Micropile, bending allowable stress
Micropile, bending allowable stress
(OP)
Hi everyone,
I am designing a foundation consisting of micropiles (10" OD steel casing, filled w/ grout). Since my design assumes a fixed-head, i have to design the micropile for max fixed head moment. I am having difficulty to find what is the allowable bending stress specifically for micropiles. I know that AISC ASD allows 0.66Fy (lateraly supported "column"). Please include any references with your response.
Thank you
I am designing a foundation consisting of micropiles (10" OD steel casing, filled w/ grout). Since my design assumes a fixed-head, i have to design the micropile for max fixed head moment. I am having difficulty to find what is the allowable bending stress specifically for micropiles. I know that AISC ASD allows 0.66Fy (lateraly supported "column"). Please include any references with your response.
Thank you





RE: Micropile, bending allowable stress
We usually specify micropiles based on the local geotechnical report, where vertical and lateral load resistances are given. The report gives the bending capacity as well sometimes, but it is very small.
Apparently, you're considering the casing steel for the bending. I don't know how you consider the moment transfer at the interface between the tube and the pilecap. Do you have reliable anchorage?
If your foundation is supported by a group of micropiles, why not just consider they are pinned?
RE: Micropile, bending allowable stress
The reason why it was considered a fixed head connection was that more latteral capacity can be achieved from the micropiles. Micropiles are emeded 20" in pile cap and i have checked that there is enough embedement to transfer the moment. What i am having trouble with is qualifying the casing for a full axial and moment load. If i could use higher allowable than 0.5Fy i would be in a better shape.
To clarify: geotechnical capacity of micropiles is adequate, structural capacity is not that satisfactory.
RE: Micropile, bending allowable stress
In addition, is battered piling feasible for your case?
RE: Micropile, bending allowable stress
AISC LRFD is mostly for building members (above surface), which is not the case for micropiles. Micropiles could be demaged during driving or rusted after some time, and keep in mind that inspection and accessebility are very limited in the case of foundation.
RE: Micropile, bending allowable stress