Grading relationships provide detailed control of elevation relationships between Allsite objects. An example may be where a split building pad with walkout basement is required, in this case the 2x building pads have a 'fixed' relationship between them.
You can add a grading relationship between the following objects:
Building
Road corridor extent
Road centerline
Road centerpoint (ie cul-de-sac head / intersection)
Road modifier (ie curb)
There are different relationship types, up to 3x relationship types can be added to any relationship:
Fixed - used in isolation where there is a fixed elevation relationship between 2x items
Minimum - the minimum allowed elevation between the 2x items
Maximum - the maximum allowed elevation between 2x items
Fixed Or - used in conjunction with Min / Max relationships. An example of this is when defining a small step between 2x building pads, say a garage and the living area, it either needs to be flush (ie "Fixed" to 0ft offset) or at least 1 step (ie 8 inches).
If adding a vehicle crossing relationship on a vacant parcel, use the Vehicle crossing min/max relationship on a parcel, not a grading relationship.
The parcel setting is the only one that constrains against the vehicle crossing location itself. A grading relationship can only target a road feature (corridor extent, centerline, centerpoint or curb modifier), so it ties the building to the point it is snapped to on that feature. On a lot that does have a building, a grading relationship is the correct tool — the parcel's fall-to-VC values apply to vacant lots only.
Relationships can cause Runaway errors if they constrain the model in a way that results in other grading parameters to not work (ie cross fall of a road, min / max grades in a parcel, building protective slopes, flood fill to work on parcels). Use the runaway overlay to help diagnose the root cause.
Bulk adding relationships (buildings)
You can bulk add relationships between buildings, to do this follow the steps outlined below:
Building to Road Relationship
Select the buildings in the model you want to add relationships to
Add up to 2 relationship types
Run Level AI Prepare, this generates the relationships.
Adjust any relationships that are snapped in the incorrect direction (ie corner lots above where want the relationship to the other road)
Group edit the relationships to set the relationship types (up to 3) and the relationship elevation difference. This can be negative or positive depending on what sort of relationship is required. In the example below all 129 buildings are set to a 2ft offset from the curb
The offset is a signed elevation difference — positive places the building above the road feature, negative below it. Where both a Minimum and a Maximum are used, the Minimum must be the lower (more negative) of the two values.
Building to Building Relationship
If defining a split pad you will need to ensure the surrounding ground (ie parcel / ground control) can grade with the relationships. To start, set the relationship on the building to "BUILDING".
After running prepare a relationship link is created, specify the offset. Next, add grade breaks / ground control with appropriate max heights to allow the ground to grade around the relationship. In the example below the 8 foot relationship between the pads would not work as the parcel max grade is set to 5% - this would cause a non viable design or potentially design 'run-away'.
Adding a grade break with maximum height set to 8ft resolves this. NOTE - The grade break needs to extent to the boundary otherwise the land next to building is also too constrained.
