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From page 173... ... 173 A p p e n d i x d Bearings are an important bridge element that must be considered when evaluating potential ways to extend overall bridge service life. Bridge superstructures experience translational movements and rotations caused by traffic loading, thermal effects, creep and shrinkage, wind and seismic forces, initial construction tolerances, and other sources. Read the entire page →
From page 174... ... 174 demonstrated the properties and wear behavior of PTFE. Key results of these studies are summarized in later sections, which are "Other PTFE Research" and "Phase Two Conceptual Design of the Experiment." This previously reported behavior was used as a starting point for the research reported here. Read the entire page →
From page 175... ... 175 and PTFE, respectively, after testing. The PTFE photo represents a total accumulated sliding length of 10,000 m (6 mi) Read the entire page →
From page 176... ... 176 Further testing on unlubricated samples, however, will indicate whether this product could be a true sliding surface alternative for conventional-type bridges in U.S. practice, which typically use unlubricated, plain PTFE. Read the entire page →
From page 177... ... 177 performing wear tests on multiple sliding materials to simulate various travel speeds and contact pressures. Test specimens were also designed as part of this phase. Read the entire page →
From page 179... ... 179 horizontal movement for a simple-span bridge, because most bridges are designed to have lower midspan deflections due to live loads (L/800 is the upper limit) Read the entire page →
From page 180... ... 180 amplitude of xi to an amplitude of xi+k can be calculated from Equation D.4: N x x i i k 1 ln (D.4) = δ + The number of cycles required to reduce the free vibration amplitude to 10% of the first cycle's amplitude can be determined from Equation D.5: N 1 ln 10 1 1 2 ln10 0.366 1 0.366 (D.5) Read the entire page →
From page 181... ... 181 2. After the truck clears the span, the bridge bounces back to its original position, and then continues upward to a deflection slightly less than the initial downward deflection caused by the truck during its passage. Read the entire page →
From page 182... ... 182 Bearing Movements Due to Temperature Variations Temperature fluctuations, including daily and seasonal temperature changes, also contribute to total horizontal movement of expansion bearings. The accumulated movement of the prototype bridge bearings with 100-plus years of service life due to daily and annual temperature variations was evaluated. Read the entire page →
From page 183... ... 183 Table D.4 shows the same calculations for other truck speeds, with unit conversion to inches per minute, for movements representing FE analysis and the approximate analysis. Sliding Speed due to Bridge Free ViBration aFter truck paSSage Once a truck has crossed the bridge, the bridge continues to vibrate freely until the vibration is damped out. Read the entire page →
From page 184... ... 184 based on the initial movement from the FE analysis and assumes a 10% damping ratio. Natural Frequency of the Bridge Structure The natural frequency of the bridge can be determined by considering the structure as a single degree of freedom (SDOF) Read the entire page →
From page 185... ... 185 Lubrication is not used much in normal U.S. practice because of the uncertainty of how long it will last. Read the entire page →
From page 186... ... 186 lubricated PTFE is the PTFE most resistant to wear. However, it is uncertain that sliding material lubrication in a bridge bearing will stay in place over the life of the bridge. Read the entire page →
From page 187... ... 187 studies were performed on samples with diameters of 3.0 and 6.1 in., with most tests performed on 3.0-in.-diameter samples. Previous studies have also shown that the size of the sliding surface specimen has a minimal effect on its behavior, including its COF. Read the entire page →
From page 188... ... 188 Table D.5. Experimental Program: Test Specimen Parameters Type of Specimen Total No. Read the entire page →
From page 189... ... 189 The sliding platform was sandwiched between the two stationary sliding surface specimens mounted on steel backing plates. The two horizontal hydraulic jacks applied horizontal pressure perpendicular to the surface of the sliding specimens to create the required contact pressure. Read the entire page →
