*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

Design-oriented stress–strain model for FRP-confined concrete

This paper presents a review of the different models for concrete based on continuum damage theory, formulated at the Laboratoire de Mecanique et Technologie (Cachan, France). Derived in the framework of the thermodynamics of irreversible processes, each formulation is based on physical observation. Induced anisotropy, ductile behavior, and directional effects such as the closure of cracks are discussed and adequate damage models are proposed. Finally, the numerical implementations performed give a good description of the failure process as well as an accurate prediction of the behavior of concrete and reinforced concrete structures.

Continuum damage theory - application to concrete

Performance and application of a design-oriented stress-strain model for FRP-confined concrete

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

Synopsis The state of stress in the concrete due to bond forces from deformed reinforcing bars is analysed. For determination of the cracking resistance of the concrete cover, a concrete ring model is used. The stresses are calculated for an elastic stage, a plastic stage, and an elastic stage with internal ring cracks. The appearance of the concrete cover cracks along the deformed bars in the bond zones for normal cover thickness can be determined by using the mean of the values obtained for the two last stages. The partly cracked elastic stage gives cracking loads just on the safe side.

Cracking of concrete cover along anchored deformed reinforcing bars

The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders.

Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

A bond theory for deformed reinforcing bars in concrete is elaborated taking into account different stages in development of final rupture occurring as splitting or pull-out. The concrete cover splitting resistance is modelled for a thick-walled concrete ring in elastic and plastic stages. Different final possible failure modes are analysed. Stress distributions along the spliced bars and in surrounding concrete are investigated. The theory is applied on overlapped tensile reinforcement splices. Tests have been performed on more than 300 spliced beams and results show plausible agreement with theory. The influence of different types of confinement on splice strength as stirrups and spirals has been investigated. Fatigue of overlapped splices is discussed and investigated.

A theory of bond applied to overlapped tensile reinforcement splices for deformed bars

Fatigue Strength of Plain, Ordinary,and Lightweight Concrete

A method is presented for the assessment and calibration of the elastoplastic behaviour of FRP confined concrete. The method is based on the evaluation of permanent deformations from observed experimental deformations and theoretical elastic response of confined concrete. The inelastic response of concrete and the parameters of its mathematical modelling are investigated. Closed form expressions are produced to relate the model parameters to the mechanical properties of the material. A strain-hardening Drucker–Prager model is developed which simulates both the hardening and softening material response with reasonable agreement to the experimental observations. The predictive ability of the model is verified through comparisons to numerous published experimental data and analytical models.

Ralejs Tepfers

Papers

Cracking of concrete cover along anchored deformed reinforcing bars

Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

A theory of bond applied to overlapped tensile reinforcement splices for deformed bars

Fatigue Strength of Plain, Ordinary,and Lightweight Concrete

Analytical modelling of plastic behaviour of uniformly FRP confined concrete members