A line constraint, also known as an edge constraint, may be applied to the edge of a shell or solid object. When applied along an edge, the line constraint will constrain all interconnecting objects to the joints selected. These joints will then displace, along those DOF selected, as a function of interpolation between the two master joints which govern constraint behavior.
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NOTE: Slight displacement discontinuity should be expected along any edge constraint. This discontinuity is sufficiently small relative to other deformations.
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NOTE: When an edge constraint is assigned to a series of joints, and some of those joints fall within the auto-merge tolerance of the end nodes, a rigid-body constraint is applied to avoid ill-conditioning within the stiffness matrix. This may cause coupling within the constraint, leading to unintended behavior.
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Example
An example edge constraint is shown in Figure 1:
Figure 1 - Edge constraint along shell element
Here, two edge constraints are applied at each end of a shell object which simulates the span of a bridge deck. Each of the four edge constraints has a master joint at either end, and a dependent joint at the intermediate-column intersection. If the joints circled in Figure 1 are numbered, from left to right, 1, 2, 3, 4, 5, then joint 2 is governed by masters 1 and 3, and joint 4 is governed by masters 3 and 5. Given this edge-constraint condition, each dependent-joint displacement is then interpolated from the displacement of the two master joints.
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