Seismic Vulnerability of the Highway System

Task C3-1: Steel Truss Bridge Braced Pier and Substructure Connection Behavior
Subject Area: Long Span Bridges — Structural Studies

Principal Investigator(s) and Institution(s)
Michel Bruneau and John Mander, University at Buffalo

A large number of steel truss bridges have been built throughout the Untied States, many in zones of moderate to high seismicity. These bridges have typically been designed to resist wind forces, but not earthquakes. Structural analyses of such bridges often reveal that many key structural members along the load path followed by the seismically-induced forces may buckle or suffer brittle fracture of their non-ductile connections. However, seismic evaluation remains difficult due to the lack of knowledge on the cyclic inelastic behavior of built-up members of the type typically found in these bridges, and on their riveted connections. The objective of this task is to analytically and experimentally develop and improve knowledge concerning the seismic behavior of steel truss superstructures.

Although some testing of bridge-specific components has been conducted by other researchers, results to date have mostly been project specific; as a result, it is difficult to draw general conclusions from them. This task will therefore attempt to provide theories and results that can be broadly applicable to many steel truss bridges which share similar structural characteristics and details.

Commonly encountered built-up brace details and configurations, and foundation anchorage details, will be collected from in-service bridges through a few selected consulting firms experienced in the rehabilitation of existing steel truss bridges. Particular attention will be paid to identifying those details that are germane to bridges in the Eastern U.S., but given the fact that most bridges were designed in the absence of earthquake-resistant details, it may be possible to select details that are commonly encountered nationwide.

This task will focus on braced piers in steel truss bridges, with a particular emphasis on the behavior of built-up braces with riveted connections. The behavior of typical base-of-column to pier details (including riveted/gusseted steel (sway) frame connection details, column base plates/seats, bearings, anchor bolts, and masonry plates and/or pedestals of concrete or masonry piers) will also be examined as any one of these details could be the weak link in the chain of lateral load resistance. To be able to perform reliable seismic vulnerability evaluations, strength and deformation limit states must be quantified using mechanistic based models.

A limited experimental program will be conducted to investigate the behavior of typical base-of-column to pier details, and identify potential vulnerabilities. Analytical studies will also be conducted for a range of parameters of typical built-up braced members to identify their potential vulnerabilities, and help formulate a suitable experimental program.

Results from large-scale cyclic inelastic testing of built-up braces and riveted connections assemblies will be used to formulate hysteretic models for these assemblies. Such models could be implemented in non-linear inelastic time-history analysis computer programs (e.g., IDARC or DRAIN-3DX) that are frequently used to investigate the seismic resistance of bridges and other structures.

Knowledge developed through this two-year study will also provide a sound basis for the development of economical and effective retrofit solutions in subsequent years.

Anticipated Start Date and Duration
January 1, 1999 - 24 months