• Wind and Structures
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• v.12 no.4
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• pp.333-347
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• 2009

Many tower-supported steel stacks have been constructed in Japan, primarily for economic reasons. However the dynamic behavior of these stacks under a strong wind is not well known and the wind load design standard for this type of a stack has not yet been formulated. In light of this situation, we carried out wind response observation of an operating tower-supported steel stack with and without a tuned-mass damper. The observation revealed the performance of the tuned-mass damper installed on the stack in order to control the wind-induced vibration. Based on the observed data, we performed a wind tunnel test of a specimen of the stack. In this paper we report the results of the wind tunnel test and some comparisons with the results of observation. Our findings are as follows: 1) the tuned-mass damper installed on the specimen in the wind tunnel test worked as well as the one on the observed stack, 2) the amplitude of the vortex-induced vibration of the specimen corresponded approximately to that of the observed stack, and 3) correlation between Scruton number and reduced amplitude, y/d, (y is amplitude, d is diameter) was confirmed by both the wind tunnel test and the observed results.

• Smart Structures and Systems
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• v.22 no.5
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• pp.509-525
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• 2018

Sensors and systems in Civionics technology play an important role for continuously facilitating real-time structure monitoring systems by detecting and locating damage to or degradation of structures. An advanced materials, design processes, long-term sensing ability of sensors, electromagnetic interference, sensor placement techniques, data acquisition and computation, temperature, harsh environments, and energy consumption are important issues related to sensors for structural health monitoring (SHM). This paper provides a comprehensive survey of various sensor technologies, sensor classes and sensor networks in Civionics research for existing SHM systems. The detailed classification of sensor categories, applications, networking features, ranges, sizes and energy consumptions are investigated, summarized, and tabulated along with corresponding key references. The current challenges facing typical sensors in Civionics research are illustrated with a brief discussion on the progress of SHM in future applications. The purpose of this review is to discuss all the types of sensors and systems used in SHM research to provide a sufficient background on the challenges and problems in optimizing design techniques and understanding infrastructure performance, behavior and current condition. It is observed that the most important factors determining the quality of sensors and systems and their reliability are the long-term sensing ability, data rate, types of processors, size, power consumption, operation frequency, etc. This review will hopefully lead to increased efforts toward the development of low-powered, highly efficient, high data rate, reliable sensors and systems for SHM.

• Computational Structural Engineering : An International Journal
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• v.1 no.1
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• pp.1-9
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• 2001

Collapse behavior of Mission-Gothic Undercrossing under Northridge earthquake is studied by performing nonlinear time-history analysis and three-dimensional nonlinear finite element method for flared columns. Bridge structural model is characterized as three-dimensional with consideration of columns, superstructures, and abutment conditions. Three components of ground motion, corresponding to bridge's longitudinal, transverse, and vertical direction and their combinations are used to investigate bridge collapse. Studies indicate that bridge collapse is dominantly caused by transverse ground motion and the consideration of three-dimensional ground motion leads to a more accurate assessment. Failure mechanism of flared columns is analyzed applying nonlinear finite element method. Reduction of column capacity is observed due to orientation of flare. Further investigation demonstrates that the effects of flare play an important role in predicting of bridge failure mechanism. Suggestions are offered to improve the performance of bridges during severe earthquake.

• Steel and Composite Structures
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• v.12 no.3
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• pp.231-248
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• 2012

This research aims to investigate the structural behavior of concentrically braced frames after element loss by performing nonlinear static and dynamic analyses such as Time History Analysis (THA), Pushdown Analysis (PDA), Vertical Incremental Dynamic Analyses (VIDA) and Performance-Based Analysis (PBA). Such analyses are to assess the potential and capacity of this structural system for occurrence of progressive collapse. Besides, by determining the Failure Overload Factors (FOFs) and associated failure modes, it is possible to relate the results of various types of analysis in order to save the analysis time and effort. Analysis results showed that while VIDA and PBA according to FEMA 356 are mostly similar in detecting failure mode and FOFs, the Pushdown Overload Factors (PDOFs) differ from others at most to the rate of 23%. Furthermore, by sensitivity analysis it was observed that among the investigated structures, the eight-story frame had the most FOF. Finally, in this research the trend of FOF and the FOF to critical member capacity ratio for the plane split-X braced frames were introduced as a function of the number of frame stories.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.77-84
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• 2010

Annealing characteristics of an oxygen free copper (OFC) processed by differential speed rolling (DSR) were investigated in detail. An OFC sample with a thickness of hum was rolled to 35% reduction at ambient temperature without lubrication, varying the differential speed ratio from 1.0:1 to 2.2:1, and then annealed for 0.5h at various temperatures from 100 to $400^{\circ}C$. Different recrystallization behavior was observed depending on the differential speed ratio, especially in the case of annealing at $200^{\circ}C$ Complete recrystallization occurred in the specimens annealed at temperatures above $250^{\circ}C$ regardless of the differential ratios. The hardness distribution in the thickness direction of the rolled OFC sheets varied depending on the differential speed ratios. These annealing characteristics were explained by the magnitude of shear strain introduced during rolling.

