Concrete cover separation failure of overlay-strengthened reinforced concrete beams

A Design Proposal for Concrete Cover Separation in Beams Strengthened by Various Externally Bonded Tension Reinforcements

“…Current models used to explain the concrete cover separation of a strengthened beam fall into the following categories: (1) derivation of the elastic stress concentrations at the FRP laminate end, (2) the strengthened beam's shear capacity and (3) the concrete tooth model. However, none of the current models can sufficiently predict the failure loads or failure modes (Gao et al 2004a;Smith and Teng 2002;Zhang et al 2012). Recently, Zhang et al (2012) developed an analytical model based on the modified concrete tooth model and verified its accuracy.…”

“…However, none of the current models can sufficiently predict the failure loads or failure modes (Gao et al 2004a;Smith and Teng 2002;Zhang et al 2012). Recently, Zhang et al (2012) developed an analytical model based on the modified concrete tooth model and verified its accuracy. This study further examines the applicability and reliability of this proposed model for steel plate and FRP laminate strengthening.…”

“…According to the debonding criteria, concrete cover failure occurs when the concrete tensile stress σ A is greater than the concrete's tensile strength. According to Zhang et al (2012), by assuming that all the teeth within the length L p ranging from the overlay end to the shear flexure crack (Point C in Fig. 2) are assumed to have the same tooth spacing S cr and fail simultaneously, and based on the experimental fact that the peak load is reached after the yielding of tension reinforcement at point C in the substrate beam after debonding, the concrete cover separation failure load for overlaystrengthened beams is determined by the following equation:…”

“…6, the tooth spacing (S cr ) is initially assumed to be the average flexural crack spacing (S fl ). If the calculated debonding load (P dy ) is greater than the diagonal shear cracking load (V cd ), the diagonal shear cracks occur before the concrete cover separation, after which the tooth spacing is taken as two-thirds of the average flexural crack spacing following suggestion of Zhang et al (2012), and the debonding load (P dy ) has to be recalculated. If the recalculated debonding load is smaller than the diagonal shearcracking load, concrete cover separation occurs right after the diagonal shear cracks are formed (P dy =V cd ).…”

Experimental and Analytical Investigation of Crack Spacing and Width for Overlaid RC Beams at Elevated Temperatures

“…Overlaid reinforced concrete (RC) beams were investigated in various studies, and the efficiency of overlaying for increasing the flexural stiffness and strength of beams under normal temperature conditions (~20 ℃) was verified (Rashid et al 2016, Rashid et al 2015a, Satoh and Kodama 2005, Zhang et al 2012). In practice, many RC structures are exposed to large daily temperature fluctuations, with maximum temperatures reaching 60 ℃ in peak summer, especially in the Middle East and some parts of North America (Al-Jabri et al 2005).…”