Issue 47

Y. Mizuno et alii, Frattura ed Integrità Strutturale, 47 (2019) 209-220; DOI: 10.3221/IGF-ESIS.47.16 212 the acting forces. In this figure, the relationships between the four fundamental bridge types are integrated into a diagram with six arrows indicating the continuity or symmetry in structure and form among them. This figure also shows three classifications of structural systems: a suspension system, beam systems, and an arch system. We can consider not only the linear relationships shown in Fig. 3, but also more complex relationships among the various bridges. The relationships shown in Fig. 3 are altered to obtain two (upper and lower) triangular coordinate systems with bilateral symmetry in Fig. 4. Furthermore, the vertical position of the main structure and the floor system is illustrated in the depth direction of the figure. A bridge consisting of a suspension system, a web system, and a diagonal system is shown in the upper half of the figure (triangular prism S1G1T1-S3G3T3), while a bridge consisting of an arch system, a web system, and a diagonal system is shown in the lower half of the figure (triangular prism A1T1G1-A3T3G3). Bridges that have a symmetrical relationship in structure and form would be placed at symmetrical points with respect to the central plane (G1T1T3G3), as shown in Fig. 4. Figure 4 : Correlation chart expressed by triangular coordinate systems [5]. T RANSITION OF STRUCTURAL FORM he structural form changes during the life cycle of a bridge (Fig. 5). In this study, the states are separated into three parts: construction state, completed state, and retrofitted state. Furthermore, retrofitting is defined as a new structural system applied to an existing structure. Figure 5 : Transition of structural form in a typical life cycle of a bridge. T