This study is carried out to introduce the methodology of modal testing technique using dynamic testing to measure the efficiency or to make sure of repair works. One of bridge bays was severely damaged and as a result of this damage a decision to remove this bay had been taken. As a result of the bridge bay situation and its site boundary condition, the removal process was necessitated to ensure the stability of the damaged bay and that it will not collapse completely during the removal process. To maintain the stability of the damaged bay splice plates were welded to join the damaged places in the main steel plate girders. The welding process was implemented from difficult positions and done only for the accessible damaged places. As a result of the limited quality control for welding process as well as the lack of knowledge of the damage full picture, it was necessary to conduct the necessary tests to ensure the stability of the bridge bay or to evaluate the interim repair process. Modal testing technique using dynamic testing was used to evaluate the repair process because its easiness, fastness and its acceptable accuracy. Two dynamic tests were carried out one for similar undamaged bay while the other test was carried out for the repaired damaged bay. Finite element model was used to validate experimental results. The results for the two tests were compared to each other and compared with numerical analysis results. The undamaged case was the reference to judge for how much the damaged bay restore its original stiffness.