• Steel and Composite Structures
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• 제5권4호
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• pp.271-287
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• 2005

The seismic behavior of two steel moment-resisting frames, which satisfy all the current seismic design requirements, are evaluated and compared in the presence of pre-Northridge connections denoted as BWWF and an improved post-Northridge connections denoted as BWWF-AD. Pre-Northridge connections are modeled first as fully restrained (FR) type. Then they are considered to be partially restrained (PR) to model their behavior more realistically. The improved post-Northridge connections are modeled as PR type, as proposed by the authors. A sophisticated nonlinear time-domain finite element program developed by the authors is used for the response evaluation of the frames in terms of the overall rotation of the connections and the maximum drift. The frames are excited by ten recorded earthquake time histories. These time histories are then scaled up to produce some relevant response characteristics. The behaviors of the frames are studied comprehensively with the help of 120 analyses. Following important observations are made. The frames produced essentially similar rotation and drift for the connections modeled as FR type and PR type represented by BWWF-AD indicating that the presence of slots in the web of beams in BWWF-AD is not detrimental to the overall response behavior. When the lateral displacements of the frames are significantly large, the responses are improved if BWWF-AD type connections are used in the frames. This study analytically confirms many desirable features of BWWF-AD connections. PR frames have longer periods of vibration in comparison to FR frames and may attract lower inertia forces. However, calculated periods of the frames of this study using FEMA 350 empirical equation is longer than those calculated using dynamic characteristics of the frames. This may result in even lower design forces and may adversely influence the design.

• Structural Engineering and Mechanics
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• 제23권4호
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• pp.409-430
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• 2006

The aim of this study is to investigate the reliability of strong motion records processed by causal and acausal Butterworth filters in comparison to the results obtained from a synthetic accelerogram. For this purpose, the fault parallel component of the Bolu record of the Duzce earthquake is modeled with a sum of exponentially damped sinusoidal components. Noise-free velocities and displacements are then obtained by analytically integrating the synthetic acceleration model. The analytical velocity and displacement signals are used as a standard with which to judge the validity of the signals obtained by filtering with causal and acausal filters and numerically integrating the acceleration model. The results show that the acausal filters are clearly preferable to the causal filters due to the fact that the response spectra obtained from the acausal filters match the spectra obtained from the simulated accelerogram better than that obtained by causal filters. The response spectra are independent from the order of the filters and from the method of integration (whether analytical integration after a spline fit to the synthetic accelerogram or the trapezoidal rule). The response spectra are sensitive to the chosen corner frequency of both the causal and the acausal filters and also to the inclusion of the pads. Accurate prediction of the static residual displacement (SRD) is very important for structures traversing faults in the near-fault regions. The greatest adverse effect of the high pass filters is their removal of the SRD. However, the noise-free displacements obtained by double integrating the synthetic accelerogram analytically preserve the SRD. It is thus apparent that conventional high pass filters should not be used for processing near-fault strong-motion records although they can be reliably used for far-fault records if applied acausally. The ground motion parameters such as ARIAS intensity, HUSID plots, Housner spectral intensity and the duration of strong-motion are found to be insensitive to the causality of filters.

• Structural Engineering and Mechanics
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• 제17권3_4호
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• pp.527-537
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• 2004

Consequence-Based Engineering (CBE) is a new paradigm proposed by the Mid-America Earthquake Center (MAE) to guide evaluation and rehabilitation of building structures and networks in areas of low probability - high consequence earthquakes such as the central region of the U.S. The principal objective of CBE is to minimize consequences by prescribing appropriate intervention procedures for a broad range of structures and systems, in consultation with key decision makers. One possible intervention option for rehabilitating unreinforced masonry (URM) buildings, widely used for essential facilities in Mid-America, is passive energy dissipation (PED). After the CBE process is described, its application in the rehabilitation of vulnerable URM building construction in Mid-America is illustrated through the use of PED devices attached to flexible timber floor diaphragms. It is shown that PED's can be applied to URM buildings in situations where floor diaphragm flexibility can be controlled to reduce both out-of-plane and in-plane wall responses and damage. Reductions as high as 48% in roof displacement and acceleration can be achieved as demonstrated in studies reported below.

