*Co-chairs of the subcommittee that prepared this document. Note: The committee acknowledges the contribution of associate member Paul Kelley. ACI encourages the development and appropriate use of new and emerging technologies through the publication of the Emerging Technology Series. This series presents information and recommendations based on available test data, technical reports, limited experience with field applications, and the opinions of committee members. The presented information and recommendations, and their basis, may be less fully developed and tested than those for more mature technologies. This report identifies areas in which information is believed to be less fully developed, and describes research needs. The professional using this document should understand the limitations of this document and exercise judgment as to the appropriate application of this emerging technology.

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Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures

A concise state-of-the-art survey of fiber-reinforced polymer (also known as fiber-reinforced plastic) composites for construction applications in civil engineering is presented. The paper is organized into separate sections on structural shapes, bridge decks, internal reinforcements, externally bonded reinforcements, and standards and codes. Each section includes a historical review, the current state of the art, and future challenges.

Fiber-Reinforced Polymer Composites for Construction—State-of-the-Art Review

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is one of the latest and most promising strengthening techniques for reinforced concrete (RC) structures. Research on this topic started only a few years ago but has by now attracted worldwide attention. Issues raised by the use of NSM FRP reinforcement include the optimization of construction details, models for the bond behaviour between NSM FRP and concrete, reliable design methods for flexural and shear strengthening, and the maximization of the advantages of this technique. This paper provides a critical review of existing research in this area, identifies gaps of knowledge, and outlines directions for further research.

Near-surface mounted FRP reinforcement: An emerging technique for strengthening structures

Intermediate crack-induced debonding in RC beams and slabs

Experimental data obtained from strengthened, precracked, reinforced concrete (RC) specimens are presented together with the results of material characterization. Strengthening was attained with the adhesion of carbon fiber-reinforced plastic (CFRP) sheets to the concrete surface. The CFRP was applied as in situ (i.e., working under the beam). Several variables were investigated, including: two CFRP material systems, two concrete surface preparations, two RC cross sections, and the number and location of CFRP plies. For two specimens, the presence of applied load (simulating the total service load) as well as external prestressing during the adhesion of the CFRP reinforcement, were investigated. It is shown that the effect of CFRP strengthening was considerable, but the effect of some of the tested variables was modest. An existing analytical model has been extended to simulate the load-deflection behavior as well as the failure mode of the precracked RC specimens. Different failure mechanisms from ductile to brittle were simulated and verified, adopting the mechanical properties of the constituent materials obtained via standard tests or using a simple test for concrete-adhesive interface.

Behavior of Precracked RC Beams Strengthened with Carbon FRP Sheets

Analytical and numerical models are presented to simulate the failure of RC beams strengthened with FRP plates and flexible sheets Different failure mechanisms, from ductile to brittle, can be simulated and verified The proposed analytical model takes into account the influence of concrete confinement in the compression zone due to the presence of the stirrups and the tensile softening properties of concrete This allows following more accurately the crack propagation and the failure mechanism of the flexural member The numerical model is based on finite element analysis (FEA), follows the smeared crack approach, and uses standard elements available in a commercial package Comparisons with experimental data obtained from strengthened RC beams tested in the laboratory are presented Analytical and numerical models show good agreement with the experiments It is shown that FRP type, thickness, and bonded length produce different types of failure ranging from FRP rupture to concrete shear failure Particularly important is the characterization of the interface (FRP-concrete) mechanical properties, for which a simple test is proposed

Brittle failure in frp plate and sheet bonded beams

FRP reinforcement may be externally bonded to the soffit of existing flexural members in order to increase their strength and rigidity. A parametric analysis is conducted to investigate the effects of FRP reinforcement on serviceability, strength, and failure mechanisms of repaired RC beams. FRP reinforcement parameters considered in the analysis are: stiffness, bonded length, thickness, and the adhesive stiffness. The choice of the repair material parameters is important in the design phase in order to obtain the desired results of strengthening or stiffening without other unforeseen effects. In this paper, three typical RC beam cross sections are considered with height-to-width ratios of 0.5, 1, and 4. Two characteristic compressive strength levels (20 and 30 MPa), and two shear span-to-reinforcement depth ratios (4.5 and 7) are considered. All other parameters related to material and geometry of the beams are maintained constant. The results of the analysis are shown in terms of repaired-to-un-repaired strength and deflection ratios. They indicate that brittle failure mechanisms can develop at loads much lower than expected when considering only flexural performance controlled by concrete crushing and FRP tensile rupture. The analytical model used for the parametrization accounts for brittle failure mechanisms induced by debonding of the FRP reinforcement or shear-tension failure in concrete in the plane of the main longitudinal steel reinforcing bars. Even when considering the limitation of the RC member due to its un-modifiable shear resistance, it is shown that the application of FRP reinforcement can considerably increase load resistance capacity and limit deflection at service.

Parametric Study of Beams with Externally Bonded FRP Reinforcement

Research is given from experimental work conducted on full-scale 1-way reinforced concrete (RC) slabs. 26 slabs with and without an overhang at 1 extremity were tested under simply supported conditions. The geometry and loading configuration allowed for the study of positive and negative moment regions. The slabs were strengthened with unidirectional carbon fiber-reinforced polymer (CFRP) laminates installed by manual lay-up. Different failure mechanisms--namely, concrete shear and crushing, CFRP rupture, and CFRP peeling--were obtained by varying the CFRP laminate cross-sectional area and amount of internal steel reinforcement. Findings from an analytical model that simulates and interprets the experimental results are also provided. These findings confirm the notion that peeling of the CFRP laminate affects the system performance but can be predicted by monitoring interface shear stresses.

Marco Arduini

Papers

Behavior of Precracked RC Beams Strengthened with Carbon FRP Sheets

Brittle failure in frp plate and sheet bonded beams

Parametric Study of Beams with Externally Bonded FRP Reinforcement

Performance of One-Way Reinforced Concrete Slabs with Externally Bonded Fiber-Reinforced Polymer Strengthening

Shear Failure of Concrete Beams Reinforced with Plates