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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-10 of 13 Abstracts search results
April 1, 1996
T. S. Lok and J. S. Pei
Load-deflection responses of simply-supported (SS) and simply-supported all-round (SSAR) steel fiber reinforced (SFR) concrete square slabs subjected to a central point load have been obtained. The slabs measured 810 mm x 810 mm x 50 mm. The elastic response alone is of particular interest and presented here because this has a major influence on the durability of SFR concrete. Results for each SFR concrete slab are compared with theoretical elastic solutions for both boundary conditions and also with the behavior of identical plain concrete and weldmesh reinforced slabs in each case. A modified depth instead of the full slab thickness is proposed for estimating the elastic response of SFR slabs for the two boundary conditions; the depth effectively reduces the elastic stiffness of the cross section. The limiting load level at which the initial response may be considered as linear is established, but the limiting load is dependent on the behavior of the slab. This limiting load level is compared with results calculated from a modified empirical expression for predicting the load at which first crack is perceived to occur. In the empirical expression, a triangular linear stress block with the modified depth is used. On average, the modified depth is about 0.7 times the overall SFR concrete slab thickness for both the SS and SSAR boundary cases. The influence of fiber type, fiber concentration, and boundary condition on the modified depth is not significant.
R. Ganeswaran and B. V. Rangan
Presents the results of a study on long-term deformations of high-strength concrete. Shrinkage and creep deformations of high-strength concretes, as well as deflections of beams and one-way slabs made of high- strength concrete are reported. The measured deformations are compared with the values predicted by the ACI method, the CEB-FIP Model Code, and the Australian Practice. The comparison shows several discrepancies between measured and predicted values.
P. R. Chakrabarti
In this project, an attempt is made to study the instantaneous load- deflection behavior of partially prestressed beams with unbonded post- tensioning tendons. Thirty-three beams with the following variables were tested: different mixes of reinforcing and prestressing steel, T-beams and rectangular beams, normal and high-strength concrete, low and high ratios of span/depth, and different effective stresses in tendons. Cracking was observed and deflections measured at precracking and postcracking stages. A suitable method for deflection calculation at precracking and postcracking stages is proposed. The proposed deflections and the deflections obtained by current ACI 318-89/92 code equations are compared with the measured deflections.
N. J. Gardner and J. Zhang
North American design codes offer two methods to insure deflection serviceability. The design engineer can calculate the live load and sustained load deflections and check that they are less than code specified limits. Alternatively, the codes give maximum span/depth ratios for which serviceability can be assumed to be satisfied and deflections do not need to be calculated. However, the span/depth provisions of ACI 318-89 and CSA A23.3- M84 do not consider many of the factors which influence the deflection behavior of reinforced concrete beams and may not be consistent with the code specified deflection limits. The immediate and long term deflections of reinforced concrete beams were calculated using a layered, nonlinear finite element model. The long term deflections were calculated by a hybrid technique using an effective reduced modulus for concrete creep and a conventional finite element, time-dependent load vector for shrinkage and tensile cracking. The modelling technique was verified using the extensive experimental data of Christiansen. Span/depth ratios are proposed, which include the effects of concrete strength, tension steel ratio, and compression steel ratio, for incremental deflection criteria of span/500 and span/250. Long term deflection multipliers are given for sustained moments of 30, 50, and 70 percent of the design ultimate moment.
M. A. Bhatti, B. Lin,
and J. P. Idelin Molinas Vega
The usual design practice for analysis of reinforced concrete slabs with openings is to neglect holes if their area is less than 10- 12% of the total slab area. This practice is based in part on studies conducted in early sixties regarding the effects of holes on the elastic behavior of plates. A literature survey revealed no specific studies regarding the effects of holes on deflection and strength of reinforced concrete slabs with openings. This paper presents a numerical study of the effects of openings of different sizes on the behavior of reinforced concrete slabs. A nonlinear finite element model for reinforced concrete slabs is developed using three dimensional brick elements taking into account cracking and crushing of concrete, and plasticity of both reinforcement and concrete. Distributed and concentrated loads are applied to slabs until collapse. Results show that when slabs are subjected to uniformly distributed loads, the openings do not have much effect on their strength and serviceability. The openings should be considered, however, when designing slabs subjected to concentrated loading where the opening ratios are larger than 2.5% .
