• Structural Engineering and Mechanics
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• 제8권3호
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• pp.285-297
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• 1999

A method is presented to find the location and magnitude of damage in a structure using data from dynamic tests. The test data include a combination of natural frequency measurements, taken before and after the occurrence of damage, and response measurements taken after damage. An algorithm is developed to identify localized increases in the flexibility of the structural members. Increases in flexibility are attributed to damage. The algorithm uses the sensitivity of the flexibility matrix to changes in the natural frequencies of the structure to identify the damage. A set of under determined equations is solved using an objective function which is derived from measurements of the system moments. Damage ranging from 10 to 60% increase in the flexibility of a member was successfully identified in a 50 d.o.f. structure, using a small number of natural frequency and velocity measurements.

• Structural Engineering and Mechanics
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• 제73권2호
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• pp.167-179
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• 2020

This study provides a simplified method for the evaluation of shear lag stress in rectangular box T-joints. The occurrence of shear lag phenomenon in the box T-joint generates stress concentration localized at both web-flange junctions of the beam, which leads to cracking or failure in the weld region of the joint. To prevent such critical circumstance, peak stress at the weld region is required to be checked during a preliminary design stage. In this paper, the shear lag stresses in the T-joints were evaluated using least-work solution in which the longitudinal displacements of the beam flange and web were presumed. The evaluation process considered particularly the effect of column flange flexibility, which was represented by an axial spring model, on the shear lag stress distribution. A simplified method for stress evaluation was provided to avoid solving complex mathematical problems using a stress modification factor β_s from a parametric study. The results showed that the proposed method was valid for predicting the shear lag stress in the box T-joints manually, as well compared with finite element results. The results are further summarized, discussed, and clarified that more flexible column flange caused higher stress concentration.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.247-261
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• 2003

The technique of posttensioning has been used successfully to improve the performance of existing concrete structures. However, very few applications of this technique can be found in steel structures. Posttensioning by means of high strength cable or bar can be used to effectively increase the working load capacity of Truss Bridges. The benefits of posttensioning trusses can be achieved in strengthening of existing structures as well as in the design of new structures. In this paper, the elastic behavior of posttensioned trusses with straight and draped tendon profiles is examined. For the analysis of posttensioned trusses in the elastic range of behavior, two methods are presented, namely, the flexibility method and the mixed-method, i.e., a combination of the stiffness and flexibility methods. Using the presented methods, the effects of design variables such as the tendon profile, truss type, prestress force, and tendon eccentricity on the working load and deflection of trusses are studied. The results show that the allowable load of truss increases proportionally with increase in prestress force and eccentricity. Posttesioning enlarges the elastic range, increases redundancy, and reduces deflection and member stresses. Thus, the remaining life of a truss bridge can be increased relatively inexpensively.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.271-276
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• 2004

In this paper. dynamic behavior of the cracked beam under a moving mass is presented using the finite element method (FEM). Model accuracy is improved with the following consideration: (1) FE model with Timoshenko beam element (2) Additional flexibility matrix due to crack presence (3) Interaction forces between the moving mass and supported beam. The Timoshenko bean model with a two-node finite element is constructed based on Guyan condensation that leads to the results of classical formulations. but in a simple and systematic manner. The cracked section is represented by local flexibility matrix connecting two unchanged beam segments and the crack as modeled a massless rotational spring. The inertia force due to the moving mass is also involved with gravity force equivalent to a moving load. The numerical tests for various mass levels. crack sizes. locations and boundary conditions were performed.

• 비파괴검사학회지
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• 제34권6호
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• pp.447-456
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• 2014

In this paper, a new damage-detection method based on structural vibration is proposed. The essence of the proposed method is the detection of abrupt changes in rotation. Damage-induced rotation (DIR), which is determined from the modal flexibility of the structure, initially occurs only at a specific damaged location. Therefore, damage can be localized by evaluating abrupt changes in rotation. We conducted numerical simulations of two damage scenarios using a 10-story cantilever-type building model. Measurement noise was also considered in the simulation. We compared the sensitivity of the proposed method to localize damage to that of two conventional modal-flexibility-based damage-detection methods, i.e., uniform load surface (ULS) and ULS curvature. The proposed method was able to localize damage in both damage scenarios for cantilever structures, but the conventional methods could not.

