results were only comparable after inclusion of partition walls in the analysis.

Unreinforced unconfined solid brick masonry walls were experimentally tested in full scale (233x241x25cm) and reduced scale (100x100x25cm) at the laboratory of the Institute for materials and structures, Faculty of Civil Engineering in Sarajevo. Cantilever walls were loaded in cyclic shear or pushed monotonically. In order to study the nonlinear behavior in a detailed and global manner, finite element meso- and macro-models of the tested walls were created using the finite element software Diana FEA. Brick units are discretized by continuum elements in a meso-model and discontinuity in displacement field is introduced by interface elements between units. In order to account for brick cracking, an additional interface element was added in the unit middle. Continuum macro-models approximate heterogeneous masonry wall by a single material and discretization is independent of brick layout, i.e., bricks, mortar and unit-mortar interface are smeared out in the continuum. The recently developed engineering masonry model is an orthotropic total-strain continuum model with smeared cracking and it was used with shell elements. Numerical results are verified against the data obtained from the experimental research program. The walls exhibit rocking failure mode in low precompression, while diagonal cracking occurs for higher vertical stresses. The results show good matching with the experimentally obtained curves regarding the ultimate load and ductility.

This paper presents the methodology for seismic analysis of masonry structures that can be employed in commercial software packages such as SAP2000. The concept of elementary block which combines non-linear spring and linear shell elements is used for discretization of masonry walls. The proposed modelling technique with localized nonlinearity can successfully simulate in-plane wall failure modes induced by compressive or tensile axial force and transverse force. It can also be used to investigate out-of-plane collapse which makes it a good candidate for 3D static and dynamic analysis of buildings. The modelling approach is tested on two examples where pushover analysis was performed: a single slender cantilever masonry wall and a family house. The response was verified against the results delivered by 3MURI and MINEA, and reasonable agreement was obtained. It is demonstrated that the transverse walls have significant contribution to the load bearing capacity of buildings.

Low-rise residential and public masonry structures constitute a large portion of the building patrimony, yet they were erected during the massive reconstruction of Southeast Europe after World War II before any design rules existed in the engineering praxis. Unreinforced unconfined masonry buildings (URM) were proven rather vulnerable during stronger earthquake motions in the recent past. To determine lateral strength, stiffness, and capacity of energy dissipation of the URM walls, in-plane tests were performed at the University of Sarajevo. Two full-scale plain walls (233 × 241 × 25 cm) built with solid clay brick and lime-cement mortar and two walls strengthened with RC jacketing on both sides were subjected to cyclic lateral loading under constant vertical precompression. Plain walls failed in shear with a typical cross-diagonal crack pattern. Jacketed walls exhibited rocking with characteristic S-shaped hysteretic curves and significantly larger ductility compared with plain walls. Wallets were tested for modulus of elasticity and compressive strength of masonry and the results showed considerable variations.

Assessment of historical buildings presents specific engineering task, considering the ways they were built and the materials, which were used. Many of them belong to cultural heritage and merit special care and protection. This concerns also the historical buildings in Bosnia and Herzegovina. The country is situated in seismic active region of South-East Europe and the majority of the historical buildings were made of stone-masonry. In the case of stronger earthquake motion such buildings could suffer heavy damages. The damages are sometimes cumulated through many years and many causes. Substantial damages were caused by recent war disaster, as well. The aim is to preserve and reveal their aesthetic and historical values and to use original materials and original way of construction, if possible. In most cases seismic assessment procedures result in the requirements for the strengthening or retrofit of the old masonry building structures. Design and construction procedures of repair and strengthening of two medieval stone masonry buildings are presented. Equilibrium between aesthetical and structural demands is discussed.

Na Građevinskom fakultetu u Sarajevu izvršeno je eksperimentalno ispitivanje običnoga i ojačanog zida u stvarnoj veličini (2,3/2,4/0,25 m) pri djelovanju cikličnoga horizontalnog opterećenja u ravnini uz konstantni pritisak. Kod običnih je zidova došlo do otkazivanja nosivosti s pojavom karakterističnih ukriženih pukotina, dok se kod zidova ojačanih armiranobetonskom oblogom javlja prevrtanje krutoga tijela. Numerička analiza provedena je primjenom programa Diana 10.1 na makromodelima pri čemu je ziđe modelirano kao ortotropan i nelinearan heterogeni materijal koji može otkazati na smicanje, zatezanje ili pritisak.

Traditional art of building in Bosnia and Herzegovina comprises brick or stone masonry structures. Most historical buildings belonging to national cultural heritage were made of stone-masonry. The country is situated in seismic active region of South-East Europe. In the case of strong earthquake motion such buildings could suffer heavy damages. Some structural elements of historical buildings, as domes and arches, cracked already by moderate earthquake but without the loss of stability. Substantial damages were caused by recent war disaster. Damages could be accumulated through the history as well. Generally, stone-masonry buildings in Bosnia and Herzegovina can be classified in vulnerability classes between A and C according to European Macroseismic Scale. Design and construction procedures for rehabilitation are presented here with examples of repair and strengthening of mosques, which present historical stone masonry structures dating from the Ottoman period in Bosnia and Herzegovina. Traditional and contemporary materials were used for their rehabilitation. It is important to preserve original forms, especially those of damaged elements. The challenge for structural engineers and architects was to find equilibrium between aesthetical and structural demands.