Force converted into Energy

[marisse]

I think this is very elemetary but i really can not figure out how can i solve this issue.....

here is my problem. I need to calculate the maximum energy a glass balustrade can resist due to impact...say caused by a running child.....i can calculate the maximum stress on the glass and i can calculate the maximum concentrated Load (F) to be applied on a given height of rail....but i can not figure out how can i convert this maximum concentrated Load (F) to Energy in temrs of Joules. Please help.

 

[prex]

The energy corresponding to a transverse load F that causes a displacement d of its point of application is Fd/2.

prex

http://www.xcalcs.com

Online tools for structural design

 

[rb1957]

if you can measure the deflection then prex's equation is ok, but then why bother (as you'll have tested the balustrade, so who cares what the internal energy is ?) ...

but i think this'll be hard to do. the other problem you have is that this is a dynamic load, the child will impact the balustrade with some force, but the energy/momentum is transferred over some time interval ... maybe there are "standard" factors for impact loading ??

i think a test (similar to a "bird" test used in aviation) ... maybe a bag of sand (lead shot) suspended from the ceiling ... different masses, different pendulum lengths, different release points will allow you to vary the test energy (which you can calculated easily)

good luck

 

[JStephen]

It's Fd/2, as stated above. This is just from integrating force (=kx) times distance.

With a brittle material, I'm not sure if that energy or the stress you calculated is real meaningful. Imperfections or scratches on the glass can lower its breaking strength, unlike, say, a steel plate.

I'd be very leery of designing something like that from scratch. Surely somewhere, somebody has a minimum thickness requirement for exposed glass. Results of running through it wouldn't be pretty.

 

[jhardy1]

This would generally be covered by building code or regulation. E.g. in Australia, we use AS 1288:1994. While only a VERY brief excerpt, the key requirements for glass balustrades are as follows:

Balustrade infill panels shall be Grade A safety glazing material (as specified in AS/NZS 2208:1996), with minimum thickness based on the glass panel area, but not less than 6 mm standard nominal thickness, for all balustrade infill panels which are not required to support the handrail loads.

Where glass is used as a structural member to support the handrail loads, only Grade A safety glass shall be used. The thickness used shall be determined using the appropriate design loads, and the allowable stresses for the glass material, but in no case shall the standard nominal thickness used be less than 10 mm.

Testing methods etc are spelt out in these two codes.

 

[14159]

I agree with JStephen:
"I'd be very leery of designing something like that from scratch. Surely somewhere, somebody has a minimum thickness requirement for exposed glass. Results of running through it wouldn't be pretty."

Surely you can get some manufacturer data or something else to help. I wouldn't do this with mechanics calculations.

DBD