Junhee Kim

Design and test of tuned liquid mass dampers for attenuation of the wind responses of a full scale building

A tuned liquid mass damper (TLMD) is proposed for bi-directional control of the wind responses of a building in orthogonal directions. It is a damper that behaves as a tuned liquid column damper (TLCD) and also as a tuned mass damper (TMD) in the orthogonal direction to the TLCD. Therefore, the TLMD provides the control performance of both a TLCD and a TMD. First, experiments are performed for the TLMD installed at angles on a uniaxial shaking table in order to describe bi-directional wind responses. The results reveal that independent TLCD and TMD behaviors are found, leading to the conclusion that the responses are controlled by one TLMD. Finally, a real size TLMD is manufactured and installed on the fifth floor of a full scale five story steel building. A hybrid mass driver (HMD) on the fourth floor is used as an exciter. Three tests are performed for the TLMD placed in the TMD direction, the TLCD direction and the coupled direction by rotating the TLMD by 45°. Independent TMD and TLMD behaviors are observed as found in the shaking table test. Therefore, it is concluded from the experiments that the new TLMD can control the bi-directional wind responses of a building by TLCD and TMD motions.

Ambient Vibration Testing for Story Stiffness Estimation of a Heritage Timber Building

This paper investigates dynamic characteristics of a historic wooden structure by ambient vibration testing, presenting a novel estimation methodology of story stiffness for the purpose of vibration-based structural health monitoring. As for the ambient vibration testing, measured structural responses are analyzed by two output-only system identification methods (i.e., frequency domain decomposition and stochastic subspace identification) to estimate modal parameters. The proposed methodology of story stiffness is estimation based on an eigenvalue problem derived from a vibratory rigid body model. Using the identified natural frequencies, the eigenvalue problem is efficiently solved and uniquely yields story stiffness. It is noteworthy that application of the proposed methodology is not necessarily confined to the wooden structure exampled in the paper.

Easy-to-tune reconfigurable liquid column vibration absorbers with multiple cells

This study proposes a retunable liquid column vibration absorber (LCVA) that can handle a wide range of natural frequencies while maintaining its original shape. The LCVA’s vertical tubes are divided into several smaller tubes (i.e., cells). Sealing a cell makes the liquid in it stand still so that only part of the liquid contained within the LCVA participates in the motion. By selecting appropriate configurations of sealed cells, the sectional area ratios of the vertical and horizontal tubes and the effective horizontal tube length are changed, which yields new natural frequencies to accommodate shifts in the natural frequency of a primary building. The proposed retunable LCVA is analytically evaluated and experimentally verified by using various patterns of sealed cells and a shake-table test to provide various natural frequencies while maintaining control performance.

A Standalone Vision Sensing System for Pseudodynamic Testing of Tuned Liquid Column Dampers

Experimental investigation of the tuned liquid column damper (TLCD) is a primal factory task prior to its installation at a site and is mainly undertaken by a pseudodynamic test. In this study, a noncontact standalone vision sensing system is developed to replace a series of the conventional sensors installed at the TLCD tested. The fast vision sensing system is based on binary pixel counting of the portion of images steamed in a pseudodynamic test and achieves near real-time measurements of wave height, lateral motion, and control force of the TLCD. The versatile measurements of the system are theoretically and experimentally evaluated through a wide range of lab scale dynamic tests.

An Electrical Wave Height Measurement at Spatial Multipoint Locations in Liquid Dampers for Structural Vibration Mitigation

Liquid dampers such as tuned liquid column dampers and tuned liquid dampers have been adopted to ensure serviceability of a vibratory building subjected to wind. In order to maximize efficiency of the vibration suppression, tuning frequency of the liquid dampers is supposed to be set to the first natural frequency of the building. Therefore, experimental evaluation of the natural frequency of liquid dampers is a primal factory task prior to their installation at the building. In this study, a novel liquid height measurement system based on variable resistance in an electric field is developed for observation of vertical motion of the liquid dampers. The proposed system can simultaneously measure the liquid height of multipoint locations in the electric field. In the experimental phase, natural frequency of the liquid dampers is experimentally evaluated utilizing the developed system. The performance of the proposed system is verified by comparison with the capacitive type wavemeter.