FRP shear strengthening of concrete beams

Sogut, Kagan (2022). FRP shear strengthening of concrete beams. University of Birmingham. Ph.D.

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Abstract

The necessity of strengthening concrete beams appears in cases where concrete beams are subjected to deterioration mainly instigated by heavier traffic loads, poor initial design, aggressive exposure conditions, natural or man-made extreme events, and steel reinforcement corrosion. All these circumstances may lead to catastrophic consequences unless immediate precautions are taken. Many cost-effective, practical, and durable fibre reinforced polymer (FRP) shear strengthening solutions have emerged in response to the increasing number of shear-deficient concrete structures. Both the externally bonded (EB) and near-surface mounted (NSM) FRP shear strengthening systems have been demonstrated to enhance the shear resistance of existing reinforced concrete (RC) beams. However, these systems require laborious surface preparation and, unless properly anchored, debond prematurely from the concrete. The Deep Embedment (DE), also known as the embedded through-section (ETS), shear strengthening technique has been developed to eliminate the shortcomings of these techniques. Previous research studies proved the effectiveness of the DE technique. However, the effects of steel-to-FRP shear reinforcement ratio, presence of existing holes, beam size, and shear span-to-effective depth (a/d) ratio on the DE FRP-strengthened behaviour have not yet been fully understood. In particular, the effects of tension reinforcement ratio and embedded length of FRP bars on the DE FRP-strengthened behaviour have not yet been identified. The DE shear strengthening technique used in this study consisted of glass FRP (GFRP) or carbon FRP (CFRP) bars embedded into the concrete core to act as additional shear reinforcement. The fifteen RC T-beams, which comprised the experimental programme of this research, were designed, fabricated, and tested at the University of Birmingham Structural Engineering Laboratory. Test parameters were steel-to-FRP shear reinforcement ratio, tension reinforcement ratio, presence of existing holes, embedded length of FRP bars, and a/d ratio. Moreover, beam size was also considered as a parameter for the investigation. The results from the experimental programme demonstrated that the concrete and DE FRP reinforcement contributions to shear resistance as well as total shear force capacity all decreased with increasing steel-to-FRP shear reinforcement ratio. The total shear force capacity of strengthened beams decreased by up to 33.7% with increasing steel-to-FRP shear reinforcement ratio from 1.35 to 3.82. The DE FRP and concrete contributions to the shear resistance also decreased by up to 39.2% and 62.8%, respectively, when steel-to-FRP shear reinforcement ratio was increased from 1.35 to 3.82. The tension reinforcement influenced the failure mode of tested beams but had an insignificant impact on shear strength enhancement. Existing holes instigated premature shear failure in RC T-beams before reaching their nominal shear force capacity. The shear strength reduction due to existing holes ranged from 7 to 22%. The embedded length of FRP bars had a clear effect on shear resistance. Both the DE FRP reinforcement contribution and the total shear resistance increased by up to 197.8% and 91.1%, respectively, with increasing embedded length from 262.5 to 300 mm. The concrete contribution to the shear resistance and total shear force capacity increased with decreasing a/d ratio, whereas the contribution of DE FRP reinforcement decreased with decreasing a/d ratio. Experimental results also suggested that DE FRP reinforcement significantly mitigated the size effect in the strengthened beams. The reduction in shear stress at failure of the unstrengthened and strengthened beams was 50% and 18%, respectively. The corresponding values for deep beams were 26% and 10%, respectively.

Moreover, a nonlinear finite element (FE) model was developed, validated, and used to conduct parametric studies. The crucial parameters impacting the shear behaviour of strengthened beams were examined numerically after validating the FE model by comparing experimental results reported in this study and published literature with numerical predictions. Limitations in current shear strengthening design guidance and existing design models were also identified, and new design equations were proposed and demonstrated to give accurate predictions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):