• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.263-266
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• 2005

Many RC structures built without seismic provisions have exhibited brittle shear failures in the beam-column joint area, and resulted in large permanent deformations and structural collapse. This paper presents the results of an experimental investigation pertaining to the use of carbon fiber-reinforced polymer(FRP) for strengthening of RC beam-column connections. The selective upgrade is obtained by choosing different combinations and locations of carbon FRP sheets to determine the effective way to improve the structural performance of joints. Experimental results demonstrate significant improvement of flexural capacity and ductility of beam-column connections originally built without seismic details.

• Wind and Structures
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• v.10 no.3
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• pp.249-268
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• 2007

Past experience indicates that the majority of failures of electrical transmission tower structures occurred during high intensity wind events, such as downbursts. The wind load distribution associated with these localized events is different than the boundary layer wind profile that is typically used in the design of structures. To the best of the authors' knowledge, this study represents the first comprehensive investigation that assesses the effect of varying the downburst parameters on the structural performance of a transmission line structure. The study focuses on a guyed tower structure and is conducted numerically using, as a case study, one of the towers that failed in Manitoba, Canada, during a downburst event in 1996. The study provides an insight about the spatial and time variation of the downburst wind field. It also assesses the variation of the tower members' internal forces with the downburst parameters. Finally, the structural behaviour of the tower under critical downburst configurations is described and is compared to that resulting from the boundary layer normal wind load conditions.

• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.703-712
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• 2017

The composite blades of offshore wind turbines accumulate structural damage such as fatigue cracking due to harsh operation environments during their service time, leading to premature structural failures. This paper investigates various fatigue crack models for reproducing crack development in composite blades and proposes a stochastic approach to predict fatigue crack evolution and to analyse failure probability for the composite blades. Three typical fatigue models for the propagation of fatigue cracks, i.e., Miner model, Paris model and Reifsnider model, are discussed to reproduce the fatigue crack evolution in composite blades subjected to cyclical loadings. The lifetime probability of fatigue failure of the composite blades is estimated by stochastic deterioration modelling such as gamma process. Based on time-dependent reliability analysis and lifecycle cost analysis, an optimised maintenance policy is determined to make the optimal decision for the composite blades during the service time. A numerical example is employed to investigate the effectiveness of predicting fatigue crack growth, estimating the probability of fatigue failure and evaluating an optimal maintenance policy. The results from the numerical study show that the stochastic gamma process together with the proper fatigue models can provide a useful tool for remaining useful life predictions and optimum maintenance strategies of the composite blades of offshore wind turbines.

• Journal of the Korea Safety Management & Science
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• v.2 no.4
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• pp.91-102
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• 2000

Nowadays, every kind of system is changed so complex and enormous, it is necessary to assure system reliability, product liability and safety. Fault tree analysis(FTA) is a reliability/safety design analysis technique which starts from consideration of system failure effect, referred to as “top event”, and proceeds by determining how these can be caused by single or combined lower level failures or events. So in fault tree analysis, it is important to find the combination of events which affect system failure. Minimal cut sets(MCS) and minimal path sets(MPS) are used in this process. FTA-I computer program is developed which calculates MCS and MPS in terms of Gw-Basic computer language considering Fussell's algorithm. FTA-II computer program which analyzes importance and function cost of VE consists. of five programs as follows : (l) Structural importance of basic event, (2) Structural probability importance of basic event, (3) Structural criticality importance of basic event, (4) Cost-Failure importance of basic event, (5) VE function cost analysis for importance of basic event. In this study, a method of initiation such as failure, function and cost in FTA is suggested, and especially the priority rank which is calculated by computer-aided decision analysis program developed in this study can be used in decision making determining the most important basic event under various conditions. Also the priority rank can be available for the case which selects system component in FMEA analysis.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.25 no.3
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• pp.74-80
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• 2017

As for A rotary wing aircraft, the configuration change about split yaw swaged rod was executed to improve hit treat capability for dealing with a long rod. The purpose of this study was to analyze if or not the quality of the split yaw swaged rod was obtained, and so the flight safety was ensured or not. Buckling analysis, Coupling Thread Strength Analysis, Thermal Stress analysis and Rod Natural Frequency Analysis were executed for structural analysis. The results of the analysis were presented that the split rod had the sufficient margin of safety and so there were no anomalies in the limit load and no failures in the ultimate load. And there were no resonances in result of natural frequency analysis. In conclusion, this study showed that the split yaw swaged rod had structural safety, so flight safety of rotary wing aircraft was secured and there was no problem in aircraft operation. It is certain that the technology of splitting the yaw swage rod will contribute to the operational Safety of the rotary wing aircraft in the future.

