(upbeat music)
- [Instructor] Thanks to some of the latest research
from engineers with the Center for Transportation Research,
bridge designers can now build more economical structures.
As part of this project
a new analytical method was developed
that proves TxDOT bridge beams
have a higher load carrying capacity
than previously thought.
- So in our current analysis method
there's a provision in the spec
that limits the shear stress at our beam ends
and when we exceed this, the spec tells us
that we have to do a strut-and-tie analysis.
The strut-and-tie analysis is very calculation intensive.
So most designers opt to not do it
and just add in a beam line to reduce the shear stress.
So adding in this beam line adds cost to the project.
- If you can permit a higher level of shear stress
in a typical bridge design where the span lengths
are being pushed to their extremes,
you can actually eliminate a beam line.
And if you're eliminating a beam line in this bridge,
a beam line in the next bridge, and some other bridges
before you know it with those settings,
you can construct another bridge to serve communities
faster, better in the state of Texas.
- So what we did here is we had the researchers
look at the strut-and-tie models of all the beam ends
of all of our standard beams
and let us know when the strut-and-tie model
tells us that you can't go above a certain shear stress.
- We constructed a variety
of different strut-and-tie models
for different types of standard precast concrete builders
and we were able to change that limiting shear stress
from 18% to some cases
where we can go all way up to 25%,
in other cases greater than 18 but less than 25.
- This will help us reduce the number of beam lines
which will reduce the cost of projects
specifically on projects
where we're stretching the span limits.
- The result of this work can really be summarized
and has been summarized in a simple table
where a TxDOT will be able to better use
its precast concrete sections to their actual capacities
as opposed to the more conservative
way of handling this problem.
- This is a really early stage.
The research has just completed.
So we need to review it in house
and determine how we're going to implement it.
Right now the researchers have suggested
different stress limits for each individual beam.
So it's likely that we would combine them together
and make it a bit more simple.
- [Instructor] For more information
and to find the publications for this project
please visit the TxDOT Research Library
at the link shown below.