Shear capacity of slider element

[h.nribet]

Hello all,

I am currently developping a EFM (equivalent frame model) for a URM (un-reinforced masonry) building with concrete slabs. I have chosen to model piers and spandrels by means of elastic frame elements, and to concentrate non-linearities at the extremities of the piers with plastic hinges, as well as mid-span with a shear "slider". This is accomplished through the use of link-elements.

Ideally, the link-element associated to the shear slider should follow a linear-brittle constitutive law, to model brittle failure. Since this isn't available in Seismostruct I have chosen a bilinear model, which will inadequately model the behaviour under cyclic loading or during a pushover: the drops in bearing capacity resulting from shear failure will not show up.

My question is the following: could I artificially introduce a small non-linear FB frame element (associated with equivalent material properties, section and using a brittle constitutive law such as the concrete tri-linear model) instead of the slider link-element, in order to make use of a shear performance criteria with no or a small residual capacity? Would this assumption be correct?

Hugo

[seismosoft]

Hello Hugo,

Probably the best way is to use one of the Modified Ibarra-Medina-Krawinkler curves that are available in SeismoStruct 2018. They all very versatile and they all have a maximum and a residual strength.

Seismosoft Support

[h.nribet]

Dear Seismosoft support,

Thank you for answering my query. I have played around with the Modified Ibarra-Medina-Krawinkler curve to draw up a backbone curve corresponding to my situation, plotting shear shear vs lateral displacement. However, after multiple tests (simple reponse control pushover analyses) on single links with the newly assigned curve in the loading direction, it seems that the element cannot "capture" any force. The user manual specifies that this model can be applied to a force-displacement relationship but so far I have been unsuccessful in doing so. Is this a known issue, or I am doing things wrong?

Regards,

Hugo

[seismosoft]

No, it is not a (know at least) bug of the program. Can it be that you are using the curve in a different DOF of the link element from the one that you are loading?
Note that you can graphically display the local aces of the elements in the pre-processor; in this you can be sure of what DOF you are loading.

Seismosoft Support