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OCR for page 35
35 Figure 4-8. Idealized two-cell cast-in-place cross section. Figure 4-9. Typical five-cell cast-in-place cross section. This loading captures the effect of concentrated axle loads same as modeling the prestress tendon as a series of straight and may magnify its effect on curved bridges to some extent; lines. In case of grillage models, additional load cases were therefore, it is justified as a simplification for a conservative studied by loading only the inside and only the outside upper bound. This load was applied at the middle of the webs. bridge and transversely was located at various positions: (1) on outside web, (2) on inside web, (3) on center of bridge, Results Review and (4) on all webs, i.e., equally distributed over the bridge width. Maximum stresses occur when the entire The following results were obtained for each load case and bridge width is loaded, therefore, the results from this case compared from spine and grillage models: were studied in more detail when developing guidelines for design. Post-tensioning was also applied along all webs of Midspan Deflection at middle of center span; the section. The prestress effects are modeled as equivalent Midspan Rotation at middle of center span; loads at nodes, i.e., the axial forces along the prestress path Midspan Longitudinal Bending Moment at middle of are applied at each end of each element which in effect is the center span; Figure 4-10. Idealized five-cell cast-in-place cross section.