Explain the Anti Slip Devices - Bridge Bearing?

It has been explained earlier that elastomeric bearings have a tendency to slip if the minimum normal pressure is less than 2 MPa. Such a situation is likely to occur when elastomeric bearings are used in steel plate girders having less self weight. UIC code 772-2R cautions against the use of elastomeric bearings if they are required to undergo simultaneously light loading and large longitudinal movements. For steel girders of spans ranging from 12.2 m to 30.5 m the minimum bearing pressure is less than 2 MPa. All such bearings, therefore, require some anti-creep or anti-slip device.