## Staad finite element analysis

## Staad finite element analysis

(OP)

Greetings

How accurate is Staad finite element analysis.In case of water

tank resting on soil, can we give springs only KFY value, not

releasing MX, MZ.e.g.

supports

1 to 200 KFY 24000

We get very less moments in bottom slab.

Please respond.

Regards.

How accurate is Staad finite element analysis.In case of water

tank resting on soil, can we give springs only KFY value, not

releasing MX, MZ.e.g.

supports

1 to 200 KFY 24000

We get very less moments in bottom slab.

Please respond.

Regards.

## RE: Staad finite element analysis

a

## RE: Staad finite element analysis

## RE: Staad finite element analysis

Having said that, we can see from the numerous posts that many are just finding out how error prone this software can be. You would think that Research Engineers would take to heart some of the feedback they have gotten over the years. In my experience, they view the problems to be mostly with the user, not the software.

## RE: Staad finite element analysis

So this will be short...I second what RON has noted and urge the original poster to check out the other staad post for some real feedback.

## RE: Staad finite element analysis

support on soil as FIXED BUT KFY 12000(variable)

Regards.

## RE: Staad finite element analysis

FIXED BUT MX MY KFZ 12000.

because if you do not allow rotation about X and Y axis then

you should have all nodes prevented from rotaions and you may have

only one level of displaced nodes.

## RE: Staad finite element analysis

Tank is modelled as 3D resting on ground by Staad.

Can spring support be FIXED BUT KFY 12000.

Regards.

## RE: Staad finite element analysis

I've invested the money and don't care to spend more for another engineering design system.

## RE: Staad finite element analysis

Staad will not prevent you from defining springs as

FIXED BUT KFY 12000

..BUT, it is not realistic and does not represent reality.

in my view, this is wrong. it has to be

FIXED BUT MX MY KFZ 12000

in order to represent plate supported on springs.

## RE: Staad finite element analysis

## RE: Staad finite element analysis

If you are performing an analysis which requires the accuracy of finite elements, it would be best to use a package better than STAAD. STAAD has a very limited library of elements and provides very poor description of its available elements and their strength and limitations. I have known several engineers who have used STAAD for finite element analysis and had disasterous results. Also, the user support services for STAAD is very poor compared to other products if you run into problems.

For basic structural analysis STAAD is probably all you need. It is easy to use and relatively accurate. However, you would be fooling yourself to think it does advanced analysis properly. It will give you an answer but the answer may be wrong.

## RE: Staad finite element analysis

I am a registered user of STAAD. It does have several shortcomings,

however, if you stick to "standard" problems with finite elements, you

can get good results. I have, for instance checked the plates against

an analytical solution for vertical walls with varous loadings and found

STAAD to be accurate.

As for MATS or TANK BOTTOMS on the ground you need to use:

(Joint No) FIXED BUT FX FZ MX MY MZ KFY XX.XXX.

You must release all the other DOF's or you'll induce bogus membrane

stresses, and it will affect your moment results(this is what you're after,

I presume). Under no circumstances do you want to fix moments.

Since you have now left all the other DOF's free in all the

joints, you will induce instabilities in the solution unless you FIX

FX and FZ at one of the joints in your mat and FX OR FZ(not both)

in some other joint in your mat, away from the first. This will give

you accurate moments(not very sensitive to subgrade modulus, by the way)

and a stable solution. If you are interested in lateral soil resistance, then

use lateral SPRINGS, do not FIX.

## RE: Staad finite element analysis

In my experience finite elements (true finite elements)must be evaluated for several factors to encompass the behavior or response to the change in those variables. Not the least of which is the element type itself. So, in my interpretation, you cannot just run one file and consider the matter complete. And since the heart of the finite element method is a numerical approximation there is an inherent amount error in the analysis - how does STAAD report this error or even better how does STAAD minimize this error?

## RE: Staad finite element analysis

## RE: Staad finite element analysis

## RE: Staad finite element analysis

Inspector_1998(visitor)http://www.reiworld.com/Support/Pro/Verification.pdf

They compare their answers with ANSYS.

## RE: Staad finite element analysis

over one word. Maybe I should have said "flat plate

related problems." I do not used STAAD for tubulars,

tubular junctions, or multiple curvature shells. I do

think, however, and I think the STAAD verification problems

bear me out, that mats on Winkler foundations, rectangular

tank walls, and other "flat" problems with rectangular

elements can be solved accurately assuming the user's

boundary conditions are correct. On this last point see

nades, above and my response. I am not defending STAAD.

If anyone has any further problems about the use of the word "standard", then let them scream and yell to their

hearts' content.

## RE: Staad finite element analysis

## RE: Staad finite element analysis

However, Gentlemen, we are asking you to step out into the unknown, to really apply the product to engineering problems and not textbook examples. In this area, I ask you, are you completely satisfied with the STAAD product?

I have used STAAD for a number of years and have always felt that the problems I analyzed were appropriate for the software. In that respect, I got exactly what I needed from STAAD. But I will not perform complex dynamic analysis or FEA with the program. Which that program is marketed to do but doesn't live up to those expectations.

## RE: Staad finite element analysis

irresponsible remarkes by QSHAKE. The

"baseline" used to measure the accuracy

of the STAAD solution is stated in my

original post. The type of element used

is explained in the STAAD manuals. ERRORS

in a numerical analysis are dependent upon

boundary conditions and assumptions in

the analysis itself, as well as on

the numerical method. I see in this forum

numerous examples of faulty boundary conditions

associated with the use of the STAAD elements

in foundation mats or tank bottoms. The post

I responded to as well as previous and following posts

are prime examples of this.

For 1161(visitor)

For example: A moment's thought will enlighten one

to the fact that to make joints in a soil supported

tank bottom pinned in X and Z would be an error. Also,

as suggested in another post, to fix moments in Z, X,

and Y, would be in error.

These conditions would produce nonsensical results.

To evaluate a structural force associated with a

degree of freedom, one must release that degree

of freedom.

The Example 10, which is in the STAADPro 2001 Online

Documentation, is, as far as I am concerned, in error.

I will not work a problem such as this in the manner

suggested by STAAD. I refer you to the post I placed

earlier, using springs, and limited lateral restraints for

solution stability.

Happy howling,

## RE: Staad finite element analysis

Inspector_1998(visitor)## RE: Staad finite element analysis

Inspector_1998(visitor)## RE: Staad finite element analysis

My single point was that STAAD is marketed aggressively as the best structural program out there and yet over and over again I hear engineers complain about it, seem confused about its application, and doubt its results.

I haven't used the program for some years but when I did, weird results would appear and not correspond to the results from an exact replica model built in STRUDL. This was about 12 years ago and Eng-Tips forums still have posts appearing with STAAD issues.

When someone offers me a program to use and then says "Its a great piece of software as long as you keep to standard designs"...would you feel confident in using it? Not me.

## RE: Staad finite element analysis

Inspector_1998(visitor)