Texas Department of Transportation (TxDOT) is currently designing its highway
bridge structures using the AASHTO Standard Specifications for Highway Bridges, and
it is expected that TxDOT will make transition to the use of the AASHTO LRFD Bridge
Design Specifications before 2007. The objectives of this portion of the study are to
evaluate the current LRFD Specifications to assess the calibration of the code with
respect to typical Texas U54 bridge girders, to perform a critical review of the major
changes when transitioning to LRFD design, and to recommend guidelines to assist
TxDOT in implementing the LRFD Specifications. This study focused only on the
service and ultimate limit states and additional limit states were not evaluated.
The available literature was reviewed to document the background research
relevant to the development of the LRFD Specifications, such that it can aid in meeting
the research objectives. Two detailed design examples, for Texas U54 beams using the
LRFD and Standard Specifications, were developed as a reference for TxDOT bridge
design engineers. A parametric study was conducted for Texas U54 beams to perform an
in-depth analysis of the differences between designs using both specifications. Major
parameters considered in the parametric study included span length, girder spacing,
strand diameter and skew angle. Based on the parametric study supplemented by the
literature review, several conclusions were drawn and recommendations were made. The
most crucial design issues were significantly restrictive debonding percentages and the
limitations of approximate method of load distribution.The current LRFD provisions of debonding percentage of 25 percent per section
and 40 percent per row will pose serious restrictions on the design of Texas U54 bridges.
This will limit the span capability for the designs incorporating normal strength
concretes. Based on previous research and successful past practice by TxDOT, it was
recommended that up to 75% of the strands may be debonded, if certain conditions are
met.
The provisions given in the LRFD Specifications for the approximate load
distribution are subject to certain limitations of span length, edge distance parameter (de)
and number of beams. If these limitations are violated, the actual load distribution should
be determined by refined analysis methods. During the parametric study, several of these
limitations were found to be restrictive for typical Texas U54 beam bridges. Two cases
with span lengths of 140 ft. and 150 ft., and a 60 degree skew were investigated by
grillage analysis method.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3096 |
| Date | 12 April 2006 |
| Creators | Adnan, Mohsin |
| Contributors | Hueste, Mary Beth D., B., Keating , Peter |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 2505737 bytes, electronic, application/pdf, born digital |
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