Bridges, Tunnels and other Transportation Structures
Results from an analytically based fatigue study of a riveted, steel, railway truss bridge are presented. This study is motivated by the available measured routine train loading configurations and the advanced algorithms that automated trains modelling and rain-flow count extraction process. The study is focused on a single span, double-track, through truss with a length 146.75 ft. (44.7 m) and a width of 30.5 ft. (9.3 m). Main truss diagonals, verticals and chords are either riveted members or eyebars and the floor system consists of riveted built-up I-section floor beams spaced at 24.45 ft. (7.5 m) and stringers spaced at 7.00 ft. (2.1 m). The main trusses are stabilized laterally via top and bottom lateral bracing system.
The current study compares fatigue damage estimated under the Cooper E80 design loading and under routine loading configurations provided from a weigh in motion in a close proximity to the bridge. Routine loads had a maximum axle load of 80 kips (355 kN) which is similar to the Cooper E80 maximum axle load but differed with respect to number of axles and their spacing. As a result for those major differences, the number of stress cycles and stress ranges are expected to vary significantly.
Finite element models were developed in SAP2000 and connected to MATLAB using the SAP2000 (OAPI) programming interface so that measured and predicted stresses at points of interest could be automatically quantified and compared. MATLAB rain-flow counting functions are being implemented to extract stress ranges from obtained stresses so that fatigues life estimations for details and locations of interest can be developed. These estimations will be compared for both loading configurations to quantify the difference between both loadings so that a more accurate fatigue life estimations could be achieved.