• Steel and Composite Structures
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• 제37권5호
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• pp.517-532
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• 2020

This paper firstly developed a new type of Double Skin Composite (DSC) beams using novel enhanced C-channels (ECs). The shear behaviour of novel ECs was firstly studied through two push-out tests. Eleven full-scale DSC beams with ECs (DSCB-ECs) were tested under four-point loading to study their ultimate strength behaviours, and the studied parameters were thickness of steel faceplate, spacing of ECs, shear span, and strength of concrete core. Test results showed that all the DSCB-ECs failed in flexure-governed mode, which confirmed the effective bonding of ECs. The working mechanisms of DSCB-ECs with different parameters were reported, analysed and discussed. The load-deflection (or strain) behaviour of DSCB-ECs were also detailed reported. The effects of studied parameters on ultimate strength behaviour of DSCB-ECs have been discussed and analysed. Including the experimental studies, this paper also developed theoretical models to predict the initial stiffness, elastic stiffness, cracking, yielding, and ultimate loads of DSCB-ECs. Validations of predictions against 11 test results proved the reasonable estimations of the developed theoretical models on those stiffness and strength indexes. Finally, conclusions were given based on these tests and analysis.

• 한국지진공학회논문집
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• 제17권4호
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• pp.171-180
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• 2013

The purpose of this study is to evaluate the effectiveness of the seismic retrofit performance for a reinforced concrete structure with steel damper. The nonlinear static analysis of the RC frame specimens with and without retrofit using the steel damper was conducted and the reliability of the analysis was verified by comparing the analysis and test results. Using this analysis model and method, additional nonlinear analysis was conducted considering varying stiffness and strength ratios between RC frame and steel damper and the failure mode of RC frame. As the result of the study, the total absorbed energy increased and the damage of RC frame was reduced as stiffness and strength ratios increased. The seismic retrofit performance, evaluated by means of the yield strength, increasing ratio of the absorbed energy and damage of the frame, increased linear proportionally with the increase of the strength ratio. In addition, the seismic retrofit performance was stable for stiffness ratios larger than 4~5. The energy absorption capacity of the frame governed by shear failure was better than that of the frame governed by flexure failure.

• 대한토목학회논문집
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• 제13권1호
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• pp.1-12
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• 1993

가상변수(假想變數)의 원리(原理)를 이용하여 공간박벽(空間薄璧) 및 뼈대구조물(構造物)의 비틂 및 횡좌굴해석(橫挫掘解析)을 수행하기 위한 접선강도(接線剛度)매트릭스들이 유도(誘導)된다. 구속(拘束)된 비틂을 고려하는 경우와 무시하는 경우 각각에 대하여, 탄성(彈性) 및 기하적(幾何的)인 강도(剛度)매트릭스들이 얻어지며 이때 축방향(軸方向) 변위(變位), 횡방향(橫方向) 처짐들, 그리고 비틂회전각에 대하여 적절한 Hermitian 다항식들을 형상함수(形狀函數)로 사용된다. 수치해석예제(數値解析例題)들을 통하여 본 연구(硏究)에서 제시한 이론(理論)의 정당성(正當性)을 입증(立證)한다.

• Geomechanics and Engineering
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• 제3권1호
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• pp.45-59
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• 2011

Scaled centrifuge modelling techniques were used to study the soil-structure interactions and performance of a jointed rollable aluminium roadway (or trackway) system on soft clay under light truck tyre loads. The measured performance and subsequent analyses highlighted that the articulated connections significantly reduced the overall longitudinal flexural stiffness of the roadway leading to stress concentrations in the soil below the joints under tyred vehicle loadings. This resulted in rapid localised failure of the supporting soil that in turn led to excessive transverse flexure of the roadway and ultimately plastic deformations. It is shown that the performance of rollable roadway systems under tyred vehicle trafficking will be improved by eliminating joint rotation to increase longitudinal stiffness.

• Structural Engineering and Mechanics
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• 제31권5호
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• pp.567-585
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• 2009

The aim of this study was to investigate the flexural behavior of reinforced concrete beams strengthened with a novel strengthening system. Concrete beams were strengthened with a hybrid retrofit system consisting of high strength steel cords impregnated in an inorganic fireproof matrix (Geopolymer). The strengthened reinforced concrete beams along with non-strengthened control beams were tested monotonically under four point bending loading conditions. Moreover, an analytical model is introduced, that can be used to analyze the flexural performance of the strengthened beams. The experimental results indicate that the failure of the strengthened beams was based on the yielding of the reinforcement in the tension face of the beams, followed by a local slippage of the steel cords. The flexural stiffness of the strengthened beams was significantly improved compared to the stiffness of the non-strengthened beams. In conclusion, the strengthening system can provide an effective alternative to commercially available systems.

