LRFD Gravity Wall Design

[dfranks]

Has anyone started working with the LRFD code to do simple gravity wall designs? In my work so far it appears that eccentricity checks and bearing capacity checks come out similar to previous design methodologies, but I am running into some issues with sliding. Is anyone else finding it necessary to add foundation keys to stabilize their walls?

 

[MIBridgeEng]

Yes, I've found that sliding is a huge issue with LRFD. The deadload of the wall (which helps create friction) has a small load factor (like 0.9), but the horizontal earth presures have a pretty high load factor like 1.5. It creates a "perfect storm". I've had better luck with spreadfooting retaining walls than with pile supported retaining walls. For pile supported retaining walls, it is simply very difficult to get enough reaction on the toe piles (presummably battered) for their horizontal component reaction to resist the horizontal forces. I truely believe AASHTO has more work to do to re-calibrate the load factors.....probably won't happen in my lifetime....

 

[FiniteElemet]

Here is the program to design wingwall using LRFD. Need MathCAD to run the app.

https://www.nysdot.gov/divisions/engineering/structures/design/design-analysis-programs

 

[FiniteElemet]

Sliding will always be issue using LRFD. LRFD always require bigger section and this is the reason why contractors try to avoid LRFD specially during these times when they are realizing bigger sections on already bid jobs.

 

[VoyageofDiscovery]

FoS should be 1.0

 

[dfranks]

VoyageofDiscovery:

I don't follow you.

Are you saying that MIBridgeEng and I are using the wrong factors?

Please elaborate.

 

[VoyageofDiscovery]

I assumed you were accustomed to FoS = 1.5 for sliding with WSD.

Basically the resulting factored resistance should be at least equal to the factored base shear force.