# Design spectrum seismic analysis

Dear Karamba team,

As a first step, I would like to thank you for supporting all students in Karamba facing difficulties. In my Ph.D. research, I model several tall buildings and apply seismic loads to them.
I have applied seismic loads in the past by using the statically equivalent method to tall buildings, and now I am going to apply seismic loads with a more advanced approach such as design spectrum.
Could you tell me how I can do this?
As I read the related topics, I was not able to grasp what I read.

An analysis of design spectrums on European standards found the following:
1- the several period of buildings should be calculated
2-It is important to calculate modal mass in the X, Y direction for the mentioned period
3-In order to determine the number of periods necessary, the sum of the modal mass by the last period should reach 90 percent of the total mass.
4- for each period, the design spectrum should be used to extract the response factor.
5-The forces should be applied to the stories after calculating the base shear
6. The structural responses of each mode will be collected, such as displacement, tension, moment, etc.
7- some sources, for combing the result of all modes, suggest with the square root of sum of squares of all modes

According to my understanding, I have these problems in Karamba:
1-I don’t know why a tall building’s first period is 4.7 (as in the spectrum, the maximum amount of period is 4). When a fixed joint becomes pinned, the period will also change significantly.
2- Second, I was unclear as to why you changed the weight of a structural element to near zero, and then applied a point mass load. I worked with a tall building, and my floor slabs were modeled as a shell with appropriate heights and weights to behave as concrete slabs.
3-The modal mass for the natural vibration component is calculated in a single direction, and there are no separate X and Y values.
4-The main issue is that I am unable to extract a result for each mode; for example, the number of modes is 5. When I connect a model view or beam view component by changing the mode, I can see the deformation, but when I connect a nodal displacement component, there are not five calculations for each mode. For each mode, how should I extract the structural response results?
Overall, would it be possible to conduct a design spectrum analysis using Karamba?
For my next step, can time history analysis be applied to seismic analysis in Karamba?

Sincerely yours,
Pooyan.