This paper describes a case study addressing analysis, design, installation,load rating, load testing, numerical verification and monitoring of the strengthening ofan old deficient bridge under a field validation research project. The strengthening wasperformed by means of two composite technologies: the common manual lay-up CFRPsystem and a mechanically fastened FRP (MF-FRP) system. The later consisted of pre-cured FRP laminates having high transverse bearing strength (i.e., bidirectional fibers)attached to the structural element by means of wedge anchors. Although considered atemporary solution, the technique is attractive because it requires minimum surfacepreparation. The bridge will be monitored for 5 years to evaluate the long-termperformance of the techniques. In this sense, load tests were performed to evaluatethe bridge structural behavior prior to and after the strengthening, showing that therehabilitation performed as predicted by numerical analysis and therefore created thepossibility to remove the bridge load posting.

The preliminary results of an experimental investigation on under-designedRC square columns are presented in the paper. The seismic upgrade was achieved bycombining steel spikes and GFRP laminates. Two parameters are investigated: the lapsplice of the longitudinal steel reinforcement and the level of axial load. A comparisonbetween as-built and strengthened columns is presented in terms of strength andductility. The shear-top displacement relationships of strengthened columns areanalyzed to assess the influence on the global performance of the lap splice. Thispreliminary analysis confirms that the proposed solution for the seismic strengtheningof under-designed columns is very effective when it is necessary to relocalize thepotential plastic hinges of columns by increasing their flexural strength. The obtainedresults will represent the basis for developing design criteria for the strengthening ofsimilar interventions and will represent a reference for the calibration of a model of thestrengthened column.

Experimental study has been performed in order to investigate the behaviorof RC beams strengthened with externally post-tensioning CFRP (Carbon FiberReinforced Polymer) strips. A total of 11 specimens have been manufactured of whichspecimens strengthened with bonded or unbonded CFRP strips considering the level ofpost-tensioning as experimental variable, and a specimen with simply bonded CFRPstrips. The following phenomena have been observed through the experimental results.The specimen with simply bonded CFRP strips failed below 50% of its tensile strengthdue to premature debonding. On the other hand, all the specimens strengthened withpost-tensioning CFRP strips showed sufficient strengthening performance up to theultimate rupture load of the CFRP strips. Also, it was observed that the cracking loadsand yield loads of the strengthened beams were increased proportionally to the post-tensioning level, but the ultimate loads were nearly equal regardless of the post-tensioning level and bonded or unbonded system. In addition, the yield loads andcracking loads of the beams with bonded post-tensioning systems were increasedabout 20% compared with those of the unbonded post-tensioning systems. However,the beams strengthened with unbonded post-tensioning CFRP strips showed ductilebehaviour with large deflections resulting from the reduced member stiffness.

Aramid fibres have been used in rope construction and for prestressingtendons, but when subjected to a constant static load the fibres creep with time andmay rupture, leading to a catastrophic failure of the rope. To understand this behaviourmany life-time models have been suggested but they suffer from the lack of long termcreep rupture data to make firm conclusions on rupture times and load levels. Suchdata is expensive to obtain using conventional creep testing as it takes a long timebefore failure of a specimen. To overcome this problem, and to obtain the creep-rupture data at low stress levels within a reasonably short time scale (hours),accelerated testing methods, the Stepped Isothermal Method (SIM) and TimeTemperature Superposition (TTSP), have been investigated. In SIM testing a single yarnspecimen is tested at a specific stress level under a series of increasing temperaturesteps from which a single response curve, known as the master curve, is obtainedwhich predicts the long-term behaviour. Some manipulation of the data is required, butthe technique has many advantages over the TTSP and conventional creep testing andit can be automated to obtain the long-term creep-rupture data points relatively easily.

Corrosion of prestressing steel in precast concrete is a significant problemfor coastal bridges in Florida. Replacement of prestressing steel with carbon fiber-reinforced polymer (CFRP) reinforcement provides a potential solution to this costlyproblem. The Florida Department of Transportation (FDOT) structures research centerhas teamed with the University of Florida (UF) to evaluate CFRP reinforced piles thatemploy two types of carbon reinforcement: (a) CFRP reinforcing bars and (b) CFRP grid.The CFRP bars act as flexural reinforcement while the CFRP grid provides confinement tothe concrete core. The focus of this paper is on the confinement provided by theembedded CFRP grid, which is tied into a circular shape and cast into the concrete in asimilar configuration to spiral ties. Existing confinement models are based onconfinement provided by FRP wraps. Consequently, their use in predicting confinementmust be validated with tests on embedded FRP grid. Standard (152 mm x 304 mm)concrete cylinders were cast both with and without the embedded CFRP grid. Thecylinders were tested in compression to determine the effect of the CFRP grid on theirstrength and ductility. A significant improvement in ductility was observed for thecylinders with the embedded CFRP grid compared to the control cylinders.