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4.2 Effect of Coefficient of Friction
It is seen from Figs. 4.3 to 4.6 that for a particular time period and coefficient of critical damping, as
the coefficient of friction increases, the peak displacement decreases in the case of building with free
sliding base. This is logical, since the resistance against sliding of the system decreases as the
coefficient of friction between the sliding surface decreases and the buildup of a large inertia force in
the superstructure becomes restricted. Thus, the spectral acceleration of such a system decreases.
Similar trend is generally true in the buildings with restricted base sliding system. The slight departure
in this trend observed in few cases is due to the fact that positions of stopper are different in different
building parametric cases.
4.3 Time Period Effect
It is observed from Figs. 4.3 to 4.6 that for both the El Centre and Koyna shocks, the acceleration of
the restricted base sliding buildings -decreases in general as the time period increases for a particular
viscous damping coefficient and coefficient of friction. For same building systems, the acceleration
values are more when they are subjected to Koyna shock than that in the case of El Centre shock. But,
the acceleration response of the free sliding system is independent of its time period for different
values of coefficient of friction.
4.4 Influence of Stopper's Position
It is seen from Figs. 4.3 to 4.6 that if the stopper is placed close to the building (before its sliding), then
its acceleration approaches to the corresponding values as obtained in the case of fixed base. But, if the
stopper is placed at a distance approximately equal to the peak displacement of the free sliding system,
far away from the building, then its acceleration is very near to that of the corresponding values of the
free sliding system. This trend is observed in all the building systems subjected to both the earthquakes
(Koyna and El Centro).
Table 3.1 shows the position of the stopper for different time periods of the system ranging from 0.4 to
0.8 seconds subjected to Koyna and El Centro shocks. These are the most feasible ranges of stopper
positions for different mass ratios. This study shows that if the stopper is placed anywhere in this
range, then the absolute acceleration of the top mass of the system is much less than the corresponding
fixed base system. The occupants of the multistory buildings will have psychological comfort by
providing stopper in the sliding base system.
4.5 Effect of Mass Ratio
From Figs, 4.3 to 4.6, it may be observed that as the mass ratio increases, generally, the acceleration
response decreases in all the cases of parametric combinations for a particular time period and
damping coefficient in the case of free sliding base. But, generally, no definite pattern of acceleration
response variation has been observed in the case of buildings with restricted base sliding with varying
values of the mass ratio.
5. CONCLUSIONS
The following conclusions are drawn from the seismic response study of multistory masonry building
with restricted base sliding system: