S. Hosni et Ac. Heidebrecht, INFLUENCE OF SITE EFFECTS AND PERIOD-DEPENDENT FORCE MODIFICATION FACTORS ON THE SEISMIC RESPONSE OF DUCTILE STRUCTURES, Canadian journal of civil engineering, 21(4), 1994, pp. 596-604
A foundation factor, F, is incorporated in the National Building Code
of Canada (NBCC) design base shear formula to account for amplificatio
n of bedrock ground motions as these propagate upwards through the loc
al soil deposit (site effects). In the NBCC, the value of F is specifi
ed as a function of the local soil type and depth, irrespective of the
ductility capacity for which the structure situated at the surface of
the soil deposit is to be designed and detailed. On the other hand, t
he ductility capacity of the structures is taken into account in the c
ode by the force modification factor, R, for which values are specifie
d depending on the type of the structural system. The current study in
vestigates the influence of the ductility capacity of engineering stru
ctures in mitigating the site effects. Simple bilinear single-degree-o
f-freedom models are used to simulate the seismic response of structur
es, underlain by soft or stiff soil deposits and subjected to seismic
ground motions. These structural models are also used to investigate t
he effects of the period-dependent force modification factors on the s
eismic response of structures. The results show that site effects are
less significant for ductile structures, as compared with structures t
hat respond elastically. The results are then used to evaluate the cur
rent code provisions for site effects. The current study also shows th
at using period-dependent force modification factors to derive the cod
e design base shear not only is recommended for short period structure
s but also is necessary to provide a realistic simulation of the seism
ic response of these structures.