两端固定梁，中间作用扭矩，用Staad/pro求解有问题。
Date Posted: 9/14/2002
Problem: My model is a simple rectangular beam fixed at both ends, with an applied torsional moment at the mid-span point of the beam. Results shows zero moment at one end. At the other end, the value equals the full amount of the applied torsional moment. The results are unchanged even in the case of uniform torsional moment applied throughout the span.
STAAD/Pro 的解决方法：
Version: ALL Build No: ALL
Solution: If you defined the beam as a single member, with fixed supports at both ends, it becomes a model with zero degrees of freedom. Under those conditions, there are no displacements to solve for. For such a case, STAAD by default releases the torsional degree of freedom at one end, and a message to this effect will appear in your output file. So, look at the output file and see if the following message is present
***STAAD.Pro WARNING - ALL DEGREES OF FREEDOM FIXED.
STAAD WILL RELEASE MOMENT-X AT FIRST JOINT ENTERED.
If you see such a message, go back to your model, and change the support at one of the nodes from
FIXED
to
FIXED BUT MY.
Alternatively, break up the beam into 2 members, so that a node is create at the mid-span point. This will change the model from a zero d.o.f system to a 6 d.o.f system, which hence wouldn't require STAAD to release anything on its own. Then change the applied load from a concentrated moment to a joint load MX at the middle joint. You will get the answers you expect.
专家的评论：
Thanks for the copy of the REI explanation (see above) of why STAAD cannot solve a structure with no free degrees-of-freedom at the joints (i.e., all joints defined as fixed support joints).
However, the explanation provided by REI is only one example among numerous severe deficiencies in STAAD. Although the suggested changes to the model will then permit a solution by STAAD, this approach is unacceptable. For example, suppose that the engineer desires to calculate a value of stiffness associated with a particular degree-of-freedom in a more complex structure than a fixed-fixed beam. In such a case, all joints in the structure would be fixed, and a unit value of support displacement would be applied as a support settlement load to the particular dof for which stiffness factors will be calculated. The calculated reactions at all of the supports (i.e., at all fixed joints) will be the stiffness factors associated with the unit support displacement. STAAD CANNOT do this!
Any comments?
|