• Steel and Composite Structures
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• 제29권1호
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• pp.91-106
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• 2018

This paper investigates the deflection of the steel-concrete composite truss beam (SCCTB) at the serviceability limit state. A precise solution for the distributed uplift force of the SCCTB, considering five different loading types, is first derived based on the differential and equilibrium equations. Furthermore, its approximate solution is proposed for practical applications. Subsequently, the shear slip effect corresponding to the shear stiffness of the stub connectors, uplift effect corresponding to the axial stiffness of the stub connectors and shear effect corresponding to the brace deformation of the steel truss are considered in the derivation of deflection. Formulae for estimating the SCCTB deflection are proposed. Moreover, based on the proposed formulae, a practical design method is developed to provide an effective and convenient tool for designers to estimate the SCCTB deflection. Flexure tests are carried out on three SCCTBs. It is observed that the SCCTB stiffness and ultimate load increase with an increase in the shear interaction factor. Finally, the reliability of the practical design method is accurately verified based on the available experimental results.

• Structural Engineering and Mechanics
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• 제67권3호
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• pp.233-244
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• 2018

This study aims at evaluating the performance of repairing technique with CFRPs in recovering cyclic performance of damaged columns in flexure in terms of structural response parameters such as strength, dissipated energy, stiffness degradation. A 2/3 scaled substandard reinforced concrete frame was constructed to represent the substandard RC buildings especially in developing countries. These substandard buildings have several structural deficiencies such as strong beam-weak column phenomenon, improper reinforcement detailing and poor material properties. Flexural plastic hinges occurred at the columns ends after testing the substandard specimen under both constant axial load and reversed cyclic lateral loading. Afterwards, the damaged columns were externally wrapped with CFRP sheets both in transverse and longitudinal directions and then retested under the same loading protocol. In addition, ambient vibration measurements were taken from the undamaged, damaged and the repaired specimens at each structural repair steps to identify the effectiveness of each repairing step by monitoring the change in the natural frequencies of the tested specimen. The ambient vibration test results showed that the applied repairing technique with external CFRP wrapping was proved to recover stiffness of the pre-damaged specimen. Moreover, the lateral load capacity of the pre-damaged substandard RC frame was restored with externally bonded CFRP sheets.

• Structural Engineering and Mechanics
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• 제67권2호
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• pp.165-173
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• 2018

A simple predicted model using a modified Shear-lag method was used to represent the moisture absorption effect on the stiffness degradation for $[0/90]_{2s}$ composite laminates with transverse cracks and under flexural loading. Good agreement is obtained by comparing the prediction model and experimental data published by Smith and Ogin (2000). The material properties of the composite are affected by the variation of temperature and moisture absorption. The transient and non-uniform moisture concentration distribution give rise to the transient elastic moduli of cracked composite laminates. The hygrothermal effect is taken into account to assess the changes in the normalised axial and flexural modulus due to transverse crack. The obtained results represent well the dependence of the stiffness properties degradation on the cracks density, moisture absorption and operational temperature. The composite laminate with transverse crack loaded in axial tension is more affected by the hygrothermal condition than the one under flexural loading. Through this theoretical study, we hope to contribute to the understanding of the moisture absorption on the composite materials with matrix cracking.

• Smart Structures and Systems
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• 제16권4호
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• pp.593-606
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• 2015

This paper presents a novel concept of healing some of the damages in wind turbine blades (WTBs) such as cracks and delamination. This is achieved through an inherent functioning autonomous repairing system. Such wind turbine blades have the benefit of reduced maintenance cost and increased operational period. Previous techniques of developing autonomous healing systems uses hollow glass fibres (HGFs) to deliver repairing fluids to damaged sites. HGFs have been reported with some limitations like, failure to fracture, which undermines their further usage. The self-healing technique described in this paper represents an advancement in the engineering of the delivery mechanism of a self-healing system. It is analogous to the HGF system but without the HGFs, which are replaced by multiple hollow channels created within the composite, inherently in the FRP matrix at fabrication. An in-house fabricated NACA 4412 WTB incorporating this array of network hollow channels was damaged in flexure and then autonomously repaired using the vascular channels. The blade was re-tested under flexure to ascertain the efficiency of the recovered mechanical properties.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1438-1441
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• 2005

To establish of standard technique of nano-length measurement in 2D plane, new AFM system has been designed. In this system, measurement uncertainty is dominantly affected by the Abbe error of XY scanning stage. No linear stage is perfectly straight; in other words, every scanning stage is subject to tilting, pitch and yaw motion. In this paper, an AFM system with minimum offset of XY sensing is designed. And XY scanning stage is designed to minimize rotation angle because Abbe errors occur through the multiply of offset and rotation angle. To minimize the rotation angle optimal design has performed by maximizing the stiffness ratio of motion direction to the parasitic motion direction of each stage. This paper describes the design scheme of full AFM system, especially about XY stage. Full range of fabricated XY scanner is $100um\times{100um}$. And tilting, pitch and yaw motion are measured by autocollimator to evaluate the performance of XY stage. Using this AFM system, 3um pitch specimen was measured. As a result, the uncertainty of total system has been evaluated.