Experimental investigation of unbonded fiber reinforced elastomeric isolators with modified support geometry

Document Type

Conference Proceeding

Publication Date


Publication Title

NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering


Fiber reinforcement is an attractive alternative to conventional steel reinforcement and an important component in the advancement of low cost elastomeric isolators for application in developed and developing countries. The fiber reinforcement is substantially lighter than steel reinforcement but has comparable tensile properties, which provides sufficient restraint for the elastomeric layers. Positioning Fiber Reinforced Elastomeric Isolators (FREIs) unbonded between the supports eliminates the requirement for large steel end plates, further reducing the cost and weight of the isolator and simplifying the installation. FREIs exhibit a unique rollover deformation when displaced horizontally. The rollover deformation is a consequence of the unbonded application and the negligible flexural rigidity of the fiber reinforcement. As rollover occurs, the effective shear area of the isolator is reduced, consequently resulting in an advantageous softening response. This softening continues until the initially vertical faces of the isolator complete full rollover and contact the horizontal supports, which prevents further softening and begins to stiffen the isolator. The occurrence of full rollover can be accelerated or delayed by modifying the support geometry of the isolator. Accelerating full rollover can be used to control excessive displacement, whereas delaying full rollover can increase the displacement capacity of the isolator, including expanding the softening regime. A proof-of-concept experimental program is conducted evaluating the effective horizontal stiffness of an isolator tested with Modified Support Geometry (MSG). It is demonstrated that MSG does not influence the performance of the isolator prior to full rollover and full rollover can be delayed while still maintaining a positive incremental forcedisplacement relationship.