VIBRATIONS OF HORIZONTALLY CURVED CONTINUOUS COMPOSITE CELLULAR BRIDGES

The use of cellular-shaped cross sections for highway bridges, especia lly on curved alignments, is an economical solution because of the hig h flexural and torsional strength of such sections. This paper summari zes the dynamic characteristics of curved composite multi-cell (contig uous boxes) bridges, continuous over two and three spans. An extensive parametric study, using the finite-element method, was conducted to e valuate the key parameters that may affect the natural frequencies and the corresponding mode shapes for this type of bridge. These paramete rs are end-diaphragm thickness, number of cross-bracings, aspect ratio , span-to-depth ratio, degree of curvature, number of cells, and span- to-span ratio. The effect of cracking of the concrete deck slab in the vicinity of interior supports is also investigated. Results obtained from tests on a 1/12 scale two-span continuous curved composite three- cell bridge model are used to substantiate the analytical modelling. B ased on the data generated from the parametric study, empirical formul as for the dominant frequency are deduced. An illustrated design examp le is presented. A study is also conducted to determine the dynamic de flections caused by a moving truck over the bridge with a view to impr ove human discomfort and perception to vibration.