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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 14 Abstracts search results
Document:
JL82-32
Date:
May 1, 1985
Author(s):
James E. Wailer and John E. Zimmerman
Publication:
Journal Proceedings
Volume:
82
Issue:
3
Abstract:
Designing post-tensioned multistory building frames frequently results in significant construction cost savings. The reluctance of structural engineers, clients, and developers to employ post-tensioning in building designs is often the result of misunderstanding the behavior and design requirements of this type of structure rather than the extra cost entailed in contractor, labor, and material evaluation as compared with other conventional construction methods. This paper illustrates the structural behavior of post-tensioned building frames, presents a moment-balancing design procedure for unbonded, draped, post-tensioned tendons, and discusses several aspects of primary and secondary post-tensioning forces which must be considered to properly design mild steel reinforcement in accordance with ACI 318-77.
DOI:
10.14359/10343
JL81-30
July 1, 1984
Alan H. Mattock
81
4
Eq. (18-3) of ACI 318-77 is an approximate equation for f(ps), the stress in bonded prestressed reinforcement at nominal moment strength. It was orginally proposed by joint ACI-ASCE Committee 423 in 1958 in "Tentitive Reccommendations for Prestressed Concrete". A study was made of the influence on the accuracy of Eq. (I8-3) (a) prestressing steel for which f(py) = 0.9Of(pu), (b) high-strength concrete, (b) additional unprestressed flexural tension reinforcement, (d) compression reinforcement, and (e) use of a slender T-ztion beam rather than a rectangular section beam. A modified version of Eq. (18-3) was developed that takes into account the above factors and yields values of fps in closer agreement with values obtained from an analysis based on simultaneous satisfaction of compatibility of strains and equilibrium of forces. This modified version of Eq. (M-3) has been included in ACI 318-83.
10.14359/10687
JL81-23
May 1, 1984
Bekele Mekonnen
Simple approximate equations for the design of rectangular and circular columns are proposed based on a study of dimensionless load-moment- interaction charts, aimed at deriving closed form equations closely approximating the charts. The resulting proposed equations achieve this aim and may therefore be used, instead of interaction charts, for the design of columns. The fact that the equations are presented in closed form also enables applications outside routine design. The equations are applicable to both the ACI and CEB approaches of strength design, as well as to the alternate design method of A CI Standard 318-77. A design example is presented in the Appendix to demonstrate the advantages of using the proposed equations. Finally, a proposal is made that allows use of the same interaction charts by ACI and CEB.
10.14359/10680
JL80-23
May 1, 1983
Hans Gesund
80
A " flexural punching" mechanism has been derived for individual concentrically-loaded column footings. It has been shown that with use of this mechanism flexural strength of square individual column footings is less than that predicted by the cantilever design method specified in ACI318-77. The deficiency in strength is in the lopercent range for rectangular column cross sections and the I5 percent range for circular columns. When the footing is rectangular, the Code required concentration of reinforcement in the central band width will compensate for the defciency if the designer uses increased reinforcement over the entire lengih of the footing. Otherwise, because the mechanism spreads well beyond the presently spectfied central band width, strength gained from the additional reinforcement under and near the column will be dissipated by the reduced flexural strength outside the central band wrdth. Suggestions are made for revisions in the expression for the width of the central band and for the portion of the reinforcement to be placed within it, which should help to overcome the problem.
10.14359/10838
JL80-09
March 1, 1983
J. F. Mulcahy and J. M. Rotter
2
The response of flat plane and column structures to lateral loading is closely associated with the stiffness of the slab/column joints. Many previous theoretical and experimental investigations have studied the linear elastic response of sway systems but few experimental results are available on the nonlinear behavior of concrete slabs/column joints. Results from experiments on reinforced concrete models are presented and show a nonlinear response from very low load levels. The behavior of the test specimens is compared with both linear elastic and empirical predictions.The results are also compared with an equvilant slab derived from th equvilant frame method of ACI 318-77. This is found to give a closer description of the observed behavior than the elastic theories.
10.14359/10464
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