Drilled pier allowable lateral

[haynewp]

IBC has the following limit on lateral loads on drilled piers. But is there any limit for lateral induced moment transferred from a fixed base column directly into the top of a pier?

1808.2.9.3 Allowable lateral load.
"Where required by the design, the lateral load capacity of a pier, a single pile or a pile group shall be determined by an approved method of analysis or by lateral load tests to at least twice the proposed design working load. The resulting allowable load shall not be more than one-half of that test load that produces a gross lateral movement of 1 inch (25 mm) at the ground surface."

 

[FixedEarth]

If I understand you correctly, are you saying you have a drilled pier with fixed head condition? If you assume you have a "fixed head" condition, then you can only take shear load (moment = 0 in a fixed head condition) and use beam on elastic equations to get your appropriate embedment depth. Alternatively you can use the constrained formula in IBC to get your embedment length.

Since it is hard to obtain a true fixity, it may be more conservative, to assume a "free head" condition. With this assumption, you can take shear and moment from the column and apply it to the pier head by using beam on elastic equations. You will get larger induce moment and larger top of pier head deflection by using a "free head" condition.

The only limit for lateral induced moment is based on your top of pier head condition (fixed head or free head).

 

[haynewp]

It's a free headed pier, just a large concrete column doweled directly into the pier, no cap.

Do geotechs a normally give a range of combined allowable lateral moments and shears that would cause 1/2" head deflection (for example)or just shears? I have only received allowable shears from the geotech for this project.

 

[FixedEarth]

For commercial jobs or taller wall projects founded on drilled piers, yes we give shear, moment, and deflection once we are given the structural loads and fixity condition. However, for residence and shorter walls, we only provide skin friction, passive earth resistance and lateral subgrade modulus values. This practice may vary based on firm size and location.

If you have access to Roark's Formulas and Bowles Foundation Analysis & Design book, you can set up your own spreadsheet in few hours. The geotechnical inputs are very minimal.