Effect of NCO content on working principle and structural behavior of laminated polyurethane seismic bearings

With the increasing constraints on urban development spaces and the rapid rise in traffic flow, there is a growing demand for urban overpasses and elevated bridges that utilize less land while exhibiting superior performance. Laminated polyurethane seismic isolation bearings (LPEB) have been widely adopted due to its high load bearing capacity. However, the isocyanate (NCO) content of polyurethane elastomer (PUE) materials has a serious effect on the mechanical properties and fatigue life of LPEB. In this study, PUEs with Shore hardness values exceeding 80 HA were synthesized by varying the NCO content from 8.4 % to 9.2 %, achieving tensile stresses ranging from 22.89 to 52.41 MPa and elongation at break between 358.01 % and 530.71 %. Notably, the PUE demonstrated high vertical stiffness and deformation resistance under 25 MPa compressive stress. Micromechanical analysis revealed that increasing NCO content to 9.2 % enhanced hardness and stiffness but reduced damping properties and low-temperature flexibility, accompanied by an elevated glass transition temperature. Conversely, the load carrying capacity and susceptibility of PUEs with lower NCO content are affected under high stress loading. Therefore, three PUE samples with NCO contents of 8.6 %, 8.8 % and 9.0 % were fabricated into LPEB and tested for mechanical properties. Their seismic effectiveness and fatigue life were further analyzed using numerical simulations in Opensees, Abaqus, and FE-Safe. The result indicated that LPEB with 9.0 % NCO exhibits vertical stiffness, horizontal equivalent stiffness, and damping ratio that are 1.15, 1.23, and 0.88 times higher, respectively, than those of the LPEB-8.6 % NCO. Moreover, under identical ground vibration energy, the LPEB-9.0 % NCO reduced deformation displacement by 5.98–31.89 % and extended service life by 33.2–44.1 %. This study provides a reference for the application of LPEB with different NCO.