Balustrade Loading Clarification

[nonplussed]

I have searched for this in other posts but have not found anything specifically related, so my apologies if this has already been answered.

In the British and Australian codes there are generally 3 horizontally distributed line loadings at the top of balustrades: 0.75kN/m, 1.5kN/m, and 3.0kN/m. Prior to 2002, the Australian code didn't even have a 1.5kN/m loading condition and instead said every balustrade "shall be designed to resist a static load of 0.75kN/m..." and "On railings or balustrades which may be called upon to restrain crowds or people under panic conditions, a load of up to 3kN/m run may be exerted."

I am currently designing several balustrades where the loading requirements and type of occupancy are not clear, for example the external balcony of a private golf club or surf club, or the external balcony adjacent to a function room. Am I right in saying that loadings larger than 0.75kN/m are a result of people trying to get to the fire exit or exiting after an event and therefore being pushed against the balustrade by the crowd behind them? Therefore, if the balustrade is at the opposite end of the floor from the exit, there will not be people getting pushed into it in an emergency and it can be designed for 0.75kN/m?

Thanks

 

[Guastavino]

I'm in the U.S., so take it for what it's worth, but here we have a 50 lb/ft linear load OR a 200 lb concentrated load for guardrails (which I think is the same?). I'm going off of memory right now but I don't think it's occupancy specific. So, maybe convert those to SI units and see if they are comparable. Obviously, your code is different, but the balustrade doesn't know that. I hope that is somewhat helpful.

 

[nonplussed]

Thanks mate. I might look into the US codes. Hopefully they have more explanation.

 

[racookpe1978]

Much of the time, the typical verticals are 4 ft apart (or slightly closer - for example, 1 flight of stairs has 3x verticals in less than 8 feet run) so 50 lbf/ft x 4 ft = 200 lbf at the post.

Lots of discussion about it, but there really isn't much "theoretical basis" for either value. Even the "failure mode" (how do determine of a design did not pass the 50 lbf/ft limit?) is not clear: The post deflects? How much yield is "good enough" and how far is "too far"? The post breaks the mounting? It deflects (yields) but holds the person back successfully?

Why 200 lbf? Has that value ever been justified, or is it just written down because somebody wrote it down? Treat it as a requrement.

 

[nonplussed]

I didn't mention that what I am certifying is cantilevered frameless glass balustrades with proprietary base fixings, both bolted and spigot fixing. Testing has been carried out on each type of fixing for 12mm heat soaked toughened glass. Testing loads were only for 0.75kN/m (approx. 50 lb/ft) and the associated point loads but the panels were not tested to failure so I don't know if they had reserve capacity or not.

In order to use any of the glass system it is crucial that I am able to justify using the max 0.75kN/m loading. The problem is that all the codes are ambiguous as to when higher loadings are required and do not provide clarity as to why they chose various values.

 

[hokie66]

The higher rating is not related to fire exits. It is rather intended for areas where crowds can congregate. Such areas would include balconies around a hotel or shopping centre atrium, where the atrium can be used for performances. The golf club or surf club balconies may also be subject to crowding, dependent on their accessibility and usage.

file:///C:/Users/Al/Downloads/BALUSTRADPOLICY110726.pdf

 

[hokie66]

Another reference.

http://harkk.com.au/technical_information/load_capacities/

 

[IronCityEngineer]

Thanks for sharing this. I was unaware that the euro codes gave this guidance. Are the loads you quote working or ultimatzied?

Interestingly, ASCE-7 doesn't classify rail loadings by occupancy, except that the 50plf load is waived for industrial railings. Importantly, the commentary of ASCE-7 says that for special conditions where "extreme loads can be anticipated" from crowds "appropriate increases in loading shall be considered" but no guidance is given.

OSHA gives similar load requirements for rails to ASCE but uses fracture as the limit state.