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Abstract. More than 50 cable-supported bridges have been built in Korea since 1980. While maintaining those infrastructures for last 30 years, we have experienced unexpected problems from operational field monitoring of long-span bridges. This paper discusses on what we have observed, learned and how we responded to those events. As an example, a vortex-induced vibration was observed in 2011 in parallel-disposed twin cable-stayed bridges. Operational monitoring and wind tunnel tests successfully identified that the close distance between two bridges was one of the main cause of the vibration. However, an operational modal analysis revealed that unexpected low damping ratio of the bridge was also contributed to the realization of this serviceability problem in an operating bridge. Another observation of vibration in a long-span suspension bridge also attracted our attention on the potential low damping ratio, which may invoke serviceability issues in assessment of bridges. This paper introduces the details of the cause investigations, assessment and mitigation of the serviceability problems, validation through field tests and operational monitoring, and concluding suggestions to bridge owners and engineers.

The wind tunnel test is one of the most reliable methods for evaluating the dynamic response of high-rise buildings considering wind-structure interaction. In conventional aeroelastic wind tunnel tests, the calibration of stiffnesses, masses and the damping properties of a scaled specimen is required. This takes extensive time and effort, especially when the tests need to be repeated with various geometric designs during design iterations. This study introduces a new testing method that combines a numerical simulation and the conventional aeroelastic wind tunnel test through the real-time hybrid simulation method. The stiffness, damping and partial mass of a scaled building model are represented numerically, while the rest of the mass, the wind-induced pressure around the model and the wind-structure interaction are represented physically in a wind tunnel. The building model in the wind tunnel rests on a base-pivoting system, which is controlled with a linear motor. The base moment induced by wind pressure and the inertial force from the mass of the physical specimen is measured; those measurements are then fed back into a numerical integration scheme. A delay-compensation scheme is implemented to minimize the effects of actuator delay on the dynamic response of the system. Several tests are carried out to validate and calibrate the developed test apparatus and control scheme including (1) tests for the identification of actuator delay, (2) free vibration tests for characterization of the dynamic properties of the hardware and the control system, and (3) wind tunnel tests for system validation through aeroelastic real-time hybrid simulation. This paper presents the overall design of the experimental apparatus, the adopted delay compensation and numerical integration schemes, and a summary of the test results. Test results confirmed that the developed experimental technique can replace the conventional aeroelastic wind tunnel tests of a building model, thus improving the efficiency of the aeroelastic wind tunnel testing.

An unexpected vibration was observed on the Yi Sun-sin Bridge on October 26th, 2014. Since the bridge was subjected to a single mode vibration in limited amplitude for one and half hours, it was regarded as a vortex-induced vibration (VIV). Since the bridge was aerodynamically well designed for the VIV as well as flutter instability, the cause of the vibration was investigated via a series of two-dimensional wind tunnel tests. The one-side lanes were closed to traffics and the epoxycoated wearing surface was being replaced at the time of the VIV. Since the primary source was estimated as the temporal screens applied on the bridge railings for maintaining curing temperature of the replaced wearing surface, wind tunnel tests were carried out for the section model of the deck section with and without the screens. This paper presents the screen effects on VIV of the investigated bridge and the illustration of the observed vibration based on in-depth investigation with a series of two-dimensional wind tunnel.