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 599

tural material and liquefaction potential are jointly present with geometri-
cal non-linearities (Brandenberg et al. , 2011).

22.3 Embankment-backfi ll-abutment-superstructure
interaction
22.3.1 Static embankment-backfi ll-abutment interaction

Various static spring-based approaches have long been developed for the
study of soil-abutment-deck interaction (Shamsabadi et al. , 2007; Spyrakos
and Ioannidis, 2003; Stojadinovic and Mackie, 2002). Despite the impor-
tance of modeling complex bridge lateral boundary conditions and the
existence of specifi c guidelines in the US (Caltrans, ATC, MCEER) and in
Europe (Eurocode 8-2) for the design of pile foundations and abutments,
only minor guidance is provided by codes for numerical modeling of the
entire coupled soil-bridge system. As a result, engineers resort to the simpli-
fi ed relationships prescribed by Caltrans to estimate the abutment-backfi ll
soil capacity and stiffness (CALTRANS, 2006). Based on passive earth
pressure tests and the force defl ection results from large-scale abutment
testing at UC Davis, a value for the initial stiffness is derived proportionally
to the backwall height:

=×× (

)

KKwh
i

1. [22.3]

abut

where w is the width of the backwall and ( h /1.7) is the proportionality factor
based on the 1.7 m height of the UC Davis abutment specimen. The ulti-
mate abutment load can be assumed to be limited by a maximum static soil
passive pressure of 239 kPa. In the transverse direction, the abutment stiff-
ness and strength obtained for the longitudinal direction can be modifi ed
using factors corresponding to a wing wall effectiveness and participation
coeffi cients of 2/3 and 4/3, respectively (Maroney and Chai, 2004).
Another simplifi ed alternative is the performance of a separate pushover
analysis that can be performed for the abutment and foundation systems
in order to quantify the lateral support stiffness of the bridge (Kappos
et al. , 2007). The advantage of this approach is that both soil and (abutment
and foundation) concrete nonlinear behavior can be considered as a means
to provide case-specifi c force-defl ection (i.e. P - y ) relationships that can, in
turn, be used as nonlinear spring boundary constitutive models in the push-
over analysis of the overall bridge structure.
Another effort was recently made (Sextos et al. , 2008) to extend the
above concept by performing a set of 3D nonlinear FE analyses on typical
Californian overpass abutment-embankment systems in order to provide
simplifi ed P - y relationships of the lateral supporting system as a function