M. Baena

Serviceability Limit State of FRP RC Beams

Owing to the particular mechanical properties of FRPs, the design of Fiber Reinforced Polymer (FRP) Reinforced Concrete (RC) structures is often governed by serviceability requirements, rather than ultimate capacity. The low stiffness of FRPs generally results in large strains being mobilized already at low levels of externally applied load, and in turn can lead to significant crack widths and deflections. This paper reviews and discusses the serviceability limitations inherent in current design codes and guidelines in terms of stress limitation, cracking and deflection control. The predictions obtained in accordance to these code equations, as well as other existing proposals for the design of FRP RC structures, are then compared to the results of an experimental program on 24 GFRP RC beams tested under four-point load.

Experimental study of the influence of adhesive properties and bond length on the bond behaviour of NSM FRP bars in concrete

AbstractThe near-surface mounted (NSM) fibre reinforced polymer (FRP) technique is a relatively recent system for strengthening concrete structures. Bond is a key factor in its behaviour, and is affected by many factors whose influence can only be tested through experimental studies. In this study, the modified pull-out test was used to study the effect of epoxy properties and bond length on the behaviour of NSM FRP bars. Three epoxy types, two FRP materials (carbon and glass) and four bond lengths (6db, 12db, 24db and 30db) are used. The load capacity, slips at the loaded end and free end and average bond stress are all analysed. The test results indicate that the role of epoxy properties appear to be a key factor in bond performance in the NSM FRP strengthening technique, and that their effect varies depending on bond length and FRP properties.

Experimental Study of Time-dependent Behaviour of Concrete Members Reinforced with GFRP Bars

This study presents the results and discussion of an experimental tests program in which 8 concrete beams reinforced with glass fibre reinforced polymer (GFRP) were maintained under a constant load for a period of 150 days. Two different ratios of reinforcement and two different levels of sustained load were used. The beams were instrumented and monitored to analyze the time-dependent behaviour due to concrete creep and shrinkage. The measured deflections are compared with those calculated using methodologies available for steel reinforced concrete structures as CEB procedure, as well as with ACI 440.1R-06 and CSA-S806-02 for FRP reinforced concrete structures. The comparisons of the theoretical and experimental long-term deflections indicate that CEB procedure gives reasonable predictions in all 8 beams. However, some differences can be found when ACI 440.1R-06 or CSA-S806-02 procedures are applied.

Comparative Study of Deflection Equations for FRP RC Beams

The mechanical and bond characteristics of Fibre Reinforced Polymers (FRP) used as internal reinforcement for Reinforced Concrete (RC) elements result in larger deflections and crack widths compared to the conventional steel RC elements. Consequently, serviceability requirements may govern the design of such members. In the last 20 years, several approaches and codes of practice have been published to predict the theoretical deflection of FRP RC elements.

Experimental Study on the Tension Stiffening Effect of GFRP RC Elements

Direct tension test experiments are accepted to be adequate to study the tension stiffening effect of fibre reinforced polymer reinforced concrete (FRP RC) members. In this paper, an experimental program on direct tension tests on GFRP RC is presented. Four different reinforcing ratios were considered; the ties were instrumented to analyze the member behaviour (load-strain relationship and crack width). Measured member deformation and crack widths are compared with those calculated using the procedures of available codes for steel reinforced concrete, like EC-2 and ACI 224, as well as with ACI 440 for FRP reinforced concrete structures.