From page 190... ... 190 Backing Plate to PTFE Stainless Steel Mating Surface Splice Plate Linkage Component to Actuator Test Specimen Sliding Platform Connected to Actuator Guide Rail T-Assembly for the Guide Rail Mounting Plate for the Backing Packing Bearings* Read the entire page →
From page 191... ... 191 3.0" 3.0" Ø 1316" Typ. PL 22" x 8" x 1" PL 22" x 10" x 0.75" 2.0" 9 " 2-Ø 2.1200" 2.75" 4 " Web of T-Assembly Flange of T-Assembly T-Assembly for the Guide Rail Guide Rail (Will be supplied) Read the entire page →
From page 192... ... 192 Figure D.18. Test frame and MTS actuators being assembled on the strong floor. Read the entire page →
From page 193... ... 193 cycle frequency was initially set to 0.1 Hz (25 in./min) for all tests. Read the entire page →
From page 194... ... 194 4. The mounting plates for the sliding material specimens were pushed toward each other until the samples touched the stainless steel mating sheet. Read the entire page →
From page 195... ... 195 Figure D.24 and Figure D.25, respectively, show the maximum (static) and minimum (dynamic) Read the entire page →
From page 196... ... 196 set of PTFE specimens, which are not shown in Figures D.23 through D.25, showed lower COF values, of about 3% to 3.5% at this pressure and speed [see Figure D.28] Read the entire page →
From page 197... ... 197 Lubricated Specimen reSuLtS The MSM specimens and the second set of PTFE specimens, which were both dimpled, were initially tested using silicone grease lubrication that was shipped together with the test specimens from the manufacturer. The samples were cycled for 50- and 150-cycle intervals. Read the entire page →
From page 198... ... 198 results in NCHRP Report 432, which reported COFs of about 1% for lubricated PTFE at this pressure and sliding speed. effect of contact preSSure Variation In the second set of PTFE samples (dimpled, unlubricated) Read the entire page →
From page 199... ... 199 Figure D.29. COF of MSM samples at high pressure of 5,000 psi (V 5 25 in./min) Read the entire page →
From page 200... ... 200 travel. In PV2, the travel speed was increased to 50 in./min to accelerate testing. Read the entire page →
From page 201... ... 201 • For PTFE and Fluorogold, there were combinations of contact pressure and velocity in which the wear rate was virtually zero. This behavior was not observed for the MSM material, possibly because of material compressibility. Read the entire page →
From page 202... ... 202 with MSM manufacturer representatives, it was concluded that MSM experiences some thickness reduction from compression and creep while not necessarily losing thickness due to wear. Because of this, it is difficult to determine consistent wear rates for MSM, and PV may not be a suitable wear characteristic, as it is for PTFE-based materials. Read the entire page →
From page 203... ... 203 Table D.8. PTFE Wear Rates with Constant 3,000-psi Pressure Material Lubrication V (in./min) Read the entire page →
From page 204... ... 204 (low K) , and one associated with severe wear regimes (high K) Read the entire page →
From page 205... ... 205 where wear rate = total thickness reduction (mil) per mile of travel distance; base wear rate = defined as a function of material type, contact pressure, and velocity from PV curves based on experimental tests for plain PTFE, glass-filled PTFE, or braided PTFE; CT = modification factor for the effects of low temperature (function of material type) Read the entire page →
From page 206... ... 206 Movement due to thermal load, however, is high-amplitude, low-cycle movement with slow movement speed, and is less likely to cause wear. Fast sliding speed combined with high contact pressure and low temperatures all contribute to PTFE wear. Read the entire page →
From page 207... ... 207 material specimen sizes (3-in. diameter) Read the entire page →
From page 208... ... 208 Recommendations for Future Work Only proof of concept testing was performed in this study. To establish more reliable wear rates for the materials sampled, additional testing with various contact pressures and velocity combinations is required. Read the entire page →

From page 173...

... 173 A p p e n d i x d Bearings are an important bridge element that must be considered when evaluating potential ways to extend overall bridge service life. Bridge superstructures experience translational movements and rotations caused by traffic loading, thermal effects, creep and shrinkage, wind and seismic forces, initial construction tolerances, and other sources.