Guard Rail Detail

[radiocontrolhead]

Am I being unrealistic with my design here?

parameters:
-Handrail load = 200 lbs
-moment arm from hand rail to deck framing resultant = 5'-0"
-diaphragm capacity = 480 lbs (asd)
-distance between tension rods = 6"
-deck joist spacing = 16" o.c.

The biggest challenge was resolving the tension force into the deck diaphragm. The deck subframing for drainage has already been installed or a strap or B.N. from above would be considered.

Thanks all in advance.

 

[DaveAtkins]

You don't need two tension rods, just one. It is not reasonable to expect someone will pull inward on the guardrail.

DaveAtkins

 

[structSU10]

See attached bulletin from Simpson:

https://embed.widencdn.net/pdf/plus/ssttoolbox/mh8yhuxhda/T-C-GRDRLPST17.pdf?u=cjmyin

They have a statement that if inward force is required to be resisted, to add a tension tie at the bottom. Technically the codes states 200 LB. load in any direction.

I'm not sure why they state the detail they show is code compliant, yet also state the 200 LB. load is in any direction, and that you should add a tension tie if the force is inward...

 

[Ron]

Check compression of the wood member at the mounting plate. If sufficient to resist the force couple with tension rod in the center of the plate, you only need one rod. Looks like you have your mounting plate thicknesses backward. The one against the wood should be thicker than the perpendicular one or at least the same thickness. 3/4" seems a bit hefty for a guardrail mount.

 

[radiocontrolhead]

Ron and all,

I was able to reduce the design to (1) rows of rods in lieu of 2 rows by considering the bearing pressure of the plate against the wood.

Last question I have remaining: Is developing the rods back as shown the correct approach or am I misunderstanding the load path? Because access from above cannot be made, I've took tension force, in this case : 5'-0" x 200 lbs / Moment arm = T. Then I took T/Diaphragm shear capacity to determine development length req'd. I'm having a hard time terminating the rods just past the first block as my PM is suggesting.

Thanks all again.

 

[KootK]

..am I misunderstanding the load path?

Probably, I don't know if one space will be enough but the extent that you showed definitely caught my eye. I see the diaphragm development force just being 200 lbs and the moment getting resolved via up/down forces in the joists. Obviously, that means that you need some vertical connection between the blocking and the joists.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[radiocontrolhead]

200 lbs makes more sense as the diaphragm development force.

I mistakenly used the internal moment (block and guardrail baseplate) for external stability, which I have since addressed (attached).

Thank you all for the help and clarifications.

 

[TehMightyEngineer]

I suspect if you model this that the torsional stiffness of the joists combined with the diaphragm capacity makes this connection have more than enough strength for the demand. Shouldn't be too hard to model this assembly in a structural design software to accurately reflect the stiffnesses and load paths.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[KootK]

Thank you all for the help and clarifications.

Happy to help. Don't shoot me but I feel as though the pendulum may have swung back to far now. I'd expect to see at least two spaces worth of blocking here. Those vertical forces in the joists that form the resisting couple can tax the joists and, probably more critically, the uplift connection between the joists and other things.

 

[radiocontrolhead]

KootK,

I actually added another row of blocking after I checked the joists for the vertical reaction loads. My last attachment was made before checking the joists which were indeed being overtaxed. Take 3 attached.

 

[TehMightyEngineer]

Just out of curiosity, but why are you using the Simpson A35 angles when an A23 angle uses fewer nails for equivalent strengths?

Also, I assume the reason you're using clips on the connection to the sheathing is you wont have access to nail down into the blocking?

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[radiocontrolhead]

I didn't go through the connection detailing fully and could use different connectors at joists/blocking, I'll need to take a final look over.

Correct, access from above cannot be made as the roofing assemblies have already been installed where A35s with spax #6 screws are used