C. Barris

Design of FRP reinforced concrete beams for serviceability requirements

Abstract Serviceability Limit States (SLS) may govern the design of concrete elements internally reinforced with Fibre Reinforced Polymer (FRP) bars because of the mechanical properties of FRP materials. This paper investigates the design of Fibre Reinforced Polymer reinforced concrete (FRP RC) beams under the SLS of cracking, stresses in materials, and deflections. A formulation to calculate the bending condition at which crack width and stresses in materials requirements are fulfilled is presented based on principles of equilibrium, strain compatibility and linear elastic behaviour of materials. The slenderness limits to comply with the deflection limitation are redefined and a methodology to calculate the optimal height of an FRP RC beam to satisfy all of these serviceability requirements is proposed. This procedure allows optimising the dimensions of an FRP RC beam taking into account the specific characteristics of the element, such as the mechanical properties of materials and the geometric and load...

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.

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.