Construction Guardrail 3

[mmarlow]

Hello,

I'm sure someone has posted about this before, but I'm having trouble finding it.

I'm designing a temporary construction platform out of wood. The contractor is proposing 2X4 posts at 4' O/C (in the weak direction). I've seen this on construction sites before, but am unable to get this to work with the 200 lb point load requirements. Flexure isn't close, never mind the connection to the platform.

I suppose my question is, how is this allowed on construction sites? Does OSHA have scaffolding load criteria for rails that differs from the 200lb point load? Im not having a lot of luck searching around.

Thank you for your help.

-MMARLOW EIT

 

[WinelandV]

In a previous job, I analyzed these guardrails. The big thing to get flexure to work is load sharing between posts - that is, the top rail will (might?) held share the 200# point between posts. This assumption means you have to make sure the top post spans in such a way to actually share the load.

Concerning the connection, we eventually forced the field personnel to use a bracket on the end posts of the platform. We were looking predominately at Bridge OH brackets and the associated platform. The OH bracket supplier had a nice, steel end bracket that you'd fit over the wood 4x4 (top bracket member) that had a vertical pocket for the guardrail post. They had test values for those, so no muss and fuss.

 

[mmarlow]

Winelandv,

Thank you for the response. I have used load sharing before, but in this case I have end posts with pinned top connections that will not be able to transfer any load over to the other posts. This might work for center posts that have adjacent posts on either side, as the pin top rail connection will be able to transfer the load each way.

I will look into those brackets

-MMARLOW EIT

 

[Ron]

Look at 29 CFR 1926.451, OSHA Construction regulations. A 200 lbf lateral load resistance is required and the guardrail must be 42 inches high. This is different than permanent guardrails under 29 CFR 1910 which only requires a height of 36 inches. Construction is different and has been stated so in OSHA official interpretations of standards.

The Code of Federal Regulations (CFR) can be confusion and you often have to look in numerous places to get a full answer. 29 CFR 1926 has the OSHA regulations pertaining to construction. 29 CFR 1910 has the regulations pertaining to general industry.


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[WinelandV]

Ron,

GREAT GREAT point. Totally forgot about the 1910 vs 1926.

 

[mmarlow]

Thank you Ron

-MMARLOW EIT

 

[JoelTXCive]

Here is another product if you have room on your platform.......

It's called Safety Boot, by a company named Safety Maker. The company has testing data on their product.

We used to use them on residential homes. They were super easy for the framers to install.

https://www.safetyboot.com/safety-boot.html

Link

 

[mmarlow]

Joel,

Very cool. Thank you!

-MMARLOW EIT

 

[DTGT2002]

And do note, you are guarding against failure - no FOS noted.

That said, we have not been able to resolve the figure 4 style brackets either. There may have been prescriptive guidance giving construction criteria at some point. If so, I don't have it.

That said, one typically sees plywood or 2x4 gussets that help the flag pole loading get closer to the ballpark, but the anchoring is still an issue.


Even with the safety boots, anchoring is often an issue as the requirements for decking are not always achievable.


Big challenge with wood - how do you attempt to model true ultimate behavior?



Daniel

 

[WinelandV]

And do note, you are guarding against failure - no FOS noted.

Even worse, they don't define failure. Is the guardrail supporting the load but being left with excessive deflection a failure? When I did construction engineering, this was the question that got asked all the time.

how do you attempt to model true ultimate behavior?

Poorly.

 

[JStephen]

If they're building it out of wood on the jobsite, it may be quicker to test a section with actual 200 lb load than to show it works on paper.
On the deflection- that has come up on cable railings, and I think somewhere, OSHA specifies that it can't deflect over a certain amount with the design loading.

 

[mmarlow]

JStephen,

I will keep this in mind. Thank you

-MMARLOW EIT

 

[dauwerda]

Just to add to what Ron pointed out, the newest edition of 1910 requires that guardrails be 42" +-3" [1910.29(b)(1)], so it does coincide with 1926.

https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.29

 

[Ron]

Thanks, dauwerda! Also, OSHA does mention 2" of deflection is considered failure.


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[WinelandV]

Ron,

I've never seen 2" listed before. Can you point me to the standard number for that?