H-Piles bearing on bedrock

[8vb76]

I have a project in Piedmont geology in Virginia (bedrock is schist/gneiss) where I'm recommending that steel (grade 50) H-Piles be founded on bedrock (some in groups of up to 4 piles/cap). The schist/gneiss bedrock is of relatively good quality (generally above 60% RQD). IBC 2003 indicates that allowable axial stresses on steel piles should not exceed 35% of the steel yield strength. Where justified, axial stress is permitted to be increased above 35% but not greater than 50%.

Questions for both you geotech & structural folks out there:

1) Is it excessive to design an H-Pile group based on let's say, 45% of yield stress?

2) If dynamic testing is to be used to confirm drivability criteria and capacity, should I expect a PDA device to be able confirm a pile capacity on the order of about 300-350 tons?

H-Piles are unfortunately relatively new to me. Thanks for any help in advance!

 

[Qshake]

As a structural engineer, I can't say that I've ever seen allowable stress exceed say 11,000 psi. Most are governed by 9,000 psi or 0.25Fy. In some cases with really bad rock or karst area I've seen 6,000 psi.

I hope this helps.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[DRC1]

Skyline Steel's website,

http://www.skylinesteel.com/products/h_pile/default.aspx

has their piling handbook online. Bring your favorite unit converter because it is metric. Curl up by the fire with this baby and you will know more than you ever wanted about sheet piles and H piles. The following quote may shed some light on your question:

"It should however be noted that traditional load capacity tables
were based on a working stress of 30% of the yield strength of
the steel to give a factor of safety of 2 on the load and some
additional capacity to prevent damage should the driving stresses
increase. When driving piles through relatively soft soils onto rock,
a working stress of 50% of the yield strength of the steel could be
adopted giving a factor of safety of 2 on the applied loading. The
tabulated values below need to be factored to give comparable
load capacities for the various pile sections.

The ability of the rock on which the pile is founded to withstand
the foundation loads must be determined by establishing the
compressive strength of the strata (MPa) from site investigation."