The Ingenieur Vol 59 July-Sept 2014 The Ingenieur Vo. 59, July-Sept 2014 | Page 31

slabs. The piers consist of double octagonal
columns with edge dimension D=2m, with rubber
bearings connected to the deck. Both pier heights
are 5.91m. The bridge is simply supported through
a pair of bearings allowing free sliding and rotation
in and about both horizontal axes. The piers are
founded on piles cap. The configuration of the
bridge is shown in Figure 1. While Figure 2 shows
bridge cross section and bearing arrangement.

calculated using the British Standard. Furthermore,
the stiffness of seismic isolator bearing was
calculated based on the actual design of seismic
isolators following Eurocodes and the capacity of
the bridge (Figure 3b). The calculation shows that,
the shear stiffness of the seismic isolator is lower
than the stiffness of the rubber bearing pad which
is important in providing a longer period.
Table 1: Bearing Stiffness and design period
Bearing Type

Figure 2: Bridge Cross Section and Bearing
Location

Shear Stiffness
(kN/mm)

Period
(Sec)

Rubber
Bearing Pad

Figure 1: The configuration of the bridge

Compressive
Stiffness
(kN/mm)
713.0

2.160

1.13

Seismic
Isolator
Bearing

99.1

0.700

1.98

Figure 3a

Bearing stiffness is an important factor to
be considered in the analysis. Table 1 lists the
compressive and shear stiffness of both bearings
used in this study. The bearing design period (T)
is an important design factor and has a direct
correlation with bearing stiffness as shown in;
T = 2Π

W
KS g

where Ks is the shear stiffness of the bearing
and W is the total weight and g is the gravity. In
design practices of seismic isolators, the 2 second
design period is normally considered. Table 1 shows
the properties of both bearings used in this stud