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(electronic tones)

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- [Narrator] Lean-on bracing
applications are being used

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at a greater rate in steel bridge systems.

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This has highlighted a
need for improved rules

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of configuration and design expressions.

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The Center for Transportation Research,

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the Texas A&M Transportation Institute,

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and the Texas Department of Transportation

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monitored a recently designed bridge

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with lean-on bracing to
come up with guidelines

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for bracing design and
improve accuracy in stiffness

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and strength components.

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- If you've ever gone
underneath a steel bridge,

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you may have noticed these Xs underneath,

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steel cross frames underneath.

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The function of those is for stability,

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primarily during construction,

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to keep the girders from buckling.

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However, because they're
these cross frames

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and they're welded together
and they're hard to fit up,

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they look small as compared to a bridge,

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but compared to a man
trying to put it up there,

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they're quite heavy.

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So this lean-on bracing concept

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removes a lot of the diagonals,

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simplifying the construction
and fabrication dramatically.

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However, the cross frames
that you were removing

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were doing something before.

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So now there has to be
a new design methodology

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to make sure that the cross
frames that you do have

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are sized appropriately

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and then also placed throughout
the structure appropriately

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so that you still have the
stability that you need.

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- What happens with cross
frames and diaphragms

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is that there are regions

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where there's usually
concerns about fatigue.

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And also, when we have
cross frames and diaphragms,

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they usually represent one of
the most expensive components

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on a per pound basis

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because there's lots of
fabrication associated with them.

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So in lean-on bracing,
what we did 20 years ago

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is we developed a concept

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where we were able to
selectively go into a bridge

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and eliminate some of
these full cross frames,

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and instead, just make use
of some much more simple,

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we call them lean on struts,

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that allow several girders to
lean on a single cross frame.

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And while some of the
suggestions we had done

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and the systems we had
designed 20 years ago,

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they started to be
implemented into design.

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It was found that we
probably left too much of it

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for interpretation by a designer,

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where some designers
were having a hard time

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applying some of those concepts,

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and a number of questions came up.

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So to try to get in on
those design concepts

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we developed 20 years ago

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and really try to develop
some refined procedures

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that make it easier
for designers to apply,

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but also try to answer
some of the questions

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and so on that came up.
- The benefits of this project

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are really stem from the fact

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that cross frames are some of
the most expensive components

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on a steel bridge, though
they are obviously essential.

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They're difficult to fabricate,
difficult to install,

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they're also difficult to inspect,

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and can have trouble spots in them.

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So being able to safely reduce

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the number of these cross frames

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really leads to a more
economical structure,

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both in the short term and long term.

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- And then over the last six years,

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there have been some
applications where TxDOT

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has essentially utilized
these methods on the design

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of a few different bridges.

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One was up in Fort Worth, which
was a heavily skewed bridge,

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which is just a geometrical configuration

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that happens with the bridge.

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Then we had a bridge over the Brazos River

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that had normal support.

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So it's been used on a couple
of different geometries.

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So it's already starting
in implementation,

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but these concepts actually

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are seeing a lot more widespread usage,

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because the National Steel Bridge Alliance

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has been pushing these concepts,

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and there was a design guide

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that was based upon our
original work that was put out.

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So we're gonna start seeing
a lot more applications

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of these, not just within Texas,

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but actually around the country.

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- We plan to take the
findings of the report

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and put directly into our design guidance,

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so that engineers can use
it readily and quickly.

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- [Narrator] For more information

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and to find the publication
for this project,

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please visit the TxDOT research library

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at the link shown below.