Development of Design Specifications and Commentary for Horizontally Curved Concrete Box-Girder Bridges (2008) / Chapter Skim
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Pages 31-43
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From page 31... ...
, and skewed abutments on curved bridges. Model Verification 3-D finite element analysis using plate and shell elements is accepted as the most accurate level of analysis available for boxgirder bridges.
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From page 32... ...
It was assumed that the pier and abutment diaphragms were relatively stiff, i.e., they had a moment of inertia of 5000 ft4. Each of the above 32 bridges was configured as a straight bridge and as curved bridges with radii of 200, 400, 600, 800, and 1000 feet, resulting in 192 bridge configurations.
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The actual member property used in analysis was 33 Figure 4-3. Typical single-cell cast-in-place cross section.
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Figure 4-6. Idealized single-cell precast cross section.
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From page 35... ...
This loading captures the effect of concentrated axle loads and may magnify its effect on curved bridges to some extent; therefore, it is justified as a simplification for a conservative upper bound. This load was applied at the middle of the bridge and transversely was located at various positions: (1)
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From page 36... ...
• Midspan Transverse Bending Moment at middle of center span; • Midspan End Shear at first abutment in single span and at start of middle span in 3-span case; • Midspan Normal Stress at bottom outside corner of cross section, at middle of center span; and • Midspan Normal Stress at bottom inside corner of cross section, at middle of center span. The graphical review of results included scatter-grams of each response quantity from spine and grillage models.
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From page 37... ...
Figure 4-18 shows that longitudinal stresses will be 37 Figure 4-11. Typical curved line (spine beam)
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From page 38... ...
• Curved bridges with length-to-width ratios of less than 0.2 and an L/R larger than 0.2 also require detailed analysis as revealed by the unconservative results for tightly curved short-span 5-cell bridges in Figures 4-16 and 4-18.
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From page 39... ...
Skewed Abutments A two-cell single-span (200 ft long) and a two-cell three-span bridge (200ft-300ft-200ft)
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From page 40... ...
40 All 3-Span fr/fsDead Load 0.96 0.98 1 1.02 1.04 1.06 1.08 1.1 0 0.2 0.4 0.6 0.8 1.61.41.21 Length/Radius (L/R) fr/ fs CIP1_6x18_sp3l_dl CIP1_6x18_sp3m_dl CIP1_6x18_sp3s_dl CIP1_6x6_sp3l_dl CIP1_6x6_sp3m_dl CIP1_6x6_sp3s_dl PC1_6x18_sp3l_dl PC1_6x18_sp3m_dl PC1_6x18_sp3s_dl PC1_6x6_sp3l_dl PC1_6x6_sp3m_dl PC1_6x6_sp3s_dl CIP2_6x18_sp3l_dl CIP2_6x18_sp3m_dl CIP2_6x18_sp3s_dl CIP2_7x7_sp3l_dl CIP2_7x7_sp3m_dl CIP2_7x7_sp3s_dl CIP5_6x18_sp3l_dl CIP5_6x18_sp3m_dl CIP5_6x18_sp3s_dl CIP5_8x8_sp3l_dl CIP5_8x8_sp3m_dl CIP5_8x8_sp3s_dl Figure 4-17.
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From page 41... ...
The final outcome of these results is that the curved alignment does not aggravate the effect of skewed abutments and therefore, any consideration taken for straight bridges can be equally valid for curved bridges. These corrections will be necessary when the bridge is designed using a spine beam analysis.
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From page 42... ...
The end span and radii of these bridges are shown in Table 4-8 The long-term deflection of Models 1 through 3 did not appear to be affected by the radius of the bridge. Therefore, methods used for adjusting cambers for straight bridges would appear to be applicable to curved bridges analyzed as three-dimensional spine beams.
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From page 43... ...
In the case of a grillage analysis, the same adjustment can be made by resolving bearing reactions into a torsional moment, increasing that moment by 20%, and recalculating the new bearing forces. 43 Model Number Radii (ft)
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