Steel Pile Design 1

[BoydZander]

I'm designing some steel pipe piles, an H section may perhaps be used.

The piles will restrain some lateral load due to wind. I have obtained moments and shears from a program for an acceptable deflection.

My question is how do I evaluate the section for stresses.

IBC 2006 1809.3.2 Specifies that the Allowable axial stresses shall not exceed 35 percent of yield strength.

Is this telling me that the maximum stress

P/A + M/S < 0.35Fy

OR, is the required stress check one of pure axial less than 0.35Fy and the combinaiton of axial and flexure would be a more conventional flexural check?

P/A < 0.35Fy AND

P/A + M/S < .66Fy

OR

(P/A)/0.35Fy + (M/S)/0.66Fy < 1.0

Any responses would be most appreciated.

Thanks

Boyd

 

[miecz]

IBC 1809.3.2 merely requires that P/A < 0.35*F_y. IBC 1809 is mum on combined or bending stress limits. I'm not aware of any code or design guide that addresses combined or bending stress limits for steel piles.

 

[civilperson]

Piles are usually assumed to be continuously supported against bending by the soil. If your pile extends many feet above grade, then the combined axial and bending stresses must be checked for that portion with no soil.

 

[BoydZander]

The piles I'm working on extend down from the bottom of pile caps whose base is 5 feet below grade. They are completely braced by the soil.

Standard output for such a pile from LPile, AllPile etc will provide curves for shear and bending moments when a lateral load is applied to the head of the pile. These attenuate to zero at some point in the upper portion of the pile. However, the top portion of the pile does have bending moments applied to it. My expectation is that the steel member does have moment applied to it and in addressing this I would assume that the steel section should be sized such that flexural stresses from said moment are below some allowable stress limit.

Comments?

Boyd

 

[miecz]

Besides meeting the criteria above, I limit combined stresses to: f_a+f_b<0.6F_y. Would be interested to hear what others do.