Determination of entrance loss coefficients for pre-cast reinforced concrete box culverts.
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2012-12-01
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Edition:Final report.
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Abstract:There is an increased interest in constructing Pre-Cast (PC) Twin and Triple Reinforced Concrete Box (RCB) culverts
in Iowa due to the efficiency associated with their production in controlled environment and decrease of the construction
time at the culvert sites. The design of the multi-barrel PC culverts is, however, based on guidelines for single-barrel cast-inplace
(CIP) culverts despite that the PC and CIP culverts have different geometry. There is scarce information for multiplebarrel
RCB culverts in general and even fewer on culverts with straight wingwalls as those designed by Iowa DOT. Overall,
the transition from CIP to PC culverts requires additional information for improving the design specifications currently in
use. Motivated by the need to fill these gaps, an experimental study was undertaken by IIHR-Hydroscience & Engineering.
The goals of the study are to document flow performance curves and head losses at the culvert entrance for a various culvert
geometry, flow conditions, and settings. The tests included single-, double- and triple-barrel PC and CIP culverts with two
span-to-rise ratios set on mild and steep slopes. The tests also included optimization of the culvert geometry entrance by
considering various configurations for the top bevel.
The overall conclusion of the study is that by and large the current Iowa DOT design specifications for CIP culverts can
be used for multi-barrel PC culvert design. For unsubmerged flow conditions the difference in the hydraulic performance
curves and headloss coefficients for PC and CIP culverts are within the experimental uncertainty. Larger differences
(specified by the study) are found for submerged conditions when the flow is increasingly constricted at the entrance in the
culvert. The observed differentiation is less important for multi-barrel culverts as the influence of the wingwalls decreases
with the increase of the number of barrels.
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