Sidewalk Overhead Falling Object Protection - Applicable Loads 2

[KootK]

I've been looking at the design of some of these overhead protection systems that get installed above pedestrian sidewalks. You know, to ensure that anvils aren't falling into baby carriages when work is being performed on the building exterior. Does anybody know of any standards or guidance that might be available with respect to the applicable loads for these systems?

It may be that I'm just not using the right search terms but I've run up against a surprising paucity of design guidance on this. I've got a friend that designs these things regularly and he swears that, in our jurisdiction, there is no loading requirement other than to understand the nature of the construction activities and to design accordingly for impact. On the other hand, I keep seeing 50 PSF crop up in the work of others.

My practice location is Alberta Canada. That said, I would be interested in design guidance originating from any geographical location that may have it.

 

[GC_Hopi]

OSHA seems to be more stringent. "Employee entrances to multistory structures being demolished shall be completely protected by sidewalk sheds or canopies... and shall be capable of sustaining a load of 150 pounds per square foot.
Link to documentLink

 

[GC_Hopi]

Here is an old NYC Department of Buildings (DOB) code for comparison. "Sidewalk sheds for buildings 100ft or more in height shall be designed for a live load of 300psf. For buildings under 100ft in height, the minimum sidewalk design live load is 150 psf and no storage is permitted."

 

[Ussuri]

Presumably it isn't as straightforward as applying a UDL? Small heavy objects may have a tendency to punch though (akin to a ballistic impact) if the structure is stiff. The question then becomes, what are you protecting against? To use your analogy, a 90kg anvil dropped off a 150m building would deliver an impact energy of 132kJ.

In my line of work (oil and gas/subsea) we always have to consider protection for dropped objects. Industry standard (ISO 13628) is to design for a 5kJ impact over a 100mm diameter and a 50kJ impact over a 700mm diameter. I'm not sure if that helps though.

 

[KootK]

In my line of work (oil and gas/subsea) we always have to consider protection for dropped objects. Industry standard (ISO 13628) is to design for a 5kJ impact over a 100mm diameter and a 50kJ impact over a 700mm diameter. I'm not sure if that helps though.

That does help. I'll add it to my heap of things to consider if I can't find any regionally specific guidance.

 

[jayrod12]

The 50 psf is likely due to the old construction loading adage. Which I still use for random checks regarding stability during construction.

However I like OSHA's specs a little better for stuff like this. and I agree with Ussuri about impact load. Think of the damage a framing hammer could cause being dropped from 45ft in the air.

 

[TehMightyEngineer]

From what I recall from a construction netting design I had to do in the past it wasn't really a load I designed for but rather an impact force based on the assumed weight of an item dropped, the fall height, and the headroom height for the net deflection. You obviously wont have the headroom issue since you're not using a net but I feel that a static load of X PSF doesn't convey the issue that a hammer dropped from 10 ft is completely different from a hammer dropped from 1,000 ft.

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

 

[KootK]

While I do agree that a dynamic, falling object load is the critical thing for these systems, in a non-industrial setting where the load is specified (NYC apparently), it's specified as a a large uniform load. My presumption is that's an attempt to provide a reasonable capacity without making a science project out of each and every one of these things. I may design the first thing that a falling object would touch for an individual impact load and then design the rest of the system for a uniform load. We'll see what additional guidance manifests itself here.

 

[TLHS]

Section 8.2.1 of the NBCC has requirements for 'Covered Ways'. It says to design them for the expected loads, with a minimum of 2.4kPa.

Worksafe BC's requirements are identical. Don't know about Alberta OHS.

 

[KootK]

Section 8.2.1 of the NBCC has requirements for 'Covered Ways'.

There it is! Thanks TLHS.

While we're at it, does anybody know of any design requirements for the vertical debris netting that usually accompanies these things?

 

[TehMightyEngineer]

You want 320(1) of the OHS code.

I also found this, not sure what these changes got applied to but maybe you can figure it out?

http://www.ihsa.ca/pdfs/committees/...-netting-working-group-submission-to-clrc.pdf

If you want the OSHA provisions it's in 1926 Subpart M - Fall Protection

https://www.osha.gov/laws-regs/regulations/standardnumber/1926

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