Structural Analysis

[audu1985]

I am a bit confused about the difference between the following:

-I know there is a deformation method for the analysis of indeterminate trusses.
-I also know that there are force methods for same...
-Is there a force-displacement method separate and distinct from the above two? I have not seen a lot of literature dealing with this. and I want to apply it to the analysis of trusses. Please help me. also want is the difference between using this for the analysis of trusses and using the direct stiffness matrix?

Rgds,

John Audu
Nigeria

 

[14159]

"-I know there is a deformation method for the analysis of indeterminate trusses.
-I also know that there are force methods for same...
-Is there a force-displacement method separate and distinct from the above two? I have not seen a lot of literature dealing with this. and I want to apply it to the analysis of trusses. Please help me. also want is the difference between using this for the analysis of trusses and using the direct stiffness matrix?"

I only know of two real distinctions - force methods and displacement methods and the difference is in what you're solving for as the unknowns in your system of equations. Displacement methods would be slope deflection, matrix displacement, etc. I haven't used force methods for so long that I've forgotten them. People give these methods lots of different names.

Are you designing these things for real in an office? If so, then there's only one reasonable method and that's the matrix displacement method. The reason it's reasonable is that there are zillions of programs out there that can be used to do the analysis and many of them are very cheap. Any reasonable structural engineering operation can afford at lest a 2D analysis/design package. In the last 10 years, I haven't heard of a single instance of somebody calculating something like this by hand. Even if the engineer knows the method very well and is very efficient, the program is the way to go. For example, if you use a classical manual method to get your results, then the architect moves something by 2-feet, you wad your papers up and throw them in the trash, start over in its entirety. If you use the program, then you open your file, move some nodes for about 4 minutes and hit "run" again. Classical structural analysis must be known and understood for the good of the engineering world, but in the design office, it's as dead as a doornail.

DBD

 

[rb1957]

DBDavis,

now you have! i'll sometimes solve single redundant structures by hand just to keep my brain working ! i prefer the unit force method.

i would also like to see more people (particularly young engineers starting to use FEA) checking their FE results with hand calcs.

audu1985,

there are many hand calc methods, Bruhn is a reasonable text. as DBDavis mentions, most of these methods are little used these days, 'cause of FEA. if you want to research this, look for structure's texts from before FEA, back in the 40s and 50s.

good luck

 

[mrMikee]

audu1985,

Back in college the textbook I used was "Matrix Methods of Structural Anaylsis" by Wang which I think has a pretty good approach to teaching matrix methods. When I took the course I did most of the homework by hand. It has both displacement and force methods. Costs about $17 used US$.

-Mike