Estimating Time-Dependent Deformations of Prestressed Elements: Accuracy and Variability


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Title: Estimating Time-Dependent Deformations of Prestressed Elements: Accuracy and Variability

Author(s): M. W. Paulsen, S. D. B. Alexander, and D. M. Rogowsky

Publication: Special Publication

Volume: 227


Appears on pages(s): 195-216

Keywords: camber prediction; case study; creep, prestressed; shrinkage variability

Date: 3/1/2005

Continuous highway overpass structures are often governed by serviceability rather than ultimate conditions. Deflection prediction and control is vital to avoid cracking. A two span overpass in Calgary was chosen as a case study. Deflections and strains in two precast prestressed girders were monitored from fabrication to erection, and a comprehensive material testing program was done on the concrete mix. The results of the case study show that the CEB MC-90 model code underestimated the time-dependent response by a maximum of 16% while ACI 209 overestimated by 19%. By tuning ACI 209 and CEB MC-90 to the concrete material testing data, predictions were increased to within 8% and 7%, respectively. A variability analysis on the two tuned models showed that while they give nearly the same prediction, the CEB MC-90 format induces less uncertainty in predictions. In addition, extrapolation to long-term ages shows a substantial divergence between predictions of the two models.