SENSITIVITY OF RESPONSE OF ISOLATED BRIDGES TO MODELING AND DESIGN PARAMETERS - A CASE STUDY

The concept of base isolations in bridges implies that structural components should experience limited inelastic behavior associated only with minor damage. Most isolation systems are designed to eliminate altogether inelastic behavior. The estimation uncertainties during the design process of the future ground motions, associated with the uncertainties involved in the constructed practice, leave the possibility that the entire system will experience inelastic behavior with permanent deformations and damage. The fundamental objective of providing pertinent protection against undesired failure modes of base isolated bridges relies on estimates of the piers properties, such as flexure or shear capacities, or estimates of foundation deformation limits. It relies also on good knowledge of isolation properties. Design choices based on nominal material properties may miss the physical features of the structure, rendering the isolation system inefficient in preventing large ductility demands on the substructure. One of the objectives of this paper is to examine the effect of variation of the ratio of isolator and pier yield characteristics on the response of isolated bridges. It has been recognized that, due to low redundancy and domination of the deck mode of vibration, isolated bridges are extremely sensitive to the characteristics of the ground motion. After yielding the stiffness properties and the periods of the deck-bridge system may be entirely dominated by the secondary stiffness of the isolators because of the larger mismatch with the support stiffness. This study investigates the sensitivity of bridge response to small variations of the post-yield stiffness of the isolation system. Since most of the mass of the bridge is contributed by the deck, analytical models for design tend to diminish the attention to the masses of the piers and to the vibration modes for design tend to diminish the attention to the masses of the piers and to the vibration modes they induce. However, in deck isolated bridges the local modes of tall massive columns may contribute substantially to the drift demand of the respective isolator-pier systems. This paper also studies the response implications of neglecting the column mass in modeling of bridges.

• Corporate Authors:

  Multidisciplinary Center for Earthquake Engineering Research

  State University of New York, 107 Red Jacket Quadrangle, P.O. Box 610025
  Buffalo, NY  United States  14261-0025
• Authors:
  • Reinhorn, A M
  • Simeonov, V K
  • DeRue, G
  • Constantinou, M C
• Conference:
  • Proceedings of the U.S.-Italy Workshop on Seismic Protective Systems for Bridges
  • Location: Columbia University, New York, NY
  • Date: 1998-4-27 to 1998-4-28
• Publication Date: 1998-11-3

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 213-223

Subject/Index Terms

• TRT Terms: Bridge decks; Bridge foundations; Bridge piers; Bridge substructures; Bridges; Deformation; Ground penetrating radar; Isolation (Chemistry); Stiffness; Structural design
• Subject Areas: Bridges and other structures; Design; Highways; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 00779883
• Record Type: Publication
• Report/Paper Numbers: MCEER-98-0015
• Contract Numbers: DTFH51-92-C-00106
• Files: TRIS
• Created Date: Dec 22 1999 12:00AM