Rowe's Moment Reduction
Rowe's Moment Reduction
(OP)
For anybody that replies to my previous questions, the wall is anchored only one tier towards the top and is a 30 foot excavation. Piles are embedded 22 feet.
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RE: Rowe's Moment Reduction
RE: Rowe's Moment Reduction
RE: Rowe's Moment Reduction
RE: Rowe's Moment Reduction
I would still look at drilled in anchors. If you need to shorten the anchors, multi stage anchors can give you a desired capacity in a much shorter length than the traditional drilled in anchors.
RE: Rowe's Moment Reduction
RE: Rowe's Moment Reduction
We are around 15 kps/ft. We're using a continuous block and have it back far enough with anchors every other pile to a waler. We want to avoid drilling for cost purposes. We're trenching, installing PVC sleeves and pushing the anchors through later.
Yes, this is only temporary to remove 1/2 of a bridge's abutments. Logistically, this is the way the contractor wanted to go. Dollars!
One more question if you don't mind. Would one apply the active earth pressure below the dredge line to the pile flange width or the effective passive resistance width (3 Bf)?
Thank you.
RE: Rowe's Moment Reduction
HOWEVER, I believe that the newer LRFD AASHTO may not say the same thing. Somewhere, for no apparent reasons, AASHTO "fixed" something that wasn't broken.
RE: Rowe's Moment Reduction
Thanks for the useful insight.
Its much more than a 10% reduction I beleive because the active wedge above the embedded portion is calculated using the height of excavation as opposed to the passive resistance which is based on only embedement depth. Would you concur?
Thanks again.
RE: Rowe's Moment Reduction
Another thing - when designing by hand calculations, it has been very common for many, many years to assume a hinge at subgrade, find the "ground reaction", and then calculate a passive depth with a safety factor. When computers came along, the programs didn't assume a hinge at subgrade and automatically solved for the embedment depth. When a program solves for the embedment depth, you get larger soldier beam bending moments and sometimes longer embedment lengths. This results in a more conservative design. Don't be afraid to assume a hinge at subgrade and then solve by hand for the required embedment depth. This could help you greatly with the design you are now doing.
RE: Rowe's Moment Reduction
RE: Rowe's Moment Reduction
The following results for this 32.6 foot deep excavation with piles at 3'-8" oc(also 3B) are as follows:
Embedment: 15'
Pile: W14x120
Anchor Load: 13.2 kips/foot.(located 5 feet below grade)
Does this embedment seem reasonable now?
Thanks
RE: Rowe's Moment Reduction
AASHTO and PADOT's design manuals do show 3b on back of the toe. If you look at the equations for the actiove and passive pfrces, you can derive each one except the active one with the 3b. I spoke to Jerry Dimaggio of FHWA about this active 3b being a mistake. He told me it was wrong but that I should be using the LRFD method for sheeting design. So, in the end, he wasn't much help and basically ignored the problem. I never uses anything more than b on the back of the soldier beam toe, and only for permanent walls or sheet pile walls.
Re run your design with a hinge at subgrade. You will get even better results. Are you using any particular sheeting design program?
Where is ground water? Are you using buoyant weight below subgrade? Does your 15' toe include any safety factor? 15' doesn't sound too bad for a one-tier system with the tie so high. Who established deflection criteria? Are you supporting any critical utilities or structures - or just roadway traffic?
RE: Rowe's Moment Reduction
RE: Rowe's Moment Reduction
I like the hinged pile at subgrade approach. I will try it. Also, ground water is at excavtion bottom and yes, I am including bouyant weight. Just supporting roadway traffic. What do you think?
RE: Rowe's Moment Reduction
Are you running the calcs by hand or are you using a computer program? If so, which program?
Very rarely does anyone use FE analysis to design sheeting walls. Specialty contractors who design and build earth retention systems almost never use FE analysis.