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.

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.

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.

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.

Coupled thermo-mechanical analysis of reinforced concrete slab at elevated temperatures from a fire accounting for nonlinear thermal parameters is carried out. The main focus of the paper is put on a one-way continuous reinforced concrete slab exposed to fire from the single (bottom) side as the most typical working condition under fire loading. Although contemporary techniques alongside the fire protection measures are in constant development, in most cases it is not possible to avoid the material deterioration particularly nearby the exposed surface from a fire. Thereby the structural fire resistance of reinforced concrete slabs is mostly influenced by a relative distance between reinforcement and the exposed surface. A parametric study with variable concrete cover ranging from 15 mm to 35 mm is performed. As the first part of a one-way coupled thermo-mechanical analysis, transient nonlinear heat transfer analysis is performed by applying the net heat flux on the exposed surface. The solution of proposed heat analysis is obtained at certain time steps of interest by a-method using the explicit Euler time-integration scheme. Spatial discretization is done by the finite element method using a 1D 2-noded truss element with the temperature nodal values as unknowns. The obtained results in terms of temperature field inside the element are compared with available numerical and experimental results. A high level of agreement can be observed, implying the proposed model capable of describing the temperature field during a fire. Accompanying thermal analysis, mechanical analysis is performed in two ways. Firstly, using the guidelines given in Eurocode 2 - Part 1-2 resulting in the fire resistance rating for the aforementioned concrete cover values. The second way is a fully numerical coupled analysis carried out in generalpurpose finite element software DIANA FEA. Both approaches indicate structural fire behavior similar to those observed in large-scale fire tests.

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.