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Live Load Effect in Reinforced Concrete Box Culverts Under Soil Fill

Live Load Effect in Reinforced Concrete Box Culverts Under Soil Fill. Sarah Orton, Erik Loehr, Andrew Boeckmann, and Garrett Havens University of Missouri. Research Motivation. Load Rating required for all bridge size culverts (span > 20ft)

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Live Load Effect in Reinforced Concrete Box Culverts Under Soil Fill

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  1. Live Load Effect in Reinforced Concrete Box Culverts Under Soil Fill Sarah Orton, Erik Loehr, Andrew Boeckmann, and Garrett Havens University of Missouri

  2. Research Motivation • Load Rating required for all bridge size culverts (span > 20ft) • In the case of culverts under deep fill, effect of dead load much greater than live load – negligible live load effect • Missouri has approximately 3000 culverts. About 700 (23%) have fill depths greater than 6 ft. • Impact – significant reduction in number of man hours required to load rate culverts and reduction of unnecessary load posting of culverts

  3. Research Methodology • 10 culverts were selected for testing • Culverts ranged in fill depth from 2.5 feet to 13.5 feet • Determine the fill depth which Live Load becomes negligible • Live Load utilized a Dump Truck loaded and parked at specific locations to maximize strains • Effects of loadings were recorded via strain transducers, and an accelerometer attached to the underside of the culverts

  4. Research Methodology • Tests were conducted in Two Rounds. • Five culverts with similar geometrics but varying fill heights made up first round • Second round focused on various cell sizes, arrangements and design loads at depths near where live loads become negligible during the first round • Computer models of each culvert were created to fully analyze the results

  5. Culverts • 10 culverts with fill depths from 2.55 ft to 13.25 ft were tested • Culverts were built between 1954 and 2001 • Design Load H10 and H15

  6. Instrumentation • Each culvert was instrumented with 12 strain transducers, 11 LVDTs , and one accelerometer to capture maximum strains and displacements as truck moved over culvert Phase 1 Phase II

  7. Live Loading • Truck loaded to approximately 50 kips was positioned in 7 static positions above the culvert to induce maximum strains and displacements in gages Position 4 Front rear tire middle primary span Position 1 Centered over secondary span Position 5 Centered over primary span Position 2 Rear tire in middle of secondary span Position 6 Rear tire in middle of primary span Position 3 Centered middle wall Position 7 Centered over far wall

  8. Results from data - Strains • Maximum strain measured in top slab vs fill depth 1.0 E-05 ~ 40 psi

  9. Results from data - LVDT • Maximum displacement vs fill depth

  10. Conclusions • Culvert testing was successful and reasonable trends found in both strain and displacement data • Culvert design is very conservative, especially at shallower fill depths • A possible point for cutoff of load rating is around 6 ft.

  11. Future Research • NCHRP Study selected to evaluate Live Load Impact on Culverts • Expand study to other states? • Reduce need for load rating in deep fill culverts • Improve load rating procedures • Reduce over-conservatism in design of culverts by better understanding load distribution through soil and pavement

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