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I have a problem understanding the construction of a wooden house, regarding the joint of the beam and truss in 3D. In my perception all wood joints should be flexible, i.e. joint should transfer shear forces and axial forces only.
So I have made a model of the house with pillars in the walls assign as trusses and wooden braces in the wall also assigned as trusses. Rafters running from the ridge of roof to the wall plate of external walls are assigned as beams. Wall plates are assigned as beams.
All beams in the model have “end released” ends. In that way I shouldn’t have any internal moment in any end joint.
The program will not allow that construction. It demand that I put rx ry rz restraints in the nodes of the jonits I have end released. But what is the point of end releasing beams when I have to put restraints in the joint afterwards?
Hello,
please clarify your question, in particular the final one. The program allows any kind of modelling, hence simply check end releases at the end. I see from your model that the moment is correctly released at the top of the pillars.
It is not clear why you want to apply restraints on the joints; you may want to apply only internal constraints or releases.Hello Keymaster
Thank you for support.
To help clarify my question I have uploaded 2 new models which are simpler than the one in my first letter. Again the models are dealing with beams and trusses. If you set view “colour by section” the beams should be shown in green and the trusses in red colours.
Both models have pillars set as “truss” and rafters and horizontal beams set as “beam”. The load is point load pointing downward in every roof node.
Both models have end released horizontal beams.
The first model “wooden house MIDDLE RAFTERS END RELEASED.nxt” have the middle rafter end released. The second model “wooden house ALL RAFTERS END RELEASED.nxt, have all rafters end released.
The first model does work fine. The second model does not function and comes with error
ERROR:Likely lability detected at node 6 – dof rxIf restraints are set in nodes of the roof corners (Rx Ry & Rz) and restraints are set in the end of roof ridge (Ry) the second model will also work fine.
Q1: If I put rotational restraints in the nodes at the end of an end released beam, do I have then a rotational beam or a fixed end beam? Wouldn’t it just be the same as if I didn’t released the end of the beam?
Q2 I have put restraints instead of constraints, because I don’t know how to apply constraints yet. Would it do a difference if I used constraints?
Thank for a great software
Hello,
here we’re discussing about the static scheme to adopt, this is up to you to decide assumptions for your model. Answering your questions:
1. End releases are a constraint inside the beam, while resraints are applied to the nodes. Hence, if you release moments in a simply supported end, this is redundant: use only a simple simple support without end releases, or a fixed support and rotational end release. So yes, it’s just the same behaviour without end releases, but the contemporary presence of both can cause labilities
2. no, constraints tie degrees of freedom of 2 different nodes together, this is not your case.Trusses have only axial response – no releases for them. Only beams can have releases.
I hope this clarifies, regardsNo sorry, it did not clarify my confusion. Maybe it is easier to tell what I want
I want all rafters to be simple supported on both top plate and ridge beam. The rafters have to be set as beam so I can assign distributed load on the rafters.
If I draw the rafters, top plate and roof ridge as beams then they all are fixed together as a fixed frame, and that is not what I want.
In the joints of two beams I want only transfer of share and axial forces, not the moment forces.
How do I draw that?
Best regards
The rafters and roof ridge then should be beams with end releases for both moments at ends. Don’t apply restraints on the internal nodes, use them only at the base.
Beams with end releases are generally labile, so you have to take care of the assembly. Your model “wooden-house-ALL-RAFTERS-END-RELESED” is correct, except that the side beams is deforming too much (see displacements in case LOAD 1 – 33cm!). In any case, the moment is not transmitted as tou can see in Diagrams view.
Sorry my model “wooden-house-ALL-RAFTERS-END-RELESED” have restraint in the roof corners. (I must have forgot på save the model with the restraints). If I remove the restraints i get error:
ERROR:Likely lability detected at node 5 – dof rx
The new file below is without the restraints
Hello,
yes, there are 2 problems:
– all the columns must be beam, otherwise the assembly is obviously labile. Considering for instance node 5, you have all trusses and beams with end releases.
– you must restraint the rotation (torsion of columns) at the base.Please find attached the corrected model.
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