| The Texas Department of Transportation (TxDOT) Bridge Division has developed a new type of rectangular, scupper deck drain with two different sizes, 4'' x 8'' and 6'' x 8'' It allows runoff to drain via free fall without a pipe system. The new drain is designed to fit between the deck reinforcement and not interfere with the structural connection of the rail to the deck; therefore, it is less susceptible to clogging and requires less maintenance. However, no equation is available to accurately predict its hydraulic performance.;A slotted drain method developed by Federal Highway Agency (FHWA) is adopted to estimate the hydraulic performance by assuming the 2'' width difference of the drains is not significant. The objective of this study is to assess whether the adopted slotted equation is an accurate prediction, whether a correction factor can be applied to the adopted equation or whether a new set of equations needs to be developed. A physical model was constructed to study the hydraulic performance of the drains. The decking was constructed to simulate bridge decking and to easily change the cross and longitudinal slope of the model. Eight hundred and twenty-two (822) tests were run for different parameter settings of the approach discharge, number of drains, drain size, cross slope and longitudinal slope, and data were collected to determine the discharges. The data analysis was carried out using linear and non-linear regression methods. The results suggested the slotted drain method underestimates the new drainfs performance ranging from 21% to 1600% versus measured discharges. A new equation has been developed to characterize the hydraulic performance of the rectangular deck drain and has high agreement with the measured capture discharges (R2 = 0.985). Using the statistics tool in Microsoft Excel and IBM SPSS statistics data editor, the data analysis demonstrated the capture discharge is proportional to the number of drains and drain size. The new equation is a function of the drain width, the drain length, the number of drains, approach discharge, the cross slope, the longitudinal slope and the Manningfs roughness coefficient. Design guidance was implemented with the new equation. |
