Load Distribution in Reinforced Concrete Slab Span Bridges
Publication: Journal of Bridge Engineering
Volume 29, Issue 9
Abstract
Changes in vehicular loading over time have caused some concrete slab span bridges to rate poorly when considering modern truck weights, which leads to load posting and restrictions that in turn lengthen trucking routes. A potential way to allow heavier vehicles to cross these bridges would be to increase the load rating by utilizing a more accurate live load distribution factor generated from field testing and computational modeling. The focus of this study was to determine the live load distribution factor for two slab span bridges using results from live load testing and plate model analysis. Field testing utilized a suite of instrumentation, and simple isotropic or orthotropic plate models of the slab span bridges were validated with field data to further investigate live load distribution. Field-test estimates of equivalent width computed using displacement data were more precise than those using strain data, but modeling indicated that strain data may better capture the distribution of stresses in the slab. Despite significant visible damage, the field bridge behaved more like an isotropic plate. AASHTO equivalent widths were conservative when compared with those computed from the field results and isotropic model for single-lane truck loading but were similar to each other for multilane loading. However, model results also indicated that the equivalent width depends on the load configuration, such that single-axle loading will be concentrated into a narrower strip compared with tandem loading. In addition, an orthotropic slab will further narrow the equivalent width compared with an isotropic slab, such that AASHTO equivalent widths may no longer be conservative for single-axle loading of a slab so degraded that it may be treated as effectively orthotropic.
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Data Availability Statement
All data, models, or codes that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
The authors would like to acknowledge the Minnesota Department of Transportation for providing funding (1036194) for this project as well as resources necessary to complete field testing and computational modeling. The opinions, findings, and conclusions are those of the authors and do not necessarily reflect the views of the funding agency.
Notation
The following symbols are used in this paper:
- At
- area under the strain or displacement curve between the two truck wheel patches in one axle;
- Aɛ
- area under the strain or displacement curve taken across the width of the bridge;
- beff
- distribution width for one wheel path;
- c
- criterion value varying from 0 to 1, with 1 describing perfect correlation between modes f and m;
- D
- distance from edge to inside of barrier;
- E
- equivalent width;
- Ei
- elastic modulus in direction i;
- Emin
- minimum value obtained from Eqs. (5) or (7);
- Gij
- shear modulus in directions i and j;
- L1
- modified span length in feet, equal to the lesser of the actual span length or 60 ft;
- NL
- number of design lanes taken as the road width divided by 3.66 m (12 ft) per lane;
- Rmax
- maximum strain or displacement sensor reading;
- W
- edge-to-edge width of bridge;
- W1
- modified bridge width in feet, equal to the lesser of the actual bridge width and 30 ft for single-lane loading or 60 ft for multilane loading;
- wt
- width of the truck;
- Δ
- vertical displacement;
- Δf
- vector containing field-test displacement data across the transverse profile of the bridge;
- Δm
- vector containing analytical displacement results across the transverse profile of the bridge that correspond to each value in the field-test vector;
- ɛ
- strain;
- ɛf
- vector containing field-test strain data across the transverse profile of the bridge;
- ɛm
- vector containing analytical strain results across the transverse profile of the bridge that correspond to each value in the field-test vector; and
- νij
- Poisson’s ratio in directions i and j.
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Published In
Journal of Bridge Engineering
Volume 29 • Issue 9 • September 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Aug 25, 2023
Accepted: Apr 17, 2024
Published online: Jun 27, 2024
Published in print: Sep 1, 2024
Discussion open until: Nov 27, 2024
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