Introduction

Cosmec TeXLon™ spherical bearings are a range of structural bearings allowing large angular rotation, with a minimum of resistance, about any horizontal axis.

Comprised of a convex base with a mating concave element, the basic bearing offers rotation of ±0.04 radians (2 1/4°) by sliding at the curved interface of the two plates. Greater rotations are also available. This is a fixed-point rotational bearing.

Provisions can be made for horizontal movement by the addition of an upper plate with a horizontal slip plane between it and the concave rotational element. Figure 1 illustrates the complete system.

Practical bearings of this type can be designed for almost any combination of loads, structural movements, and rotations found in today’s bridges. They have the following performance advantages:

• High Rotation Capacity: This is easily obtained in a spherical bearing by modest dimensional differences between mating parts. By contrast, bearings with elastomeric rotation elements must be made progressively thicker for increasing rotation, which in turn demands larger shear devices or bigger pots in pot bearings. If the elastomer is not confined, the added thickness means greater vertical deflection.
• Minimal Rotation Resistance: In a spherical bearing, this is assured by low friction between the mating parts. Resistance is lower than any current bearing design for rotations over 0.02 radians. This is most important when assessing bending moments imposed on the substructure.
• Constant Rotational Resistance: In Cosmec spherical bearings, rotational resistance is constant because the frictional force is constant at all degrees of rotation; thus, eccentricity of loading is one low figure even in extreme rotations. All other bearing designs have rising eccentricities that cause commensurate increases in bending moments; increases that can be extreme in elastomeric disc or pad bearings.
• Rotational Preset: This is easy with spherical bearings; a particular advantage for some erection procedures on cable-stayed, segmental, or cantilever structures. Rotational preset is virtually impossible with bearings having elastomeric rotational elements.
• Negligible Vertical Deflection: Under load, spherical bearings offer no deflection-related problems with expansion joints, rails, service ducts, or other inter-structure details.