This paper aims to review and critically assess experimental research efforts on the seismic retrofit of existing reinforced concrete (RC) beam-column joints with fiber-reinforced polymer (FRP) sheets of the past 20 years. A review of the literature revealed several promising features of FRP strengthening schemes. FRP retrofits can be used to address a number of different deficiencies in nonseismically designed RC members framing into beam-column joints. A majority of studies concentrate on joint shear strengthening, and strengthening in the principal stress axis is found to be most effective. Other strategies include counteracting the weak-column/strong-beam in nonseismically designed specimens by means of column flexural strengthening, as well as plastic hinge relocation within the beams, away from the joint. Only a limited number of studies evaluate combining several of these retrofit objectives into a more complete retrofit of the joint subassemblage. In most studies, simple FRP wrapping is observed to be used for anchorage, which is not always effective. Instead, anchorage by means of FRP anchors or mechanical anchors is shown to be required to achieve adequate strengthening in most cases. Next to the detailed discussion of the literature, a database of all tested specimens is compiled and analyzed. Shear strengthening design equations from major design guidelines are assessed based on the experimental results collected in this database, highlighting the need for their further improvement. Moreover, an analysis of the database reveals a lack of tested specimens with realistic test set-ups, including scaled specimens, testing without axial load, and lack of slab and transverse beams. These parameters are found to heavily affect retrofit effectiveness and may lead to nonconservative results. Moreover, on average, the effectiveness of repairing predamaged specimens is found to be similar to that of retrofitting specimens without damage.

The effective strain in composites, along with their potential rupture and debonding, plays a crucial role in predicting the strength of retrofitted reinforced concrete (RC) beams. However, only limited experimental data on these phenomena are available, mainly because of the inadequacy of traditional deformation and strain measurement techniques. This paper presents a comparative analysis of instrumentation for monitoring retrofitted RC elements. In particular, the paper addresses beams retrofitted with composite materials, FRPs (fiber-reinforced polymers), and FRCMs (fiber-reinforced cementitious mortars). It also considers strain gauges, fiber Bragg grating (FBG) sensors, LVDTs, digital image correlation (DIC), and acoustic emission (AE) sensors for monitoring strain, displacement, cracking, and debonding. Experiments on six beams are carried out, and the measured data from the monitoring devices are compared. The accuracy of DIC for strain and displacement monitoring is shown to match the performance of traditional methods, with the added benefit of providing full-field monitoring. The use of AE for detecting cracks and debonding, which is not readily possible using traditional methods, is also demonstrated. This is of particular interest for composite-strengthened RC elements, where accurate measurements of effective strain and debonding of the composite material can lead to the development of more precise design formulas.