DYNAMIC ASSESSMENT OF RC BEAMS FLEXURALY STRENGTHENED WITH CFRP STRIPS

In the last few decades externally bonded FRP strips and sheets have been the most commonly used technique for strengthening of RC structures and bridges. The fact that FRP does not corrode and good mechanical performance have made this material very popular to use. Prior to design and application of FRP strengthening, it is of great interest for design engineers to evaluate condition of deteriorated and damaged RC structures. One of the most popular non-destructive techniques to evaluate structural health is modal testing. In this work Experimental Modal Analysis (EMA) is used as a technique to evaluate loss of beam stiffness due to damage and also effectiveness of FRP strengthening in terms of stiffness recovery. This experimental technique is based on fact that changes in local stiffness influence on global dynamic parameters (frequencies, mode shapes and modal damping). This paper presents experimental results of experimental modal analysis carried out on damaged concrete beams strengthened with CFRP strips and sheets. Three RC beams with rectangular cross section were tested. Beams were subjected to monotonic loading with increasing load steps with four-point bending setup in order to generate different damage levels in specimens. CFRP strengthening was applied on the specimens after they were damaged by loading to 50% of their flexural capacity. Modal tests were carried out after each loading-unloading cycle. Beams were excited by the impact hammer. Frequency response functions were processed using Dewesoft software to obtain natural frequencies, mode shapes and damping ratios. Keywords: FRP strengthening, dynamic parameters, experimental modal analysis, concrete beams