Wall Rail Bracket Anchor Design 2

[271828]

Greetings All,

I'm working on a handrail project that has a very typical situation: Wall handrail with brackets and sleeve anchors into clay brick. Surely there are a million lineal feet of these in service.

Attached is how I would approach this problem. The rail is subjected to either 200 lb or 50 plf. If I sum moments around the bottom of the bracket, I get an anchor tensile force of 816 lb. This value far exceeds the 3/8 in. sleeve anchor allowable strength shown in the Hilti Table 6.

I'm trying to figure out how people make these "calc out."

Am I missing something big here? Are the 200 lb and 50 plf excessive? Is there some way to justify not considering the eccentricity like I did? etc.?

Is the 4.0 factor of safety (Hilti table footnote) required? In this case, the FS would be about 1.8. I could not find a code provision requiring 4.0, but maybe one exists. Is there something stopping me from saying 1.8 is good enough?

Something else?

Any advice would be appreciated!

 

[dik]

Do these help at all?

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1703465869/tips/NHandrail_HSSc_C3_prn_pzbzmb.pdf

[/url][URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1703465869/tips/NHandrail_HSSc_C3_nx3b5a.sm[/url]

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

-Dik

 

[XR250]

If these are not guardrails, do they still need those loads?

 

[dik]

handrail or guardrail? They have different loads... and loadings are for Canadian codes.

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

-Dik

 

[dik]

For handrails based on the code for Manitoba... I don't usually do residential stuff... for industrial stuff... as indicated on the SMath program. Even ordinary handrails in a house require these design loads. The two wood screws are prescribed and likely don't accommodate the loadings (no size stipulated? #6 or #14?). This is for houses and small buildings only (Part 9).

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

-Dik

 

[dik]

To answer the OP's question, the fastener loads can be high... in particular going into wood. The prescribed attachment noted above likely will not calculate out, especially is you have a small mounting plate, and there is no stipulated screw size. The SMath program I attached is representative of maybe a dozen programs I have for dealing with different handrail conditions. I have a larger collection for guards, which have different loading conditions. Part of the work I do is designing connections for metal fabricators.

I usually check design capacities by allowing an increase of 1/phi to allow for an overload or at least flag something that may be close for closer review.

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

-Dik

 

[Enable]

Calcs seems right to me.

I imagine you're stuck with these off the shelf brackets, but if you can convince the contractor to fabricate their own, one configuration we use for hand rails on clay brick is 3 KWIK-CON screw anchors (2 fasteners ~ 700lbs capacity with ~2" moment arm and 1 anchor for shear). This will work for the loads you have as long as it's aesthetically viable. Pretty cheap to fabricate, though not as cheap as a mass produced part I'm afraid.

As an alternative maybe you can contact the part supplier and see if they have any test data on the bracket? They should have something if this is a high volume part.

 

[dik]

Fasteners should be FH fasteners with countersunk holes... and fastener circle is important... KwikCons are good; I use them often and occasionally use #14 screws designed as screws and not as lag screws... I stipulate that they are designed as screws and have not had anything 'bounce back'.

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

-Dik

 

[271828]

Do these help at all?

Yes, it helps to see how someone else would approach this. Very impressive program BTW.

 

[271828]

If these are not guardrails, do they still need those loads?

I wondered that myself, as I scratched my head on how people make these calc out.

Here's how I read the requirements on this:

IBC (2021) 1011.11 Handrails: "Flights of stairways shall have handrails on each side..."

ASCE 7 (2022) Section 4.5.1 is entitled "Handrail and Guard Systems."

I don't see a code distinction between a handrail preventing falling over the edge of the structure vs a handrail attached to the wall for someone to grab for balance.

The "spirit" of the provisions seems to be about preventing falling over the edge. Thus, if the 4.0 factor of safety isn't a requirement, then it might be OK to go with a lower factor of safety when falling over the edge isn't possible. For example, in my case, the factor of safety would be 1.84.

Anybody have an opinion on that?

 

[271828]

So it seems you guys are using more favorable brackets. That makes sense to me, and at least now this question doesn't mean I'm off the deep end. LOL

I will contact Wagner to see if they have another bracket with multiple anchors, or if they have test data showing their single anchor bracket is strong enough.

Thanks dik and Enable for sharing your program and detail, respectively. Much appreciated, and I know you had to spend time and energy developing those. Hopefully I can pay you back along the way.

 

[dik]

Three hole, circular plates are more common in these environs. I also have programs for 2 hole circular as well as 2 and 4 hole rectangular mounting plates. I maybe do one or two of these a week. They are just a small part of my work... done about 960 projects in the last three years, most of them only a few hours... but includes a six storey building addition (one of the larger ones).
Different horizontal and vertical distances, different spacings, different cantilever distances, different plate sizes and different fastener circles. I even have a *.pdf stamp that I can add to shop drawings I review.

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

-Dik

 

[dik]

I just use limit states with DL and LL factors 1.25, and 1.5 and phi factor of 0.9... factor of safety 1.666

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

-Dik