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Re: Precast Concrete C-shaped Joists

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Joel:
 
The proper way to assess the safe capacity of an undocumented concrete structure is by conducting a load test.  Paul and I have overseen several such tests.  The specifications are quite explicit.  You will find them in the back of ACI 318.  If you want to discuss this, just call me.
 
Stan

On Wed, May 26, 2010 at 9:49 AM, Adair, Joel <jadair(--nospam--at)shwgroup.com> wrote:

Correction to below:  “…one of four numbers: 9.060, 9.070…”

 

Sorry about the typo.

 

-- Joel

 

From: Adair, Joel [mailto:jadair(--nospam--at)shwgroup.com]
Sent: Wednesday, May 26, 2010 9:24 AM


To: seaint(--nospam--at)seaint.org
Subject: Precast Concrete C-shaped Joists

 

Hi, Everyone –

 

I’m trying to determine the load capacity of the floor of a building designed in 1970.  This is a ground floor structural slab with a crawl space below it.  The drawings indicate that the floor is constructed of precast “C”-shaped joists, sitting on pier-supported grade beams, with a 2”-3” topping slab.  The “C”-shaped joists are like double-T’s without any wings, and are laid next to each other, then topped.  It is unknown whether they’re prestressed.  From the details, it is clear that they are two different depths – 9” and 12”.  On plan, they’re called out as “Precast reinforced concrete joist X.XXX 2’-0” wide fillers cast as required” (plus additional information about the thickness and reinforcement of the topping slab).  The “X.XXX” in the callout is one of four numbers: 0.060, 9.070, 12.070, or 12.080.  Obviously, the 9 or 12 is the depth.  I’m having a hard time figuring out the “.060”, “.070” or “.080”, though.  Might this indicate the capacity in some way?  There aren’t any general notes or plan notes that would provide any other direction to the precast designer regarding loading, so it seems that these numbers must indicate design capacity somehow.

 

If anybody has experience with this type of a floor system, I’d really appreciate any help you could provide.

 

Thanks.

 

-- Joel

 

Joel Adair, P.E.

SHW Group

Plano, Texas

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NOTICE:
This e-mail transmission is intended only for the use of the individual or entity named above and may contain information that is confidential, privileged, and/or exempt from disclosure under applicable law. If you are not the intended recipient, you are hereby notified that any review, disclosure, copying, distribution, or other use of any of the information contained in this transmission is strictly prohibited. If you have received this transmission in error, please immediately notify the sender by e-mail at the above address and delete it from your computer system; you should not copy the message or disclose its contents to anyone. The content of the message and or attachments may not reflect the view and opinions of the originating company or any party it is representing.