During vibrations, the structure passes through different behavior areas (elastic or inelastic). Different areas of behavior correspond to different approaches to analysis and design. Modeling vibrations as a phenomenon includes its presentation in the form of a mathematical model, with certain parameters specific to the system, which define and control the vibration process itself, namely mass, stiffness and damping. While mass and stiffness can be more accurately described mathematically, damping modeling involves the state and medium in which the system resides. Due to differences in understanding of the state variables that control damping forces, there is still no single accepted model of damping. The wrong selection of damping model in the dynamic analysis of structures can result in the response of the structure being underestimated, which can be the cause of the collapse of the structure. The paper analyzed the response of the bridge structure to pedestrian excitation, applying different numerical damping models and the damping determined experimentally. At the end of the paper, a comparative analysis with conclusions is given.

Textile-reinforced concrete (TRC) is a reinforced concrete, where steel reinforcement is replaced with textiles or fibers. Textile reinforcement is a material consisting of natural or synthetic singular technical fibres processed into yarns or rovings which are woven into multi-axial textile fabrics having an open mesh or grid structure. In the paper an overview of tests results related to mechanical properties, deformation properties and durability characteristics of textile meshs are presented. Applications of different textiles as reinforcement in TRC is analyzed through some realized projects. TRC has been successfully employed for strengthening or repair of damaged structural elements and lightweight, thin structural elements (precast thin-walled elements, shells, tanks, pipes, pedestrian bridge, waterproofing structure, integrated cladding systems, external insulation system).

Dinamičan razvoj tehnologije materijala doveo je do primjene različitih novih materijala za poboljšanje svojstava nosivosti i trajnosti betonskih nosača. Jedan od pristupa jeste primjena sistema zaštite obložnog dijela betonskog nosača (zaštitni sloj betona). U ovu svrhu, razvijeni su polimerni materijali armirani karbonskim, staklenim ili aramidnim vlaknima (FRP – Fiber Reinfored Polymer). Novi pravac razvoja ovih sistema jeste primjena tekstilom armiranih sitnozrnih betona, gdje se koriste tekstili s vlaknima u više pravaca. Fabrički proizvedena ravninska tekstilna struktura sačinjena je od vlakana upletenih na razne načine, kao što su tkanje, pletenje, filcovanje ili štrikanje. Za potrebe istraživanja i razvoja ovog sistema ojačanja betonskih greda, formirana su dva istraživačka centra u kojima se sprovode projekti pod nazivom „Textile Reinforced Concrete (TRC) -Technical Basis for the Development of a New Technology” (SFB 532) RWTH Aachen University i „Textile Reinforcements for Structural Strengthening and Repair” (SFB 528) Technische Universitat Dresden. U ovim istraživačkim centrima sprovode se istraživanja mehanizama trajnosti, prionljivosti i kapaciteta nosivosti. Pored dva navedena velika projekta, postoji i niz projekata koji se odnose na tekstilom armirani beton, a sprovedeni su u Izraelu, Sjedinjenim Državama, Grčkoj, Belgiji, Ujedinjenom Kraljevstvu i Kanadi [3]. Utvrđeno je da količina i raspored tesktilne strukture imaju značajan uticaj na ponašanje tekstilom armiranog betona. Istraživanja su posvećena:

The paper provides an overview of ambient vibration tests and numerical analysis performed in the framework of Project NATO SfP 983828. The aim of the research is the definition of the dynamic characteristics of bridges on the examples. The paper considers three case studies: two older existing bridges and one newly constructed bridge. A comparative analysis of natural frequencies and mode shapes, obtained by ambient vibration measurements (AVM) and mathematical models (AMs), was carried with the aim to demonstrate the usefulness of ambient vibration tests for identification of the modal parameters of the tested bridge structure. Agreement between AVM and AMs results is very good. The mode shapes are very similar. Some differences between computed and measured frequencies were obtained, which can be attributed to the real nature of the boundary conditions, the uncertainty in the material properties of structure elements, and the mathematical models assumptions.

Original scientific paper An overview of research performed in the framework of the NATO Project SfP 983828 is given in the paper. The scope of the research was to identify the parameters affecting the dynamic response of an existing R/C girder bridge, based on ambient vibration measurements and numerical simulations using finite element models (FEM). For this purpose, the bridge across the river Bosnia near Sarajevo and the soil surrounding the bridge were instrumented. Ambient vibration tests and geophysical investigations were performed. The results are studied and a refined three-dimensional (3D) FEM is developed that takes into consideration the soil-structure interaction and superstructure-substructure interaction. The FEM’s with designed parameters and parameters obtained by measurements were developed. The developed FEM models are comparatively assessed and FEM model with congruence between the measured and computationally predicted dynamic characteristics of the structure was defined. The results of the analysis show that the adequate determination of the pier, deck and bearings stiffness is the key parameter for reliable system identification.

The available experimental and numerical results of many studies of behavior of reinforced concrete connections for different stages of loading, up to fracture loading, are presented and analyzed in this paper. The problem of beam-column connection (or plate-wall connection) in prefabricated monolithic structures is emphasized. Fracture mechanisms of RC structures, the theoretical basis for their analysis, and the use of fracture mechanics in RC structures were also considered, as well as the mathematical models of prefabricated connections. In order to formulate an adequate mathematical model for calculating the connections, the dominant parameters influencing the behaviour of these connections were analyzed. A failure model for the prefabricated wall - monolithic RC plate connection was formulated. In building the model, the results of implemented experimental and numerical research of prefabricated connection in the MMS system from 2007 were used. Experiences with the implementation of the aforementioned construction system in structures in Tuzla, in the 1980's last century, were additionally used. The proposed mathematical models provide a sufficiently accurate failure assessment of prefabricated reinforced concrete connections.