Strut modelling in modelling masonry infills in RC frame

[Anonymous]

I am trying to model masonry infills as struts in the context of a RC frame and the initial idea was simply jointing them to the frame by introducing strut compression-only elements with no weight, but same physical properties of the masonry by means of the definition of a new material. This has also been described in the link below.

(https://forums.autodesk.com/t5/robot-structural-analysis-forum/infill-wall-modeling/td-p/6395335)

To this regard would it be fine to simply joint the new strut to the structural node?

However, some methodologies propose the introduction of rigid links in the nodes, plastic hinges at a calculated distance from the nodes to account for the local plastic failure in ultimate conditions of the structure (see picture plastic hinges) and assign a force-displacement relationship not just to define the hinge, but for the strut as well.

Unfortunately, I did not find where in Robot it is possible to assign this force-displacement relationship to the strut, or if it is simply not possible and I should use a different element.

Another question is: when the implementation of the rigid link is mentioned(picture strut model) in the text it is described as the area around the node "modelled with elements of infinite stiffness". If I would like to apply this concept to a whole structure, and logically I assume it would not be the same thing as defining a fixed constraint when it comes to find an equivalent tool in the software. Conversely, should I define a local rigid link with the master node in the node itself and the slave node where the plastic hinge is?

Many thanks for your help (and patience in reading) in advance.

[Artur.Kosakowski]

Hi @Anonymous

IMHO creating  such complex model may cause you more harm than good. I'd rather use compression only bars alone but it is up to you.

You may use short bars with large(r) stiffness as well as rigid links with the master nodes in the corners. The force -  displacement can be defined in the release definition (if so you cannot use compression bar for the strut at the same time). 

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Thank you very much for your prompt reply.

I totally agree and that was my fear too because that conceptualisation might be useful for understanding local effects but overall in the structure I don't honestly know if the benefits might worth the effort. 

In conclusion (just as a confirmation), your recommendation would be to either use plastic hinges, short columns (to simulate a higher stiffness) and a strut OR alternatively not defining the plastic hinges and instead introducing the compression bar. Is it correct?

Many thanks again.

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

Personally I'd try to avoid plastic hinges and keep the model simpler (with compression only bars) but you may want to create a simple test example and decide what works better for you.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.