Seismosoft | Earthquake Engineering Solutions

Hi,
I would like to know if discretizing the structure in more elements the chord rotation can be considered correct or to have the correct value must refer to a single element.
thanks

Hi,

The values provided by SeismoStruct correspond to the chord rotation observed for each computed element. This is, if you define 3 elements to model one beam, the chord rotations provided correspond to each individual element of the beam, an the actual value need to be computed based on the displacements and rotations observed at the end nodes of the actual beam (3 elem.). Nevertheless, based on ongoing studies, the use of a "simplified" beam corresponding to one single FB with the cross section equal to the actual beam end's, might lead to similar results, especially if your structure is govern by a column sway mechanism (usual present in structures design without seismic provisions).

Note that usually, columns can be modeled with a single FB element and, this way, you can directly extract the columns chord rotations from SeismoStruct.

Hope this (long) comment can help you,
Romain

Many thanks Romain, will shape the column with a single element.

is the chord rotation calculated in program base on plastic+yield rotation or not calculated only for plastic rotation? .what i should enter for this value in performance criteria? enter plastic rotation in performance criteria or no enter ultimate rotation (plastic+yield)

The chord rotation calculated is the total chord rotation.

Note that the chord rotation is directly comparable to code-based limits only when the element has not been discretized.

Do a search on "Material Inelasticity" in the Help system to get some additional guidance on this with regard to preferred element type, etc.

thank you huffle

are you sure about ultimate rotation? ,if we choose inelastic plastic-rotation force base in element class, should we check rotation for this element in ultimate rotation?(i.e (plastic+yield)) .according to your opinion if we want to check rotation according to fema356(asce41) we should add yield rotation to the value which in exist charts in those code yes? was this clearly mentioned in help that chord rotation is ultimate rotation ?i want to be sure because i should reference this in my thesis if i use ultimate rotation in performance criteria

Well, you are right that FEMA 356 limits are placed on plastic rotation only. I have merely assumed that chord rotations reported in SeismoStruct are the total values becasue I see nothing to indicate otherwise. I still believe this to be the case.

So, I believe you will either have to estimate the yield rotation by hand and add it to the permissible plastic rotation from FEMA 356 before comparison with SeismoStruct values, or subtract the yield rotation from the SeismoStruct values for direct comparison with FEMA 356 limits.

Confirmed.

Seismosoft Support