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Can anyone tell me the difference between RESTRAINED & CONSTRAINED?3Q
- Thread starter ericyuxin
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Joint restraints can be assigned to any joint in the model, not just those on the ground. A joint restraint restrains movement in any or all degrees of freedom depending on which DOF you select.
Joint constraints are different from restraints. Constraints are used to connect 2 or more joints together in any or all degrees of freedom, including the effects of the offset distance between the joints. Select joints, then Assign menu>Joint>constraints
Joint constraints are different from restraints. Constraints are used to connect 2 or more joints together in any or all degrees of freedom, including the effects of the offset distance between the joints. Select joints, then Assign menu>Joint>constraints
Joint Constraints
I had difficulty with joint constraints, when I constrained a number of joints together. What happened is, static equilibrium was not satisfied for the model. The lateral loads times the moment arm about the base (a point) did not equal the reaction loads about the same base (a point). This is pretty easy to check, by putting a single load on the structure.
So, if I use joint constraints, I will check that these constraints have not extracted some moment out of the problem, and this could be substantial. What I ended up doing is using rather stiff spring connectors between joints rather than joint constraints between joints.
I had difficulty with joint constraints, when I constrained a number of joints together. What happened is, static equilibrium was not satisfied for the model. The lateral loads times the moment arm about the base (a point) did not equal the reaction loads about the same base (a point). This is pretty easy to check, by putting a single load on the structure.
So, if I use joint constraints, I will check that these constraints have not extracted some moment out of the problem, and this could be substantial. What I ended up doing is using rather stiff spring connectors between joints rather than joint constraints between joints.
Hi jrmack, constraints should satisfy static equilibrium unless you've tripped across a bug.. which is always a possibility. You can easily verify static equilibrium by creating a simple model with 2 joints, one joint 10 ft above the other and assign a body constraint to both joints for all 6 dof. Assign restraint on the bottom joint in 6 dof. Assign a lateral load to the top joint of, say 1 kip. Restraint reaction is 10 kip-ft moment as expected. The constraint automatically considered the offset distance
I wonder if maybe the self weight or some other loads got included in your reactions and that threw you off?
Maybe I misunderstood, but I don't see how SAP's constraints 'extract out the moment' in a model. Maybe you can provide more details. And when you say you used 'spring connectors', are you referring to a 2 point link?
I wonder if maybe the self weight or some other loads got included in your reactions and that threw you off?
Maybe I misunderstood, but I don't see how SAP's constraints 'extract out the moment' in a model. Maybe you can provide more details. And when you say you used 'spring connectors', are you referring to a 2 point link?
Stressed
I also tried the model you suggested.
>>one joint 10 ft above the other and assign a body constraint to both joints for all 6 dof. Assign restraint on the bottom joint in 6 dof. Assign a lateral load to the top joint of, say 1 kip. Restraint reaction is 10 kip-ft moment as expected<<
But it doesn't work. The error message says "more than one constraint, restraint and/or substructure external connection applied at DOF ... at joint ...". Even if I apply only one restraint (rotation about 2) it doesn't work. Any thoughts?
I also tried the model you suggested.
>>one joint 10 ft above the other and assign a body constraint to both joints for all 6 dof. Assign restraint on the bottom joint in 6 dof. Assign a lateral load to the top joint of, say 1 kip. Restraint reaction is 10 kip-ft moment as expected<<
But it doesn't work. The error message says "more than one constraint, restraint and/or substructure external connection applied at DOF ... at joint ...". Even if I apply only one restraint (rotation about 2) it doesn't work. Any thoughts?
I see dawn836 posted with exclamation marks (!!) for emphasis. Older versions of SAP2000 do not permit users to assign constraints and restraints to the same point. But this limitation was removed approx. 2 years ago, so yes, you absolutely can assign constraints and restraints to the same joint if you have SAP version 8.
My point was that use of constraints do satisfy static equilibrium in every case that I've seen and considers offset distance between constrained joints. I am still confused by jrmack's comment about SAP2000 constraints 'extracting out the moment'.
My point was that use of constraints do satisfy static equilibrium in every case that I've seen and considers offset distance between constrained joints. I am still confused by jrmack's comment about SAP2000 constraints 'extracting out the moment'.
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