Includes bibliographical references. / The focus of the dissertation was to provide an in depth investigation towards the fatigue performance of Carbon Fiber Reinforced Polymers (CFRP) which were externally bonded onto concrete beams as a repair and strengthening technique for internally corrosion damaged RC beams. It was identified that more research concerning the fatigue performance of externally bonded CFRP laminates used as a composite material for originally damaged concrete structures was required. Therefore, there was a need to study the failure mechanisms between the externally bonded CFRP, corrosion damaged internal steel, and patch repaired section and the original substrate concrete with respect to the long term performance, whilst treating the system (CFRP, substrate concrete, patch repair and bonding agents) as a composite material. The methodology of the dissertation included the introduction of accelerated corrosion techniques to degrade the internal steel reinforcement. The damaged RC beams were repaired by removing the damaged concrete, treating the corroded internal steel reinforcement, replacing the damaged concre te section removed with a rapid-hardening high strength patch repair mortar, and finally externally bonding CFRP laminates along the patch repaired section and entire tensile face to restore the bending capacity lost due to the reduction of internal steel and subsequent patch repair. Two of the six RC beams which were patch repaired and CFRP strengthened, were subjected to a monotonic load in order to establish the ultimate static load at failure for the RC beams. The ultimate static load at failure was then used to derive the maximum imposed cyclic fatigue loading that was applied. The remaining four RC beams were then subjected to constant sinusoidal cyclic loads at varying amplitudes, the range of amplitude dependent on the corresponding static load at failure for the identical RC beam. The aim of the cyclic load tests was to determine the long term behaviour of the repaired and strengthened RC beams at different degrees of loadings . The test specimens were tested until fatigue failure was reached. At utimate fatigue failure, the RC beams exhibited excessive concrete cracking, but eventual fatigue failure was determined when the CFRP finally delaminated along a portion or the entire length of the tensile face. It was evident that once fatigue failure occurred due to concrete cracking, the fully laminated CFRP would then withstand a large majority of the tensile stresses still being applied. The CFRP momentarily restored the overall strength of the repaired and strengthened RC beam until ultimate failure occurred at the point of CFRP delamination. The outcome of the dissertation observes and describes the failure mechanisms during RC beam and CFRP fatigue failure. The results obtained from the extensive testing plot a failure curve for each RC beam which had been corroded, patch repaired and finally CFRP strengthened. The cumulative results captured display a predicted failure curve graph. This graph indicates the percentage of ultimate cyclic load applied which was a function of the corresponding ultimate static load applied for an identical RC beam versus the number of cycles applied until failure. This curve can be used as a guideline to predict the number of cycles until failure for a repaired and CFRP strengthened RC beam of similar dimensions for a specific percentage of static loading, this loading being dependent on the increased ultimate static load at failure for a patch repaired and externally strengthened CFRP reinforced concrete beam. The predicted failure curve clearly indicates that for repaired and CFRP strengthened RC beams experiencing low fatigue cyclic amplitudes equaling 45% of the corresponding total static loading at failure, the fatigue performance is significantly increased versus the identical test specimens with increased loading of approximately 55 % and 67% of the corresponding ultimate static loads, these beams exhibit considerably decreased long term performance. The static load tests also indicated that the influence of the accelerated corrosion on the ultimate capacity of the RC beam is minimal since the addition of the externally bonded CFRP doubled the ultimate static capacity of the identical RC damaged beams. The experimentation was also able to capture the failure mechanisms for each tested beam throughout the cyclic loading phase. Identifying the failure mechanisms was useful when conducting on site investigations which focused on the long term performance of either the reinforced concrete beams that were patch repaired and strengthened or not As expected, the combination of combining a high strength patch repair mortar and external CFRP strengthening scheme significantly increased the long term performance of the RC structure. Finally, due to the investigations performed in this dissertation, the increased long-term performance of a patch repaired and CFRP strengthened RC beam can now be empirically quantified and the failure mechanisms physically observed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/14554 |
| Date | January 2012 |
| Creators | Gregan, Steven Ivan |
| Contributors | Moyo, Pilate, Beushausen, Hans-Dieter |
| Publisher | University of Cape Town, Faculty of Engineering and the Built Environment, Department of Civil Engineering |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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