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# Re: Base plate design forces in SDC D

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Base plate design forces in SDC D
• From: Tom.Hunt(--nospam--at)fluor.com
• Date: Thu, 7 Jan 2010 15:20:52 -0800

Ravi,

Some quick thoughts.  Unless your piperack is over 65 feet tall I would use an OMF with R = 3.5 (see footnote c) for the transverse direction and an OCBF with R = 3.25 (see footnote b) in the longitudinal direction.  Typically the R = 1.0 for connection design is one method of complying with the code where you are allowed to design for "The maximum load effect, indicated by analysis that can be transferred to the ....".  The thought being that the largest load that can be transferred by the system is the largest load that can be delivered to the structure (i.e. the largest seismic load being R = 1.0).

Thomas Hunt, S.E.
Fluor

"Vasu, Ravi" <Ravi.Vasu(--nospam--at)jacobs.com>
01/07/2010 01:14 PM
 To cc Subject Base plate design forces in SDC D

List,

I am designing a Piperack(R = 2.5) base plate & Anchor bolt in SDC 'D'.  Per AISC 341-05, section 8.5(given below), I am getting very large design forces

I am not sure whether this is the general procedure, other engineers follow.

Section 8.5 a.  - AXIAL FORCE

Need to follow section 8.3, that is, the force should be lesser of the following:

b.  1.1Ry*(Area of column)

Section 8.5 b.  - SHEAR

The critical force should be lesser of the following:

b.  1.1Ry*(Area of column)/H.

H = Height above & below of the column considered.

Section 8.5 c.  - Flexural Strength  (for column fixed base?)

The critical force should be lesser of the following:

b.  1.1/1.5Ry*(Fy * Zx)

Per discussion with AISC, I am using R = 1 for beam moment connection & comparing with 1.1RyFy*Z (design per AISC design guide # 4) to get the design force.

I think for other connections(base plate/anchor bolt/bracing) also,  using R =1  gives big forces but not as huge as section 8.5.

Can you pl. give any input in this design forces?

Thanks

Ravi Vasu

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