• Smart Structures and Systems
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• 제5권6호
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• pp.681-697
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• 2009

Limited, noisy data in vibration testing is a hindrance to the development of structural damage detection. This paper presents a method for optimizing sensor placement and performing damage detection using finite element model updating. Sensitivity analysis of the modal flexibility matrix determines the optimal sensor locations for collecting information on structural damage. The optimal sensor locations require the instrumentation of only a limited number of degrees of freedom. Using noisy modal data from only these limited sensor locations, a method based on model updating and changes in the flexibility matrix successfully determines the location and severity of the imposed damage in numerical simulations. In addition, a steel cantilever beam experiment performed in the laboratory that considered the effects of model error and noise tested the validity of the method. The results show that the proposed approach effectively and robustly detects structural damage using limited, optimal sensor information.

• 한국정밀공학회지
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• 제23권6호
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• pp.128-135
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• 2006

Rational dynamic modeling and analysis method f3r complex structures are studied with special attention to slide way joints. For modeling of slide way joints, a general modeling technique is used by using the influence coefficients method which is applied to the conversion of detailed finite element model to the equivalent reduced joint model. The theoretical part of this method is illustrated and the method is applied to the structure with slide way joint. In this method, the non-linearity of the contact surfaces is considered within a proper range and the boundary effect of the joint model could be eliminated. The proposed method was applied to finite element modal analysis of a clamp jointed cantilever beam and slide way joints of the vertical type lathe. The method can also be used to other kinds of joint modeling. The results of these analysis were compared with those of Yoshimura models and rigid joint models, which demonstrated the practical applicability of the proposed method.

• 대한간호학회지
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• 제36권3호
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• pp.484-492
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• 2006

Purpose: The purpose of this study was to investigate the effects of a rehabilitation nursing program(RNP) for persons with disabilities. Method: a quasi-experimental pretest and post test study was used to examine the changes of patient's muscle strength, flexibility, self efficacy and health related quality of life at the completion of an 8-week education and physical exercise with a Thera-Band and Exercise Ball course. The subjects consisted of 40 adults who were disabled. Twenty-two experimental and 18 control subjects completed pre and post-test measures. Outcome variables were flexibility, hand grip, elbow flexor and extensor, knee flexor and extensor, self efficacy and quality of life. Independent t-test and ANCOVA were used to examine group differences by using SPSS 12.0 Result: Mean comparisons of the change scores revealed that the experimental group increased significantly in knee extremity flexor(p=0.035), extensor(p=0.039), flexibility(p=0.008), self efficacy(p=0.000), and quality of life(p=0.000). No significant group differences were found in each patient's hand grip, elbow flexor and extensor. Conclusion: RNP can improve lower extremity flexibility, muscle strength, self efficacy and health related quality of life in people with disabilities. The intervention to tailor exercise and education to the unique needs of the disability was suggested for further study.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2007년도 정기학술발표대회 논문집
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• pp.943-946
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• 2007

최근 가변성능에 관하여 공간, 재료, 구조, 공법 등 건설 산업 전반에 걸쳐 많은 연구가 진행 중이다. 시대적인 주거환경 변화, 미래지향적인 건설 트랜드 변모 그리고 수요중심적인 인식을 만족하기 위해서 주택의 모습과 공간, 형식이 진화되어가고 있다. 이에 따라 본 연구에서는 가변성을 지니고 있는 건축의 성능요소들을 비교 분석하여 대안을 제시하고자 하며, 적용 가능한 다양한 분류예시를 통하여 실제적인 차세대 장수명화를 실현시키기 위한 방향과 지침을 제시하고자한다.

• 한국군사과학기술학회지
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• 제13권3호
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• pp.405-412
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• 2010

The purpose of this paper is to compare complexity and to assess flexibility of competing transponder architectures for satellite communication services. For performance comparison, we consider three channelization techniques: digital down converter(DDC) based on the use of the cascaded integrator-comb(CIC) filter, tuneable pipeline frequency transform(T-PFT) based on the tree-structure(TS) and variable oversampled complex-modulated filter banks(OCM-FB) based on the polyphase FFT(P-FFT). The comparison begins by presenting a basic architecture of each channelization method and includes analytical expressions of the number of multiplications as a computational complexity perspective. The analytical results show that DDC with CIC filter requires the heavy computational burden and the perfect flexibility. T-PFT based on the TS provides the almost perfect flexibility with the low complexity over DDC with the CIC filter for a large number of sub-channels. OCM-FB based on the P-FFT shows the high flexibility and the best computational complexity performance compared with other approaches.