Truss foundations for frost-heave and other reactive soil environments
A truss foundation for single-axis trackers that are installed in climates that experience frost heave or reactive soils. Truss legs are oriented to be substantially plumb, to eliminate adfreeze moment on below-ground components in the frost zone. Elbow couplers are attached to the upper end of each embedded component and used to change the leg angle from plumb to angled.
1 . A truss foundation for a single-axis tracker comprising:
a pair of screw anchors, each anchor of the pair embedded into underlying ground at a substantially plumb orientation and terminating above ground in an elbow coupler, wherein each elbow coupler comprises a connecting portion extending at an angle relative to a central axis of the screw anchor;
a pair of upper leg sections, each joined at a first end to one of the elbow couplers to form a pair of bent truss legs; and
a truss cap having a pair of opposing connection portions received in a second end of respective ones of the upper leg sections, the truss cap having at least one planar mounting surface for supporting a tracker component.
2 . The truss foundation according to claim 1 , wherein the tracker component is selected from the group consisting of a tracker bearing, a tracker drive motor, and a tracker center structure assembly.
3 . The truss foundation according to claim 1 , wherein each screw anchor extends below an active soil layer of the underlying ground.
4 . The truss foundation according to claim 3 , wherein connections between the upper leg sections and the screw anchors and between the upper leg sections and the truss cap are crimp connections.
5 . The truss foundation according to claim 1 , wherein the elbow coupler comprises a feature for registering the position of a crimping device with respect to crimp features on a connecting portion of the elbow coupler.
6 . A truss foundation for supporting a single-axis tracker above underlying ground comprising:
a pair of adjacent truss legs, each leg comprising a substantially plumb-driven screw anchor, an elbow coupler and an upper leg section that is oriented at an angle relative to the screw anchor via the elbow coupler; and
a truss cap joining open ends of each upper leg section, wherein the truss cap comprises a pair of connecting portions that are received in respective ones of the truss legs.
7 . The truss foundation according to claim 6 , wherein each substantially plumb-driven screw anchor extends below an active layer of the underlying ground.
8 . The truss foundation according to claim 6 , wherein the truss cap comprises at least one planar mounting surface for supporting a tracker component.
9 . The truss foundation according to claim 8 , wherein the tracker component is a component selected from the group consisting of a bearing assembly, a drive motor, and a center structure.
10 . The truss foundation according to claim 6 , wherein the truss cap comprises a bearing adapter.
11 . A method of assembling a truss foundation comprising:
embedding a pair of adjacent screw anchors at a substantially plumb orientation;
attaching an elbow coupler to an upper end of each driven screw anchor;
orienting a truss cap above the pair of elbow couplers; and
sleeving respective upper leg sections over connecting portions of the truss cap and over the connecting portion of one of the couplers while the truss cap is held at the correct orientation; and
while maintaining the orientation of the truss cap, crimping portions of each upper leg that overlap with the truss cap and the elbow coupler.
12 . The method according to claim 11 , wherein attaching an elbow coupler to an upper end of each screw anchor comprises passing at least one bolt through the elbow coupler and screw anchor.
13 . The method according to claim 11 , wherein crimping the portions of each upper leg that overlaps with the elbow coupler comprises registering a crimping device with a feature on the elbow coupler.