BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Publicat de Universitatea Tehnică „Gheorghe Asachi” din Iaşi Tomul LXI (LXV), Fasc. 4, 2015 Secţia CONSTRUCŢII. ARHITECTURĂ COMPARISON OF THE EXPERIMENTALLY OBTAINED DYNAMIC CHARACTERISTICS OF A BRIDGE WITH AMBIENTAL AND FORCED VIBRATIONS BY CONSTANTIN GAVRILOAIA * , RALUCA ONOFREI, NICOLAE ŢĂRANU and MIHAI BUDESCU “Gheorghe Asachi” Technical University of Iaşi Faculty of Civil Engineering and Building Services Received: December 10, 2015 Accepted for publication: December 280, 2015 Abstract. The paper presents a study case performed on a bridge over the Danube, located in Cernavoda, Romania. The tested structure was subjected to several vibrations, resulted from the natural movement of the bridge and from the movement of a truck, a train and an excavator. The monitoring system used to record the in situ data was composed of four seismic transducers positioned in the first span of the bridge. The speed integration and vibration modes identification was performed using ARTeMIS Extractor. Emphasis is placed on analysing the mode shapes and observing the relation between frequency and modal coordinates. Key words: dynamic characteristics; frequency; vibration modes; FDD; MAC. 1. Introduction The in situ determined dynamic characteristics of a structure are an indicator on the degradation state of the building. Because the excitation of the rigid structures is hard to accomplish, the frequencies and the vibration modes are identified using ambiental (e.g. wind) and forced (e.g. traffic on the bridge: * Corresponding author: e-mail: gavriloaiaconstantin@gmail.com