An analytical approach towards determining the strength of FRP-reinforced/prestressed concrete beams Sameh R. Salib, George Abdel-Sayed, and Nabil Grace Abstract: Non-corrosive fiber-reinforced polymers (FRP) are becoming a desirable replacement to steel bars in rein- forcing/prestressing concrete structures. However, the difference between the two materials is not only related to the properties in the longitudinal direction of the bars as most of the current research work and design guidelines are con- cerned with. The properties in the transverse direction of the bars have basic differences, which may influence the beam strength and its mode of failure. This paper presents a comprehensive analytical modeling for evaluating the strength of concrete beams reinforced and (or) prestressed with FRP bars and the corresponding mode of failure. It takes into account significant parameters such as the crack path geometry, the crack width, and the properties of the bars in both longitudinal and transverse directions. The proposed analysis identifies any premature failure of beam due to the dowel failure of FRP reinforcement and determines the contribution of stirrups, if any, based on the number and actual tensile strain of the stirrups crossing the failure crack. A good agreement has been observed between the results of the developed model and the results of an experimental program conducted at the University of Windsor, as well as other published experimental programs. Key words: ACM, FRP, cracks, dowel action, reinforced concrete, strength. Résumé : Les polymères non corrosifs renforcés de fibres (« FRP : fiber reinforced polymer ») sont un substitut sou- haitable aux barres d’acier qui servent à renforcer/pré-contraindre des structures en béton. Cependant, la différence entre les deux matériaux n’est pas seulement liée aux propriétés dans la direction longitudinale des barres, comme sem- blent s’en préoccuper le travail de recherche actuel et les guides de construction, dans leur majorité. Les propriétés dans la direction transverse des barres diffèrent fondamentalement, ce qui est susceptible d’affecter la résistance des poutres et leur mode de rupture. Cet article présente un modèle analytique complet permettant d’évaluer la résistance des poutres en béton renforcées et/ou précontraintes par des barres en FRP, et le mode de rupture correspondant. Il prend en compte des paramètres significatifs tels que la géométrie des lignes de fissure, la largeur des fissures, et les propriétés des barres dans les directions longitudinale et transverse. L’analyse proposée identifie toute rupture préma- turée de la poutre due à la rupture du goujon du renforcement en FRP et détermine la contribution éventuelle des étriers, en se basant sur le nombre et la déformation réelle en tension des étriers qui sont au travers de la fissure. Un bon accord a été observé entre les résultats du modèle développé et ceux d’un programme expérimental mené à l’Université de Windsor, ainsi qu’avec d’autres programmes expérimentaux qui ont été publiés. Mots clés : ACM, FRP, fissures, action du goujon, béton renforcé, résistance. [Traduit par la Rédaction] Salib et al. 315 Introduction Most of the current design codes for concrete structures reinforced and (or) prestressed with steel bars evaluate the beam strength in two independent steps. The first step is to calculate the beam flexural strength, corresponding to a flex- ural crack, based on the compressive force induced in con- crete and the tensile force carried by longitudinal reinforcement. The second step is to calculate the beam shear strength, corresponding to a diagonal crack with a given slope and considering the contribution of both con- crete and shear reinforcement (ACI 1995; CSA 1994). The current design guidelines for FRP-reinforced concrete struc- tures (ACI Committee 440H 2001; CHBDC 2001; BIR 1997) recommend the same procedure with few modifica- tions to account for the difference in the longitudinal proper- ties of steel and FRP bars (e.g., modulus of elasticity and tensile strength), as well as to consider the damaged/highly stressed fibers at bent locations of FRP stirrups. The ACI Committee 440H (2001) considers the shear strength, V n , for concrete beams reinforced for flexure with FRP bars and for shear with steel stirrups (as for the tested beams listed herein) to consist of two components, similar to Can. J. Civ. Eng. 29: 301–315 (2002) DOI: 10.1139/L02-001 © 2002 NRC Canada 301 Received 30 April 2001. Revised manuscript accepted 19 December 2001. Published on the NRC Research Press Web site at http://cjce.nrc.ca on 10 April 2002. S.R. Salib and G. Abdel-Sayed. 1 Department of Civil and Environmental Engineering, University of Windsor, Windsor, ON N9B 3P4, Canada. N. Grace. Department of Civil Engineering, Lawrence Technological University, Southfield, MI 48075-1058, U.S.A. Written discussion of this article is welcomed and will be received by the Editor until 31 August 2002. 1 Corresponding author (e-mail: sayed@uwindsor.ca).