• Computers and Concrete
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• v.22 no.6
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• pp.515-525
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• 2018

This paper presents a numerical study on the performance of reinforced concrete (RC) bridge structures subjected to heavy goods vehicle (HGV) collision. The objectives of this study are to investigate the dynamic response and failure modes of different types of bridges under impact loading as well as to give an insight into the simplified methods for modeling bridge structures. For this purpose, detailed finite-element models of HGV and bridges are established and verified against the full-scale collision experiment and a recent traffic accident. An intensive parametric study with the consideration of vehicle weight, vehicle velocity, structural type, simplified methods for modeling bridges is conducted; then the failure mode, impact force, deformation and internal force distribution of the validated bridge models are discussed. It is observed that the structural type has a significant effect on the force-transferring mechanism, failure mode and dynamic response of bridge structures, thus it should be considered in the anti-impact design of bridge structures. The impact force of HGV is mainly determined by the impact weight, impact velocity and contact interface, rather than the simplification of the superstructure. Furthermore, to reduce the modeling and computing cost, it is suggested to utilize the simplified bridge model considering the inertial effect of the superstructure to evaluate the structural impact behavior within a reasonable precision range.

• Journal of the Mineralogical Society of Korea
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• v.10 no.2
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• pp.148-161
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• 1997

Based on the X-ray powder diffraction (XRD) and M ssbauer spectroscopy, the thermal behavior and phase transformations of two clays are investigated for raw and fired conditions, which are collected from Kwangryeongli and Ildo district in Cheju Island. M ssbauer spectra at room temperature and 20for two clays show that paramagnetic Fe3- is the structural iron of the layer silicate and ferrihydrite, and superparamagnetic goethite has about 50% of total iron contents. The XRD peaks of hematite for the fired clays appear from 80$0^{\circ}C$ in Kwangryeongli clay and from $600^{\circ}C$ in Ildo district clay, respectively. The structural Fe2+ was completely oxidized into Fe3- at 40$0^{\circ}C$ for Kwangryeongli clay and 50$0^{\circ}C$~$600^{\circ}C$ for Ildo district clay, respectively. The structural Fe2+ was completely oxidized into Fe3- at 40$0^{\circ}C$. For the temperature ranging from 40$0^{\circ}C$ to $700^{\circ}C$~80$0^{\circ}C$, two fired clays exhibit the dehydroxylation of the clay mineral. A disintegration of the clay mineral structure is observed from $700^{\circ}C$~80$0^{\circ}C$ to 110$0^{\circ}C$, followed by the onset and spread of vitrification process. It is also shown that well-crystallized hematite phase is formed at the temperature higher than 110$0^{\circ}C$ and the relative absorption area decreases, which might be related to the recrystallization of alluminosilicate matrix.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.202-208
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• 2015

Alumina dispersion strengthening copper(ADSC) alloy has great potential for use in many industrial applications such as contact supports, frictional break parts, electrode materials for lead wires, and spot welding with relatively high strength and good conductivity. In this study, we investigated the oxidation behavior of ADSC alloys. These alloys were fabricated in forms of plate and round type samples by surface oxidation reaction using Cu-0.8Al, Cu-0.4Al-0.4Ti, and Cu-0.6Al-0.4Ti(wt%) alloys. The alloys were oxidized at $980^{\circ}C$ for 1 h, 2 h, and 4 h in ambient atmosphere. The microstructure was observed with an optical microscope(OM) and a scanning electron microscope(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS). Characterization of alumina was carried out using a 200 kV field-emission transmission electron microscope(TEM). As a result, various oxides including Ti were formed in the oxidation layer, in addition to ${\gamma}$-alumina. The thickness of the oxidation layer increased with Ti addition to the Cu-Al alloy and with the oxidation time. The corrected diffusion equation for the plate and round type samples showed different oxidation layer thickness under the same conditions. Diffusion length of the round type specimen had a value higher than that of its plate counterpart because the oxygen concentration per unit area of the round type specimen was higher than that of the plate type specimen at the same diffusion depth.

• Smart Structures and Systems
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• v.15 no.3
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• pp.505-522
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• 2015

Variation of temperature is a primary environmental factor that affects the behavior of structures. Therefore, understanding the mechanisms of normal temperature-induced variations of structural behavior would help in distinguishing them from anomalies. In this study, we used the structural health monitoring data of the Shanghai Yangtze River Bridge, a steel girder cable-stayed bridge, to investigate the mechanisms of thermally induced vertical deflection ($D_T$) at mid-span of such bridges. The $D_T$ results from a multisource combination of thermal expansion effects of the cable temperature ($T_{Cab}$), girder temperature ($T_{Gir}$), girder differential temperature ($T_{Dif}$), and tower temperature ($T_{Tow}$). It could be approximated by multiple linear superpositions under operational conditions. The sensitivities of $D_T$ of the Shanghai Yangtze River Bridge to the above temperatures were in the following order: $T_{Cab}$ > $T_{Gir}$ > $T_{Tow}$ > $T_{Dif}$. However, the direction of the effect of $T_{Cab}$ was observed to be opposite to that of the other three temperatures, and the magnitudes of the effects of $T_{Cab}$ and $T_{Gir}$ were found to be almost one order greater than those of $T_{Dif}$ and $T_{Tow}$. The mechanisms of the thermally induced vertical deflection variation at mid-span of a cable-stayed bridge as well as the analytical methodology adopted in this study could be applicable for other long-span cable-stayed bridges.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.69-77
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• 2009

An underwater structure is made to put with serious damage state by special environmental factors. If this damage phenomena persist, as for the structure, it is generated a structural serious problem because of the corrosion of a reinforcing bar and the loss of the concrete cut end. Repair work of an underwater structure is very harder than repair work in land, and it is actual that certification about a maintenance effect is uncertain. And the existing repair method is applied to a structure damaged with you without verification of a repair effect by a foreign reward and experience. In this study, a repair method about an underwater structure was proposed and observed a behavior characteristic and interface failure of an specimens. and comparison analyzed an effect of a proposed maintenance method.