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.

The paper presents analysis of results from fourteen full-size tests on reinforced concrete members subject to different ratios of bending and in-plane loads. The tests examined the influence of bond between concrete and reinforcement on the deflections and cracking of the members. The parameters in the test program included reinforcing bar diameter, ratio of in-plane to bending loadings, reinforcement ratio and concrete cover. Two types of specimens were involved: one set with a larger number but smaller diameter bars, and one with a smaller number but larger diameter bars. Since reinforcement sized varied, the bond characteristics of these bars varied, leading to different load-deflection responses. The test results showed that different longitudinal reinforcement configurations, for the same reinforcement ratio and the same loading and boundary conditions, result in different cracking loads, post-cracking stiffness and deflections.

Throughout the history of concrete construction, numerous construction failures have occurred involving excessive deflections and cracking of the completed structure. This paper presents two building construction cases where concrete slabs developed extensive cracking and excessive deflections soon after the slab construction and formwork removal. The effects of the shoring-reshoring operations, the rate of concrete strength development, as well as the effects of design details on the slab cracking and deflections, are investigated. The ACI 318 requirements of minimum thickness and deflection control are applied to both construction cases, and the adequacy of these code requirements is discussed. Based on the findings of this work it was concluded that the ACI 318 long term creep and shrinkage deflection calculation method does not adequately account for the early-age high construction loads.

A procedure for calculating the instantanious deflections of irregular reinforced concrete flat plate floors is presented. The method is applicable throughout the entire loading stages from the uncracked state to the fully cracked state and even up to the ultimate limit state. Based on the familiar effective moment of inertia approach, the proposed procedure also uses the ACI Direct Design Method with some generalization. The total static moment in a particular design strip will be distributed to the midspan and support sections according to the distribution coefficients of the ACI Direct Design Method, taking into account column sizes and irregularity of slab geometry around the edge slab-column connections. At high loads, the modulus of elasticity of the concrete can be reduced to better reflect the nonlinear behavior of concrete slabs. The definitions of effective span, width of design strips, torsional rigidity of transverse torsional members, and column sizes and orientations will be generalized as far as practical. The accuracy of the proposed procedure has been compared with measured deflections of two multiple-panel irregular flat plate floors tested at Nanyang Technological University - Singapore. The comparison between the calculated deflections and the experimetnal values show that the proposed procedure is reasonably accurate.

Although limit state design blends both serviceability and strength limit states, most engineers tend to be less confident in serviceability limit states than in strength limit states, especially when deflections of reinforced concrete slabs are considered. A major source of the lack of confidence is the existence of many uncertain variables in calculating slab deflections of reinforced concrete slabs are considered. A major souce of this lack of confidence is the existence of many uncertain variables in calculating slab deflections such as concrete properties (e.g., modulus of elasticity, modulus of rupture), creep coefficient, curing regime and duration, and the existence of construction loads. The absence of any reliability ocefficients in deflection calculations or deflection limits gives the impression that engineers are expected to evaluate the exact deflection that will take place on site. To make matters worse, the introduction of high-performance concrete (HPC) has increased the uncertainty about concrete properties. While HPC enhances the overall material's performance, it is usually reported to have higher shrinkage strains, and it is more susceptible to plastic shrinkage than normal-strength concrete (NSC). The possible reduction of curing periods from the recommended one week to two or three days due to tight construction schedules can result in substantial microcracking which would significantly reduce the concrete modulus of rupture. Therefore, serviceability performance is dependent on many inter-related factors that the engineer cannot control in the design assumptions. Unless the band of errors in deflection calculations is known to the engineer, the lack of confidence in deflection claculations will always be there. This paper describes a mathematical model utilizing the theory of error propagation to predict the error in the calculated deflections of simply-supported, one-way reinforced concrete slabs. Parametric studies have been carried out to examine the effect of changing the concrete properties as a result of changed site conditions on the accuracy of the estimated deflections.