Pedestrian railing with handrail

[OSUCivlEng]

I'm working on the design of the railing for a pedestrian bridge. The railing is 54" tall and will have a handrail attached to the railing mounted 36" above the deck. AASHTO handrail loads are straightforward, but I'm wondering what loading I should check the handrail for, or if I should just consider deflection? If the handrail fails, the railing is still behind it, so it seems absurd to apply the same loads I designed the railing for. However you don't want the handrail to deflect against the railing behind it and pinch a hand or finger.

The weakness of the handrail seems to be the connection of handrail support as ADA requirements limit the diameter of the handrail to between 1 1/4" to 2".

 

[BridgeSmith]

What material are you planning to use for the handrail and what is the spacing of the handrail supports?

At our typical 8' - 10' spacing for handrail supports, the deflection for a steel pipe in the required diameter range is a small fraction of an inch. The standoff distance for the handrail is somewhere around 3"-4". Where required for the pedestrian railings and fences on bridges we've done according to AASHTO, it hasn't been difficult to meet the loading requirements. OSHA requirements appear to be the same - 50lb/ft horizontal and vertical + 200lb point load.

 

[bridgebuster]

I use 50 plf and compare it to A 200 pound concentrated load. Even OSHA limits the rail diameter to 1.5" for metal pipe and 2" for wood. It' not difficult to design the connection for the 200 pound load. Google Julius Blum, their catalog has a good example for railing design and plenty of fixtures.

One odd thing though, the minimum OSHA requirement for hand rail height is less than ADA.

 

[BridgeSmith]

Not sure about the requirements for the handrail itself, but the AASHTO requirements for the top rail and posts for the railing system are 50plf horizontal and 50 plf vertical and a 200lb point load applied at any location in any direction.

Edit: Loads are applied at the top rail or 5ft above the walking surface, if the rail/fence is taller than 5ft.

 

[OSUCivlEng]

Heh that whole unit conversion thing will get you every time! Couldn't figure out why my deflection calc kept blowing up to over 1.5". I was using kip/foot when everything else was in kips and INCHES.

My handrail is 1 1/4 Schedule 40 pipe with supports at 5' on center. That's good for 50 plf and 200 lb point load and a deflection of 1/4".

 

[OSUCivlEng]

HotRod, I've already been through this with the architect between rail and handrail. The way ADA defines a handrail is something between 34" and 38". My rail is 54" tall (due to bicycles), while the handrail is mounted at 36". The handrail is there to provide something to hold on to for balance. The 54" rail is designed for the AASHTO loads you mention so someone doesn't fall off the bridge. Actually it may be slightly over designed because I think I applied the 200 lb point load in both directions.

 

[BridgeSmith]

We do a similar thing for pedestrian railings above retaining walls and pedestrian fence on bridges. We apply the AASHTO loading to the top rail of the railing system (or 5ft up on the fence) and check the rails and posts. We check the handrail bar and mounting supports for the similar ADA loading.