Drilled Pier with Lateral Loads

[DaveAtkins]

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

 

[jdonville]

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

 

[Riggly]

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!

 

[JAE]

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.

 

[miecz]

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.