Shear strengthening of reinforced concrete beams using an external carbon fibre reinforced polymer (CFRP) composite of low elastic modulus

Beam-column joints designed seismically are considered impractical due to the congestion of steel stirrups. Currently, CFRP is used for strengthening reinforced concrete structures that have reduced integrity due to corrosion of steel reinforcement or unintentional overloading. The aim of this thesis is to mitigate the congestion of steel stirrups in the beam-column joint regions using an externally bonded CFRP composite and to possibly propose initial 'new build' design rules. Experimental work was conducted on 24 reinforced concrete beams with different percentages of steel shear reinforcement and varying amounts of CFRP. Six of these were tested under cyclic load. Significant reduction was observed as the RC beams were subjected to load reversal significantly higher than their service load. 18 beams were tested under static load in order to find the contribution of the CFRP to the shear capacity with varying percentages of steel stirrups. The results show that the CFRP contribution to the shear capacity is significant at zero and low ratios and decreases with an increase in the percentage of steel stirrups. The CFRP contribution is reduced significantly at high percentages of steel stirrup as the mode of failure becomes flexural. For strengthened beams having no steel shear reinforcement, the CFRP contribution is evaluated using current design rules. Load sharing between the CFRP and steel stirrups was observed and this relationship is very important for development of the current design rules. An alteration in the mode failure for the strengthened beam having a moderate percentage of steel stirrups was observed and similar behaviour was noticed with the beam conventionally reinforced with high ratio of steel stirrups. This is very beneficial in practice where the congested steel causes problems. Finite element analyses were carried out using ANSYS to attempt to predict the behaviour of further beams, caveats for which are highlighted within the thesis. The results for load sharing between the CFRP and steel stirrups shows that the relationship between the CFRP contribution to the shear capacity and the percentage of steel stirrups is not proportional as observed experimentally. Future work recommends a repeat of the experimental test with more instrumentation. Experimental tests on more complex structures (i.e. beam-column joints) are recommended where the shear reinforcement and confinement could be provided through the CFRP and hence reduce the congestion of steel stirrups. Using other FE codes is also recommended with an increased budget.EThOS - Electronic Theses Online ServiceGBUnited Kingdo