Large Deflection Theory

[PrashVJ]

Hi,
I am doing a project on retrofitting of concrete beams.I am going to determine the response of the retrofitted structure analytically.As most of the journals regarding retrofitted structure performed elastic beam theory to find out the deflection and the corresponding moment of the structure,i am trying to find out response of it using large deflection theory.Please help me out in understanding "what is large deflection theory","why it is used" and "how to use it."

 

[paddingtongreen]

I found this, it is old (1956) but to the point.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[dtex]

There's plenty of stuff on the internet concerning Large Deflection Theory.

If your project "actually" requires this type of analysis, you might want to find someone else to work with you on it. It's not something that you can just read about for a few hours and then expect to use in a practical application.

Dan

 

[JoshPlumSE]

If you're talking about large deflections for concrete then you should more precise than to say only "large deflection theory". Large deflection theory, essentially, just assumes that the stiffness of the structure is affected by the deflection. That's certainly a simplification, but basically valid.

When most people say large deflection theory, they probably mean a geometrically non-linear analysis. The basic concept is that in your analysis, you apply a small fraction of the total load and analyze the structure. Then you re-evaluate the stiffness of the structure based on its new deformed shape and apply the next small fraction of the total load. Continuing each increment of load until all the load is applied or the solution diverges.

But, this isn't as relevant to concrete. In concrete you have to address MATERIAL non-linearity more than geometric non-linearity. Because at larger deflections, the cracking and yielding of concrete members is probably more important than geometric non-linearity.

Therefore, if you are using a program that uses "large deflection theory" don't just assume that it also handles the material non-linearity.