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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 12 Abstracts search results
Document:
SP203-10
Date:
August 1, 2001
Author(s):
R. I. Gilbert
Publication:
Symposium Papers
Volume:
203
Abstract:
An experimental program of long-term testing of large-scale reinforced concrete flat slab structures is described and the results from the first series of tests on five continuous flat slab specimens are presented. Each specimen was subjected to sustained service loads for periods up to 500 days and the deflection, extent of cracking and column loads were monitored throughout. The measured long-term deflection is many times the initial short-term deflection, due primarily to the loss of stiffness associated with time-dependent cracking under the combined influences of transverse load and drying shrinkage. This effect is not accounted for in the current code approaches for deflection calculation and control. Recently proposed procedures to improve deflection calculation (1) are evaluated against the test results and good agreement between the measured and calculated deflections is obtained.
DOI:
10.14359/10810
SP203-06
N. J. Gardner
Predicting the deflection serviceability of reinforced concrete members in service is fraught with uncertainties which include imperfect knowledge of the limiting serviceability criteria, the material properties and the load history including construction loads and the service load. The serviceability criteria can be immediate deflection/curvature or incremental deflection/curvature. Most codes offer two methods for control of deflections. The designer may choose to calculate the deflections and check that these computed deflections are less than arbitrary, specified allowable limits. Calculating the immediate deflections of reinforced concrete members is difficult due to the concrete cracking in the tension zones of such members. Calculating the additional deflections due to the shrinkage and creep of the concrete and the consequent redistribution of stress is extremely difficult. Alternatively the codes give specified maximum span/depth ratios for which serviceability can be assumed to be satisfied and deflections do not need to be calculated. This paper compares the deemed-to-comply span/thickness limits of AC1 318-99, CSA A23.3-94, BS 8110-85, AS 3600-94, Eurocode 2 (1992 draft), AC1 435-78 and the proposals of Gardner and Zhang (1995), Thompson and Scanlon (1988), Asamoah and Gardner (I 997) and Scanlon and Choi (1999).
10.14359/10806
SP203-11
B.-S. Choi and A. Scanlon
Research has shown that design expressions previously developed for material properties such as modulus of elasticity, modulus of rupture and creep coefficient used in the calculation of beam deflections may not be appropriate for high-performance-high-strength concrete. Also, the uncertainties associated with regular and high-performance concrete material properties as characterized by probability distribution functions may be different. Since high strength concrete may be used to reduce the size of structural members, assessment of deflections will be an increasingly important design consideration. This paper discusses these issues and demonstrates through Monte Carlo simulation techniques some differences between the variability of deflections in beams made with regular and high-strength concretes.
10.14359/10811
SP203-09
B. Vijaya Rangan and P. Kumar Sarker
Reinforcing bars with a minimum yield strength of 500 MPa (72.5 ksi) are currently in use in Australia. The paper examines the effect of this high strength reinforcement on the bending stiffness of flexural members. The influence of tensile steel ratio, concrete strength and shrinkage of concrete on the bending stiffness is studied using a parametric analysis. It is found that for the same service load the bending stiffness of members with 500 MPa (72.5 ksi) reinforcement varies between 85 and 100 percent of that of members reinforced with 400 MPa (60 ksi) steel depending on tensile steel ratio. Also shrinkage of concrete should be included in the bending stiffness calculations for members with tensile steel ratio less than about 0.008.
10.14359/10809
SP203-01
A. Scanlon, D. R. Cagley Orsak, and D. R. Buettner
AC1 Building Code requirements for deflection control are critically reviewed. Provisions for minimum thickness, deflection computations, and permissible computed deflections are reviewed. Differences in the approaches to deflection control for one-way and two-way construction are identified. Limitations in the application of the prescribed deflection calculation method are discussed. Results of a survey of consulting firms concerning deflection control in design offices are presented. The paper concludes by suggesting possible directions for future changes in building code requirements for deflection control.
10.14359/10801
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