Al, Your suggestion to bring it to the engineer is standard ops and what I would normally do or have done in the past. Therein lies the problem. This project like most of my work is a Public Work project. 12 years of experience doing this type of contracting has indicated to me that either the engineers don't know this technically minor detail as they should or because they are designing other elements of the project- rebar, structural members, concrete of which some do fall under D1.1 and to keep it simple they just throw out a wide net. Either way, the loads on the railing we will be building are obviously far less than a supporting structural member. And in truth, I don't think any of them want to have that code distinction brought to their attention either for reasons of convenience or embarassment.
That said and with no intent of malice or defamation what I usually do these days is to present the missing information of the contract drawings in my submitted shop drawings for their review and approval. We provide details in our shop drawings, missing in their design which we've used with success following best construction methods. Design is their responsibility; if they think we have encroached on their area of expertise they will/should direct us as such in their review. I suspect most of them don't really enjoy designing commercial railing and seem to appreciate our filling in the blanks as it were. If I ever had a seconds doubt as to our ability to provide a safe, strong, functional fabrication under any code I would out of self preservation bring any detail or discrepancy to their attention. Even having done so, I'm sure you wouldn't be surprised how many times it was approved as submitted or simply quietly went away.
As an example: the horizontals on these railings are 1 X 1 X .120 Sq. HSS. That material is only readily available in A513, an unqualified metal under D1.1. This was brought to the owners attention a week before bid. The Owners answer was that his "consultant" was not available to answer that question before bid. Our bid proposal addressed that issue specifically, again ignored by the primes. I specifically informed them in the proposal of the unqualified material and the 12 week lead time for the mill to certify the tubing to A500. These questions have been ignored for 2 months. Now I will submit my shops which will specify A513 for the horizontal rails and I have completed the full expectation of my responsibility. I cannot reinvent the Bureacracy into a more efficient framework. They will make a decision, direct my course of action and I will let them know how much more it's going to cost and how much longer it's going to take. Likely it won't come to that. I know that tube will work and it's up to them to do their jobs. What's a guy to do? I showed them where the clear waters ran, if they like the mud it's all theirs. Oh, and thanks for listening. If you have any suggestions it's always appreciated.
I find it interesting that when I had my shop my insurance carrier would not cover railings, stairs, or fire escapes. They said the exposure with too high should there be a claim.
I have testing some railings. The test loads were 200 pounds of horizontal force at the top of the posts and 50 pounds per linear foot of horizontal and vertical load for the top rail. Each section was load tested. It passed, but the railing was not what I see in most installs. I suspect about 25% of the railing installs I see would actually pass such a test without excessive deflection. Most would fail long before the max loads were attained. Another point, the testing was required by the Owner's insurance.
One of the engineers I deal with provides expert witness testimony for deck failures, railings, etc. and judging by his workload, I can see why my insurance carrier shied away for providing coverage.
Best regards - Al
That's interesting Al but makes me wonder what kind of railings you are comparing this to. A 200# man with momentum and full force mule kicking a 42" high railing will [in my estimate] produce very nearly a 200# concentrated force, which I have carried out in order to justify my estimate and theory. Granted, this was not a controlled scientific study. The only thing that happened was a sore foot for me. Most of the stuff we do is 1 1/2" schedule 40 pipe or HSS equivalent. Embedded 8" into sleeves grouted into concrete and the PE who provides occasional consultation for me assures me they meet the load requirements of IBC. A lot of the light residential railing I look at makes me wonder though. My insurance agent has at times indicated she would sleep better if I increased my coverage but the fact is there's railing I built 10 years ago for a highly used public park full of athletes and skateboarders that 's still as solid as the day it went in the ground. New England [where I believe you practice?] may have a more conservative insurance industry.
The next project lined up after this is a Pedestrian Guardrail in Aluminum with bolted base plates to concrete. That one IS giving me the occasional jitters. But it's a few months off and lucky guy that I am the engineers on that one decided to exclude specifying the anchorages [again brought to the EOR prior to bid] so there's going to be some wiggle room and adjustments.
Do you have any thoughts on the backing material/configuration/tolerance referenced above that you'd share?
yojimbo,
You'd asked about further comments regarding the "backing material closeness to base metal material tolerance". Although technically the .120 material thickness doesn't fall within the parameters of the structural code, paragraph 5.22.1.1 addresses faying surfaces: "The separation between faying surfaces of plug and slot welds, and of butt joints landing on a backing, shall not exceed 1/16".
I don't know how many splices you'll have, but I was thinking yesterday, one option could be to plasma cut some short, solid bars to fit inside, and you could just grind the small radius on the edges to clear the corner radius of the tube. If it's not a seamless tube, you'd also need to grind away enough to clear the seam. Not really a whole lot of grinding, unless you have a lot of splices.
I was going to suggest using a solid piece of plate(punch a vent hole in the center if hot dip galvanizing) to be inserted inside as backing.....but Scott has already mentioned that.
Aluminum on concrete, not a very good combination. You will have to isolate the aluminum from the concrete or there will be hell to pay. 18-8 stainless anchorage should work.
Al
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