• Steel and Composite Structures
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• v.23 no.3
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• pp.351-362
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• 2017

This paper presents an experimental study on the behavior of composite floor slab comprised by a new steel sheet and concrete slab. The strength of composite slabs depends mainly on the strength of the connection between the steel sheet and concrete, which is denoted by longitudinal shear strength. The composite slabs have three main failures modes, failure by bending, vertical shear failure and longitudinal shear failure. These modes are based on the load versus deflection curves that are obtained in bending tests. The longitudinal shear failure is brittle due to the mechanical connection was not capable of transferring the shear force until the failure by bending occurs. The vertical shear failure is observed in slabs with short span, large heights and high concentrated loads subjected near the supports. In order to analyze the behavior of the composite slab with a new steel sheet, six bending tests were undertaken aiming to provide information on their longitudinal shear strength, and to assess the failure mechanisms of the proposed connections. Two groups of slabs were tested, one with 3000 mm in length and other with 1500 mm in length. The tested composite slabs showed satisfactory composite behavior and longitudinal shear resistance, as good as well, the analysis confirmed that the developed sheet is suitable for use in composite structures without damage to the global behavior.

• Structural Engineering and Mechanics
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• v.60 no.1
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• pp.51-69
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• 2016

A large number of welded steel moment-resisting framed (SMRF) structures failed due to brittle fracture induced by ductile fracture at beam-to-column connections during 1994 Northridge earthquake and 1995 Kobe (Hyogoken-Nanbu) earthquake. Extensive research efforts have been devoted to clarifying the mechanism of the observed failures and corresponding countermeasures to ensure more ductile design of welded SMRF structures, while limited research on the failure analysis of the ductile cracking was conducted due to lack of computational capacity and proper theoretical models. As the first step to solve this complicated problem, this paper aims to establish a straightforward procedure to simulate ductile cracking of welded joints under monotonic tension. There are two difficulties in achieving the aim of this study, including measurement of true stress-true strain data and ductile fracture parameters of different subzones in a welded joint, such as weld deposit, heat affected zone and the boundary between the two. Butt joints are employed in this study for their simple configuration. Both experimental and numerical studies on two types of butt joints are conducted. The validity of the proposed procedure is proved by comparison between the experimental and numerical results.

• Journal of Welding and Joining
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• v.29 no.3
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• pp.76-81
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• 2011

Recently, the structural failures due to fatigue occur frequently with the increase of size of ships and offshore structures. In this respect, the assessment of fatigue life and the residual strength are very important. Currently, the smart materials technology has demonstrated a variety of possibilities for a diagnosis of structural strength and structural health condition for large structures. The benefits and feature of the MFC sensor are more flexible, durable and reliable than conventional smart material. In this study, Micro Fiber Composite (MFC) sensor for the measurement of stress intensity factor (SIF) of two dimensional cracks induced in a structure is developed. Two MFC sensors are placed in the vicinity of the crack tip close to each other with the crack tip in between them. The SIFs of Mode I($K_I$) as well as of Mode II($K_{II}$) based on the piezoelectric constitutive law and fracture mechanics are calculated. In this study, the SIF values measured by MFC sensors are compared with the theoretical results and measured value.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.185-192
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• 2011

A CFRP (Carbon Fiber-Reinforced Plastic) strengthening method being widely used to increase the load-carrying capacity of structures is very suitable for existing bridge structures. However, not only flexure and shear failures but also debonding failure might be additionally occured in reinforced concrete(RC) beams strengthened with the CFRP plates. The CFRP debonding failure would cause a brittle fracture of the beam. Therefore, health monitoring for the CFRP bonding condition is strongly required. In this study, a feasibility of the impedance-based damage detection method using PZT sensors was investigated through a series of experimental studies for realtime structural health monitoring(SHM) for the CFRP laminated concrete structures.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.351-361
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• 2015

External reactor vessel cooling (ERVC) for in-vessel retention (IVR) has been considered one of the most useful strategies to mitigate severe accidents. However, reliability of this common idea is weakened because many studies were focused on critical heat flux whereas there were diverse uncertainties in structural behaviors as well as thermal-hydraulic phenomena. In the present study, several key factors related to molten corium behaviors and thermal characteristics were examined under multi-layered corium formation conditions. Thereafter, systematic finite element analyses and subsequent damage evaluation with varying parameters were performed on a representative reactor pressure vessel (RPV) to figure out the possibility of high temperature induced failures. From the sensitivity analyses, it was proven that the reactor cavity should be flooded up to the top of the metal layer at least for successful accomplishment of the IVR-ERVC strategy. The thermal flux due to corium formation and the relocation time were also identified as crucial parameters. Moreover, three-layered corium formation conditions led to higher maximum von Mises stress values and consequently shorter creep rupture times as well as higher damage factors of the RPV than those obtained from two-layered conditions.