Jae-Seung Hwang

Bracing Systems for Installation of MR Dampers in a Building Structure

In this study, the effects of bracing systems for installing a magnetorheological (MR) damper in a building structure on seismic response control are analytically and experimentally investigated. The performance of the toggle brace system which enables the installed damper to generate larger effective control force due to its response amplification mechanism than a conventional brace system is evaluated. In addition, the nonlinear velocity amplification factor for the toggle brace—MR damper system and the effect of toggle configuration are considered. Analytical and experimental results show that control performance can be enhanced using the toggle brace system especially for the case in which the MR damper installed using non-amplifying brace system cannot provide sufficient response reduction.

The Numerical Analysis of Heavy Weight Impact Noise for an Apartment House

ABSTRACT In this study, numerical analysis is performed to investigate the sound radiation characteristics of an apartment house according to the type of the slab system. In order to satisfy the boundary condition of the apartment house, the whole floor is modelled with FEM model for three different structural system: wall, RC, flat slab system. From the analytical results, it is shown that heavy weight floor impact noise of wall type slab is larger than that of the other slab systems and the noise radiated from the wall have great effect on the sound pressure level. The results also show that the vibration energy of RC or flat slab system is widely distributed over the whole slab, which is main reason that the noise induced by the slab systems is reduced in comparison with wall slab system. 1) 1. 서 론 현재 중량충격음 차단성능을 바닥슬래브의 중량 증가와 뜬바닥구조를 통해 소음의 저감을 얻으려고 하는 시도는 현재 그 성능 개선의 한계에 도달해 있다. 210 mm의 슬래브 두께와 그 상부의 뜬바닥 구조로 구성되는 표준바닥구조라 할지라도 50 dB을 만족하지 못하는 차단성능을 갖고 있는 경우가 상존하고 있어 바닥충격음 차단성능을 확보하기 위해 많은 연구가 진행되고 있다

An Analysis of Characteristics of Floor Dynamic Properties and Bang-machine Impact Force on Floating Floor Using System Analysis

Heavy-weight floor impact noise is directly related to the impact source and floor vibration property. Dynamic properties of the standard floating floor that is used in Korea was investigated using accelerance, acceleration energy spectral density(ESD), and structural modal test. In the standard floating floor, natural frequency was decreased by the finishing mortar mass and the damping ratio was increased. Bang-machine force spectrum acting on the concrete slab can be calculated using inverse system analysis. Impact force acting on concrete slab is changed by interaction of finishing mortar and resilient material. The amplitude of the bang-machine force spectrum was amplified in low frequency range(below 100 Hz), and over 100 Hz was decreased. Changed force spectrum influence to the response of structure vibration, so the heavy-weight floor impact noise level was changed.

Control of floor vibration and noise using multiple tuned mass dampers

The floor impact noise that occurs between upper and lower households in residential houses has been known as one of major causes that adversely affects residential environments and can lead to serious social troubles in a residential community. In order to alleviate this problem of floor impact noise and to improve the residential conditions, regulations are applied in many countries to reduce the floor impact noise. The floor impact noise can be divided into two categories - light weight floor impact noise and heavy weight floor impact noise - depending on the standard impact sources and the frequency range where the noise is dominant. The light weight floor impact noise generated in the high frequency ranges can be easily reduced by resilient material used in a conventional floating slab system, whereas the heavy weight floor impact noise induced by flexural vibration modes in the relatively lower frequency ranges is difficult to reduce using the traditional methodologies such as a floating slab system or increasing the thickness of slab. In this study, a new method is presented to effectively reduce the heavy weight floor impact noise induced by the vibration of slab using the multi tuned mass dampers (MTMDs). A substructure modal synthesis technique based on the FEM model is utilized to develop an analytical model of the slab coupled with MTMDs. Further, the acoustic power and acceleration responses are analyzed to evaluate the performance of the MTMDs in reducing floor impact noise. Numerical analysis is carried out to investigate the effect of the MTMD on the vibration and noise control of the simply supported slab

Vibration and Noise Control of the Simply Supported Slab Using the Multi-tuned Mass Damper

In this study, it is outlined that heavy weight floor impact noise induced by the vibration of slab can be reduced using multi tuned mass damper(MTMD) effectively. Substructure synthesis is utilized to develope analytical model of the slab coupled with MTMD and acoustic power is introduced to evaluate the performance of noise control for simplicity. Numerical analysis is carried out to investigate the effect of the properties of MTMD on the vibration and noise control of the simply supported slab. Numerical analysis shows that mass ratio of MTMD is critical on the vibration and noise control of the slab and it is also essential to reduce the vibration in higher modes of slab in the light of its great effect on the radiation of sound.

