Example for Civil 3D & Hecras

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c Hand On Training For

Bridge Hydraulic Analysis Via CIVIL-3D-2009 & HEC-RAS c c c Example: BRIDGE AT STATION 65+870 (AN05107-Benguela-Lubango Road Project) c c c c

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  G G  HEC-RAS is the one of popular programs that is made for hydraulic analysis. It has been designed to perform one-dimensional hydraulic calculations for a full network of natural and constructed channels. In spite of many benefit of this program, some shortcomings are experienced while running HEC-RAS. The most significant shortcoming is the geometric input data. HEC-RAS conventional data entry procedure requires lots of manual work and gives engineers a burden of manipulating. AutoCAD Civil 3D could be an excellent assistant to aid this time-consuming work. AutoCAD Civil 3D allows engineers to develop geometric data for import in HECRAS and view exported water surface profile result data. As a result, the engineer could concentrate on hydraulic principle, rather than time-consuming work, during model analysis.

G   The example presented in hand is for a bridge crossing with an ephemeral wadi stream in Angola. The main goal of this example is designated to perform a complete hydraulic analysis of a wadi bridge by using the integrated package that includes the following programs: AutoCAD Civil 3D and HECRAS. The objectives of this comprehensive ³hand-on training´ example are to train the workshop participants to be able to carry out the following tasks: - How to generate automated river/wadi cross-sections using AutoCAD Civil 3D. - How to import the generated cross-sections to HEC-RAS. - How to carryout Hydraulic analysis using HEC-RAS and how to get the corresponding water surface profile and velocity variations through a bridge. - How to carryout scour analysis using the HD module in HEC-RAS in order to estimate the contraction scour as well as the local abutment and piers scour.

G    !" The following software should be available and installed in order to be able to carry out the hand on training example: -c HEC-RAS version 3.1 or up. -c AutoCAD Civil 3D 2007 or up.

G #   The bridge is located in Benguela-Lubango , Angola. The catchment area equals 158.67 Km2. The stream length is estimated as about 22 km and the average catchment slope is 0.01 m/m. The following data are used in the design: a)c Roadway data and site data survey: PGL at the bridge site = 514.524 Roadway width = 15m Natural wadi bed level at bridge location (u/s side)= 509.68 Natural wadi bed level at bridge location (d/s side)= 509.60 b)c Rainfall data Rainfall depth corresponding to the 50 yrs event (P50) = 142.5 mm Rainfall depth corresponding to the 100 yrs event (P100) = 167.3 mm c)c Catchment data Catchment area = 158.67 km2 Max. stream length = 22 km Average catchment slope = 0.01 m/m Time of concentration (Bransby William) = 495.32 min. d)c Design flow data 50yrs Peak discharge (Q50) = ’
c 100yrs Peak discharge (Q100) = 
 c c e)c Initial bridge span Based on the given data, the initial expected bridge span ranges from 3.2 to 4.7 ¥Q = 60m to 90m. Based on this simple analysis, the initial guess of the proposed bridge span will be taken as ½
with 2 sets of piers (interspacing = 20m). It should be noted that the aforementioned initial bridge span dimensions will be checked using the following HEC-RAS Hydraulic Analysis.

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