• Smart Structures and Systems
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• 제17권1호
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• pp.135-147
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• 2016

This paper describes a smart structural system, which uses smart materials for real-time monitoring and active control of bolted-joints in steel structures. The goal of this research is to reduce the possibility of failure and the cost of maintenance of steel structures such as bridges, electricity pylons, steel lattice towers and so on. The concept of the smart structural system combines impedance based health monitoring techniques with a shape memory alloy (SMA) washer to restore the tension of the loosened bolt. The impedance-based structural health monitoring (SHM) techniques were used to detect loosened bolts in bolted-joints. By comparing electrical impedance signatures measured from a potentially damage structure with baseline data obtained from the pristine structure, the bolt loosening damage could be detected. An outlier analysis, using generalized extreme value (GEV) distribution, providing optimal decision boundaries, has been carried out for more systematic damage detection. Once the loosening damage was detected in the bolted joint, the external heater, which was bonded to the SMA washer, actuated the washer. Then, the heated SMA washer expanded axially and adjusted the bolt tension to restore the lost torque. Additionally, temperature variation due to the heater was compensated by applying the effective frequency shift (EFS) algorithm to improve the performance of the diagnostic results. An experimental study was conducted by integrating the piezoelectric material based structural health monitoring and the SMA-based active control function on a bolted joint, after which the performance of the smart 'self-monitoring and self-healing bolted joint system' was demonstrated.

• Steel and Composite Structures
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• 제20권2호
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• pp.267-293
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• 2016

It is well known that, in order to accurately predict the behaviour of steel structures a requirement the definition of the mechanical behaviour of beam-to column joints is of primary importance. This goal can be achieved by means of the so-called component method, which, in order to obtain the whole behaviour of connections, provides to break up joints in basic components of deformability and resistance. One of the main joint components used to model bolted connections is the so-called equivalent T-stub in tension, which is normally used to predict the behaviour of bolted plates in bending starting from the behaviour of the single bolt rows. In past decades, significant research efforts have been devoted to the prediction of the behaviour of bolted T-stubs but, to date, no particular attention has been devoted to the characterization of their plastic deformation capacity. To this scope, the work presented in this paper, taking into account the existing technical literature, proposes a new theoretical model for predicting the whole behaviour up to failure of bolted T-stubs under monotonic loading conditions, including some complexities, such as the bolt/plate compatibility requirement and the bolt fracture, which are necessary to accurately evaluate the ultimate displacement. After presenting the advances of the proposed approach, a comparison between theoretical and experimental results is provided in order to verify its accuracy.

• 한국안전학회지
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• 제34권5호
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• pp.1-6
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• 2019

The mobile elevated work platforms(MEWPs) consist of work platform, extending structure, and car, and it is a facility to move persons to working positions. MEWPs are useful but composed complex pieces of equipments, and accidents are caused by equipment defects. Among them, accidents caused by fracture of the bolts fixing the extension structure and the turntable are increasing. In this study, fatigue failure and fatigue life of a turntable fixing bolt subjected to irregular fatigue load were analyzed by FEA. For this purpose, finite element modeling is proposed and structural analysis and fatigue analysis are performed simultaneously for fixing bolts. As a result of the structural analysis, it was confirmed that there is no risk of permanent deformation because the maximum stress acting on the fixing bolt is lower than the yield strength, and fatigue analysis was confirmed that the fatigue life is less than the design standard. The fatigue analysis results of this study can be effectively used for the design and the documentary assessment of the safety certification of the MEWPs by examining the fatigue life of the turntable fixing bolt.

• 한국안전학회지
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• 제36권4호
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• pp.12-19
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• 2021

This paper presents a safety assessment method for FTA-based induction heating systems; the failures and causes of electrical fire are first analyzed for each part and module qualitatively, and methods to manage high probabilities of failure and electrical fire are considered, thereby improving the reliability of the induction heating system. The cumulative importance value (ACC) of the minimal cut set is drawn by setting failure as the top event, and STACK and SMPS are observed to account for about 70% of the induction heating system failures. Thus, intensively managing the basic events contained in the minimal cut set of failures for STACK and SMPS is expected to provide effective and stable operation of the induction heating system. When electrical fire is set as the top event, the STACK percentage is 90%. Accordingly, the current IGBT is changed to a FET to increase the applied voltage and prevent induction heating system failure, and a heat sink plane is installed to prevent FET heating caused by switching, thereby preventing an electrical fire. By classifying the parts and modules of the induction heating system in detail and by applying FTA based on actual failure rates and relevant data, more practical and reasonable results may be expected. Hence, continuous research must be conducted to ensure safety when using induction heating systems.

• 한국강구조학회 논문집
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• 제20권2호
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• pp.279-288
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• 2008

본 논문에서는 압축력을 받는 고장력 볼트 마찰이음부의 미끄러짐 거동을 3차원 유한요소 해석 및 실험을 통하여 규명하였다. 모재의 두께가 고장력 불트이음부에 끼치는 영향을 미끄러짐 하중, 볼트의 변형 및 파괴하중과의 관계와 함께 파악하였다. 초기 미끄러짐 하중 이후의 볼트의 강성을 고려한 이음부의 거동 모델을 제시하고 유한요소해석 및 실험을 통하여 비교, 분석하였다. 범용 유한요소해석 프로그램인 ABAQUS에서 지원되는 고체요소를 사용하여 해석모델을 작성하였고 모재 사이의 마찰 및 미끄러짐이 발생한 이후 볼트와 모재 사이의 마찰 등을 고려하였다. 기존의 문헌에 제시된 여러 가지 강재의 응력-변형도 관계를 적용하였으며 미끄러짐 변위와 볼트 주변의 축응력들을 비교하였다. 모재의 두께가 볼트의 직경보다 작은 경우에는 압축력에 의한 휨좌굴에 시험체에 발생하였고 모재의 두께가 볼트 직경보다 두꺼운 경우에는 볼트의 전단파괴가 이음부의 극한강도를 나타냄을 파악하였다.

