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Re: Joist Modification

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Jonathan,

       You didn't say anything about code compliance.  If someone added loading to existing joists, as seems to be the case, the entire joist may be overloaded.  You will need to check this out.

        Assuming this is not the case why not try to make use of the steel you already have?  I think I would approach the problem as follows:

1.)    Jack (shore) the joists as required to provide the necessary camber.

2.)    Install side A of a new double L bottom chord (Ls back to back with the existing web members in between) at the required level (8" above the existing bottom chord).  Install additional web members as required to create the proper bottom chord panel points necessary to eliminate bending due to joint eccentricity in the bottom chord.

3.)    Install side B of the new double angle bottom chord on the opposite side of the joist.  The existing and new chords should be tied together and I would prefer bending or cutting and splicing the NEW chord rather than the existing chord.

4.) You probably have to reinforce the top chord and possibly (but not necessarily) the web members also.

        I hope this is helpful.

Regards,

H. Daryl Richardson

"Meyer, Jonathan" wrote:

 

I have encountered a situation where a joist bottom chord prevents proper head room clearance. The joists (24LH 09 - Bottom of metal deck ~30' AFF) are in a controlled atmosphere building built in the 60's. A platform was installed to provide a means of egress from the upper walkways in the building. This platform is partially hung from the roof steel and supported by the existing columns and the exterior tilt-up wall panels. Joists span 45 feet and support the roof (EPDM, insul & metal deck). As fate would have it there is only 6'-0" clear below the joist to the platform (min required is 6'-8") One suggestion is to weld a beam to the bottom of the top chord for a distance of 8 feet at the end of the joist. Then  cut the joist bottom chord and attach it via members sloped to tie into the bottom flange of the beam and the bottom chord of the joist. The webs would also be modified to attach to the beam.

I have never tried such a modification nor seen one like this, which leads me to believe that it has rarely (if ever) been done. I am not enthusiastic about such a modification, but I would like to ask if anyone has ever designed anything similar or seen such an animal. If so I would appreciate your input. If anyone has any suggestions for modifying the end of a joist I would also be interested in hearing them. Thanks for any advice that you may provide.

Jon Meyer
Webber Smith Associates
Lancaster, PA