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Next step is to draw orphan joints/nodes to the location where the centerline of the trunnion will be welded to the elbow. In this example we click the Draw joint icon where we enter -18" in the Z direction and click the two elbow joints as shown below left to add joints where the trunnion will be welded to the elbow. Next, assign a Body constraint to each pair of joints in order to create a zero weight rigid connection. You will need to assign a different Body constraint to each pair of joints. As shown below right, there needs to be a a separate Body constraint for each of these pairs of joints. You don't want to select all 4 joints and assign the same Body constraint.
Next, draw additional 2 orphan joints/nodes below to the base of the trunnion. The offset distance of that newly drawn joint will define the length/height of the trunnion. In this example we'll make the trunnion 16" long. Click Draw Pipe icon, change the pipe property set to the 8"STD section which we imported earlier, clicking the base joint then double click the joint above it in order to draw the trunnions. Draw anchors at the base of the trunnions to complete.
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Use the Draw frame icon to draw the frame section. In this example, we will rotate the local axis of the frame elements by 90 degrees. Select the frame elements that we want to rotate and use Assign menu>Frame>Local axes and type 90 degrees as shown below. After the frames are rotated, they display local axis arrows. Red/Green/Blue arrows correspond to local axes 1/2/3. Click 'Show Undeformed shape' icon to clear the display of the local axis arrows. Local 1 axis (red arrow) is axial/longitudinal direction.
As an alternative to importing a pipe section and defining a pipe property set for the trunnion, users can use Define>Structural sections to import or custom define a structural pipe section. The library of structural pipe sections is small, so you may end up having to click the "Add new" button to enter the pipe OD, wall thickness, and material. Using a structural pipe has the advantage of not having the program do a code check on the trunnion, and it does not require the user to define a new pipe property set.
Trunnions on elbows can reduce elbow stiffness. Users can reduce elbow flexibilities by selected selecting one or more elbows with a trunnion, then Design menu>Assign Design Properties for Object Type Elbow as shown below left. Users can also select elbows then assign Pipe>Property modifiers to scale the moments of inertia and stiffness in other directions of selected elbows using the dialogue shown below right.