• 한국철도학회논문집
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• 제12권6호
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• pp.1037-1042
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• 2009

국내 사면안정성 설계기준은 우기 건기시로 제안되어 사용되고 있지만, 한계평형해석의 결과로 산출되는 안전율이 외부조건에 의해 변화되며, 특정한 변곡점이 없기 때문에 사전에 안전을 확보하기 어렵다는 점에 착안하여 경보발령, 서행 및 열차정지 등과 같은 안전규정의 설정이 가능한 대안을 검토하였다. 이를 위하여 본 연구에서는 불포화토질역학과 신뢰성해석에 기초하여 현행 안전율을 보조할 수 있는 부가적인 지표를 도입하였다. 강우침투에 따라 안전율과 신뢰지수는 지수함수형태로 감소하는 특징을 보이며, 파괴확률은 누적확률분포함수 형태로 증가함을 확인할 수 있었다. 본 연구에서 검토한 부가지표인 파괴확률 변화속도는 현재의 기준 안전율 부근에서 명백한 변곡점을 갖는 특징이 있다. 이를 이용하면 사면의 안전관리와 모니터링 시스템에 대한 적정 규정으로 적용이 가능할 것으로 판단된다.

• 터널과지하공간
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• 제16권6호
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• pp.437-450
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• 2006

암반구조물의 파괴는 초기응력의 크기, 무결암의 강도 그리고 단층이나 절리와 같이 암반 내에 존재하는 불연속면의 상태에 의해 좌우된다. 일반적으로 고심도에 건설되는 암반구조물의 경우 높은 현지응력과 공동굴착에 따른 유도응력으로 인해 공동 경계면에서 스폴링이나 슬래빙과 같은 취성파괴가 발생할 수 있다. 최근 고심도에 건설되는 암반구조물이 증가함에 따라 취성파괴의 발생사례가 증가하고 있으며, 더욱이 국내의 저심도 구간에서도 스폴링 현상이 보고되어 취성파괴에 대한 연구의 필요성이 요구된다. 그러나 아직까지 취성파괴에 대해 명확하게 규명되지 않아 본 보고에서 취성파괴 현상을 규명하기 위해 수행되었던 기존 연구결과를 중심으로 취성파괴와 그 특징에 대하여 요약 정리하였다.

• 마이크로전자및패키징학회지
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• 제21권4호
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• pp.15-24
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• 2014

Recently, a variety of printing technologies, including ink jet, gravure, and roll-to-roll (R2R) printing, has generated intensive interest in the application of flexible and wearable electronic devices. However, the actual use of printing technique is much limited because the sintering process of the printed nanoparticle inks remains as a huge practical drawback. In the fabrication of the conductive metal film, a post-sintering process is required to achieve high conductivity of the printed film. The conventional thermal sintering takes considerable sintering times, and requires high temperatures. For application to flexible devices, the sintering temperature should be as low as possible to minimize the damage of polymer substrate. Several alternative sintering methods were suggested, such as laser, halogen lamp, infrared, plasma, ohmic, microwave, and etc. Eventually, the new sintering technique should be applicable to large area, R2R, and polymer substrate as well as low cost. This article reviews progress in recent technologies for several sintering methods. The advantages and disadvantages of each technology will be reviewed. Several issues for the application in R2R process are discussed.

• 마이크로전자및패키징학회지
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• 제21권1호
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• pp.25-29
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• 2014

본 연구에서는 기존의 PCB의 한계를 극복할 수 있는 광 PCB에 대한 연구를 수행하였으며, 고효율 수동정렬을 위한 플러거블 렌즈구조를 제안하였다. 제안된 구조는 광 도파로 수동 정렬시 발생할 수 있는 렌즈와 도파로 간의 정렬 오차를 개선하고자 도파로와 렌즈를 합한 형태이다. 또한 탈착에 의해 손상되는 렌즈표면을 보호하기 위한 보호벽 형태를 지님으로써, 고효율의 수동정렬이 가능하게 하였다. 최적화 시뮬레이션을 통하여 구조를 설계하였고, 반복적 포토 리소그래피와 열적 리플로우 공정을 통하여 플러거블 렌즈 구조 제작을 위한 공정 연구를 수행하였다. 렌즈일체형 플러거블 접속구조의 광도파로를 PDMS복제공정으로 제작된 mold를 이용하여 임프린트 공정을 통해 제작하였다. 따라서 본 논문에서는 수동정렬이 가능한 광PCB접속용 플러거블 렌즈 구조의 제작이 가능함을 확인하였다.

