The key feature of molded, steel reinforced bearings is their functionality in a wide array of uses and conditions.
Earthquake Bearing Designs
Custom designs are available with the following features: Structure supported on DYMAT® multi-directional bearings with no internal bearing guiding. Connection between the supports and concrete deck is made with a custom unit that disconnects at maximum design horizontal force. These are fixed and unidirectional connectors. When the horizontal force exceeds the maximum design force, as in an earthquake, large molded steel reinforced bearings support the structure and supply the horizontal returning force due to the shear stiffness of the material. DYMAT® offers a design service to incorporate this system into the structural design.
Vibration & Acoustic Isolation Pads
The selection of vibration and acoustic properties of a pad is a special study and the material compound and exact shape of the pad must be carefully selected. DYMAT® offers the service of proposals of pad designs at no obligation. Special type “U” and “L” pad standards are available with reduced shape factors.
Design, Materials & Testing
Elastomeric material meets all AASHTO and MTC specifications
Standard Durometer A 55±5 Durometer
Maximum dead plus live load 6.89 MPa (1,000 psi)
Maximum dead load 4.14 MPa (600 psi)
Per AASHTO Specifications
Initial deflection less than 7% between zero and 5.52 MPa (800 psi)
Allowable shear deflection ±25% of effective rubber thickness
Per MTC Specifications
Initial deflection less than 4% between 1.38 MPa (200 psi) and 6.89 MPa (1,000 psi)
Allowable shear deflection ±50% of effective rubber thickness
High quality neoprene and natural rubber elastomers are compounded to meet engineering requirements. Standard bearings in the table are compounded to meet current AASHTO and the Canadian MTC current specifications. Custom material specifications can be manufactured.
DYMAT® Plain Bearing Pads
Available in all Sizes and Thicknesses
The material is standard AASHTO and MTC neoprene or natural rubber in 50, 55, 60 and 70 Durometer A (±5). DYMAT® will manufacture special material specifications on request.
The least plan dimension of the bearing must be equal to, or greater than, five times the thickness.
Compression - Deflection
The initial deflection due to load should not exceed 6% of the thickness when measured between 200 and 1,000 psi.
Abnormal Design Conditions
See Transport and Road Research Laboratory Report 708 (1976), Transport and Road Research Laboratory, Crow Thorne, Berkshire, England.
Design Criteria for Non-Standard Bearings
Design engineers should be knowledgeable in all aspects of the bearing design.
Reference is made to:
Design of Neoprene Bearing Pads, E.I. DuPont Company
Natural Rubber in Bridge Bearings, Technical Bulletin No. 7
Natural Rubber Bureau, 19 Buckingham Street, London, W.C.2
Since it is not possible to list all potential bearing sizes required for every structure, DYMAT® offers custom sizing service at no obligation to engineers.
Calculation of Shear Stiffness
DYMAT® has tested shear stiffness on the standard bearing. Use the following method.
KS = G x L x W per unit length / Et
KS = Shear Stiffness
G = Shear Modulus
L = Length of Pad
W = Width of Pad
E = Number of Internal Elastomeric Layers
t = One Layer of Elastomeric Thickness