Debonding of Steel Plate‐Strengthened Concrete Beams

The behavior of damaged concrete beams strengthened by externally bonded steel plates is analytically investigated using linear elastic fracture mechanics and the finite element method. The study includes investigation of the failure by interface debonding of the steel plate and the adhesive layer due to interfacial shear stress which exists at the interface. The principles of the conservation law of elasticity are used to determine the critical strain energy release rate required to cause the interfacial crack to propagate. Simply supported beams under monotonically increasing symmetrical loads are considered exclusively. It is found that the failure by debonding is dependent on the stress near the interfacial crack tip and on the critical strain energy release rate required for crack propagation. For the beam size [$4\times 4\times 96\mathrm{in}\text{.}$ $(101.6\times 101.6\times 2\text{,}438.4\mathrm{mm})$] and the loading configuration [two symmetrical point loads spaced 24 in. (609.4 mm) apart] studied in this investigation, the results indicates that the most critical case occurs when five flexural cracks exist within a short region in the midspan of the beam. Furthermore, the results suggest that critical separation of debonding load is relatively insensitive to the thickness of the adhesive layer for the range of thickness [$0.1<0.25\mathrm{in}\text{.}$ $\left(2.59<t<6.35\mathrm{mm}\right)$] studied in this investigation.