Hinged Frame with Diagonal Bracing

[aodonne1]

I am trying to develop a simple model of a totally hinged frame of rigid elements that only uses diagonal braced members for lateral resistance. Can someone please give me some advice regarding the simplest way to build this model. For example, which elements to use and how to ensure the end of each element is pinned and not carrying any moment.

Thank you,
Andrew

[vesna]

You can use elastic beam-column or truss elements for your rigid elements. The type of elements you want to use depends on what rigidity you want to achieve. In case you use elastic beam-column elements to define pins you need two nodes at each element end.

Lets say you have nodes 1 and 2 at node i and nodes 3 and 4 at node j. If your element is from nodes 2 to 3, you can define pins in the following way:
equalDOF 1 2 1 2
equalDOF 4 3 1 2

In case you use trusses for rigid elements, by definition they are pinned at their ends.

[Djeras]

Hello Vesna

I´m modelling a CBF. Concerning this problem but in 3D moddeling,

What if one of the master nodes, let´s say node 4, a slave node of a rigid diaphram? Would that be a problem ?

[fmk]

depends on the constraiint handler you use .. the transformation constraint handler cannot folllow constraints, i.e. one node constrainied to another constrained to another. use Penalty method for such cases

[Djeras]

Ok, Thank you on that one

How about this proc for creating an hinge at the end of the braces --->>

where,
matID_HINGE ----> is the material associated to the rotation around local 2 & local 3 axis
matID_Rot -------> is the material associated to the rotation around local 1 axis

set matID_HINGE 3
set E_RH 1E-7;
uniaxialMaterial Elastic $matID_HINGE $E_RH

set matID_Rot 4
set E_RH 1E7;
uniaxialMaterial Elastic $matID_Rot $E_RH

proc Hinge_Frame1_LeftBrace {eleID nodeR nodeC matID_HINGE matID_Rot} {

element zeroLength $eleID $nodeR $nodeC -mat $matID_Rot $matID_HINGE $matID_HINGE -dir 4 5 6 -orient 0 4.5 4 0 4 -4.5

equalDOF $nodeR $nodeC 1 2 3
}

# nodeR has already a rigid diaphragm constraint
# #### Is this a correct approach ?

Another question regarding 3D analysis,
in a CBF structure can we only represent X bracing part of the frames in 3D ? ´Cause even if the elements are physically disconnected in the model , the rigid diaphragm ensures all the structure is connected and therefore stable right on the very first step of the Static analysis.

The Problem here is that I believe constraints are not well defined ´cause on Static analysis the Newton-Raphson algorithm fails on the very first step

[colco]

Dear Djeras
Hi
I am modeling CBFs in 3D. The beams and braces are pinned at their ends. I am modeling pin connection by zeroLength elements and equalDOF command. I have encountered the same problem as you mentioned. I was wondering if you have possibly reached to a definite conclusion about this problem by now.
Your reply would be greatly appreciated.
Best regards

[Gholamreza]

informative