Numerical Analysis of Heavy-weight Impact Noise for Apartment Units Considering Acoustic Mode

Numerical analysis was performed to investigate the heavy-weight impact noise of apartment houses. The FEM is practical method for prediction of low-frequency indoor noise. The results of numerical analysis, the shape of the acoustic modes in room-2 are similar to that of acoustic pressure field at the fundamental frequency of acoustic modes. And the acoustic pressure was amplified at the natural frequency of the acoustic modes and structural modes. The numerical analysis result of sound pressure level at 63 Hz and 125 Hz octave-band center frequency are similar to the test results, but at 250 Hz and 500 Hz have some errors. Considering most of bang-machine force spectrum exists below 100 Hz, the noise at 250 Hz and 500 Hz are not important for heavy-weight impact noise. Thus, the FEM numerical analysis method for heavy-weight impact noise can apply to estimate heavy-weight impact noise for various building systems.

Numerical Study on the Control of Heavy-weight Floor Impact Noise for PC Slab Coupled with Viscoelastic Material

In this study, a new slab system where a part of precast slab is connected each other by viscoelastic material is proposed and numerical analysis is performed to evaluate the effect of the connection between the material and PC slab on the vibration and noise control. Substructuring is introduced to develop the equation of motion for the slab system. In addition, the optimal properties of viscoelastic material are investigated. For the performance evaluation of the new slab system, the sound power and acceleration responses of the slab are compared with those of two way slab and one way slab, respectively. Numerical analysis results show that the sound power of the new slab system can be reduced by viscoelastic material significantly.

Prediction of Heavy-Weight Floor Impact Sound in Multi-unit House using Finite Element Analysis

In this study floor impact noise and structure acceleration response of bare concrete slabs were predicted by using Finite Element Analysis(FEA). Prediction results were compared with experimental results to prove the accuracy of numerical model. Acoustic absorption were addressed by using panel impedance coefficients with frequency characteristics and structural modal damping of numerical model were applied by modal testing results and analysis of prediction and test results. By using frequency response function, the floor acceleration and acoustic pressure responses for various impact sources were calculated at the same time. In the FEA, the natural frequencies and the shapes of vibration and acoustic modes can be estimated through the eigen-value analysis, and it can be visually seen the vibration and sound pressure field and the contribution of major modes.

The Effect of Dynamic Property of Absorbing Sheet on the Amplification of Heavy Weight Floor Impact Noise

Previous experimental results performed by many researchers for a couple of decades in South Korea have shown that an absorbing sheet inserted in a conventional floating slab system for thermal insulation or vibration absorption may amplify the vibration of the slab system at specific frequency ranges depending on the material properties of the sheet. The amplified vibration, consequently, results in the heavy weight floor impact noise exceeding the sound level limit for an apartment house, 50 dB. In this study, the amplification mechanism is examined through numerical analysis and a new slab system is proposed to reduce the amplification and control the noise. The new slab system consists of studs connecting the base slab and upper concrete finishing yielding the dramatically increased stiffness of the slab. The numerical simulation is performed to investigate the effect of the slab system with studs on the vibration and noise control. The results show that the performance of the slab is sensitive to the number and location of studs, and the heavy weight floor impact noise can be reduced up to 6~7 dB compared to the conventional slab system at the optimal stud location.

Experimental study of instantaneous probabilistic energy control for seismically excited structures

In the previous study, authors developed a probabilistic algorithm for active control of structures. In the probabilistic control algorithm, the control force is determined by the probability that the structural energy exceeds a specified target critical energy, and the direction of a control force is determined by Lyapunov controller design method. In this paper, an experimental verification of the proposed probabilistic control algorithm is presented. A three-story test structure equipped with an active mass driver (AMD) was used. The effectiveness of the control algorithm was examined exciting the test structure using a sinusoidal signal, a scaled E-Centro earthquake and a broadband Gaussian white noise. Specially, experiments on control had been performed under a different condition to that of system identification in order to prove the stability and robustness of the proposed control algorithm. Experimental results indicate that the probabilistic control algorithm can achieve a significant response reduction under various types of ground excitations even when the modeling error exists.