Seismosoft | Earthquake Engineering Solutions

Hi all

Am modelling a braced concrete frame with a vertical shear link (eccentric bracing) and I modelled the behaviour of the shear link by a link element with zero length carrying only F3 and M2 and the other DOF set to be a very high value representing two springs; a translational spring and a rotational spring and before and after the link element a rigid steel arm to make sure all the deformations are resisted only by the link element (springs). But when I run the analysis with the link element and without it, nothing differed in the results. This means that the program didn't feel the link element. So what's wrong ?

Thanks a lot

Dear Mohamed Meshaly,

There are many things that can be wrong with your model, such as local axes definition, element connections, response curve parameters, analysis type, loading, etc.

With the limited details you have provided us with, we are afraid that it is virtually impossible to provide you with any further guidance or hints.

Seismosoft Support

Mohamed Meshaly,

We looked into your model and found out a number of modelling issues that you should address, such as, for instance:

- one of your columns was wrongly superimposed with a beam (this was conspicuously visible on the model rendering, hence we are surprised that you did not notice such a blatant modelling error)

- instead of using 'constraints' to model the rigid arms, you were employing inelastic frame element with a cross-section of 5 mm x 100 metres (yes, 100 metres!). This is a very dubious modelling choice, which, again, did surprise us

- according to the local axes you have defined, the translational degree-of-freedom of your shear link elements should be F1, not F3

- we cannot quite understand why you are using two rigid arms below and above the shear link elements. We would rather suggest you to employ only one rigid arm, placing the link element right above the truss, and then a rigid arm from there to the beam mid-span

- you state that you are experiencing difficulties in verifying the shear link correct behaviour, but the model you sent us is one with several bays and multiple storeys, which inevitably renders it complicated to verify the modelling. As we keep on stating in this Forum, you should instead start with a much simpler model (e.g. single bay one storey portal), make sure you get things to work there (in your case by "playing" with the shear link properties until you get the expected behaviour), and only after that pass onto more complex models

- you will notice that if you assign zero stiffness to all degrees-of-freedom of the shear link element, and then replace such zero values with e.g. 1E+15 and rerun the analysis, the results do change significantly (it is therefore simply a question of you adequately defining the shear link properties)

Seismosoft Support

Thanks a lot for your notes. I put the rigid arm properties like this (100m * 5mm) to be sure that it will be rigid enough to make sure all the deformations happen only in the springs (shear link). This was the same reason to use rigid arms before and after the two inelastic springs.Again, is it ok to define both springs (translational and rotational) in one shear link model ?

Really thanks for your time

Dear Mohamed Meshaly,

We suspect you are missing a bit the significance of the remarks we have made, but, ok, anyway, yes, the answer to your specific query is indeed "yes".

Seismosoft Support