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Truck Live Load- Exterior Girder Design

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KMA

KMA

Structural
Feb 19, 2003
17
For bridge design with prestress concrete girders and slab deck..I have an exterior girder carrying sidewalk that is protected from roadway traffic with conc barrier. This is what I would call a barrier protected (or unmountable curb). Regardless of the sidewalk being protected from vehicle traffic, it still resists truck load, right? As per the definition of LLDF, lateral distribution will occur.
Why do we use the terms mountable and unmountable curbs for bridge design? Somewhere a truck load is always being distributed....If the sidewalk were not protected and did not by definition have a sloped (mountable) curb, I would still consider a 6" curb mountable. Is this evaluation incorrect?
 
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AASHTO Standard Specs 3.23.2.3.1.4 states that an exterior stringer must have the same carrying capacity as an interior stringer.

6" curb is definitely mountable.
 
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The term "mountable" or "unmountable" is being used to describe if the vehicle could accidentaly mount the sidewalk. This accidental loading could lead to higher design forces in the exterior girder than these being used to size interior girder, due to typically cantilevered slab.
AASHTO 3.23.2.3.1.4, as pointed by Bridgebuster, states that exterior girder should have no less carrying capacity than inerior girder, but in some cases, with long cantilevered overhangs, it well could be than your design moments be higher than for interior girder.
 
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Wiktor,

I used to work with a fellow with the same name at firm in NYC (A&H Engineers).
 
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KMA,

The barrier work like it is state, do not allow the truck go to the walkway.

If the girder it is parallel to the ones on traffic lanes and using rigid transverse beam that don't allow the deck behave like a flexible deck.

The torsional behavior of the deck transfer the load to the external girder due the transverse beam nevertheless there are or not truck on it.

When checking the fraction of the loads have to take the max between analysis and codes.

I agree with wiktor about definition.
 
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The definitions are the same for subdivision design...

mountable curb = rounded curb

barrier curb = square curb can be 6 -8" high or check New Jersey Turnpike Barrier (NJ DOT for more info).

 
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