Theoretical Investigation of Structure-Property Relationships in Cross-Linked Polyurethane Elastomers for Seismic Isolation Bearing Applications in Nigerian Infrastructure

Seismic isolation bearings incorporating elastomeric elements provide a proven strategy for protecting critical infrastructure from earthquake damage, with increasing relevance for Nigerian infrastructure exposed to moderate seismicity in the Benue Trough and other seismically active zones. This research theoretically and experimentally investigates the structure-property relationships in cross-linked polyurethane elastomers designed for seismic isolation bearing applications, developing a predictive framework for engineering target mechanical and dynamic properties from molecular architecture. The theoretical framework employs rubber elasticity theory extended with network topology corrections, Mooney-Rivlin and Ogden hyperelastic constitutive models, and linear viscoelasticity formulations. Polyurethane elastomers were synthesised from three diisocyanate types, four polyol molecular weights, and two chain extender types in a systematic formulation matrix. Cross-link density was determined by equilibrium swelling and compared with theoretical prediction from stoichiometric formulation. Static mechanical characterisation included uniaxial, biaxial, and planar tension testing to parameterise hyperelastic models. Dynamic mechanical analysis over seismic frequency ranges of 0.1 to 10 Hz and temperature ranges representative of Nigerian service environments characterised viscoelastic behaviour. Full-scale bearing prototype testing was conducted under simulated seismic displacement histories. Results demonstrate that Ogden model with N=3 terms provided superior fit to multiaxial data compared to Mooney-Rivlin representation. Cross-link density control through stoichiometry achieved target horizontal stiffness values within 7 percent. Temperature sensitivity of dynamic modulus was lowest for ester-type polyol systems, confirming their preference for tropical climate applications. The research provides a complete molecular design-to-performance framework for polyurethane seismic isolation bearing elastomers applicable to Nigerian infrastructure engineering. Keywords: polyurethane elastomer, seismic isolation, structure-property relationships, hyperelastic model, cross-link density