B. Chen and E. G. Nawy
Use of prestressed prisms as main reinforcement has been demonstrated to be effective in limiting cracks and reducing deflections in high-strength, high performance concrete beams. To further understand the load-deformation history of such type of structural members, computer-simulated analysis has been conducted. A nonlinear analytical model based on strain compatibility was established. Theoretical predictions are compared with the experimental data obtained by the authors. Comprehensive computer-simulated flexural tests were also performed on a theoretical member section to further identify the variables which may affect the structural behavior. Parametric study suggests that the section ductility is mainly controlled by the reinforcing index. The influences of the effective prestress and concrete strength on ductility is found to be insignificant. Fiber optic Bragg-grating sensor technology was developed and used to internally and externally measure the deformations and cracking in the specimens.
P. L. Fuhr, D. R. Huston, and A. J. McPadden
An optical technique has been developed whereby two angles and linear displacement can be simultaneously measured in a noncontact manner. The method depends upon the usage of a diffraction grating with linear variation of period along its length. The grating is attached to a structure at a point of interest, while all other system components are placed at a remote location. Evaluation of this measurement technique has been demonstrated on a laboratory- based structure, which simulated conditions found at deep trench (or tunnel) walls or bracing systems. In a construction site configuration, this sensor allows the user to determine if the walls are undergoing structural deformation. In addition, the magnitude of deformation may be measured and alarm conditions may be monitored. Experimental results obtained using this technique are presented and compared with theory.
Y. L. Mo and H. C. Lai
Although structures with elastic response are fairly well understood, structures with inelastic response are more difficult to analyze. Furthermore, in studies of inelastic response, attention has generally been paid to the response of reinforced concrete structures with relatively little attention being given to pounding of reinforced concrete buildings. Generally, the mutual collisions, or pounding, result from excessive deflections of adjacent buildings. In this paper, an algorithm is described for computing the pounding response of reinforced concrete buildings. In this situation, the buildings are idealized as two-dimensional multi-degree-of-freedom systems with nonlinear force-deformation characteristics. Collision between adjacent masses can occur at any level and are simulated by means of impact elements. Using real earthquake motions, the effect of deflection is investigated. In this study, the following conclusions are found. 1. Pounding can cause high overstresses, mainly when the colliding buildings have excessive deflections. 2. The code-specified separation distance is adequate to prevent pounding. 3. Pounding problems of adjacent buildings with large difference in mass are common.
M. A. Polak, A. Scanlon, and D. V. Phillips
Presents available algorithms for deflection calculations of reinforced concrete (RC) beams, plates, and shells, using nonlinear finite element analysis. Detailed finite element formulations based on the layered approach and nonlinear constitutive laws are discussed and evaluated. The layered approach, through the rigorous treatment of the states of strain and stress can model complex behavior of both thin and thick plates. Further refinements can be incorporated using full three-dimensional modelling; this approach is briefly discussed in the paper. Alternative, simpler approaches based on the effective stiffness formulation are presented in the paper. The results of the finite element effective stiffness analyses are compared to both experimental results and the results of the layered analyses. Time-dependent effects of creep and shrinkage have a significant effect on deflections of reinforced concrete structures. The methods of incorporating these effects into layered and effective stiffness analyses are discussed in the paper. To demonstrate the usefulness of the finite element analysis, several examples of numerical results are presented and compared to experimental data. The examples include slabs with different loading, boundary, and reinforcement conditions.
I. N. Robertson and C. J. Ambrose
The effective beam width method is used extensively for two- and three-dimensional analysis of flat plate structures subjected to combined gravity and lateral loading. Typically, the member stiffnesses are assumed constant throughout each span. This approach is shown to produce unreliable estimates of lateral drift and slab bending moments when compared with the results of a previously reported experimental program performed by researchers at the University of California at Berkeley. This paper presents a two-beam effective width model in which different section properties are used in negative and positive bending regions of the slab. Proposed slab stiffnesses for use in this model are based on a correlation between the experimental data and analytical analysis results. The application of the two-beam model using the proposed slab stiffness factors to a typical flat-plate structure is demonstrated in a worked example.
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