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Re: Load Capacity of a Holddown Post as a Compression Member

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Nels,

        If it qualifies as a "long" column you can use the differential form of the Euler column formula to determine the critical load.  I've done it before but not recently and not for this specific load case.  It requires calculus to solve the basic differential equation and it's a bit messy.  It takes about three pages per load case.

        My reference for the above is "Elements of Strength of Materials" by Timoshenko and MacCullough, Third Edition, Thirteenth Printing, page 288.

        Alternatively, you might try dividing your column into ten or twenty shorter elements and apply your vertical load plus a small horizontal distributed load and solve using a computer analysis with P-delta turned on.  As you increase the vertical load I THINK  you will reach a critical load beyond which the horizontal deflections increase radically and/or you get error messages.

        You must apply your own safety factors to both solutions.

        If this is an important structure I think I would try both of he above.  I personally distrust computer solutions (not the computers, the programmers).  I think relying blindly on computer solutions that you haven't tested is equivalent to signing another engineer's work without knowing exactly how he did it.

Regards,

H. Daryl Richardson

"Nels Roselund, SE" wrote:

Is there a rational way to determine the design capacity of a compression member in which the applied load increases linearly along its length from zero at one end to a maximum at the other end, as for a shearwall holddown post.at the end of a shear wall?  I assume that the capacity would be greater than if the load is applied in end bearing each end. Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net