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.

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Identifikacija sustava armiranobetonskih grednih mostova utemeljena na terenskim mjerenjima i numeričkim simulacijama SYSTEM IDENTIFICATION OF R/C GIRDER BRIDGES BASED ON FIELD MEASUREMENTS AND NUMERICAL SIMULATIONS Damir Zenunovic, Mirsad Topalovic, Radomir FolicOriginal 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. Keywords: ambient vibration; concrete bridge; modal analysis; numerical simulation; soil investigation Identifikacija sustava armiranobetonskih grednih mostova utemeljena na terenskim mjerenjima i numeričkim simulacijamaIzvorni znanstveni članak U radu je dan pregled istraživanja provedenih u okviru NATO projekta SfP 983828. Predmet istraživanja je identifikacija parametara koji utječu na dinamički odziv postojećih armiranobetonskih grednih mostova, utemeljena na mjerenjima ambijentalnih vibracija i numeričkim simulacijama uporabom modela na bazi konačnih elemenata (MKE). U tu je svrhu instrumentaliziran most preko rijeke Bosne u blizini Sarajeva. Urađena su ispitivanja ambijentalnih vibracija i geofizička istraživanja. Rezultati su analizirani i urađen je poboljšani trodimenzijski numerički model koji uzima u obzir interakciju tla i konstrukcije, kao i interakciju gornjeg i donjeg stroja mosta. Razvijeni su modeli s projektnim parametrima i parametrima dobivenim mjerenjem. Urađena je komparativna ocjena razvijenih modela i verificiran model koji je imao vrijednosti dinamičkih karakteristika konstrukcije podudarne mjerenim vrijednostima. Rezultati analize pokazuju da je odgovarajuće određivanje krutosti stubova, kolovozne ploče i ležajeva ključni parameter za pouzdanu identifikaciju sustava.