United States Department of Transportation
i
Impact of overhang construction on girder design.
-
2010-05-01
-
[PDF-4.61 MB]
Details:
-
Creators:
-
Corporate Creators:
-
Corporate Contributors:
-
Subject/TRT Terms:
-
Publication/ Report Number:
-
Resource Type:
-
Geographical Coverage:
-
Edition:Technical report; Sept. 2006-Aug. 2009.
-
Corporate Publisher:
-
Abstract:Economical constraints on the design of bridges usually necessitate the use of as few girders as possible across the
bridge width. The girders are typically uniformly spaced transversely with the deck extending past the fascia girders, thereby
resulting in an overhang. While designers commonly employ rules of thumb with regard to the geometry of the overhang, these
rules of thumb generally address only the deck in-service strength and deflection requirements, and the effect due to construction
load is not considered. In particular, the impact of the overhang on fascia girder behavior during construction is not well
understood. Overhang construction often leads to a torsional load on the girder system that can lead to problems in steel and
concrete girder bridges during construction. The main issue with concrete girder bridges is excessive lateral rotation in the fascia
girder, which can cause potential problems of construction safety and maintenance. Field problems on concrete bridges have been
reported in the state of Texas where the fascia girders experienced excessive rotation during construction. For steel girder bridges,
the unbalanced overhang loading can lead to both local and global instability. Locally, the overhang brackets often exert a large
force on the web plate that can distort the web and increase the magnitude of the plate imperfection. Global stability problems
have occurred primarily on bridge widening projects where a few girders are added to an existing bridge system. The girders in
the widening are usually isolated from the existing bridge and the unbalanced load from the overhang can cause excessive twist
that intensifies the global stability of the girder system.
The objective of this study was to improve the understanding of the bridge behavior due to the unbalanced loading from
the overhangs and to identify critical factors affecting the girder behavior. The study was also aimed at developing simple design
methodologies and design recommendations for overhang construction. The research included field monitoring, laboratory tests,
and parametric finite element analyses. The data from the field monitoring and laboratory tests were used to validate finite
element models for both concrete and steel girder bridges. Based on the validated models, detailed parametric studies were
conducted to investigate the effects of the unbalanced loading. Results from the parametric studies were used to identify the
geometries of girder systems that are prone to problems with the overhangs as well as to provide design suggestions. In addition,
a closed-form solution for lateral rotation in the fascia girder in a concrete girder bridge was derived using a rigid-body model,
and was used to develop design methodology and design recommendations for overhang construction.
-
Format:
-
Funding:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type:
