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, the actual girder
behavior is not well understood due to the variability in the girder loading that the overhang
exerts on the fascia girder. Construction of the overhang is accomplished using cantilever
brackets that support the construction loads that include the weights of the formwork, freshly
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placed concrete, and the screed. The overhang brackets are connected to the top of the fascia
girder and react against the side of these girders. Due to the eccentricity of the overhang, a
torsional load is applied to the fascia girder. The forces from the overhang brackets can cause
girder deformations that are not well understood in either concrete or steel bridge systems. In
concrete girder systems the overhangs often cause rotation in the fascia girders that are locked
into the bridge system once the concrete bridge deck cures. In addition to locking this
undesirable rotation into the girders, there are safety concerns with regard to the potential for
dropping the formwork between the adjacent girders due to excessive twist of the fascia girder.
In steel girder systems, the overhang brackets can cause problems with the local and global
stability of the girders. In some bridge widening projects, the torsional loading from the brackets
coupled with the relatively large length-to-width ratio of the widening have led to systems that
were dangerously close to failure. In addition, in many instances the overhang brackets exert large concentrated forces on the webs of the steel girders.
This research investigation focuses on improving the understanding of bridge behavior as a result
of the loading from overhangs. Critical scenarios for the layouts and geometries of the overhang
brackets will be identified. The products of the research study include a design methodology for
overhang design as well as recommended details for construction bracing that can minimize
undesirable deformations in both concrete and steel girder systems. The work will be
accomplished through a combination of field investigations, laboratory testing, and parametric
finite element work.