Effect of soil–structure interaction and spatial variability of ground motion on seismic risk assessment of bridges - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 598

• Even though general purpose numerical analysis software can now effi -

ciently solve geometric non-linear problems (i.e. sliding at the pile-soil
interface, sliding and rocking at the strip footing-soil interface, closure
of deck-abutment gaps, etc.), analysis convergence is not ensured during
simultaneous material and geometrical non-linear phenomena, neither
can the results be easily verifi ed.

One solution to the above-described problem is to assess in advance the
locations of the soil-foundation-superstructure system that are anticipated
to be subjected to the highest level of inelastic demand and develop the FE
modeling strategy accordingly (for instance by prescribing refi ned mesh and
nonlinear capabilities solely to specialized areas of interest, i.e. upper soil
layers of the pier foundations and backfi ll).

22.2.4 Effect of soil liquefaction on the dynamic
bridge response
The vulnerability of bridge foundations to liquefaction-induced lateral
spreading has been clearly demonstrated by the extensive damage observed
in many past earthquakes, i.e., Alaska (1964), Loma Prieta (1989), Costa
Rica (1991) and Kobe (1995), among many others. Since then, extensive
experimental testing (on large-scale single piles and smaller centrifuge
samples) and numerical research have been conducted. The numerical
research can be classifi ed into three main categories: p -multiplier method
(Baziar and Dobry, 1995), p - y spring coupled with continuum soil material
models (Kulasingam et al. , 2004), and three-dimensional continuum method
(Elgamal et al. , 2008; Varatharaj and Muraleetharan, 2004). More recently,
liquefaction has also been considered in the framework of vulnerability
analysis (Bayram et al. , 2011; Brandenberg et al. , 2011; Elnashai et al. , 2009;
Kwon et al. , 2008), clearly demonstrating the signifi cant effect of liquefac-
tion on the seismic fragility of bridges through multiple different excitation
mechanisms. An example of the effect of liquefaction on ground motion
and soil stiffness (Zhang et al. , 2008) involves strong shaking, non-linear,
response history analyses where lumped spring and damping models are
used to represent the soil and foundation and consideration of lateral
spreading through incremental static analyses with prescribed displacement
of the laterally spreading soil. It is believed that future research will focus
on improved computational methods to establish a more reliable relation-
ship between ground motion intensity measures (IMs) and structural
demand in the presence of liquefaction. However, determining the optimum
IM is still a challenge especially for systems where variability in soil, struc-