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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 1-5 of 13 Abstracts search results
April 1, 1996
Presents American and European design provisions for the control of deflections. Both minimum and computed versus allowable deflections of CEB-FIP Model Code (MC 1990) and ACI Code (ACI 318-89) are considered. The methods in both codes for predicting deflections and applying span/depth-thickness ratio are evaluated in design examples. Based on the simplified method for computing the long term deflection, no significant difference is found between the codes.
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% .
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.
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.
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.
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