Serviceability related to deflections and cracking often controls design of fiber reinforced polymer (FRP) reinforced concrete. The existing approach prescribed in ACI 318 for computing deflection of steel reinforced concrete overestimates member stiffness when FRP is used as the reinforcement. Deflection is then underestimated. Numerous proposals have consequently been made for computing deflection of FRP reinforced concrete, and have mostly involved modifications to Branson’s original ACI expression for the effective moment of inertia Ie. This paper reviews the different procedures used in the past by ACI Committee 440 to compute deflection of FRP reinforced concrete members, and discusses deficiencies of past and present ACI 440.1R deflection calculation guidelines. A case is made for the need to adopt a more rational approach to compute deflection and the basis for proposed changes are reviewed and explained in detail. A statistical comparison of past, present, and proposed approaches for computing deflection are compared with an experimental database that justifies the need for a more rational approach to computing deflection. The paper ends with a clear set of deflection procedures for carrying out serviceability design of FRP reinforced concrete.

This paper presents detailed investigations into the effective moment of inertia for concrete beams prestressed with aramid fiber reinforced polymer (AFRP) tendons, including an assessment of the existing predictive methods. A three-dimensional nonlinear finite element analysis (FEA) model is developed, based on three different experimental programs reported in literature, to predict the effective moment of inertia of concrete beams prestressed with AFRP tendons. The investigation includes the effect of different sectional properties and various prestressing levels in the tendons. The solved FEA models are compared with several predictive models. The prestressing level in the AFRP tendons significantly influences the transition of the moment of inertia from uncracked section (Ig) to fully-cracked section (Icr) . The existing design standards may not be applicable for beams having a large Ig/Icr ratio (typically over 50) with a low level of prestress (e.g., below 40% ultimate).

To understand and predict the effect of externally bonded reinforcement (EBR) on the serviceability behavior of FRP (fiber-reinforced polymer) strengthened members, four-point bending tests have been executed on reinforced concrete (RC) beams with span length 3.8 m (150 in.). This experimental campaign was further complemented with tests on strengthened tensile members. These so-called ‘tension stiffening’ tests typically consist of a tensile test on a reinforcing bar embedded in a FRP strengthened concrete prism. As the FRP EBR increases the stiffness of the beams and as a denser crack pattern with smaller crack widths is obtained, the serviceability limit state (SLS) of the strengthened members is positively influenced. Hereby, the behavior in terms of deflection and crack widths can be predicted in a fairly accurate way.

This paper describes a laboratory investigation on the flexural behavior of carbon fiber reinforced polymer (CFRP)-reinforced concrete slab specimens extracted from Laurier-Taché Parking Garage (National Capital Region - Canada) after being in service field conditions for about eight years (1997-2005). A total of four specimens, measuring 3 m long × 1 m wide × 0.19 m deep each, are extracted from the parkinggarage and then tested in flexure under four-point bending set-up. In addition, five FRP bar samples are extracted from the slabs and tested in tension to evaluate the strength or stiffness degradation of the CFRP bars, if any. The test results are presented in terms of deflection, crack widths, strains in concrete andreinforcement, ultimate capacity, and mode of failure. Based on the test results, the current provisions, provided by different FRP codes and design guidelines, are evaluated. The results showed that the CFRP bars as well as the CFRP-reinforced concrete slabs have not been adversely affected after being in service for eight years.

Design for deflection control is a critical part of the design of FRP reinforced members due to the relatively low modulus of elasticity and elastic-brittle nature of FRP reinforcement. This paper provides an overview of design for deflection control including a brief review of the basic mechanics of beam flexure and a review of methods to account for cracking, tension stiffening, shrinkage and creep. The basis for selecting appropriate deflection control criteria is also discussed and a framework is presented to incorporate deflection control into the overall design process.