COMBINATION of HIGH FREQUENCY MODES in SEISMIC ANALYSIS of IRREGULAR BUILDINGS
Seismic building codes of practice recommend dynamic analysis for the seismic analysis of irregular buildings. Further the building codes recommend complete quadratic combination (CQC) for the combination of modal responses. It is observed that CQC gives incorrect results if high frequency modes are included. Therefore some seismic codes (IS 1893:2002, BIS, India) restrict the use of use of CQC up to 33 Hz. The effect of rigid content in the high frequency modal response on modal response combination, in response spectrum method of analysis of building structures is discussed with the help of examples.