impact loading 1

[Anne651]

I have a heavy duty door, lets say 40kN. I have to design a stopper to qualify the door for design basis earthquake. Now, lets say I use the floor response spectrum, and it is acceleration of 1 g.

I need to find the design load for the stopper.

Now, I assume a force of 40kN (40/g*1g) applied during earthquake for 0.25s. So my impact load applied is 10kNs (Ft). Then door is traveling at constant velocity = mv, so velocity is 10kNs/40kNg=2.45m/s=V2,

Now assume my door stop deflects 5mm, use V1=0, v2^2=V1^2+2ax, I get deceleratoin of a=600m/s^2. Then v2=v1+at, t=0.004s. So, I assume the door will stop in 0.004s.

Ft=10kNs t=10/0.004=2500kN.

This is a huge load, 250tonn. Which is different from impact factor of 2. Is there anything wrong with what I did? Many thanks,

 

[GregLocock]

Can your stopper (and the associated structure) really stop a 4 ton door moving at 5 mph in 3/16"? I measure the static stiffnes of many things made of steel, and 50 kN/mm is of the order of a cast iron surface plate embedded in concrete, so 10 times that isn't a stopper, it is the structure.



Cheers

Greg Locock


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[Ron]

Can you provide a sketch? As Greg noted, the numbers don't pass the sniff test. Can the door actually handle being stopped without major structural duress?

 

[woodman88]

I am sorry, but do you have an existing system that equals this? Because it sounds like you need at least two door stops that deflects 50mm to 100mm. I would look around at other systems to see if you are in the ballpark with your assumptions before doing any more calculations.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[rb1957]

deceleration 600 m/s2 ... 60g ??

i think you should also worry about trying to restrain a large panel at a single point, or are you restraining the entire edge ?

 

[Anne651]

GregLocock and rb1957.

I will try to restrain at single point, if not feasible an entire edge.

Greglock, what should be the expected stiffness of a steel block of lets say 3" x 6"

Thanks,

 

[IRstuff]

Your calculations appear to be valid for a freely linearly moving object, but is that actually the case? A "door" implies hinging, which implies a rotation and not linear motion.

TTFN
faq731-376

 

[rb1957]

like IR, i doubt it's a simple problem. you're restrining one corner, the other is free (so that side of the door will be flexing; the other side is hinged, so he'll be constrained to keep aligned. you're trying to control the center of the door (the center of mass of the door) by controlling a point on the bottom edge ...

 

[Anne651]

I am assuming the hinge is frictionless. I mean, should I do some centripital force calculation?

 

[Anne651]

shouldn't the stiffness be 200 000 MPa? That is what I assumed.

 

[Anne651]

ok, I have no solution to the problem.........

 

[vpl]

Aren't you defining your door in terms of a force, not a weight?

People have been assuming that the door is a swinging type access door, but is that correct? This could also be a large "garage door" type that drops or a reinforced concrete door that slides. This will make a difference.

A drawing or sketch would help considerably.


Patricia Lougheed

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[dhengr]

Anne:
I’m not exactly sure what you are trying to accomplish without a better description and a few detailed sketches. But, consider these things in your design and analysis: if you can do something to increase the time duration and distance of travel in the stopping process, you will significantly improve your conditions. With the door hinged on one side and the stop mechanism at one of the top or bot. corners of the other side, and the center of mass about in the center of the door, you will induce a considerable torsional action on the door structure, can it take that? However that might absorb part of the energy too. Think of most heavy door stop mechanisms, they travel some distance and are pneumatically or hydraulically controlled, the flowing fluid absorbs the energy, allows time and distance of travel. A mechanical system along the same lines, assuming your stopping mechanism is mounted on the floor at the lower corner of the door, might be a set of spring loaded wedges which absorb the energy through friction and move some distance, but tighten to absorb more energy per mm trraveled, as they move. There are also some helical springs made out of flat spring steel bar stock, not round stock, wound around themselves (volutes?). They tighten upon the outer coils as they travel and absorb energy by friction. There are also, off the shelf, rubber and hydraulic energy absorbing bumpers.