Re-assessment of the structural performance of RC members strengthened using plate-bonded techniques and of patch-repaired RC members

Abstract

Over the past 25 years, many papers have been published on the structural behaviour of RC beams strengthened in flexure using the plate-bonded technique. As a result of this notable experimental and numerical research work, a better understanding was obtained of the structural implications related to this strengthening technique. However, in most of these studies only the flexural mode of failure was addressed numerically and validated, while the peeling and shear failure modes are not yet well established and validated numerically for a wide range of the design parameters. Furthermore, no numerical or theoretical basis exists for the design of anchorage systems that suppress the peeling failure mode, nor is there a significant body of work, which seeks to quantify the corresponding behaviour and the increase in strength. The primary objective of the research work presented in this thesis, is to develop a numerical method which addresses all the possible failure modes of the plate-bonded RC beam/slab with or without end-anchorage systems and which is capable of tracing its structural behaviour for the entire load path. In this manner, peeling, shear, flexural and anchorage failure modes are monitored simultaneously at each spectrum load step and, when any failure criterion violation is detected, the failure mode and failure load pattern are computed together with other useful load-history information. Therefore, it is proposed that the design of plated beams/slabs under arbitrary transversal loading could be carried out using an interactive approach of strength assessment, considering simultaneously the possibility of shear, flexure, or peeling failure in plate-bonded beams/slabs without end-anchorage systems, as well as anchorage failure in plate-bonded beams/slabs with end-anchorage systems. An incremental one-parameter load-control method is adopted to predict the failure load pattern and the failure mode. The flexural analytical model is an iterative method utilizing a secant stiffness approach. Peeling, anchorage detachment (rawlbolt or angle plate systems) and shear failure models are developed and presented. The results demonstrate a very good correlation between the proposed method and the test results carried out on plated beams not only for the prediction of the actual failure mode and ultimate load capacity, but also for the prediction of deflections and strains in the concrete, bottom steel and plate for the entire load path up to the collapse load. The proposed method for the design of plate-bonded RC beams/slabs with or without end anchorage systems is implemented as a subroutine of a Rehabilitation Design Program (REDEPRO) developed as part of this research work for reassessment purposes of RC structures. A further scope of this thesis is to provide a numerical method developed for the reassessment of flexural capacity of RC members, which are repaired using re-casting, spraying or patch repair by hand-application. The proposed method is a non-linear secant stiffness approach of section analysis for strength assessment. Any shape of the cross-sectional repair configurations can be treated including partial patch-repair and different repair material properties, if applicable. The analytical results show good correlation with test results on RC beams repaired under load or using different load relief strategies. The analytical procedure is also implemented as a subroutine of the REDEPRO program to be used for rehabilitation design purposes.