CACK IDENTIFICATION IN A CANTILEVER BEAM FROM MODAL RESPONSE

Shin Soobong 대한토목학회 1995 대한토목학회 학술발표회 논문집 Vol.1995 No.1

Estimation of bridge displacement responses using FBG sensors and theoretical mode shapes

Shin, Soobong,Lee, Sun-Ung,Kim, Yuhee,Kim, Nam-Sik Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.2

Bridge vibration displacements have been directly measured by LVDTs (Linear Variable Differential Transformers) or laser equipment and have also been indirectly estimated by an algorithm of integrating measured acceleration. However, LVDT measurement cannot be applied for a bridge crossing over a river or channel and the laser technique cannot be applied when the weather condition is poor. Also, double integration of accelerations may cause serious numerical deviation if the initial condition or a regression process is not carefully controlled. This paper presents an algorithm of estimating bridge vibration displacements using vibration strains measured by FBG (Fiber Bragg Grating) sensors and theoretical mode shapes of a simply supported beam. Since theoretically defined mode shapes are applied, even high modes can be used regardless of the quality of the measured data. In the proposed algorithm, the number of theoretical modes is limited by the number of sensors used for a field test to prevent a mathematical rank deficiency from occurring in computing vibration displacements.89The proposed algorithm has been applied to various types of bridges and its efficacy has been verified. The closeness of the estimated vibration displacements to measured ones has been evaluated by computing the correlation coefficient and by comparing FRFs (Frequency Response Functions) and the maximum displacements.

Structural Damage Assessment Using Transient Dynamic Response

Shin, Soobong,Oh, Seong-Ho,Kwahk, Im-Jong,Koh, Hyun-Moo 한국전산구조공학회 2000 한국전산구조공학회논문집 Vol.13 No.4

강제진동을 가한 구조물의 제한된 위치에서 측정한 가속도를 사용하여 손상을 확인하고 평가하는 알고리듬을 개발하였다. 개발된 알고리듬에서는 선형적 구속-비선형 최적화에 의해 최적의 구조변수를 구하여 구조물을 인식하는 시간영역-시스템 인식기법을 사용하였다. 동적운동방정식의 오차를 최소화하도록 최적의 변수를 추정하였으며, 제한된 위치에서 측정된 가속도 자료를 이용하여 손상된 부재를 찾기 위하여 적합적 변수모음법을 적용하였다. 손상은 측정된 가속도의 시간이력에 시간창의 개념을 적용하여 통계적으로 평가하였다. 가속도가 측정된 자유도에서의 변위와 속도는 측정된 가속도를 적분하여 계산하였으며, 미측정 자유도에서는 변위를 추가의 미지변수로 추정하고, 속도와 가속도는 추정된 변위의 차분에 의해 수치적으로 계산하였다. 개발된 알고리듬의 효율성을 검증하기 위하여 트러스에 대한 수치모의실험을 실시하였다. 손상지수의 한계치를 정하고 각 부재에서의 손상가능도를 계산하기 위하여 자료교란법을 적용하였다. A damage detection and assessment algorithm is developed by measuring accelerations at limited locations of a structure under forced vibrations. The developed algorithm applies a time-domain system identification (SI) method that identifies a structure by solving a linearly constrained nonlinear optimization problem for optimal structural parameters. An equation error of the dynamic equilibrium of motion is minimized to estimate optimal parameters. An adaptive parameter grouping scheme is applied to localize damaged members with sparse measured accelerations. Damage is assessed in a statistical manner by applying a time-windowing technique to the measured time history of acceleration. Displacements and velocities at the measured degrees of freedom (DOF) are computed by integ- rating the measured accelerations. The displacements at the unmeasured DOF are estimated as additional un- knowns to the unknown structural parameters, and the corresponding velocities and accelerations are computed by a numerical differentiation. A numerical simulation study with a truss structure is carried out to examine the efficiency of the algorithm. A data perturbation scheme is applied to determine the thresholds for damage indices and to compute the damage possibility of each member.

