# Experimental Study on the Behavior of Polyurethane Springs for Compression Members
## 1 Introduction  
In recent years, we have witnessed the widespread use of elastomeric polymers in engineering applications such as base isolators, structural dampers, and vibration control springs [1, 2]. Elastomeric polymers feature a high toughness-to-density ratio and can resist large elastic deformations [2, 3, 4]. The conventional seismic design of structures tends to generate inelastic deformation in the structural member (e.g., beam and column), which results in residual drift and leads to permanent damage. However, in advanced seismic design, buildings are considered based on a low-damage self-centering system with replaceable fuse devices specially designed with the aim to sustain large deformation [5, 6, 7, 8, 9, 10, 11, 12]. In this way, some researchers have tried to design structural damper systems using materials with self-centering characteristics, such as applied superelastic shape memory alloys (SMA) [13, 14, 15, 16, 17]. [PERSON] et al. [18] applied SMA to a friction damping brace to study recentering capability and energy dissipation, and proposed an optimal design method for a smart self-centering bracing system. However, despite the excellent self-centering performance of SMA, it is thought that it will take a long time to be applied to actual structures as its price is too high and its workability is relatively poor. Therefore, studies on elastomeric polymers, such as polyurethane, that exhibit similar performance while being more economical and workable than SMA are being actively conducted. In this way, elastomeric polymers, suchas polyurethane springs, can be used in structural damper systems that offer not only self-centering but also vibration control [19; 20]. In the last decade, some researchers have examined the cyclic response of structures equipped with polyurethane elastomers. Polyurethane is a polymer developed by I. G. Farben and [PERSON] in 1937, and refers to a generic term for compounds with a urethane bond (-NHCO-O-) [21]. The urethane bond of polyurethane is generally formed by reacting a reactive isocyanate group (-NCO) with a hydroxyl group (-OH), such as TDI and MDI. In special cases, it can also be synthesized by the reaction of bischloroformates and amines [22; 23]. [PERSON] et al. [24] evaluated the behavior of axial polyurethane friction dampers by using finite element (FE) analyses and found that polyurethane springs are able to increase damper stiffness and strength. [PERSON] et al. [25] employed polyurethane elastomers in a rocking wall system and performed 14 sets of experimental tests. Their obtained results showed that the used polyurethane elastomers could produce flag-shaped hysteresis with small residual drifts. [PERSON] et al. utilized polyurethane foams in wooden house wall panels and evaluated their seismic behavior through experimental tests [26]. The results showed that polyurethane foams could simultaneously achieve a stable increase in the stiffness and damping properties. [PERSON] and [PERSON] [27] investigated a sliding isolation system, in which polyurethane elastomers were used to effectively minimize the response of buildings to seismic excitation. The obtained results demonstrated that the proposed system had an excellent damping energy dissipation capacity. [PERSON] et al. [28] experimentally evaluated the behavior of the smart damper equipped with dual polyurethane rubber springs and then concluded that these smart dampers initially exhibited rigid behavior in the quasi-static tests because of equipped polyurethane springs under precompression. [PERSON] et al. [29] revealed that polyurethane foam increased the rigidity of buildings, resulting in the mitigation of the inelastic response of the structure subjected to different seismic excitations. [PERSON] et al. [20] evaluated the seismic performance of high-voltage post insulators by using the polyurethane bearing system through a shaking table.