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Design of bridges against large tectonic deformation

I. Anastasopoulos, G. Gazetas, V. Drosos, T. Georgarakos and R. Kourkoulis
National Technical University, Athens, Greece

Abstract: The engineering community has devoted much effort to understanding the response of soil-structure systems
to seismic ground motions, but little attention to the effects of an outcropping fault offset. The 1999 earthquakes of Turkey
and Taiwan, offering a variety of case histories of structural damage due to faulting, have (re)fueled the interest on the
subject. This paper presents a methodology for design of bridges against tectonic deformation. The problem is decoupled
in two analysis steps: the irst (at the local level) deals with the response of a single pier and its foundation to fault rupture
propagating through the soil, and the superstructure is modeled in a simpliied manner; and the second (at the global level)
investigates detailed models of the superstructure subjected to the support (differential) displacements of Step 1. A parametric
study investigates typical models of viaduct and overpass bridges, founded on piles or caissons. Fixed¨Chead piled foundations
are shown to be rather vulnerable to faulting¨Cinduced deformation. End¨Cbearing piles in particular are unable to survive
bedrock offsets exceeding 10 cm. Floating piles perform better, and if combined with hinged pile¨Cto¨Ccap connections,
they could survive much larger offsets. Soil resilience is beneicial in reducing pile distress. Caisson foundations are
almost invariably successful. Statically¨Cindeterminate superstructures are quite vulnerable, while statically¨Cdeterminate are
insensitive (allowing differential displacements and rotations without suffering any distress). For large¨Cspan cantilever¨C
construction bridges, where a statically determinate system is hardly an option, inserting resilient seismic isolation bearings
is advantageous as long as ample seating can prevent the deck from falling off the supports. An actual application of the
developed method is presented for a major bridge, demonstrating the feasibility of design against tectonic deformation.

Keywords: fault rupture; earthquake; soil-structure interaction; bridge; viaduct; pile group; caisson foundation; inite
elements