Loads on Guards and Handrails 2

[dik]

Does anyone treat these loads as the factored load with the design being capable of resisting these loads (without load factors DL and LL factors = 1.0 for both). These are the maximum loads. Dik

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

No. These are live loads and are factored as such.

 

[wrantler]

ditto

 

[jayrod12]

Agreed with the above

 

[dik]

Thanks... what I thought... recent project where EOR has considered as such...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[wrantler]

So if you design to their loading and it is less than 'code'. Is that your stamp on the line? I would say probably at least 1% liable.

 

[dik]

I occasionally encounter this with safety attachments where they want to use the stipulated loading as a factored load... it's already maxxed out. It doesn't need to be increased. This is the point at the end of your 'bell' curve...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[southard2]

Just to make sure apples to apples. I always thought of these prescribed loads as raw un-factored service loads. So say the handrail consists of a steel posted bolted into a concrete footings.

If I'm using ASD (allowable stress design) I use the loads as prescribed and apply a factor of 1.0. Then when I design the foundation rebar or the bolts into the concrete I'd factor the services loads so that I'd be using ultimate loads with the concrete design. I do all my concrete design using LRFD.

I'm only bringing this up again because when I read the thread above I think someone could mis-intepret it.

I view the handrail loading prescribed in ASCE 4.5 as service loads. The actual loads being applied to the object. Then depending on whether you are using allowable stress design or LRFD design you factor the loads as appropriate. So you could say these are the maximum service loads. But I don't view them as ultimate loads. If you need ultimate loads for your design you need to multiply them by 1.6.



John Southard, M.S., P.E.

https://www.pdhlibrary.com/

 

[SE2607]

I believe when the code (ASCE-7) formally defined a guardrail load as a live load, that, to me removed any ambiguity. Much to my dismay, LL load factors apply. I, too, believe a 200 lbf is an ultimate load, but the code clearly defines it as a live load and is subject to all appropriate load factors, just like a floor live load. This is different from E or W loads where the load combinations clearly reflect 0.7E and 0.6W respectively.

 

[Eng16080]

I agree with everyone above that it's just another live load, to be used as such.

A related complication for wood guard and handrail design (per US codes) is whether you should use a load duration factor, CD, of 1.0 (typical for live loads) or 1.6 (based on a total cumulative load duration of 10 minutes). Using 1.6 seems the norm, but I think it's highly debatable.

 

[SE2607]

Eng16080 - I totally agree with you, but again, a live load has a CD = 1.0 per table 2.3.2 of the NDS. One could argue that this is not an "Occupancy Live Load" but an Impact Load, but footnote 2 excludes CD=2.0 for connections, which is the crux of the challenge of a guardrail connection in wood. CD=1.6 is clearly for wind and earthquake loads. It (a guardrail load) is also not a construction load nor a snow load. While using a CD > 1.0 makes sense to me, I believe it would leave one to a liability risk.

 

[phamENG]

I think it's important to realize that the "Dead Load, Live Load, Construction Load, etc." in the C_D table are recommendations (but go lower for those categories at your peril). The duration of loading is cumulative over the life of the structure. In other words, a 3-second gust wind load is not expected to occur for more than 10 total minutes for the entire life of the structure. A 40psf live load in a house is not expected to occur for more than 10 total years over the life of the structure. It's not about the short term duration of a particular loading event.

For more info and some references, check out this thread from last year: thread337-498986

 

[Eng16080]

SE2607, I think we're on the same page with this.

I recently did a lot of research on this for the purpose of updating my handrail/guardrail post connection details. Based on that research, I ultimately decided to use CD=1.0 for the design. In some cases, using CD=1.0 instead of 1.6 leads to some serious difficulty in getting the details to work. With CD=1.0, I found that for a guardrail height of 42", the typical 4x4 post doesn't work. Instead a 4x6 is needed.

Resisting the tension force at the base of the post using a proprietary holdown was also challenging as the published values are all based on CD=1.6, not 1.0. I divided the listed capacity by 1.6 to get a comparable value for CD=1.0. Getting a reasonable connection to work with 2x8 framing was very difficult and I'm now considering not using 2x8 framing for decks at all, only 2x10 or 2x12. As a side note, for 2x8 framing, I calculated a holdown (tension) force a fair amount higher than discussed in the paper published by Simpson on the matter. This isn't to say that my analysis method is necessarily the best and theirs is wrong. I just found it interesting.

(My apologies if this is getting slightly off topic from the original question.)

 

[dik]

I'm not sure... I use load factors, the a question has been raised. I've not been able to confirm this is stipulated anywhere. SE2607... I didn't know that about ASCE 7... I'll take a look... maybe someplace to hang my hat.

The use of a reduced load has a real impact on attachment. Many clients are trying to attach these things to the flimsiest of materials using the most feeble connections... a recent project had 3/8 x 2" lag screws connecting to something...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Not to worry... it's appreciated...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

I almost never use design to code as a criteria... I like 'safe'. When I was younger, when a new code came out, I used to carefully go through it, looking for 'exceptions'... I've outgrown that...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JLNJ]

I will go to my grave believing that the ASCE folks chickened out when they made the 200# (which was likely a legacy from OSHA) into a regular live load.

 

[phamENG]

JLNJ - hopefully this doesn't put you in an early grave, but I'm going to disagree with you on this. Those loadings have been floating around in various places since well before the rise of strength or limit states design. The only indication that it might be an 'ultimate load' came between 2000 and 2006 while the IBC put in a provision to increase the allowable stress for guardrails. It was the only standard/code document that did that. And they removed it at the insistence of the engineering community.

Check out this thread for some references to these loads predating LRFD: thread507-357633

 

[phamENG]

That thread does reference an old standard from the 70s that's no longer on the NIST website:

NBSIR 76-1131 | A Model Performance Standard for Guardrails

It gets into load combinations for allowable stress design. Factors are 1.0 for typical situations, but it actually factors those loads up in some cases. The base loads are also higher in some cases - up to 300lbs for some point loads and 100lbs/ft distributed.

 

[KootK]

Setting aside the question of what makes sense (sounds as though pham's got that covered), British Columbia has a guide out for guard design that, in my mind, clarifies their expectations: Link. One would hope that this would be uniformly applied across the provinces.