Principal Investigator(s) and
Institution(s)
Michel Bruneau and John Mander, University at Buffalo
Objective
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.
Approach
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
9/23/99 |