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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
October 1, 1982
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.
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.
An appropriate time-dependent constitutive relation of concrete based on the physical principle of superposition is derived. This simple stress-strain relation is discussed in solving relaxation problems in which the change of stresses is asked for under given strain conditions. In the discussion of special problems in prestressed concrete, first demonstrated are the differential settlements of supports of continuous beams. The time-dependent deformations and changes of stresses in steel and concrete are illustrated. An especially useful equation is given for calculating the so-called loss of prestress force under the real conditions of the bonded steel in the concrete section.
The integral relationship between stress and dilatation of concrete has been presented in an algebraic form. This makes the solution of problems for stress changes of concrete structures easy. Expressions for determinations of stress changes in singly reinforced concrete sections on the basis of integral relationship applying the aging theory are given. For determination of stress losses and dilatations, convenient diagrams are presented for single and multilayer reinforced concrete sections.
Osama El-Shafey, Ian J. Jordaan,
and Robert E. Loov
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.
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