| This thesis describes the field Dynamic Resonance Tests, Analysis of the field Data and its results of the Strawberry Park Underpass, a two simply supported spans railway bridge located in Los Angeles, California. These tests were performed by using an eccentric mass dynamic shaker and twenty five FBA-11 accelerometers. The bridge was shaken in both the longitudinal and the transverse directions. To identify the effects of the rails, the tests were performed initially with the rails in place and then with the rails disconnected at the abutments. The first natural frequency of 4.93 Hz and a damping value of 2.15% were found in the transverse direction with rails in place. In the same case, a frequency of 6.75 Hz and a damping value of 4.5% were found for the second transverse mode. When the rails were cut in the transverse direction, a "localized" mode was triggered, which allowed a greater dissipation of energy and significant reduction of the structural acceleration response levels. The fundamental longitudinal frequency was 6.5Hz with a corresponding modal damping of about 5.0%. In the vertical direction, the fundamental frequency was 6.0Hz with a modal damping of 1.6%. Significant participation of the adjacent roadbed was also observed. A three dimensional finite element model of the bridge was developed, in order to predict the experimentally developed results. These predictions were reasonably accurate. This model will be the first step towards further analytical studies, which are currently under development. |
