Construction Safety: Dropped Object Offset Distance from a 280 Meter tall Bldg.

[racookpe1978]

On a different forum, a question was asked that has me puzzled:

User asked how far an object would be blown sideways in a 4 m/sec westerly wind if dropped from a 280 meter tall building. Turns out it was not a "college physics homework question" at all but a dropped object safety review. Guy has a existing 2 story building 50 meters from the new building. Owner of the existing building wants to know how he (his building) is going to be protected against falling objects.

How do today's projects manage that issue in downtown congestion to build/design the plywood "sidewalk tunnels" under high rise building construction? Is it a "Code issue" with standard assumptions, or a "Tell the scaffoldors/carpenters to put up the usual boards"?

What would even be considered the "average object" that could be dropped?

In this case, 50 meters is well within the 60 degree "cone" we consider for working underneath regular scaffolding against dropped objects, particularly a floor level or roof level 280 meters high. But that "cone" is for dropped solids (wrenches, bolts, tools) falling in a complex crowded place in scaffolding or platforms, each objects being likely bounced sideways as it hits irregular stuff below the work level. Straight down drop? Seems like some items (planks, plywood, boards) would "sail" and heavier items would not be blown at all.

 

[GregLocock]

If they were unlucky a plywood board could fly, wind or no wind.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[1503-44]

In the absence of air, a feather and a hammer fall at the same velocity. Got nothing to do with being heavy. In air, the feather will most likely travel the farthest horizontally. It has more aerodynamic drag.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[racookpe1978]

Right: It is why I asked about the "real world" not some physics classroom thing.

A 2x10 plank will "fall" rather than "fly" but it will be more affected by wind than, say, a scaffold pole (2 inch dia x 10 feet) or a hammer or 2x4. In turn, a plywood board or tile or loose debris will be near-unpredictable in "flight."

So, ignore the physics book of free-falling items in a vacuum. You don't build in a vacuum anyway - millwrights and carpenters couldn't work in a spacesuit anyway. 8<).

How do you protect adjacent buildings while under construction, and how far away from the taller building do you provide protection?

 

[3DDave]

Considering the number of neighboring buildings damaged by falling construction cranes I'd say it's a tough problem. Prevention is far better than protection.

 

[LittleInch]

I'm no building engineer, but I think all that anyone does is protect "people", not the building. If you drop something really big and heavy or pointy and it hits the building, what does it do? Maybe dents a few things or damages the A/C equipment - so what - fix it and claim on the insurance.

People though are a different matter. So it's about creating "safe" means of access and egress to a building, working out where the small objects could go and working out where items are lifted over anything where failures could result in items falling to the ground.

How far away? In practice I think this is just judgement and prevailing wind, but should be a reducing distance for every m up to account for acceleration vertical vs velocity sideways. Maybe some building departments have guidance in different locations.

In the case you highlight I don't think anything you put up as a temporary shield is going to stop some small but heavy object dropped from 280m.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

True - This was only a small building and it killed someone in the next set of flats.

https://www.eng-tips.com/viewthread.cfm?qid=471238

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r13]

Construction net blocks flying objects, and roofed gallery below catches falling items.

 

[1503-44]

Excavators seem to go straight down, but to be sure, there was probably little wind there anyway.
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Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.