High-capacity casting polyurethane elastomeric (HCPUE) bearing is a new elastomer isolation bearing that features excellent durability, higher vertical capacity, and a simpler production process compared with traditional rubber isolation bearings. However, HCPUE bearing exhibits significant hardening behavior at low temperatures. To expand the application of HCPUE bearings in cold regional structures, this study developed an improved low-temperature resistant 3M-HCPUE bearing by incorporating 3-methyl tetrahydrofuran copolyether glycol (3M-PTGL) in the elastomer formulation. The low-temperature performance improvement of the 3MHCPUE specimen was verified through characterization and mechanical property tests using six different compounding formulas. HCPUE materials with 15% and 25% 3M-PTGL were selected to prepare improved 3MHCPUE bearings. The shear hysteretic behavior and ultimate deformation performance of the bearings were tested at different temperatures. Seismic fragility analysis of a three-span box girder bridge with 3M-HCPUE bearings was conducted using different isolation periods and ambient temperatures. The 3M-PTGLimproved 3M-HCPUE bearing exhibited excellent low-temperature performance and effectively alleviated the hardening behavior of the HCPUE bearing at low temperatures. The change rate in the equivalent stiffness for the 3MHCPUE bearing with 25% 3M-PTGL was degrees C reduced from 106% to 44% at -20 degrees C compared with that at 23 degrees C. The equivalent damping ratio slightly decreased from 25.2% to 19.6%. The improved 3M-HCPUE bearings effectively reduced the failure probability of the pier at low temperatures, but increases the probability of bearing failure.

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 lowtemperature 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.

Seismic isolation laminated elastomeric bearings are applied worldwide in bridges to reduce vibration and prevent collapse. Currently, the high-capacity polyurethane elastomeric bearings (HPEB) are favored in longspan bridges due to their super-high bearing capacity, low cost, and simple manufacturing process. However, there are many countries and regions in the world with extremely cold climates and are covered by ice and snow. At subzero temperatures, the stiffness of polyurethane elastomers (PUEs), which are an important component of HPEB, increases significantly, rendering HPEB ineffective in protecting bridges in cold regions from earthquake hazards. In this work, an attempt was made to modify the PUE as well as to improve the low-temperature resistance of HPEB by introducing 3-methyl-tetrahydrofuran/tetrahydrofuran co-polyether glycol (PTGL). Specifically, a series of microscopic characterization experiments (FT-IR, AFM, DSC, and DMA) were performed to study microphase separation and crystallization phenomena of the newly developed PUE. Moreover, the mechanical verification experiments were performed for the PUE and HPEB with different amounts of PTGL, including tensile, compression, and shear tests. All tests are performed at 23, 0, -10, and -20 degrees C temperatures respectively. The mechanical experiments demonstrate that the introduction of PTGL significantly reduces the shear modulus (G) and horizontal stiffness (Kh) of HPEB at low temperatures, that is, improves the lowtemperature resistance of HPEB. Therefore, this research is of great significance for the application of isolation bearings in cold regions.

Laminated elastomeric bearings are broadly used in large bridges for adjusting the deformation and ensuring the safety of the bridge structure. Interestingly, the bridge bearing’s deformation contains rich information that reflects the complex load conditions of the bridge structure. Nevertheless, the structural health monitoring (SHM) of the bridge bearings has not been carried out effectively due to the special characteristics of bridge bearings’ deformation, including the large range and the existence of varied forms. Along these lines, a novel conductive polymer composite-based flexible strain sensor was fabricated by employing a facile solution-blending method. More specifically, the proposed strain sensor was composed of thermoplastic polyurethane (TPU), multiwall carbon nanotubes (MCNTs), and silane coupling agent KH550. The utilization of the KH550 not only promoted the dispersion of MCNTs within the TPU matrix but also enhanced the interfacial bonding between the MCNTs and the TPU matrix, resulting in the large strain range (~150%) of the silanized MCNT/TPU strain sensor. More specifically, the silanized strain sensor with 3.0 wt% MCNTs demonstrated extraordinary linearity, promising gauge factor (~ 8.12), and great durability under the enforcement of a tensile strain up to the value of 150% through the application of consecutive stretch–release tests. On top of that, the compressive bending sensing tests proved the stable and repeatable bending sensing capability of the proposed silanized strain sensor. Moreover, the silanized strain sensor could effectively monitor the shear and the compressive deformation of the laminated elastomeric bridge bearings. This work provides a new way for fabricating flexible strain sensors with enhanced strain range, which validates the feasibility of the strain sensor for monitoring the bearing’s deformation and provides an experimental basis for developing the SHM of the laminated elastomeric bridge bearings.