• Steel and Composite Structures
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• 제45권6호
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• pp.797-818
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• 2022

Steel-precast ultra-high-performance concrete (UHPC) composite beams with demountable high-strength friction-grip bolt (HSFGB) shear connectors can be used for accelerated bridge construction (ABC) and achieve excellent structural performance, which is expected to be dismantled and recycled at the end of the service life. However, no investigation focuses on the demountability and reusability of such composite beams, as well as the installation difficulties during construction. To address this issue, this study conducted twelve push-out tests to investigate the effects of assembly condition, bolt grade, bolt-hole clearance, infilling grout and pretension on the crack pattern, failure mode, load-slip/uplift relationship, and the structural performance in terms of ultimate shear strength, friction resistance, shear stiffness and slip capacity. The experimental results demonstrated that the presented composite beams exhibited favorable demountability and reusability, in which no significant reduction in strength (less than 3%) and stiffness (less than 5%), but a slight improvement in ductility was observed for the reassembled specimens. Employing oversized preformed holes could ease the fabrication and installation process, yet led to a considerable degradation in both strength and stiffness. With filling the oversized holes with grout, an effective enhancement of the strength and stiffness can be achieved, while causing a difficulty in the demounting of shear connectors. On the basis of the experimental results, more accurate formulations, which considered the effect of bolt-hole clearance, were proposed to predict the shear strength as well as the load-slip relationship of HSFGBs in steel-precast UHPC composite beams.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.845-850
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• 1998

Flexural tests on 3.0m reinfored concrete beams with epoxy and anchor bolt bonded CFRF-Grid reported in these tests. The selected experimental variables are concrete compressive strength, strengthening length and strengthening method. The effects of these variables in overall behavior are discussed. The results generally shown that the main flexural mode of strengthened beams is separation failure. The strengthening of the chipping by the tensile bar is really necessary in order to prevent CFRP-Grid from rip-off failure.

• 대한기계학회논문집A
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• 제37권7호
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• pp.875-881
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• 2013

증기발생기 수직 지지대를 고정하고 있는 고강도 앵커 볼트의 응력부식균열에 대한 건전성 평가는 원자력발전소 기기 건전성 유지와 관련하여 중요한 현안 가운데 하나이다. 이에 따라 미국 EPRI에서는 고강도 앵커 볼트의 건전성 평가를 위한 기준균열계수 개념 기반의 평가 절차를 제시한 바 있으며, 본 연구에서는 EPRI에서 제시한 절차에 입각하여 증기발생기 수직 지지대 고정용 앵커 볼트의 응력부식균열 및 취성 파괴에 대한 건전성 평가를 수행하였다. 이를 위해 볼트 예비하중과 운전하중을 고려한 3차원 유한요소 응력해석을 수행하여 볼트 단면에 작용하는 공칭응력을 결정하였으며, 결정된 볼트 응력과 EPRI 절차를 이용하여 앵커 볼트의 균열 건전성을 평가하였다. 또한 3차원 탄성 유한요소 파괴역학 해석을 수행하여 EPRI에서 제시한 기준균열계수의 정확성을 검증하였다.

• 한국강구조학회 논문집
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• 제27권1호
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• pp.53-61
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• 2015

인장이음은 고장력 볼트의 체결력과 모재 그리고 고장력 볼트의 내력을 직접적으로 활용하고, 볼트구멍의 가공수나 체결개소의 감소, 피로저항성 등에 있어 유리하며 때문에 역학적으로 매우 효율적인 연결이다. 이러한 인장이음은 교량의 거더와 가로보의 이음, 주탑의 수평이음, 보-기둥 연결부, 바닥판 단부 2차부재 연결부, 브라켓 등에 적용될 수 있다. 본 연구에서는 인장이음의 역학적 거동을 파악하기 위해서 T-인장이음에 대한 정적실험을 수행하였다. 시험변수는 고장력 볼트의 직경, 플렌지 두께 및 체결력 감소이며, 인장이음의 파괴양상과 내력, 플랜지 두께와 고장력 볼트의 직경의 영향, 체결력의 영향에 대해 분석하였다.

• Steel and Composite Structures
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• 제22권1호
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• pp.45-61
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• 2016

The domestic and foreign scholars conducted many studies on mechanical properties of wave web steel beam and high-strength spiral stirrups confined concrete columns. Based on the previous research work, studies were conducted on the anti-seismic property of the end plate bolt connected wave web steel beam and high-strength spiral stirrups confined concrete column nodes applied with pre-tightening force. Four full-size node test models in two groups were designed for low-cycle repeated loading quasi-static test. Through observation of the stress, distortion, failure process and failure mode of node models, analysis was made on its load-carrying capacity, deformation performance and energy dissipation capacity, and the reliability of the new node was verified. The results showed that: under action of the beam-end stiffener, the plastic hinges on the end of wave web steel beam are displaced outward and played its role of energy dissipation capacity. The study results provided reliable theoretical basis for the engineering application of the new types of nodes.