Time-Dependent Monitoring and Modeling of I-35W St. Anthony Falls Bridge. I: Analysis of Monitoring Data
Publication: Journal of Bridge Engineering
Volume 22, Issue 7
Abstract
For the successful implementation of long-term monitoring strategies of prestressed concrete structures, the expected behavior of the structure must be accurately quantified before anomalous or damage-related readings can be properly identified. In situ structures may be subject to large variations in temperature, which can have a significant impact on measured deformations, and continued creep and shrinkage of the concrete further complicate long-term predictions. The goals of this and a companion paper are to present the methodology for extracting the time-dependent behavior of a posttensioned concrete box girder bridge from structural monitoring data in the presence of changing temperatures (this paper) and to compare predictions of long-term time-dependent deformations computed using finite-element analysis with the extracted time-dependent monitoring data (the companion paper). To investigate the interactions between temperature and time-dependent behavior for in situ monitoring data, strains and expansion joint deflections from the St. Anthony Falls Bridge, a posttensioned concrete box girder bridge on I-35W in Minneapolis, Minnesota, were collected over a period of 5 years. A methodology based on linear regression was used to separate the time-dependent deformations from the temperature-related deformations given a variable coefficient of thermal expansion (CTE). The total temperature-related deformations were captured by functions based on the average bridge temperature, the thermal gradient through the depth of the superstructure, and the average squared temperature of the bridge, which was proposed because the CTE was observed to vary with temperature. On examination of the extracted time-dependent readings, the deformation rates were found to decelerate during the winter and accelerate during the summer. To enable direct comparison between the measured results and the creep and shrinkage predictions from finite-element models assuming constant temperature, an Arrhenius-adjusted time formulation was used, which normalized the measured deformations under varying temperatures to those expected from a constant reference temperature. This procedure for processing the time-dependent measured data enables a comparison with time-dependent finite-element model results conducted at constant temperature.
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Acknowledgments
The authors would like to acknowledge the support of the Minnesota DOT. Numerical computations were performed using resources provided by the University of Minnesota Supercomputing Institute. The opinions expressed in this paper represent those of the authors and not necessarily those of the sponsors.
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Published In
Journal of Bridge Engineering
Volume 22 • Issue 7 • July 2017
Copyright
© 2017 American Society of Civil Engineers.
History
Received: Jul 13, 2015
Accepted: Jan 24, 2017
Published online: Apr 13, 2017
Published in print: Jul 1, 2017
Discussion open until: Sep 13, 2017
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