Strengthening of reinforced concrete (RC) beams by external plate bonding (EPB) technique has become very popular for the last two decades, especially in the past few
years with the increasing applications of the advanced composites. Unlike the unstrengthenedb eams, the composite structure shows an undesirable failure of plate debonding. It has been well recognized that central to this failure mode is the stress concentration at the plate end. It is prerequisite to well understand the stress characteristics
at this zone. This thesis reports a systematic investigation on the stress distribution at the interface between the concrete and the bonded plate and the prediction of the failure loads using the obtained stresses.
A Finite Element Analysis (FEA) based on elastic fracture mechanics is carried out first to provide a detailed study on the stress fields near the plate ends. This becomes
the benchmark for the analytic solutions presented in the following chapters. A completed analytical solution is developed by the principle of complementary energy and
provides consistent results with the FEA with less computational efforts. A closed form rigorous solution is proposed such that a spreadsheet package is sufficient to obtain the numerical results. This rigorous solution provides the basis to further develop a simplified solution of the interfacial stresses that are subsequently used to develop the strength models.
To consider the nonlinear properties of concrete a detailed nonlinear FEA simulation is conducted in the thesis and extensive results are computed at various load levels,
from the elastic state to the ultimate state. In addition, a Nonlinear Fracture Mechanics (NLFM) method is developed taking into account the pre- and post-cracking behaviors
and the interactions between the shear and transverse normal stresses. This solution is able to predict the load level at the onset of plate end cracking (serviceability
load) and that at the ultimate failure state (ultimate load).
Finally some of the proposed solutions are applied to selected beams whose test results are available for comparison. In combination with existing material failure criteria, the elastic simplified solutions are also used to predict serviceability loads. Two groups of serviceability loads predicted from the elastic solution and NUM solution,
respectively, and one group of ultimate load predicted from NLFM solution are all compared with the experimental data. Encouraging correlations are achieved. Other useful results, such as development length, the size of Fracture Process Zone (FPZ) are also calculated.
Before concluding the work, a series of parametric analyses are carried out to assess the impact of various parameters on the interfacial stress fields, which provides some
fundamental information related to design of the strengthening scheme.