USE OF SHM FOR INVESTIGATION OF THE PERFORMANCE FOR A CFRP STRENGTHENED CONCRETE BRIDGE

During the summer of 2006, a medium-sized concrete girder highway bridge was strengthened with CFRP plates. The total length of the bridge was approximately 100 m, in 6 spans, with a width of approx. 13 meters of the concrete slab. The slab was cast in place on three concrete beams with a height of 1.5 m and a bottom width of 900 nun. The strengthening was needed due to low load carrying capacity in the ultimate limit state. The bridge had extensive cracking in the bending moment regions and some of the cracks exceeded 1.0 mm and reached to the centre of the beam. To investigate the strengthening effect, monitoring was carried out before and after strengthening in two of the beams at one section. Electrical strain gauges were welded to the steel reinforcement and bonded to the concrete surface. In addition the deflection and the curvature was measured by LVDTs (Linear Vertical Displacement Transducers). Hence, both global (deformation and curvature) and local monitoring (strains) were undertaken. Loading was introduced by a three axle truck. The load was controlled by weighing the truck. During loading the bridge was stopped for normal traffic but monitoring was also carried out on the traditional traffic load. Similar loading was used before and after strengthening. After the strengthening work was finished, additional electrical strain gauges was mounted on the CFRP plates and the loading was repeated. The comparison between the two tests also aimed to investigate the change in stiffness in the section. This was done by calculating die change in curvature. Here we introduce a performance factor. The performance is a factor that describes the stiffness change of an existing structure due to e.g. deterioration or strengthening. The results from the tests show an increase in performance and a decrease in steel strain after strengthening.