Development of a Nonlinear Bearing for Large Movable Structures
It is not uncommon for large movable structures such as retractable roofs on stadiums to employ linear bearings which allow lateral horizontal movement that will reduce the demand on the structure - in essence creating the roller support of the classic pin-roller simply supported beam. In designing various retractable roofs in the past, Geiger Engineers has sought to improve on the typical linear bearing. Dr. Keith MacBain, one of Geiger's principals, has now developed a nonlinear bearing that will provide the desired translational movement while also allowing for rotation. With the combination of translation and rotation, the structural designer gains a greater ability to tailor the bearing's response. Dr. MacBain and Geiger currently have a patent pending on their nonlinear bearing design.
At right are snapshots of animations that illustrate various types of motion achievable with the nonlinear bearing. Each motion is described relative to the lower-left of the truss (point A). Translation only and rotation only are self-explanatory. For in-phase motion as point A moves to the left it rotates clockwise; for out-of-phase motion the rotation is counter-clockwise. Tuned motion is a general motion however in the case shown here, the radii are selected to accommodate the displacement and rotation of point A with no rotation of the lower portion (and no associated horizontal reaction).