Effects of structural symmetry of introduced polyether diol on low temperature tolerance of laminated polyurethane bearings in bridges

Abstract

Laminated seismic isolators are installed on highway bridges worldwide to minimize the risk of seismic collapse. In recent years, Laminated Polyurethane Bearing (LPB) has gained immense popularity in the field of large-span bridge construction due to its advantages such as ultra-high bearing capacity, low cost, and simplicity of production. However, Polyurethane (PU) elastomers of LPB undergo cold hardening, which reduces the ability of LPB to protect bridges from seismic damage in freezing regions. In this study, four kinds of polyether diols with varied chemical symmetry were added to PU consisting of PTHF, TDI, and MOCA, respectively. The introduced polyether diols include polytrimethylene ether diol (POTG) and polytetrahydrofuran (PTHF) with symmetric linear structures, and poly(oxypropylene) (PPG) and 3-methyl-tetrahydrofuran/tetrahydrofuran co-polyether diol (3MTHF) with asymmetric structures. The microscopic characterization performance tests and low-temperature mechanical experiments were conducted to investigate the effect of structural symmetry of added polyether diol on the low-temperature tolerance of LPB. Results prove that due to the significant structural irregularity of the chains, the 3MTHF-based PU exhibits the least amount of microphase separation and the lowest elastic modulus among all specimens, yielding the best low-temperature tolerance of corresponding LPB. It was further discovered that the Bouc-Wen model with proper parameters can accurately simulate the lateral response of the 3MTHF based LPB at different temperatures. Finally, the seismic responses of bridges isolated by 3MTHF based LPB were investigated and compared with those of the bridges with the conventional PTHF based LPB under near-fault earthquake loadings at low temperatures. The results shows that 3MTHF significantly enhances the horizontal flexibility of the LPB, thus improving the effectiveness of the isolation system in low-temperature environments.