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Bridge Widenings | Steel-Reinforced
Elastomeric Bearings
Design
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Terminology and Notation. LRFD refers to Load and Resistance Factor
Design, a design methodology that makes use of load factors and resistance
factors based on the known variability of applied loads and material properties.
Bracketed <references> reference relevant sections of the AASHTO LRFD Bridge
Design Specifications.
Load Factors. TxDOT recommends the
following permanent loads <Article 3.5>: The
engineer may reduce the maximum load factor
for wearing surfaces and utilities <DW in
Table 3.4.1-2> to 1.25.
Bridge Widenings
Slab spans can be widened with slab spans. Skewed slabs with main reinforcing
perpendicular to the bents will be weak if the edge beam is removed under
traffic. The edge should be shored under this condition. Alternatively, dowels
can be grouted into the existing slab edge and the widening placed with
reinforcing parallel to the centerline of the roadway. Curbs may be removed
after the new slab has cured.
Concrete girder spans can be widened with concrete girders, prestressed
beams, prestressed box beams, or double-tee beams. Prestressed beams are
recommended. Box beams may be used if depth is an issue.
Pan form girders can be widened with pan forms, prestressed box beams, or
double tee beams. Pan forms are recommended. Alternates using double-tee beams
may be appropriate for certain situations.
Steel I-beam spans can be widened with prestressed beams or steel I beams.
Prestressed beams are recommended. Steel I beams may be used if depth, framing,
or aesthetics is an issue.
Continuous steel I-beam units can be widened with prestressed beams or steel
I beams. Simple-span prestressed beams with the slab continuous are recommended.
The slab should have standard reinforcing and be tied to the existing slab.
Cantilever/drop-in steel I-beam units can be widened with prestressed beams
or continuous steel I beams. Simple-span prestressed beams are recommended with
expansion joints over the bents connected by longitudinal open joints to the
existing expansion joint at the notches.
Continuous steel plate girder units can be widened with continuous steel
plate girders or with prestressed beams if the span is 140 ft. or less.
Prestressed concrete beam spans and units should be widened in kind.
Steel-Reinforced Elastomeric Bearings for Prestressed Concrete Beams
Geometric Constraints – Rectangular pads are
preferred over round pads, which make it harder to satisfy rotation.
Structural Analysis – Expanding length of
prestressed concrete beam units can be taken as 1/2 total unit length.
For highly skewed bridges and very wide bridges, take expanding length
on a diagonal between slab corners to obtain the most unfavorable
expansion length.
Design Criteria – For Design Method A in
<Article 14.7.6>, shape factor S is preferred to be between 10 and 12.
Design Resources
For additional information on LRFD bridge design as implemented by TxDOT, consult the following resources:
Feedback
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bridge design policy and recommendations.
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