AASHTO Handrail on Sidewalk Check

[mikeCTE]

thread507-405072

We've been asked to check the use of a side-mounted handrail that will attach to a turn-down edge of sidewalk (5ft wide sidewalk). Project requires the use of AASHTO which shows 200lb point load + 50 PLF line load applied + 50 PLF line load in the direction of gravity. We can get the structures to all pencil out, but if we look at this from a global perspective of overturning and sliding (safety factor of 2.0 and 1.5, respectively, it looks like we need to thicken up the sidewalk to 5" (from 4") to get it to work.

We are not accounting for the weight of the person/object applying the lateral loading, so it's conservative, but I am worried our client will be unhappy when we tell them to increase their quantity of concrete by 25% to handle a stability check that's almost impossible to happen in real life.

Any thoughts on a reasonable way to justify the presence of live load (which would assist the overturning and sliding resistance)?

 

[TehMightyEngineer]

Love that old handrail thread, good stuff.

I'd definitely apply the weight of a row of people in your load case, it's unrealistic otherwise.

However, I'm a little concerned that something as light as a handrail load is giving you overturning issues. What happens when a more likely load like a snow plow blasts by and dumps 3 feet of wet snow onto the sidewalk and rail?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Ron247]

Without cranking a number, overturning and especially sliding seem unlikely. How wide a strip of sidewalk are you using?

 

[mikeCTE]

design of the sidewalk (by others) is 5ft x 4" thick. when you sum moments about the corner of the sidewalk, it overturns due to a 4'-6" railing height and 50plf horizontal, vertical, + 200lb point load.

​

 

[BridgeSmith]

The 200 lb point load can be distributed at a 45 degree angle back across the sidewalk, so over a width of 10'. So for your sidewalk/retaining wall, your lateral load is 70 lb/ft, if you want to consider it. By my reading of the AASHTO spec, the railing loads are for design of the railing system, but not for external stability of the wall that supports it.

If it makes you more comfortable using the pedestrian's weight, the provisions for vehicle impacts to a traffic railing allow for the weight of the vehicle to applied to a base slab that the vehicle crosses to impact the railing.

If you still want the added thickness, realize that the material cost is a small part of the total cost of placing the sidewalk. The major cost factors are in the labor for finishing, etc. I calculate the cost difference for an extra inch of concrete at less than $2 per linear ft for a 5ft wide sidewalk, unless your concrete prices are much higher than the $120/CY we pay around here.

 

[mikeCTE]

i think concrete here is running $600/yd or so.

my understanding of AASHTO and IBC/ASCE 7 is that you are to apply your railing load in a manner to produce the worst case outcome (including using 0.9D for selfweight). agree?

 

[BridgeSmith]

Yes, the minimum component dead load (DC) load factor is 0.9. Even at that, and factoring the railing load at 1.75 (which I don't believe is applicable either), I have it passing the overturning check (neglecting pedestrian weight). 70lb/ft * 4.5ft * 1.75 = 551 lb-ft/ft < 0.9 * .33ft * 5ft * 150pcf * 5ft/2 = 557 lb-ft/ft.

Is the $600/CY the material cost from the ready-mix supplier, or the in-place cost?