Retro-fit of Roof Rafters - Bearing Seat Reinforcing

[PSUEng11]

Good afternoon everyone,

I am working on a small project and thought I might run a question by everyone. Basically what had been going on was that a previous homeowner had cut a 6 foot section out of the bottom chord of the second and third roof trusses near the front bearing support to allow standing room on an elevated platform in their carport. We were initially going to just repair the trusses to their original integrity and layout essentially. However, the current homeowner wanted the space to be left open. Our next option was to essentially ignore the two cut trusses and retrofit new 2x8 rafter on both sides of each truss top chord with new 2x10 collar ties, located in the lower third of the roof height. The existing trusses have 2x4 top chords,roughly have a 5:12 slope, are spaced 24" oc, and a span of approximately 30 feet.

The question that I have really pertains to the bearing seat of the new 2x8 rafters. You could end up with a level cut that projects beyond the inside face of the front and rear bearing supports or you could end up with a sort of reverse birds mouth with the cut being on the interior face of the bearing support, which doesn't really leave a good bit of room for a hanger either. Either way I am not sure how to go about designing the rafter ends or reinforcing of the bearing seats to prevent any possible splitting due to reduced section area. Does anyone have any experience with this?

Thank you for your time and help,

PSUeng

 

[woodman88]

I do not think the trusses will work at the location of the forces you need to transfer to it.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[a2mfk]

sketch of what you are talking about would help

 

[PSUEng11]

a2mfk, please see the attached sketch.

 

[PSUEng11]

a2mfk, I apologize. I have never had to upload a file before to eng-tips, but that does not seem to be working. Is there a better way to do that?

Thank you for your time and help,

PSUeng

 

[asixth]

I would like to see the sketch too. I don't think cutting the bottom chord is a good idea and would not like to see how that portion of the roof would perform if it was subject to it's design loading, whether it be wind or snow.

There should be a link next to the attachments which says "upload to engineering.com". If you click on that, upload your file it will then ask if you would like to insert in into the thread after it finishes loading.