It can get a little tricky, so here's a few tips. First, make sure you have your site file linked in to your view. You need that as a point of reference. In our case, we have a project that is based on shared coordinates (site is linked center to center, then we acquired the coordinates from the site file to line our project up to those coordinates).
Next, get your levels added. You can either work from an overall relative level elevation of 0, which we do include on some of our projects. When you have this level in your project, you can use the actual invert elevations from the existing or proposed pipe.
If not, you need to do a little math - for example, you have a level defined at 303'. The pipe invert is 322.43'. You need to do the math, subtracting the level from the true invert, so our pipe is at 19.43'. You don't need to do any conversion if your project is in feet and inches instead of decimal feet - typing this value in will do the conversion for you.
You also need to know if the invert elevation is to the top, middle or bottom of pipe. That will come in handy as you start to draw the pipe.
Next up - calculating slope. This is why I decided to add this post - for the life of me, I couldn't do the basic math to convert slope to inches, so being the geek I am, I did a Google search and found a great table from a book called Basic Engineering for Builders, written by Max Schwartz. Here's the conversion table:
Before you add the pipe make sure you have the right fittings, such as the ductile iron mechanical joint library. We use a modified version of an old CADWorks library based on Clow for ours, but make sure your outside diameters are correct.
Now you're ready to add the pipe. From the home tab, select the Pipe command. Set the size and invert elevation for the offset, after doing the math. Next, select Justification to bottom, middle or top based on what you have as you invert elevation.
If the pipe is sloped, make sure you turn slope on. The direction you're drawing determines whether you use slope up or slope down. If you're starting from the highpoint, select slope down. Set the slope to the right value - if the values you were given were based on percentage, use the table to find the inch to 12 inch value (re: .5% = 1/16"/12" slope).
After you review this, pick your second point. And this is where the fun begins. Sometimes, Revit doesn't want to add a right angle to the pipe, especially if the view is not at right angles. What you want to do, when this happens, is rotate your view based on a pipe segment. Make sure your view crop region is turned on.
Select the crop region, and then pick the Rotate tool from the Modify tab. The center of rotation will show up in the middle of the view. Move your mouse over the center, pick it and drag it to the end of your pipe. After you've moved the center, you can rotate the view around this point. You can either pick a line that is orthographic first, then the center line of the pipe. That usually works, but sometimes you have to pick the first line for the rotation as the centerline of the pipe, then pick an orthographic line relative to your view. Either way, get the pipe in view flat.
Once it's flat, the fittings should work as designed. If you want to see this solution live, then join me at Autodesk University this year in Las Vegas, for my class, Revit MEP - On Steroids. We're going to have a lot of stuff revolving around site based projects in that class. If you can't make it to AU, it will be available after the event if you're signed up as an AU member. You'll have a handout with pretty pictures, and they may even have a recording of the class.
Hope this helps - happy BIM'ing...David B.
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