Nonlinear seismic analysis of quasi-isolation systems for earthquake protection of bridges

Filipov, Evgueni

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Description

Title

Nonlinear seismic analysis of quasi-isolation systems for earthquake protection of bridges

Author(s)

Filipov, Evgueni

Issue Date

2012-05-22T00:33:53Z

Director of Research (if dissertation) or Advisor (if thesis)

• Fahnestock, Larry A.
• LaFave, James M.

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Nonlinear Seismic Analysis of Bridges
• Quasi-Isolation of Bridges
• Seismic Isolation of Bridges
• Incremental Dynamic Analyses of Bridges

Abstract

Quasi-isolation is a modern bridge seismic design philosophy where nonlinearity is permitted to occur in specific bearing components such that forces transferred into the substructure are reduced and isolation is achieved by sliding of the bearings. The system is a pragmatic approach for providing earthquake resilient bridges in locations such as the eastern and central United States, as well as in many locations around the world where there is significant earthquake risk at long recurrence periods. Such a seismic risk does not typically justify the design of a rigorous classical isolation system, but instead, a low-complexity, low-cost quasi-isolation approach could provide significant mitigation of earthquake effects. The proposed system employs a set of fixed bearings at one intermediate substructure, and all other substructures are instrumented with isolation bearings that permit thermal expansion such as elastomeric bearings with an elastomer-concrete sliding interface or elastomeric bearings with a PTFE (Teflon) to stainless steel sliding interface. L-shaped steel side retainers are placed in the transverse direction of the elastomeric bearings, and along with the low-profile fixed bearings, these components prevent bridge movement during service loading, but break-off and permit sliding at high earthquake loads. This thesis outlines a base bridge prototype, with the anticipated nonlinear behaviors in the structural components defined in a finite element model of the global structure. New nonlinear elements have been formulated to capture the bi-directional stick-slip behaviors in the bridge bearings and the bilinear (and eventual fracture) behavior of steel retainers and fixed bearings. Longitudinal and transverse static pushover analyses are performed to demonstrate local limit states and progression of damage in the bridge structure. A large scale parametric study carried out to investigate the quasi isolated system performance on different superstructure types, substructure types, substructure heights, foundations and isolation bearing types. Different suites of ground motions are scaled and incremental dynamic analyses (IDA) are carried out for each parametric variation such that the sequence of damage and global seismic performance can be evaluated. Results indicate that the bearing systems with the flat PTFE slider, would likely result in critical damage from the unseating of bearings at moderate and high seismic events in the New Madrid Seismic Zone (NMSZ). The sequence of damage for many bridge cases indicates yielding of piers at low-earthquake hazards which justifies further calibration of the quasi-isolation bearing systems. Finally the, type of ground motion, foundation stiffness, pier height and bearing type were noted to have significant influence on the global bridge response.

Graduation Semester

2012-05

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http://hdl.handle.net/2142/31181

Copyright and License Information

Copyright 2012 Evgueni Filipov

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