Effects of prestressing force on natural frequency of prestressed concrete beams considering self-weight

Soobong Shin,Hokyoung Lee,이종한 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.4

This study investigated the effects of prestressing force on the natural frequency of concrete beams considering changes in the self-weight of the beam. For this, a finite element formulation was derived to account for the increase in the stiffness of a beam-tendon system due to the axial force and deformation induced by prestressing of the tendon. The developed finite element formulation was validated with the data obtained in laboratory experiments. The experimental natural frequencies of the small prestressed concrete (PSC) beam specimens were consistent with those obtained using the proposed method. The first natural frequency increased almost linearly as the prestressing force increased. The proposed method was then applied to four actual PSC bridges typically employed in the field. Different from the laboratory specimens, the first natural frequencies of the actual PSC bridges barely changed or increased with increasing prestressing force. The results of an analytical parametric study showed that the increase in the natural frequency strongly depended on the magnitude of the prestressing force relative to the total weight of the structure. Thus, the variation in the natural frequencies of the actual PSC bridges with high total weight relative to the prestressing force was negligible due to the application of the prestressing force.

Damage assessment of shear buildings by synchronous estimation of stiffness and damping using measured acceleration

Shin, Soobong,Oh, Seong Ho Techno-Press 2007 Smart Structures and Systems, An International Jou Vol.3 No.3

Nonlinear time-domain system identification (SI) algorithm is proposed to assess damage in a shear building by synchronously estimating time-varying stiffness and damping parameters using measured acceleration data. Mass properties have been assumed as the a priori known information. Viscous damping was utilized for the current research. To chase possible nonlinear dynamic behavior under severe vibration, an incremental governing equation of vibrational motion has been utilized. Stiffness and damping parameters are estimated at each time step by minimizing the response error between measured and computed acceleration increments at the measured degrees-of-freedom. To solve a nonlinear constrained optimization problem for optimal structural parameters, sensitivities of acceleration increment were formulated with respect to stiffness and damping parameters, respectively. Incremental state vectors of vibrational motion were computed numerically by Newmark-${\beta}$ method. No model is pre-defined in the proposed algorithm for recovering the nonlinear response. A time-window scheme together with Monte Carlo iterations was utilized to estimate parameters with noise polluted sparse measured acceleration. A moving average scheme was applied to estimate the time-varying trend of structural parameters in all the examples. To examine the proposed SI algorithm, simulation studies were carried out intensively with sample shear buildings under earthquake excitations. In addition, the algorithm was applied to assess damage with laboratory test data obtained from free vibration on a three-story shear building model.

UKC2014 학술대회 참가기

신수봉(Soobong Shin) 대한토목학회 2014 대한토목학회지 Vol.62 No.10

건설분야 관련 ISO 활동

신수봉(Soobong Shin) 대한토목학회 2010 대한토목학회지 Vol.58 No.12

콘크리트 분야 국제표준화 활동의 최근 동향

신수봉(Soobong Shin),최완철(Oan Chul Choi) 한국콘크리트학회 2012 콘크리트학회지 Vol.24 No.5

제 2차 3국 심포지엄 참가기

신수봉(Soobong Shin),최정욱(Jung-Wook Choi) 한국콘크리트학회 2011 콘크리트학회지 Vol.23 No.2

잔교식 항만구조물의 안전진단 및 유지관리

신수봉(Shin Soobong),이성우(Lee Sung-Woo) 동아대학교 해양자원연구소 1999 동아대학교 해양자원연구소 연구논문집 Vol.12 No.-

Baseline concepts and research outcomes associated with the developed safety inspection and maintenance manuals for pier-type port structures are summarized. Inspection procedure and the methodology of condition assessment are introduced for pier-type port structures. Differently from condition assessment on bridge structures, visual inspection is mainly applied for port structures. Through sample examples, the procedures of inspection and condition assessment are illustrated for each structural component, inspection unit, and for the whole structure.