SewerCAD Automated Design

Question

As in the screenshot I did the Automated design in SewerCAD and the program sized the first pipe 300mm which is correct but the increment in the load does not require to increase the size in the second pipe to 400mm; that has been checked in the Excel and I also forced that pipe in the sewercad to be sized as 300mm and does work. 
 I am wonder because the design constraints applied should give more flexibility to to go with smaller size because I used (Table not Simple) for Slope constraints as in the screen shot; where I expected the program to increase the slope and maintain the pipe size (300mm) as I tried manually.

Jesse Dringoli · Accepted Answer

In the example you provided, the "simple" slope constraints have a minimum of 4 mm/m whereas the "table" has a minimum of 2 mm/m for the 400 mm size. The automated design routine will try to set the slope at the minimum. After computing design with using the table, if you manually change CO-12 from 400 mm to 300 and compute analysis, you'll see that at that flatter slope (2 mm/m), the 300 mm size does not have enough capacity. The flow through the pipe is 56 l/s and the 300mm size has a capacity of 43 l/s at that slope. This is why the 400 mm size was selected. At the higher slope of 4 mm/m (when using the "simple" slope constraints), the 300 mm size pipe has a capacity of 61 l/s - since that's higher than the calculated pipe flow of 56 l/s, that size is selected. 
 
So, regarding "...if the program keeps the 300mm with higher slope will be OK" - if a higher slope was used, cover would be greater, so the minimum slope is used (and thus 400 mm size) to minimize cover. 
 
With that said, (and as Scott mentioned), automated design it also not meant to be perfect but rather to give you a good starting point for your design. If you prefer to make an adjustment to the design such as the pipe in question here, you can do that manually.

Jesse Dringoli · Answer

Mo, 
 
I think the answer to that goes back to the point about automated design being a good starting point. If you're not satisfied with the result, you can always use your judgment (based on your specific opinion or requirements) to make further adjustments.

tlfoster56 · Answer

When you say you forced the pipe to be 300mm, did you also set Design Conduit? to False?

Scott Kampa · Answer

Hello, 
 
If the slopes are very shallow, the following support solution might be useful: communities.bentley.com/.../10402.why-is-stormcad-over-designing-the-conduits-during-a-design-run-on-a-system-with-very-shallow-slopes 
 
Otherwise, you mention that you tried manually setting the conduit to the smaller diameter. Did you get any user notifications about exceeding any design priorities when you did this? 
 
Also of note is that the automated design will still require the engineers input. There may be areas where you want or need a different size conduit. As stated in the Help documentation: 
 
As with any automated design, the program's design is intended only as a preliminary step. It will select pipe sizes and pipe invert elevations based on the input provided, but no computer program can match the skills that an experienced engineer has. The modeler should always review any automated design, and should make any changes required to adjust, improve, and otherwise polish the system. 
 
Otherwise, we will need to see a copy of the model to look into this further. There are two options for sharing your model files on Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the ‘Advanced Reply editor’ before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley. 
 
 communities.bentley.com/.../7079.be-communities-secure-file-upload 
 
If you upload to Sharefile, please post here with the name of the file so that we know that it is available. 
 
Regards, 
Scott