Shear strengthening of reinforced concrete beams using an external Carbon Fibre Reinforced Polymer
(CFRP) composites of low elastic modulus

Assaf, IA

Abstract

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.

Citation

(CFRP) composites of low elastic modulus. (Thesis). Salford : University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2007