Browsing by Author "Galambos, Theodore"
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Item Distortion-Induced Fatigue in Multi-Girder Steel Bridges(2000-05-01) Jajich, Dmitri; Schultz, Arturo E; Bergson, Paul; Galambos, TheodoreThis report summarizes the findings of a project with the following goals: 1. to implement a field instrumentation and monitoring program for a typical multi-girder steel bridge on skew supports that may be susceptible to web-gap distortion; 2. to assess the frequency and magnitude of the distortional fatigue stresses at the web-stiffener connections; and 3. to evaluate the impact of these stresses on fatigue life. Measurements from 12 independent strain gauges were continuously monitored and recorded for more than three months on Minnesota Department of Transportation (Mn/DOT) bridge #27734. Truck loading tests also were conducted. Predicted web-gap fatigue life based on the long-term monitoring data from Mn/DOT bridge #27734 ranges from 45 to 75 years. Comparison of web-gap stresses with primary design stresses reveals that web-gap distortional stresses are comparatively high. The report also highlights a detailed finite element study to better understand the web-gap stress mechanism and to compare experimental results with theoretical predictions. Study results have important implications for investigators of distortion-induced web-gap fatigue. They indicate that the actual stress at the so-called hotspot may be as much as twice the stress measured at the strain gauge. The report includes a method for estimating girder deflections and web-gap stress.Item Field Instrumentation of Steel Highway Bridges(1993-02) Leon, Roberto T.; Galambos, Theodore; Schmit, Jeffrey J.; Teng, Ai-LienTwo projects dealing with field instrumentation of bridges are described in this report. In the first project, a portable, rugged and multi-purpose bridge instrumentation system was developed. This was accomplished by using fourteen removable instruments and a portable data acquisition. The instrumentation included eight reusable strain sensors and six inclinometers, which allowed load distributions, stresses, and displacements to be measured in steel girder bridges. In the second part of the project the portable data acquisition system was used to measure strains near fatigue critical details in steel bridges to determine stress ranges under both controlled and random traffic. For this part of the project conventional strain gauges were also used. Overall this acquisition and modelling system worked quite well for determining strains and deflections of simply supported bridges under static loadings. A new measurement technique for finding deflections, based on slope sensors, was developed and verified. This technique can now be readily used in bridge evaluation. The system should be extended now to various types of bridges including continuous span, concrete girder, and timber bridges.