TJI End Reaction 2

[mark1234]

I am trying to determine the design assumptions which limit the end reactions on a TJI joist.

The confusion for me lies when comparing intermediate allowable reactions and end reactions.

TIA

 

[JAE]

I think the difference is that at the ends, you have a terminated web end that can buckle more easily than within the span.

 

[mark1234]

JAE,

Would you happen to know the design check for this?

Out of curiousity, I just ran a continuous joist with point load near the end (using TJ-Beam). As end bearing the joist failed in end reaction. I then assumed 2x4 support wall and cantilevered the joist 2" over and the joist worked fine.

This little experiment in this case is going to save $8,000 on my project.

 

[JAE]

I don't know the formulaic check - attached is a Georgia Pacific Data Sheet what includes end bearings along with notes about bearing lengths, end/intermediate reactions, and what to do about them.

 

[mark1234]

Thanks JAE,

The notes for end reaction made much more sense to me. The note saying for 4" Bearing or greater set the end reaction to max. shear.

I have another reason for this post. I am sure others have encountered what I have regarding floor systems being redesigned by lumber suppliers. In a nutshell I have had numerous times where our design would be scrutinized and redesigned by the supplier. This last time was a set of shop drawings with TJI doubled in lieu of singles. The response from the supplier was our design was flawed and their program told them doubles were required. I requested the calcs and reviewed.

1) End bearing input was 3" with a rimboard (1.88" Effective). Joists bear on 2X8 plate.
2) Higher loads then required.

Using their loads and the cantilever approach I mentioned the joists work within their software. Using the intended loads the joists work either way.

I feel this is a problem in our industry regarding the suppliers of trusses, joists, etc. designing buildings using software they do not understand and with limited engineering knowledge.

 

[RARWOOD]

I raised a similair question in the past with LP. The answer was very involved, so I concluded it was easier to just follow the guidelines and limitations listed in their catalog.

 

[haynewp]

There is a lot of information here on bearing design and stiffeners.

http://www.i-joist.org/pdf/Asd_ij.pdf