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SORBTEX® Structural Bearing Pads and Expansion Bearing Assemblies

Structural Bearing Pads and Expansion Bearing Assemblies

SORBTEX® is a layered rubber and fabric composite material that is used as an elastomeric bearing pad in a wide variety of structural bearing applications. SORBTEX® is manufactured to meet, and is tested in accordance with, the requirements of MIL-C-882E. SORBTEX® also meets the cotton-duck pad (CDP) requirements as discussed in AASHTO Section, Section, and AASHTO Section 18.10.1. In addition to the above noted globally recognized specification references, SORBTEX® is also identified by a multitude of state and corporate specifications and descriptive references. The most common descriptive references for SORBTEX® are: fabric pad, preformed pad, preformed fabric pad, cotton duct pad, cotton duck pad, and CDP.

SORBTEX® offers great flexibility to the engineering community in the design of connections requiring relative movement between structural elements. When compared to other elastomeric bearing products, SORBTEX’s high load capacity, predictable vertical deflection, and rotation range allows for the design of significantly smaller and more cost effective bearing solutions. Structural bearings whose sizes require an average compressive stress of 2,500 psi (3,000 psi per AASHTO) and rotations to 0.025 radians are possible with SORBTEX®. Please see the document titled “SORBTEX® LITERATURE” for a detailed review of Voss Engineering, Inc.’s independent material testing and bearing design methodology development program.

Use of a PTFE surface on the SORBTEX® pad (lower element) and a polished stainless steel surface on a sole plate (upper element) will allow longitudinal movements limited only by the physical constraints of the related structural elements.

SORBTEX® Bearing Pads are fabricated to order and available in wide variety of plan sizes and thicknesses. Plan size is limited to 48″ (+0, -1″) in a single piece, however, lengths up to and over 120″ are possible depending on the required thickness. In addition to square and rectangular bearing pads, SORBTEX® is available in round, washer; annular ring, dovetail interlocked, and mandrel wrapped bushing formats.

SORBTEX® pads can be fabricated to meet any thickness requirement. The most economical pad thickness is achieved by utilizing any combination of the following standard gages: 1/16″, 1/8″, 3/16″, 15/64″, 9/32″, 11/32″, 1/2″, 5/8″, 3/4″, and 1″. Voss routinely fabricates SORBTEX® pads up to 5″ thick.

For further application support please contact us using the links on this website.

SORBTEX® is made of high-quality cotton or cotton-polyester duck cloth that has been impregnated with oil resistant synthetic rubber and treated with mold and mildew inhibitors. Manufactured to the specifications of MIL-C-882E, 27 January 1989.


Hardness (Shore A)90 ± 5
Compression Min. Ultimate Strength 110000 psi
Shear Modulus (G) 2450 psi
Apparent Shear Modulus (G A ) 31150 psi 1325 psi 400 psi 850 psi
Permanent Set2 ± 1%
Volume Swell (per FED-STD-60, REF)25% max.
Dielectric Strength (ASTM D149)155 VDC/mil
Volume Resistivity (ASTM D257)3.3 ohmºcm x 10 10
Thickness Tolerance± .031" (per layer)
Plan Size Tolerance 4± 1/8 in
1. 10,000 psi minimum per MIL-C-882E Section 4.4.4. Ultimate breakdown 12,000 psi to 18,000 psi depending on product thickness.
2. Based on tests conducted according to ASTM D 4014-87, Annex A1 at pure shear strain of 33 percent.
3. At compressive stresses of 500, 1000, 2000, 3000 psi, based on shear stress measurements made @ 70 ºF at a shear plus slip strain of 50 percent.
4. General shop tolerance. Provide required tolerances at time of inquiry.