Difference between a load applied constantly or time-dependent?

[Barau]

Hello all,

I have a question related problably to vicoplasticity behaviour of a statically indeterminate beam (the one annxed). There are any difference of applying this load P constantly and applying the same load just in a small period of time (for example, 1 second, almost like an impact)? If yes, how this or these differences will drive the sizing of this structure?

Thank you in advance,

 

[hokie66]

That depends on the material and on whether or not the loading is within the elastic range of the material. If creep is a factor, e.g. as in reinforced concrete, then deflection is time-dependent.

 

[cap4000]

Just checked a 2 inch slab over a 2 inch metal deck with a 4,000 pound safe rolling over it. With a pallet truck the move was done in two. The door was taken off and moved separately. Using Ram Advanse shell program the deflection was 0.25 inch. With 9.5 foot spans the floor deflected immediately. Not time dependent trust me. It was so heavy that the safe got stuck in the elevator half way up.

 

[hokie66]

cap4000,
If your deck acted as a reinforced concrete deck, i.e. composite steel and concrete, there would be additional time dependent deflection if the load is left in place. If the steel deck takes all the load elastically, then there would not be additional deflection.

 

[cap4000]

hokie,

The building was 25 years old. I believe you are correct that if the load was placed mid span on the slab for the long term the slab would have deflected much more and likely would have failed.