# Friction Behavior of Ceramic Materials for the Development of Bridge-Bearing Friction Materials
## 4 Test Results and Analysis of Bridge Bearings with Ceramic Applications  
### Test Plan for Bridge Bearings  
A test plan was developed to analyze the application of ceramic-friction materials in full-scale bridge bearings. The target bridge-bearing capacity in this study was set to 3000 kN. Tests were conducted based on the bridge-bearing test standards outlined in the AASHTO LRFD BCS. A bridge-bearing test evaluation device with a vertical load capacity of 30,000 kN, horizontal load capacity of 5000 kN, and stroke of \(\pm\)1000 mm was used to perform the compression and friction tests (Figure 7). This setup allowed a comprehensive evaluation of the performance of ceramic materials under realistic bridge-loading conditions, providing insights into the feasibility of using ceramics as materials in high-capacity bridge bearings.  
For a comparative evaluation with conventional friction materials, tests were conducted on bridge bearings using ceramic and PTFE friction materials. The PTFE material  
Figure 6: Friction test results with both ceramic-friction materials (under 15 MPa of vertical load).  
Figure 7: Test setup of bridge bearing.  
used had a thickness of 4.5 mm, diameter of 350 mm, and dimple pattern with lubricant application conditions, simulating the environment of actual bridge bearings. For the ceramic material, a roughness coefficient of 0.8 was set, as indicated by previous findings, indicated that achieving a lower surface roughness through polishing was not significantly beneficial. The ceramic material was designed to have dimensions of 50 mm width and 8 mm thickness, with the lower plate featuring side sections of 250 mm height and a central section of 350 mm, whereas the upper plate consistently measured 350 mm. This configuration was used because of the limitations of the ceramic manufacturing equipment, which constrained the achievable length and thickness. In addition, the use of ceramics in the full-plate form proved less economical than the use of PTFE. Therefore, the optimal configuration was determined to be the partial application of ceramics, considering both the manufacturing constraints and cost efficiency. As shown in Figure 8, a partial plate layout was designed to enhance the economic feasibility by selectively, rather than fully, applying ceramic materials. The detailed size and application positions were determined based on the loading conditions of the bridge bearing and typical movement ranges, with an average travel of \(\pm\)10 mm in the transverse direction and \(\pm\)50 mm in the longitudinal direction. Consequently, as shown in Figure 8, ceramic materials were arranged in a grid pattern on the upper and lower sections of the bearing to optimize the performance and cost.  
For the compression test, a load equivalent to 1.5 times the capacity of the bridge bearing was applied at a constant rate, maintained at the maximum load for 5 min, and then removed. A visual inspection was conducted after the test. To assess potential failure behaviors such as damage and defects due to excessive loading on the bridge bearing, an additional test was performed under extreme conditions with a load set to 3.0 times the bearing capacity.  
The friction test was conducted by applying a vertical load equivalent to the full capacity of the bridge bearing (1.0 times its capacity), controlling the displacement at a rate of 1.058 mm/s with a movement range of \(\pm\)25.4 mm from the origin. The COF was determined as the ratio of vertical to horizontal forces.