Load Rating of Segmental Bridges (2024)
Chapter: 7 Summary of Conclusions
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6 Execution of the Analytical Program
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Suggested Citation:
"7 Summary of Conclusions." National Academies of Sciences, Engineering, and Medicine. 2024. Load Rating of Segmental Bridges. Washington, DC: The National Academies Press.
doi: 10.17226/28597.
CHAPTER 7
Summary of Conclusions
At the conclusion of the project, the primary findings of the study can be summarized as follows:
- Live load factor depends on the limit state and target reliability index, and the HL-93 live load is acceptable for the design and load rating of segmental bridges.
- Live load MPFs are conservative for multiple lanes. For more than two lanes, MPF may be reduced to 0.75, and for more than three lanes, it may be reduced to 0.60. The recommendation is valid for span lengths up to 300 ft.
- For the Service III limit state, the recommended target reliability index βT and corresponding live load factor (λL) and resistance factor (ϕ) are as follows:
- Design load rating at inventory level: βT = 1.00 and λL = 0.80.
- Design load rating at operating level, as well as legal load rating, and permit load rating: βT = 0.00 and λL = 0.65.
- Resistance factor ϕ = 1.00.
- Reduced load factor replaces striped lanes in the design and load rating of segmental bridges. Therefore, design lanes are recommended to use for design load rating at both inventory and operating level, as well as for legal load rating, and permit load rating. The most influential factors on load rating, in the extent considered in this project are (1) assumptions about condition factor, (2) assumptions about fc′ (specified versus expected—affects allowable stress), (3) selection of CR and SH model, (4) inclusion of TG, (5) Resal effect, (6) gross- versus transformed-section properties, (7) load rating time, (8) assumed erection time, and (9) selection of model to determine fc′ (t).
- The use of Homberg charts is conservative for load rating in the transverse direction. 3D FEA is an alternative. The modeling guidance has been provided.
The final additional deliverables for the project were prepared, including the following:
- Guideline for Load Rating of Segmental Bridges (with load rating examples containing training materials provided in Appendix C).
- Proposed revisions to AASHTO LRFD.
- Proposed revisions to AASHTO MBE.
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