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Lee C.-H.,DongYang Structural Engineers Co. | Ryu J.,Korea University | Oh J.,Korea University | Yoo C.-H.,Advanced Development Team | Ju Y.K.,Korea University
Engineering Structures

This paper describes the development process of a new low-steel composite friction material and the experiments to investigate its frictional behavior. Automotive braking technology was adapted to derive an optimal friction damper for buildings, and a high friction coefficient and stable behavior were set as the primary targets for performance. To improve performance, clamping details which incorporated load washers were also proposed. In order to evaluate the performance of the friction system, pseudo-dynamic tests were conducted. In the experiments, the proposed friction dampers showed repeatable, predictable, and very stable behavior without significant fading of frictional resistance, even under hundreds of repetitive sliding excursions. The friction load tended to be proportional to the initial clamping force regardless of the real-time clamping force, thus confirming that the behavior of the proposed dampers could be predicted using the idealized Coulomb friction model. It was also verified that frictional performance could be remarkably increased through the use of conical shaped load washers, when applied correctly. Furthermore, nonlinear time history analysis was performed on a five-story example building with and without friction dampers. Based on the results, the friction damped system demonstrated effectiveness in reducing structural responses such as roof displacement, base shear force, and story drift ratio compared to the original undamped frame system. © 2016 Elsevier Ltd Source

Kim D.-H.,Korea Advanced Institute of Science and Technology | Lee C.-H.,DongYang Structural Engineers Co. | Lee C.-H.,Korea University | Ju Y.K.,Korea University | Kim S.-D.,Korea University
Structural Design of Tall and Special Buildings

In this study, a subassemblage test was performed using buckling-restrained braces with an H-shaped core element, which have been proven in a previous uniaxial component test to have good performance. The loading protocol prescribed the quasi-static cyclic pattern with stepwise incremental displacement amplitude. Two different end connections (bolted connection and pin connection) and two different buckling-restrained mechanisms (concrete-filled tube and hollow steel tube) were examined as the test parameters. The performance of the specimen was evaluated by comparing the test results with the recommended provisions for buckling-restrained braces. The test results showed that the compression strength capacity of buckling-restrained brace (BRB) with in-filled concrete increased by about 10% compared with BRB without in-filled concrete. According to test result at same story drift of 2Dbm, structural performance of pin connection specimen without bolt slippage is superior to bolted connection specimen. Also, bolted connection specimens showed similar performance for total energy dissipation and cumulative plastic ductility, regardless of the connection types and the existence of concrete filling. Copyright © 2014 John Wiley & Sons, Ltd. Source

Lee C.-H.,DongYang Structural Engineers Co. | Kim J.,Hanyang University | Kim D.-H.,Korea Advanced Institute of Science and Technology | Ryu J.,Korea University | Ju Y.K.,Korea University
Engineering Structures

A new hybrid damper which combines a friction damper and steel strip damper is proposed for improving the seismic performance of structures at multiple levels of ground motion. In order to investigate the combined behavior of the proposed damper, quasi-static cyclic tests were carried out on ten specimens. Experimental results demonstrated that hysteretic response was stable, and multi-phased behavior (i.e., activation of two different kinds of dampers) functioned as intended. However, depending on the type of strip damper applied, the behavior and failure modes showed distinct differences due to rotational motion induced during combined behavior deformation and energy dissipation capacities were enhanced when a strip damper with adequate out-of-plane stiffness was applied. Furthermore, numerical analysis based on both material strength and expected strength well represented behavioral characteristics of the damper, and dissipated energy was reliably predicted. It is expected that the proposed analytical model can be practically applied to predict the performance of structures strengthened by the hybrid damper. © 2016 Elsevier Ltd. Source

Peronto J.,Thornton Tomasetti | Sunu W.,DongYang Structural Engineers Co. | Sinn R.,Thornton Tomasetti | Huizinga M.,Thornton Tomasetti
Structures Congress 2014 - Proceedings of the 2014 Structures Congress

The ultra-modern, 245-meter-tall Federation of Korean Industries (FKI) office tower is a significant and recent addition to the skyline of Seoul, South Korea. The building, including below-grade parking and support spaces, consists of 170,000 square meters of gross floor area with 111,000 square meters above grade. A separate, free-form, glass and steel rib-shell structure at the podium also houses a 6,000-square-meter conference center. The tower structural system consists of a reinforced concrete core and composite perimeter columns coupled with steel outriggers and belt trusses to resist lateral forces. The superstructure is founded on reinforced concrete bored piles socketed into the local rock formation. Five below-grade levels were constructed utilizing top-down construction techniques. The exterior wall of the tower has been furrowed as part of the architectural expression and to provide optimal utilization of building-integrated photovoltaic panels. The unique exterior skin is a key factor in disrupting the organization of wind vortices for the purely prismatic tower geometry. All documentation was produced in 3D REVIT and TEKLA models. © 2014 American Society of Civil Engineers. Source

Lee C.-H.,DongYang Structural Engineers Co. | Lho S.-H.,Korea Agency for Infrastructure Technology Advancement | Kim D.-H.,Korea Advanced Institute of Science and Technology | Oh J.,Korea University | Ju Y.K.,Korea University
Engineering Structures

An hourglass-shaped strip damper (HSD) was proposed to improve on the conventional slit damper. The damper has non-uniform strips which have a smaller cross-sectional area close to the middle height. To find the structural capacities of HSD subjected to monotonic and cyclic loadings, experimental tests were carried out in this study. Test parameters were loading rate, material strength, and the number of damper plates. The results showed substantial load-resistance capacity under monotonic loadings, and excellent ductility and energy dissipation were exhibited under cyclic loadings, with even distribution of damage over the entire height of strips. Based on the test results, a simple hysteretic model using a combined isotropic-kinematic hardening rule was also proposed. The comparison demonstrated that it represents the tested cyclic load-displacement hysteresis well. It is expected that the proposed model can be successfully used to predict the behavior of HSD in real-world applications. © 2016 Elsevier Ltd. Source

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