G.B. SHERIF, H.E.EL KHORAIBIE, M.H. KOTB and A.A.SUMMRA
Department of Civil Engineering
Faculty of Engineering, Al-Azhar University
Ambient vibration measurements of many buildings have been recorded across the
world in the past to determine their dynamic properties, in particular, to ascertain the
properties of the fundamental modes of vibration. It is also recognized that the
experimental data from one region may not be used in another owing to the
differences in the construction methods and materials.
During an ambient vibration survey [Arlekar and Murty, 1997], a total of nineteen
buildings in Kanpur (India) seismic zone III are investigated to determine the
fundamental lateral transitional natural periods and the corresponding mode shapes of
vibration, as per the current seismic code for India. The investigated buildings are
reinforced concrete moment resisting frame (RC MRF) with un-reinforced masonry
bricks (URM) as infill walls.
Some infilled frame structures are analytically modeled using the standard analysis
software, ETABS & SAP 2000  where the diagonal strut model is considered.
Regression analysis of fundamental lateral natural period data from experiments is
performed and empirical expressions are obtained for fundamental lateral natural
periods of (RC MRF) buildings with brick infill walls.
The expressions in the current codes are found unsuitable for estimating the
fundamental natural period of (RC MRF) buildings with brick infill. As these
expressions grossly overestimate the natural periods, improved expressions are
The analytical numerical technique based on diagonal strut model, using the available
analysis software is found to be inadequate for determining the fundamental natural
periods of buildings. Thus new ratios of experimental and analytical natural periods