SUDA Tip: How to Configure a Single Structure Which Contains Two Independent Grates

Written by Robert Garrett

In a roadway with a center barrier, we often use storm drain inlets like this one.

openroads suda barrier two inlets detail

This type of structure presents a unique challenge for producing a 3D model representing the total structure while also allowing surface flow calculations independently for each grate.  Additionally, the elevations of the two grates could be different as shown here.  And on the high side of superelevation, there may be only one of the grates present.

openroads suda median barrier template

To solve this challenge we create two different feature definitions. The first feature definition is always used and is defined with a single grate, which in the library under development here is always on the low side.

openroads suda feature definition one grate openroads suda one grate 3d model

Then we configure a second feature definition which defines the other grate.

openroads suda feature definition two grates openroads suda two grates 3d model

This creates for us a workable (although not perfect) 3D model.  You will notice that the high side grate has only a minimal vault.  In fact, the vault could be modeled as nearly nothing.   Since we have two independent grates then we can also perform surface runoff and grate capacity calculations for each grate independently.

The final bit we need to account for is to make sure that the water captured by the high side grate is accounted for hydraulically in the network.  We do this by setting up a false pipe which connects the high side grate to the low side grate and thus add the high side captured flow to the drainage network. The false pipe is seen in yellow, is placed in a scratch level and is made as large as possible to eliminate hydraulic effects which could occur if we made this pipe very small.

openroads suda pipe link between structures openroads suda pipelink between structures 3d model

If you liked that solution to this unique challenge and you have your own structure challenges Contact Us to see how we can help you.

Robert Garrett

Robert has over 25 years experience as a practicing engineer and is licensed in the State of Tennessee. After graduating from Tennessee Technological University, Robert worked for the Mississippi State Highway Department, Bridge Design Division. Then he spent 12 years with the Tennessee Department of Transportation in the Roadway Design Office and later served as Regional Manager in the Design Survey Office.From 2000 to 2006, Robert worked for Robert G Campbell and Associates in Knoxville, TN where responsibilities included roadway, site, and utilities design projects.Joining Bentley Systems in March 2006, Robert wrote specifications & documentation for software development. Duties included testing, customer feedback and ensuring the products met the needs of the civil engineering user base. He also developed training material for education both internally to Bentley and for outside organizations. He served as Product Manager for Utilities Products, including the new OpenRoads Subsurface Utilities Design and Analysis software. Robert also provided guidance and implementation services for new technologies.He is a frequent presenter and trainer at user conferences.

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