I am analyzing the beam with simply supported ends . in this case i have made use of enforced but without ticking the Fy option . i am getting the warning message of instability. then is it necessary to take care of the structure or not. It is the book problem.
Hi,
Can you please attach the relevant model so that i can check the reasons for this warning?
This is the file that you wanted to see. help me as fast as you can. ok
In most finite element analysis applications (STAAD.pro, RAM Elements) the default is to treat the model as a 3D Space frame (6 degrees of freedom at each node). A single beam on two pin supports is actually not stable in a space frame analysis because the beam can spin. In your case, the beam could also rotate about node 1, pivoting on the Y axis since node 2 was not restrained in the Z direction.
Here's how I would suggest you define your supports in the B1.std file:
SUPPORTS1 FIXED BUT MY MZ4 FIXED BUT FX MX MY MZ
As per your suggestion i have made changes and i got no warnings. I have also analyze the structure with enforced but with the same condition and it showed no warnings. I want to know what is the real difference between the fixed and enforced but support.
When you use enforced, the program applies a very stiff spring along the degree of freedom that is restrained. Thus, that degree of freedom is an active one in the stiffness matrix and hence solved for, except, its value will turn out to be zero during the calculations.
When you treat it as FIXED, that d.o.f is eliminated from the stiffness matrix, and is treated as a known value of zero, and thus not calculated.
From a numerical standpoint, they both produce the same result. However, enforced has some advantages such as it is suitable for solving support settlement problems when plates and solids are present in the model. The FIXED support does not lend itself easily to such problems.
can anyone suggest what happens when i tick the forces & moments in the fixed but support option.