Dynamic/earthquake analysis - Computational Analysis and Design of Bridge Structures - page 544

17.5 3D illustrateD examPle of a high-Pier
BriDge suBjecteD to oBlique inciDence
seismic WaVes —Pingtang BriDge, PeoPle's
rePuBlic of china

The time-lag effect in seismic wave propagation has an influence on large-
span structure. This case study demonstrates the effect of the topography
and the angle of the oblique incidence waves. 3D finite element analysis
with equivalent artificial boundary is used to simulate the radial damp-
ing of continuous medium within a finite domain (Gu et al. 2014). This
equivalent artificial boundary can be represented by viscoelastic artificial
boundary elements to simulate the spring and dash system around the soil
outside boundary.
The numerical model of a continuous rigid bridge with the total length
of 560 m and its spans of 100 m + 180 m + 180 m + 100 m was built.
The pier is a RC double wall of 2 m thickness, 9 m depth, and about
30 height. The diameter of the circular pile is 2.8 m. The bridge layout is
shown in Figure 17.25(a). The numerical model of the bridge with special
topographic shape is shown in Figure 17.25(b). The parameters of the
ANSYS model elements (ANSYS 2012) and soil are shown in Tables 17.8
and 17.9, respectively.
Anza Earthquake record of a short duration was selected for this study.
The results of the internal forces are compared by inputting the seismic
wave in vertical direction and on an oblique incidence. The bottom and the
top of the pier are the most vulnerable locations in this rigid continuous
bridge. The force at the bottom is larger than that at the top in this case.
So the internal forces at the bottom of piers are studied. Locations of the
numbered piers are shown in Figure 17.25(a). The amplitudes of the internal

10000 + 2 × 18000 + 10000 = 56000

340

200

3 4

2

280 280

(a) (b)

Figure 17.25 Layout of Pingtang bridge and FEA model: (a) elevation (in cm); (b) soil-
bridge finite element model to simulate the spring and dash system.

Table 17.8 3D FEA model and elements
Element BEAM188 MASS21 SOLID45 BEAM4

structure Girder, pier, pile Lump mass Soil Rigid