Glass Guardrail to Wood Joists

[bookowski]

How are the forces resolved for a guardrail on wood framing?

See attached sketch from an architect. This is an interior 'lightwell', i.e. a floor opening that allows you to see down to the next floor. It's a single family residence. The lightwell is about 6ft x 3ft in plan, i.e. longest span of the header/trimmer joists is about 6ft. until something frames in. The members are 9.5" LVL on each side of the opening. On one side there are joists framing into the 6ft. header @ 16" o.c., at the other two sides where joists are parallel I can add blocking (4th side is exterior wall, no rail).

My instinct is that this works, but not sure how to calc it. It's partially built but I can still add blocking in there. If I did that do you count on the sheathing, i.e. a tension/compression couple between the sheathing and blocking? Forces still seem pretty high when I check that.

 

[msquared48]

Looks like a force-couple applying a torque to the stringer(s) over the length if the stringer(s)to me.

Mike McCann
MMC Engineering

 

[bookowski]

Correct. What did that add to the question?

 

[SteelPE]

If you are concerned about the torsion, couldn't you apply blocking at each support location and than provide some sort of strap that wraps from the top flange of the blocking around the lvl and under the bottom flange of the blocking (something like an Simpson LSTA strap).

This is probably one of those details that happens all the time but nobody really cares about. Well, until some engineer in a powerhouse company delegates the design responsibility of the railing to others and then complains that he doesn't like my mathematics but he can't come up with anything better.

 

[msquared48]

I guess nothing...

I do not see this as a difficult problem with additional blocking and strapping, plus the lateral restraint of whatever the platform diaphragm is, which I do not know the details of, yet.

Mike McCann
MMC Engineering

 

[jdgengineer]

Several of the cities we work in require that we detail these connections specifically. Typically, we use a horizontal holdown to a joist or blocking (Simpson DTT2Z). See the PDF below for an idea.

http://www.strongtie.com/ftp/bulletins/t-grdrlpst10.pdf

Alternatively, we wrap a coil strap around the rim @ 4'-0" to take the torsion out, similar to as described above.

 

[bookowski]

jdg - That's a great product. I was thinking of creating something similar with straps as you said, but wasn't sure if there was a more common detail. Thanks.

 

[DBronson]

bookowski:

The attached publication walks you through the calcs for the glass standoffs.

Regards,
DB

Link