J.B. Mander

Ambient vibration and seismic evaluation of a cantilever truss bridge

Abstract An experimental ambient vibration field investigation with a companion computational modeling study of a cantilever truss bridge is presented. The ambient vibration experiments were conducted on the central suspended span and two adjacent anchor spans of the North Grand Island (NGI) Bridge. Three-dimensional finite element model of the bridge is validated against the experimental results. Results from time history analyses using selected ground motions are used to assess the damage threshold of the bridge. A nonlinear static procedure using the capacity–demand spectrum approach is then employed to evaluate the expected seismic performance of the structure. Results show that sway frame members are especially prone to damage under earthquake-induced deformations. However, overall response of the structure may be considered satisfactory from a life safety standpoint.

Seismic Retrofit of Steel Deck-Truss Bridges: Experimental Investigation

Alternative seismic retrofit strategies for steel deck-truss bridges are investigated in this study. Various modified tension-only bracing configurations, which consist of tendon elements with or without supplemental systems are introduced within the end-sway frames. The effectiveness of the retrofit configurations is demonstrated experimentally and analytically on a one-third scale model of an existing steel end-sway frame tested on the shaking table at the State University of New York at Buffalo. It is concluded that proposed alternatives can efficiently improve the lateral strength and stiffness characteristics. Moreover, the load path within the end-sway frame is modified to bypass the existing nonductile steel bearings. A stable energy dissipation mechanism is provided by means of re-centering elastomeric spring dampers along with fuse elements, thus reducing the overall seismic demand on the structural systems.

Re-Shaping Semi-Active Structural Response Via Simple Applications of Embedded Computation, Sensors and Valves

Semi-active dampers and actuators hold significant promise for their ability to add supplemental damping and reduce structural response, particularly under earthquake loading. Novel devices utilizing off the shelf components and control systems are used to modify structural response. Devices are presented from design, modeling, analysis and validation via hybrid testing and experimental shake table results. All cases are compared with independent analytical predictions based on first principles analysis.Copyright