Infill Element Behaviour

[Rajen]

I have modeled a six storeyed RC frame building considering infill walls. Thereafter, I carried out pushover analysis to understand the response of the RC frame wit infill wall.

From the post processor data I can see the deformation of struts of infill panel in each direction. The struts deformation gradually increases with with load factor. Some of the struts shows sudden decrease of deformation (mostly struts at GF level). How can I determine the ultimate capacity of the infill panel from this data?
How can I also understand how this infill panel contribute to the strength of the RC frame before after they reach ultimate deformation?

[seismosoft]

Although we do not know the details of your model, note that a slight decrease in the deformation demand of some members can be expected, due to the redistribution of forces in the building. A sudden decrease of the infills deformation, especially in the Ground Floor level is very uncommon. Are you sure that there is a decrease in the deformation with increasing load factor?. have you plotted the infill deformation against the top displacement to check things?

A pushover analysis is the best tool for what you want. In general, for typical RC frames and infill panels, there is a peak of the pushover curve, after which there is a gradual strength decrease due to the failure of the infill panels.

Seismosoft Support

[Rajen]

Thanks for your reply. Yes, there is decrease in the deformation with load factor. I have plotted the infill panel deformation graph for struts (Deformation vs Load factor).

I have analysed the model using pushover analysis. How can I validate that infill panel fails when the strength degradation begin from peak? Strength degradation may occur due to different failure modes (crushing of core, crushing of unconfined concrete...) of surrounding frame also? How can I ensure at which point of pushover curve did infill frame fail?

[seismosoft]

The infill panel model that we are using is nonlinear, hence it has a failure point with a peak capacity and strength degradation after that.
In order to check things, go to the post-processor and extract the element results for the infills (Infill Panel Forces & Infill Panel Deformations).
Regards,
Seismosoft Support