Improved design and construction of large-span culverts
A comprehensive review was made of the design and construction of flexible metal and rigid reinforced concrete large-span culverts, past documented field experience of monitored culvert performance, and culvert failures. Full-scale field testing of a flexible metal and a reinforced concrete large-span culvert was conducted and the results compared with finite element computer analyses. Based on this work recommendations for improved design and construction of large-span culverts were developed.
The review of metal culvert design and construction practice revealed numerous differences among current methods as well as deficiencies. Proposed design limit states were identified and discussed for improved practice. An improved earth load thrust prediction model was developed based on past analytical work considering the flexural rigidity of the structure relative to the surrounding soil, in addition to other factors. The design curves for arching factors were extended to cover a wider range of structural backfill width conditions and shallower burial. Also, a proposed construction procedure was outlined to control construction moments based on deflection limits as a function of the expected level of construction control.
None of the existing methods explicitly deals with large-span reinforced concrete culvert design and construction practice. Therefore, a proposed design approach for these culverts was outlined. Construction practice was based on recommendations from the manufacturers.
The review of failure cases showed that most failures of large-span metal culverts occurred as a result of poor backfill procedures and/or poor backfill material selection. Other causes were excessive construction loads and invert uplift. Excessive deformation was the most common limit state reached before or at failure. Furthermore, significant variations in structural response may occur over time after construction. Therefore, better construction provisions and control are needed, coupled with consideration of flexural stiffness and moment capacity in design.
The field tests showed significant differences in structural behavior between backfilling and live load testing. The metal structure was successfully subjected to very heavy live loads at shallow cover conditions without the use of thrust beams or ribs (current practice). Finite element computer analyses of the two tests showed that earth load responses could be reasonably modeled; however, live load predictions were poor.
0794: Materials science