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- [Announcer] Deck haunches are commonly used
on both prestress concrete
and structural steel girder bridges.
The haunch is the area between the top of a bridge girder
and the bottom of the concrete deck
that helps maintain a uniform deck thickness.
A recently completed Center
for Transportation research project
conducted full scale laboratory testing
and developed computational models
on a wide range of haunch details
for both pre-stressed concrete
and structural steel girder bridges.
This work has resulted in guidelines for analyzing,
designing and detailing haunches, having different heights
and reinforcement detailing, improving the effectiveness
of current TxDOT detailing practices.
- The haunch is necessary to help keep the deck
and the beams acting together.
And so this research was all
about how we reinforce that haunch area to make it
so it all works together.
- The haunch is actually the connection, you know,
generally it's the region over the top flange or the top
of the girder to where it connects to the concrete slab.
And a lot of times we'll end up
having maybe an eight inch thick concrete slab
that we use for the bridge deck, but then
due to changes in geometry of the girders along the length,
a differential camber between adjacent girders.
A lot of times there'll be a a little bit thicker region
over the top of the girders.
Most standard haunches
in both steel and concrete bridges are usually
at the order of maybe zero to three inches.
In some cases where there might be an extreme geometry issue
with the bridge, some cross slope issues across the width
of the bridge, they may need to have a thicker haunch.
Some cases there'll be construction problems
that lead to where they have to have a much thicker haunch.
So when we talk about tall haunches here
or extreme haunches, we're talking about haunches
in the range of about five to 15 inches,
significantly higher
or larger than what we would use on a standard haunch.
A lot of times when this happens,
if it's a construction problem, the girders are up,
you know, the contractors trying to build the bridge,
we're trying to minimize the impact
on the traveling public,
but all of a sudden you have this problem
that needs to be fixed
and you have to kind of come up
with a detail that allows you to have this extreme haunch.
And there's some questions about how it impacts the strength
of a composite concrete or a composite steel girder
and that's what we were trying to focus on here.
This project, it was a relatively unique
in that a lot of times we'll
say there's a steel girder bridge project
or a concrete girder bridge project.
This considered both steel and concrete girders.
And in order to study the behavior,
we really needed to do some full scale testing.
Okay, when I say full scale,
I mean trying to test reasonable size girders
along with the geometry that would be existing
in these haunched regions.
So they consisted of,
I'll call them full scale laboratory test
doing what we call a push-out test
where even though we're simulating a girder,
we would actually do our tests
in a large frame where we subject large shear forces
between the simulated deck
and the simulated girders on them.
So we did extensive laboratory tests
on both steel and concrete, you know, girder systems.
And then we use that data to validate computer models
that allowed us to then look a little bit more
at the wider range of geometries using computational models.
- What we found, very interestingly,
is our current practice can be
expanded to deeper haunch levels
and with very minor modifications to our existing standards.
And then they also provided a bit more guidance
onto what other things we can do
that would achieve the same purpose.
- You get these problems in the field
and you want to have a solution, this is a relatively,
you know, common problem where things come up
and the geometries suddenly necessitate maybe
increasing the haunch above what you normally would have.
I think this research
provides a good solution to those problems
and hopefully trying to avoid, you know,
any delays and so on that that may end up
impacting the construction schedules.
- [Announcer] For more information
and to find the publication for this project,
please visit the TxDOT Research Library
at the link shown below.