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# Building mode shape and time period calculations for Seismic analysis

## Building mode shape and time period calculations for Seismic analysis

(OP)
Good Evening to all

I m trying to learn the dynamic analysis of a building.I hope you people help me in understanding the subject.While following the example given in a book by Mr. Duggal,I saw that it is required to find the mode shape and time period of a building before calculating the base shear,etc.

I tried to calculate the mode shape and time period of building with "n" number of floor.I m attaching a file,which containn the procedure/method which I followed.I request the concern experts and other engineers in this forum to look at it guide me to calculate the mode shape and time period of a building.

If possible please provide an example (manual method) for calculating the mode shape and time period of a building of at least 5 or 6 storied.

I hope you all will help me in learning this subject.

thanks & regards
Mofiz Ahmed

### RE: Building mode shape and time period calculations for Seismic analysis

(OP)
Hi to every one,is there anyone reading this...........I m waiting for a good reply to my question????

### RE: Building mode shape and time period calculations for Seismic analysis

If you are looking for an exact solution for the frequencies and mode shapes then there is no other way that to formulate the mass and stiffness matrix for the structure, then calculate the frequencies by calculating the roots of the system characteristic equation.  The current I-Codes basically give some rules (described by the vertical and horizontal irregularities) to assume the structure's behavior is dominated my a simple first mode and then it goes on to give some simple estimates (and I stress estimates) of the fundamental period; but again these are only rough approximations.  Chopra's Structural Dynamics book has some pretty good information on this and you may need to brush up on some Linear algebra.  I hope this helps.

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