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RE: Open Web Joist reinforcement

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Randy:

Here are a few ideas to consider:

Reinforcing for moment is difficult, since the top chord usually is 
supporting a floor or roof deck and therefore accesiblity to the top chord 
is limited or non-existent. With this condition, try to install an 
intermediate support so as to reduce the bending moment. Another option is 
to add joists between the existing joists. If adding joists in an existing 
building, specify a field splice at mid-span or field install one of the 
end bearings. Also note that the joist designer shall design the new joists 
to span between the new rows of bridging as laterally unsupported or 
provide a special lateral support detail from the deck to continuously 
brace the joist. Consider different moments of inertia between existing and 
new and cambers.

Reinforcing web members depends upon the member configuration and stress 
level. Begin by checking the capacity of the end connections. This will 
give an indication as where the reinforcement has to terminate. Some 
examples follow:

To reinforce a single angle turned 45 degrees in compression, consider a 
pipe as a strongback, U-bolted to the angle at several locations. The angle 
has to carry the full stress in compression, but it buckles at a higher 
stress level since the pipe is bracing the angle.

2 angles designed for tension may sometimes be braced together to resist a 
stress reversal (compression).

A plate may be welded to double angles to increase the compressive strength 
of the section. If the plate needs to be carried into the connection, I 
will usually require that the plate be provided in 2 pieces. It shall be 
slotted at the each end to fit around and weld to the chords and the plate 
butt welded together at the center.


I hope this helps!

Jim K.




-----Original Message-----
From:	Randy Diviney [SMTP:rsdiviney(--nospam--at)hayeslarge.com]
Sent:	Monday, December 03, 2001 2:08 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Open Web Joist reinforcement

What are some methods that could be used to reinforce existing long span 
joists for both shear and moment? I looked for a design guide and searched 
the Internet but have come up with nothing.



TIA

<bold><italic><color><param>8080,0000,0000</param>




</color></italic></bold><italic>Randal S. Diviney P.E.

Director of Structural Engineering

Hayes Large Architects

(814)946-0451</italic>

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