Energy Dissipation in a Structure

[sammy3]

I am having a hard time understanding the theory behind the physical energy dissipation involved in structures. Suppose I have two different cantilevered beams. One of them is rigid and the other one is flexible. If I apply the same concentrated force to the free end of both beams what are the consequences in regard to energy dissipation and stress distribution?

 

[GregLocock]

There's no such thing as rigid.

Howver, if one is ten times as stiff as the other, then you will only put 1/10 times as much energy into it.

Th stress distribution effect will depend on how you've made one beam more rigid than the other.

This would make a good homework question...

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[cvg]

if you apply the same concentrated force you will apply the same energy to both. the strain will be much less on the stiffer one.

 

[IRstuff]

Consider the cantilever to be a spring. Stiffness is then correlated to the spring constant. Work or energy input is proportional to k*deflection^2. Force is k*deflection. Same force results in less deflection in the stiff cantilever, hence less work is used.

TTFN

 

[rb1957]

i wonder if the point of the "problem" is that the internal stress distribution is the same for both the elastic and the "rigid" beams, it's just that the "rigid" beam doesn't deflect hence there is no energy considerations (no external work done, no internal strain energy).

 

[haynewp]

Maybe you have read about energy dissipation in seismic lateral systems and are trying to apply it to a statically loaded beam?





Mendacity is a system that we live in. Liquor is one way out and death's the other.
-Tennessee Williams

 

[drawoh]

sammy3,

Niggling technical point...

Energy dissippated is not a function of stiffness. It is due to internal damping, and whether or not you exceeded the yield stress of the material. Creep if it is present, is a factor too. Springs store energy.

JHG