Deflection of Prestressed Concrete Members


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Title: Deflection of Prestressed Concrete Members

Author(s): Osama El-Shafey, Ian J. Jordaan, and Robert E. Loov

Publication: Special Publication

Volume: 76


Appears on pages(s): 421-450

Keywords: tion; envconcrete; i beams (supports); creep properties; creep tests; deflec- . . . ronments; live loads; parklng facilities; prestressed shrinkage.

Date: 10/1/1982

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.