Impact force of sliding window 1

[GoncaloPT]

Hi! Hope you all are doing great

I'm in need of some tips/help regarding some forces for the design of a structure.
I have a sliding window that will impact on a steel square profile (represented in blue). The glazing sliding window will have a total mass around 150 kg, a impact height of around 2 meters.

Assuming a terminal velocity of 0.2 m/s (vf) what should be the impact load expected on the steel structure? Can anyone provide some guidelines on how to estimate this loads?
I understand this should also consider a collision distance and a impact duration, but i have no ideia of what are reasonable values for these.

Any input would be much appreciated

 

[LittleInch]

Whilst an interesting theory, I still think this is not a real issue. All vendors are aware of this and more importantly very aware that if anyone leaves a finger in the wrong place then it would get destroyed if they allow that to happen.

So there is usually some sort of inbuilt system to stop the heavy door slamming at speed into the closure section

And 0.2m/sec velocity is way too high

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

 

[bones206]

I think the force of 3.25 KN calculated by the elastic energy approach is reasonable. If the goal is to design the jamb and it’s anchorage, I would probably double that value and be done with it.

Not sure the approach using potential energy makes sense since this isn’t a vertical drop situation.

 

[BridgeSmith]

I would start by making an estimate of the force that can reasonably be applied to the sliding portion (by the user) to estimate the acceleration. The distance that it slides will then determine the velocity. That's the easy part.

The hard part is estimating the deceleration distance (effective cushion thickness). There has to be some distance over which the 'stopping' takes place, otherwise the force is literally infinitely high.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[GoncaloPT]

Trying to estimate some other approach for the reactions on the stiffest part of the frame, I modeled a type of support for the steel profile.
With a load of 1KN e got a total deflection of 0.046 mm that translates on a stiffness of 2.17*10^7 N/m (wich is really rigid).

With that I got a reaction of 10 kN, wich seems kind of high.

Any toughts about this results?

@LittleInch we are also the manufactorers of the sliding windows system, and we do not have any in built system to slowdown the sliding window. Thats why i'm trying to estimate like a bad scenario to give some loads to the structural engineer of the steel frame.

 

[phamENG]

I think it's a bit much...I don't know anyone who could slam a door with 2.25kips of force behind it - dynamic peak or not.

You may not have anything specifically to slow it down, but it will (unless it's riding on a friction-less rail, of course).

Discussing the engineering mechanics behind it was fun, but I think you need a more pragmatic approach rather than a technical one. Do you have any information on the effective coefficient of friction between the door and the rail that it rides on or track it rides in? Considering a normal use case, most people won't push harder than it takes to get a sliding door moving. So if you can figure out the static coefficient of friction and you know the weight, you'll know the frictional force preventing it from moving. A force just greater than that will start it moving and friction will drop off to a lower level based on the dynamic coefficient of friction. Assuming they continue to apply force all the way to the end, the force exerted on the frame will be the force of the person pushing minus the force of the dynamic friction - for simplicity's sake we can say the force applied to the frame is the difference between the force of static friction and the force of dynamic friction.

Now that you have your force, apply a safety factor that you feel comfortable with to account for a) people in a hurry b) malefactors who like to slam doors or c) over zealous building maintenance crews that grease the tracks to make the door slide more easily.

Oh - and don't put this in any sort of official document. It's a good starting point, but be sure to test it by actually slamming some doors.

 

[bones206]

I think modeling the entire jamb and all the contact points would be more realistic. Modelling the stiffest contact point and extrapolating that result as the overall jamb “spring” is likely overestimating the global stiffness of the jamb.

 

[human909]

I think it's a bit much...I don't know anyone who could slam a door with 2.25kips of force behind it - dynamic peak or not.

It depends. With simple hammer and a stiff connection almost anyone can produce a peak force of 10kN. If you have a 150kg door then producing high impact forces with human hand is trivial if you have a suitably stiff door and jamb.

Though most door jambs aren't that stiff!

 

[bones206]

GoncaloPT - It's great that you are looking at this problem using different methods. Hopefully you will see some convergence in results, but you have to keep the boundary conditions consistent between the various methods. For example, you previously used the deflection formula of a simply supported beam under uniform loading to obtain jamb stiffness. But the FEM is more akin to a short cantilever with a point load. If you can bring the boundary conditions of those two methods into alignment, I think you will see the results converge.

 

[Ron]

To the OP....

You are measuring with a micrometer, marking with a crayon and cutting with an axe. You're looking for a problem that doesn't exist.

 

[phamENG]

human909 - sure, but the energy generated there is coming mostly from the velocity in a low friction environment, and you get a bigger bang for your buck there (yes, that pun is absolutely intended). Getting a heavy door up to speed and keeping it there takes a bit more work than most people are willing to put into a sliding door.

 

[Guest090822]

Ron - that's 80% of all engineers I've ever met. They all want to gravitate to complicated first!

 

[bones206]

What's the point of having nerd muscles if you can't flex them?