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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 20 Abstracts search results
Document:
SP76-17
Date:
October 1, 1982
Author(s):
Osama El-Shafey, Ian J. Jordaan, and Robert E. Loov
Publication:
Symposium Papers
Volume:
76
Abstract:
A set of measurements of time-dependent deflections of prestressed concrete members in a parking structure is presented. Time-dependent strains for field control specimens from the same concrete batch and subjected to the same environmental conditions as the members are given, together with results from control specimens stored in the laboratory. A comparison of these strains and those determined using CEB-FIP Recommendations and the ACI Committee 209 procedure is shown. The deflection of the members was predicted by means of a step-by-step finite element analysis using the strains from the field control specimens. In the analysis, the fact that the major part of creep is irreversible is recognized. Creep and shrinkage strains predicted using the two code procedures were substantially different from those recorded in the field (up to 2.25 times the recorded values). Part of this discrepancy can be attributed to the influence of the environmental conditions (particularly temperature) on creep and shrinkage strains, but the prediction methods themselves leave room for improvement. In spite of the disagreement between the field strains and those predicted by CEB-FIP Recommendations, the measured deflections were similar to those predicted from measured field control strains and to those predicted from CEB-FIP strains. The ACI Committee 209 procedure slightly overestimates the final deflection.
DOI:
10.14359/6798
SP76-10
ACI Committee 209
This report reviews the methods for predicting creep, shrinkage and temperature effects in concrete structures. It presents the designer with a unified and digested approach to the problem of volume changes in concrete. The individual chapters have been written in such a way that they can be used almost independently from the rest of the report. The report is generally consistent with the ACI Building Code (ACI 318-77) and includes material indicated in the Code, but not specifically defined therein.
10.14359/6791
SP76-08
Marwan A. Daye
Creep of concrete is an important characteristic to the 1' design engineer particularly when dealing with prestressed concrete, more so in the design of prestressed reactor/containment buildings. Since actual testing is a long term process, an empirical formula for prediction of creep of concrete is developed. The effect of the physical properties of the aggregate and the mix proportions as well as the age at loading and the concrete temperature are considered. Creep test results for cylinders made from both normal and light weight concrete are compared with creep values predicted using the developed formula. The comparison indicated good correlation between both values. The prediction formula is computerized such that the creep values for a concrete mix could be evaluated immediately with the input of the mix properties on three computer data cards.
10.14359/6789
SP76-06
G. Chadha
A precise evaluation of prestress losses in prestressed concrete members is a simple but time-consuming problem. Nevertheless, design aids would be useful to engineers. This paper uses an iterative procedure for calculating the long-term losses. Tables for direct prediction of losses due to creep and shrinkage are presented. It uses available information on concrete creep and shrinkage and steel stress relaxation, and includes the effect of interaction of various factors contributing to the prestress losses. To illustrate the use of the tables, two numerical examples are included. The tables are applicable for all prestressed concrete structures such as buildings, bridges, or nuclear power plants. The manual computations being tedious and time consuming, the predicted prestress losses tables are highly accurate, as they are based on interaction computer program using increments of short duration.
10.14359/6787
SP76-07
M. S. Khalil, W. H. Dilger, and A. Ghali
A computer-aided, step-by-step method is presented for the study of time-dependent stresses and deformations of pre-stressed concrete frames. The method is used to investigate the effectiveness of deferring the final connections between column or walls and slabs in building frames and allowing the slabs to slide on the columns during post-tensioning. The joints are then constructed at a later date. A second investigation concentrates on the stresses developed in a cast-in-place, normally-reinforced closure strip cast sometime after post-tensioning of the floors in a long continuous frame. Results obtained for the two examples are evaluated and the possibility of excessive stresses and cracking is discussed.
10.14359/6788
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