International Concrete Abstracts Portal

This paper presents the test results of 14 full-scale concrete beams. The beams were 3300 mm long with a rectangular cross-section of 200-mm width and 300-mm depth. Twelve beams were reinforced with carbon FRP composite bars and two reinforced with steel as control. Two newly developed types of CFRP bars with different surface textures were considered: the sand-coated ISOROD bars and the ribbed-deformed C-BAR. The beams were tested to failure in four-point bending over a clear span of 2750 mm. The results presented focus on the deflection behaviour of beams reinforced with CFRP bars, which have different bond, elasticity modulus, strain, and strength characteristics. The test results were compared to the predictions of some of the available models (ISIS-M03-01 design manual, ACI 440.1R-01 guidelines, and Razaqpur model). Based on the findings of the study, the validity of the design guidelines and the effectiveness of using the new CFRP bars as reinforcement for concrete beams were established.

SP-210 This Symposium Publication contains papers presented during the 2002 ACI Spring Convention in Detroit, including six papers related to predicting the deflections of concrete members reinforced with fiber-reinforced polymer (FRP) reinforcement: one paper describes two field investigations, two unique laboratory investigations, a paper on estimating the errors in calculating deflections of high-performance concrete slabs, and a comparison of the ACI and EC2 deflection provisions. This volume should be read in association with Symposium Publication SP-203, Code Provisions for Deflection Control in Concrete.

Serviceability of concrete members reinforced with FRP often governs the design. There are two main serviceability criteria to be satisfied: crack width and deflection. Prior to cracking the behaviour of concrete members reinforced with FRP is identical tot ehat of seel reinforced concrete. After cracking, due to the mechanical characteristics of FRP, the curvature increases rapidly. Therefore deflection of FRP reinforced members is typically larger, thus more critical than deflection of comparable members reinforced with steel. Crack width is often portrayed as less significant due to the excellent corrosion resistance of FRP products. However, high sustained strain in FRP at service loads may lead to stress corrosion primarily in glass-fibre reinforced polymer (GFRP), and the width of cracks needs to be limited for aesthetic reasons. This paper deals with the design of concrete reinforced with FRP to satisfy serviceability requirements. To achieve the goal, a simplified mathematical design using charts is developed for ISIS Canada (1) by the authors. The principles involved in developing these charts, and their applicability are discussed. To satisfy the crack width and deflection limitations of these members, allowable stress limits in FRP reinforcement are introduced.

A method is proposed for calculating the deflection of FRP reinforced concete structures based on the integration of moment-curvature relationship. The moment-curvature relationship is assumed to be essentially bilinear with slopes corresponding to the flexural rigidity of the gross and the cracked sections, respectively. The proposed method is used to obtain closed-form solutions for maximum deflection of continuous beams under three common types of loading. The predictions of this method are compared with available experimental data and with the corresponding redictd values by other available methods. The available methods use the concept of effective moment of inertia, similar to the ACI method for conventional reinforced concrete, or some modifications thereof. The predicted values by the proposed method compare better with the experimental results than the effective moment of inertia methods.

ACI 318-99(1999) and EC2-92(1992) building design codes are the two major design code documents of reinforced concrete structures worldwide. Therefore, a detailed comparative analysis of these codes is justified and can be useful in understanding rational behind both codes. This type of comparative work can help identify iiscrepancies in either code and would substantiate their validity. In this regard, deflection computations and estimation of the flexural stiffness would be particularly attractive for detailed comparison. The analytical procedure adopted by ACI is particularly characterized by inconsistent correlation with test results, due to the fact that a number of factors affecting deflection have been ignored. In this study, detailed comparison with parametric analysis is conducted using the deflection provisions of ACI318-99 and EC2-92. First, the permissible deflections are compared and significant differences between the limits of the two codes are noted. The differences in the rationale of the deflection limits are identified. The span-to-depth ratio limits adopted by the two codes were found to have significant differences, with EC2 exhibiting more conservative limits. In comparing the two procedures for computing flexural deflection, all the pertinent quantities are investigated. These include: the cracking moment, the modulus of elasticity, the gross and cracked moment of inertia, the effective moment of inertia. A special form of the effecive moment of inertia equation is used to facilitate a parametric comparison between the two equations. Long-term flexural deflection is aslo compared and exhibits the differences between the two codes in relation to the impact of shrinkage, creep and compression reinforcement. This study is concluded by a numerical example that shows the differences between the codes in estimating short and long term deflection.