04-19-2010, 12:02 PM
(04-17-2010, 06:40 AM)kantiman Wrote: dear friends
i hv solve one RCC building in Etabs considering dynamic effects using response spectra method an i m getting natural period 2.37 sec an base shear 1319 kN. An i hv solved same problem manually also i got natural period 0.97 sec and base shear 1320 kN but , the problem s that natural period by manually an etabs r not matching plz some one help me i m attaching etab file also.
Hi kantiman
the period that Etabs gave you is the analytical period based on eigenvalues ((K-w~2M)=0), while the period that you calculate manually is based on the approximate formula given by your seismic design code (I guess Ct*h~3/4) that usually gives conservative value.
I roughly checked your model and it seem that every thing is ok. your numerical period is too long may be because of the story height, notice also that you didn't take into account the stiffness of the brick masonry walls which may decrease the period.
but which is strange is that with two different periods (numerical and empirical) you have the same base shear?!