A Study on Effective Mass of One Way Joist Supported Systems

Abstract

This paper focuses on the effective mass calculations of an experimental and analytical research study in which two laboratory joist supported footbridge systems were tested with static and dynamic loadings. Effective mass of different modes in laboratory footbridges were measured through experimental modal analysis and compared to the theoretical and finite element model results. For both single span (30 ft × 7 ft; 9.14 m × 2.13 m) and three span (90 ft × 7 ft; 27.42 m × 2.13 m) footbridges, acceleration data were collected on three parallel lines in the longitudinal direction of the laboratory structures. Testing was done for different bottom chord extension configurations to observe the effect of the extensions on various properties. For effective mass calculations, the average mode shapes of the three longitudinal lines were used and one way systems were treated as beams. The mode shape vectors for the first bending mode of the single span footbridge and the first three bending modes of the three span footbridge were determined for each bottom chord extension configuration. Each mode shape vector was then normalized to establish the mode shape matrix, and the effective mass of the entire footbridge for each mode was calculated to be compared to the theoretical and finite element model results.