×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*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.

Students Click Here

Jobs

Drilled Pier with Lateral Loads

Drilled Pier with Lateral Loads

Drilled Pier with Lateral Loads

(OP)
I am designing a drilled pier which supports one of those high mast lights at a weigh station along the interstate.  So, in addition to vertical load, I have a lateral load and moment at the top of the pier.  The Geotechnincal Report gives me a modulus of horizontal subgrade reaction, which varies with soil depth.

All of my design examples are "by hand," but I am doing this on RISA-3D.  So, I am asking for confirmation that I am approaching this correctly.  I model a vertical concrete pier, with horizontal springs off the side, which get stiffer as you go deeper.  For each spring stiffness, I multiply the modulus times the diameter of the pier times the spacing of the springs.

Am I missing something?

DaveAtkins

RE: Drilled Pier with Lateral Loads

DaveAtkins,

Sounds like you are on the right track. Ideally, you would have your geotech run LPILE, but there are other ways to skin that particular cat. I know that Ohio DOT gives specific guidance for the design of high-mast lighting foundations in Section 1100 of the Traffic Engineering Manual, available for download from http://www.dot.state.oh.us/drcc/

Good Luck.

Jeff

RE: Drilled Pier with Lateral Loads

Dave,
I designed several caissons with horizontal loads.  AASHTO recommends that the lateral capacity be design with COM624.  The program is available on the FHWA site as a free download, and there is also a thick manual that goes with it.  However, if you take that approach, I would recommend that you work with the geotechnical engineer for the soil input parameters with are very critical.  The program also includes reinforcement design parameters.

I also agree that your approach is in the right direction. However, the modulus of subgrade reaction is based on individual soil layers.  I would advise you work closely with the geotech engineer for when inputing those parameters - be clear as to the basis of the subgrade reaction.  

Good luck!

RE: Drilled Pier with Lateral Loads

DaveAtkins - I have done exactly what you describe, using RISA-2D however.  But Riggly's suggestion sounds interesting - you might try getting into that COM624 program and report back here what you think.

RE: Drilled Pier with Lateral Loads

I've compared COM624 (now LPile) results with a RISA-3D model, and with an old program called DCalc.  The results were quite similar.  For my RISA models, the spring constants increase linearly with depth, but are limited by the ultimate bearing capacity.  We usually ignore the first few feet of soil.

For more discussion on this, see thread256-164011: Lateral Loaded Piles - Modulus of Horizontal Subgrade Reaction.

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.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources