×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Bearing Capacity of a Pier and Pad Foundation.

## Bearing Capacity of a Pier and Pad Foundation.

(OP)
Does skin friction of the pad come into play increasing bearing capacity? Can we add the skin friction provided the sides of the pad to the bearing capacity of the foundation?

### RE: Bearing Capacity of a Pier and Pad Foundation.

NO. You can't predict what might be the situation in years to come.

### RE: Bearing Capacity of a Pier and Pad Foundation.

Beyond the uncertainty with future excavations, there is the work by O'Neill and Reese for drilled shafts. Their research indicated that the mobilization of skin friction 'shearing' along the sides occurred at much smaller displacements than the end bearing. Therefore, when the full bearing capacity is reached, the side friction has already experienced too much movement to retain its full friction value. There's interaction equations from their work now included in the AASHTO bridge design spec, but we have not bothered to use them since the first time we went through the arduous calculations, only to get a result that gained us almost nothing (we were able to utilize about 5% of the skin friction with the full bearing and vice versa).

You're supposed to ignore skin friction near the bottom anyway (in the case of drilled shafts, 2 diameters), due to the 'downdrag' effect of the bearing load on the surrounding soil. I don't know about how your geotech info was presented, but what we get is adjusted based on the size of the footing to account for that effect.

In short, OG's response of a flat "NO" is correct, but for more reasons than just uncertainty about future conditions.

### RE: Bearing Capacity of a Pier and Pad Foundation.

We typically only use skin friction for drilled piers, not pad footings.

### RE: Bearing Capacity of a Pier and Pad Foundation.

OG is right..it would not be accepted engineering practice to consider it. Also have a think too about the interface friction. If, just if, you were to consider it...some pads are constructed without any formwork so concrete is cast directly adjacent to the soil. That would provide some degree of interaction. However, some pads are cast against timber formwork with backfilled after striking of formwork. This would likely provide less interaction as the material may not be properly compacted against the pad.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!