• Structural Engineering and Mechanics
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• 제50권2호
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• pp.241-255
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• 2014

The girder of self-anchored suspension bridge is subjected to large compression force applied by main cables. So, serious damage of the girder due to breakage of hangers may cause collapse of the whole bridge. With the time increasing, the hangers may break suddenly for their resistance capacities decrease due to corrosion. Using nonlinear static and dynamic analysis methods and adopting 3D finite element model, the responses of a concrete self-anchored suspension bridge to sudden breakage of hangers are studied in this paper. The results show that the sudden breakage of a hanger has significant effects on tensions of the hangers next to the broken hanger, bending and torsion moments of the girder, moments of the towers and reaction forces of the bearings. The results obtained from dynamic analysis method are very different from those obtained from static analysis method. The maximum tension of hanger produced by breakage of a hanger exceeds 2.2 times of its initial value, the maximum dynamic amplification factor reaches 2.54, which is larger than the value of 2.0 recommended for cable-stayed bridge in PTI codes. If two adjacent hangers on the same side of bridge break one after another, the maximum tension of other hangers exceeds 3.0 times of its initial value. If the safety factor adopted to design hanger is too small, or the hangers have been exposed to corrosion, the bridge may collapse due to breakage of two adjacent hangers.

• Structural Engineering and Mechanics
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• 제44권1호
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• pp.51-60
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• 2012

Concrete sleepers are essential components of the conventional railway. As support elements, sleepers are always subjective to a variety of time-dependent loads attributable to the train operations, either wheel or rail abnormalities. It has been observed that the sleepers may deteriorate due to these loads, inducing the formation of hairline cracks. There are two areas along the sleepers that are more prone to crack: the central and the rail seat sections. Several non-destructive methods have been developed to identify failures in structures. Health monitoring techniques are based on vibration responses measurements, which help engineers to identify the vibration-based damage or remotely monitor the sleeper health. In the present paper, the dynamic effects of the cracks in the vibration signatures of the railway pre-stressed concrete sleepers are investigated. The experimental modal analysis has been used to evaluate the modal bending changes in the vibration characteristics of the sleepers, differentiating between the central and the rail seat locations of the cracks. Modal parameters changes of the 'healthy' and cracked sleepers have been highlighted in terms of natural frequencies and modal damping. The paper concludes with a discussion of the most suitable failure indicator and it defines the vibration signatures of intact, central cracked and rail seat cracked sleepers.

• Coupled systems mechanics
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• 제6권3호
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• pp.229-249
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• 2017

A new technique to mitigate irregular buildings with soil structure interaction (SSI) effect subjected to critical seismic waves is presented. The L-shape in plan irregular building for various reasons was selected, subjected to seismic a load which is a big problem for structural design especially without separation gap. The L-shape in plan building with different dimensions was chosen to study, with different rectangularity ratios and various soil kinds, to show the effect of the irregular building on the seismic response. A 3D building subjected to critical earthquake was analyzed by structural analysis program (SAP2000) fixed and with SSI (three types of soils were analyzed, soft, medium and hard soils) to find their effect on top displacement, base shear, and base torsion. The straining actions were appointed and the treatment of the effect of irregular shape under critical earthquake was made by using tuned mass damper (TMD) with different configurations with SSI and without. The study improve the success of using TMDs to mitigate the effect of critical earthquake on irregular building for both cases of study as fixed base and raft foundation (SSI) with different TMDs parameters and configurations. Torsion occurs when the L-shape in plan building subjected to earthquake which may be caused harmful damage. TMDs parameters which give the most effective efficiency in the earthquake duration must be defined, that will mitigate these effects. The parameters of TMDs were studied with structure for different rectangularity ratios and soil types, with different TMD configurations. Nonlinear time history analysis is carried out by SAP2000 with El Centro earthquake wave. The numerical results of the parametric study help in understanding the seismic behavior of L-shape in plan building with TMDs mitigation system.