Luis Mauel Bustos Karam
MODEL VALIDATION FOR AN AGED GERBER TRUSS BRIDGE
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This thesis presents the approaches utilized to model an aged Gerber Truss Bridge crossing the Shinano River in Nagaoka city, located in the central part of Niigata Prefecture, Japan. These approaches were assessed by comparing analytical results from a finite element model with data recorded during a field load test. The bridge was instrumented with 100 strain gauges on 25 truss members in addition to thirteen displacement transducers placed at the center of each span along the bridge. All gauges were read simultaneously as the bridge underwent nondestructive live loading. The installed instrumentation allowed the measurement of deflections as well as the local strain of several critical elements. The recorded gauge readings were used in the assistance of calibrating a working two dimensional finite element model, helping to understand the force and deformation mechanisms controlling the bridge behavior.
With the endeavor to collect the necessary data that allow a better understanding of the structural behavior of the bridge for then validate a model capable of accurately simulate the bridge response in the current operating conditions, field load test were carried out. Field tests involved measuring strains and vertical displacements while trucks of known weight crossed the bridge. The bridge response was monitored under two different loading scenarios, namely static and dynamic. Static load case data was recorded continuously and reduced to member forces for model validation comparisons. Vertical displacements at each bridge¡Çs span were also recorded for model validation purposes. The purpose of driving the truck at a higher rate of speed on the dynamic load case was to investigate the effects an impact load had on the instrumented members. Minimum and maximum values from the high speed measured results were compared to quantify the effect that dynamic loading had on strains and movement.
The model validation process began by developing eight simple truss models, each reflecting different expected restraint conditions, in the hopes of replicate data from recorded results at field load test. Models were refined to frames, and then frames including stringers for greater accuracy. Finally, the most accurate model in simulating the overall structural response to static vertical loads taking into account both member force and span vertical displacement was selected.
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