S.D. Campbell/Kinetics Noise Control
APPLICATION
Examples of the design of both steel- and carbon fiber mesh-reinforced pads are presented for a performing arts center. The pads were located under the support columns and rested on concrete piers. A typical column load was 111.2 kN dead and 89 kN live. The pads were required to have steel plates laminated top and bottom to allow for mounting, pre-compression of the pads, and the attachment of horizontal slider plates. The mounting plates required 25.4 mm of height out of a total allowable pad height of 114.3 mm, leaving only 88.9 mm for the pad. The target static natural frequency of the pad was 7 Hz ± 1 Hz under dead load plus 25 percent of the live load.
The design utilized five layers of natural rubber reinforced with four layers of either steel or carbon fiber mesh. The rubber layers were 6.5, 25.4, 9.5, 25.4, and 6.5 mm thick with 3.2 mm thick steel reinforcement for a total height of 86.1 mm. The same lamination was used for all the pads on the project with varying plan dimensions based on the load. The pad described herein was 203 mm square. For 50 durometer natural rubber this bearing had an estimated static natural frequency of 6.0 Hz under the design load and 6.4 Hz under the dead load only. The steel reinforced pad met the design criteria and remained within the height limitation.
A design using the carbon fiber mesh for reinforcing could take two forms. Identical rubber layers could be used, with identical performance obtained, but with a total height of only 73.6 mm. Alternatively, the center rubber layer could be increased in thickness to 20 mm (total height 84.1 mm) leading to a design load natural frequency of 5.4 Hz and a dead load only natural frequency of 5.7 Hz. This significant reduction in natural frequency was achieved while simultaneously slightly reducing the operating height. Although the increased flexibility was not required for this project, it was desirable, and could be critical in some applications.