16 A.R. Klembczyk 2.3 Intermediate Inspection After 7 Years in Service A visual inspection of each damper was performed looking for corrosion, damage to the unit from use or the surrounding environment, and for fluid leakage. The units were all found to be in 100% working condition with minimal signs of physical damage or deterioration, as well as no signs of fluid leakage. There were only minor signs of corrosion and some external contamination noted. The units had been subjected to nearly constant cycling for a period of use of over 7 years at the time of this inspection. The total estimated cycles after 7 years was as many as 2.0 108. The owner required no formal testing of installed dampers at this time. 2.4 Principal Inspection and Testing After 11 Years in Service The Principal Inspection after 11 years of service included two phases. The first was a visual inspection of all Pier Dampers and all four Vertical Dampers. All dampers appeared to be in 100% working order. A sample of five of the seventeen deck dampers were inspected per the owner’s request to minimize deck panel removal costs. Similar to the case for the Intermediate Inspection 4 years earlier, there were only minor signs of corrosion and some external contamination noted. This minor corrosion and contamination appears to have been caused by caustic chemicals from the exhaust plumes from boats and ships navigating under the bridge. Dampers located under the deck of the bridge near the shore or over land exhibited nearly new appearance. Two of the five Deck Dampers and one of the four Vertical Dampers were temporarily removed for testing purposes as outlined below. The second phase of the Principal Inspection consisted of performing dynamic tests on the three dampers that were removed. These three dampers were shipped to the Taylor Devices facility in North Tonawanda, New York so that they could be tested to the original Acceptance Test Procedure and compared to the original acceptance tests from 2001. This was done to determine if any of the performance outputs had deteriorated in any way. This Acceptance Test Procedure consisted of two types of tests. The first type consisted of subjecting the dampers to a series of sinusoidal input tests throughout the specified velocity range. These tests are referred to as the “Force vs. Velocity” tests. The second type of test was performed at approximately 0.50 mm amplitude. These tests are referred to as the “Low Amplitude” tests. The Low Amplitude test demonstrates the ability of each Damper to produce substantial damping force for very small vibrations, and demonstrate that there has been no loss of fluid. If any loss of fluid had occurred, the damper would demonstrate an inability to produce any substantial force for these small displacements. Figures 2.10, 2.11, and 2.12 show the results of the Force versus Velocity tests for each Damper, measuring the output force at several velocity inputs. These plots also show the data points recorded through the same testing methods 11 years prior. The graphical data illustrates the fact that there is virtually no difference in output characteristics when comparing the results from 2001 to the results from 2012. Figures 2.13, 2.14 and 2.15 demonstrate the results of the Low Amplitude Tests for each of the three dampers that were tested. Note that in each case, the hysteresis loops (force vs. displacement) show no signs of free-play, loss of fluid, excessive friction, wear or degradation of any sort. It should be noted that the dampers were tested with their spherical bearings in place and their end attachment brackets still connected. Therefore, no degradation to these components has occurred and the bearings have maintained their tight fit requirement that is necessary to produce damping for very low displacements. Subsequent to the successful testing of these three dampers, they were sent back to London and reinstalled on the bridge in January 2013. 2.5 Conclusions The results of the 7-year Intermediate Inspection, the 11-year Principal Inspection, and dynamic testing show that the Millennium Bridge dampers have experienced no physical or functional deterioration. The dampers displayed no measurable change in output, as well as no signs of leakage after 11 years of continuous service and nearly constant cycling.
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