Test and analysis of concrete-filled double steel and double skin tubular columns having outer stainless steel tube

Serkan Tokgoz,Sedat Karaahmetli,Cengiz Dundar 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.1

This paper presents experimental and analytical studies of eccentrically loaded concrete-filled double steel (CFDST) and concrete-filled double skin tube (DCFST) columns having outer stainless steel tube. Eighteen CFDST and DCFST column specimens were manufactured and tested to examine the strength and load-deflection responses. In the study, the main parameters were concrete strength, load eccentricity, cross section and slenderness. The strengths, load-deflection diagrams and failure patterns of the columns were observed. In addition, the tested CFDST and DCFST columns were analyzed to attain the capacity and load versus lateral deflection responses. The obtained theoretical results were compared with the test results. A parametric study was also performed to research the effects of the ratio of eccentricity (e/Ho) slenderness ratio (L/r), Ho/to ratio, Hi/ti ratio and the concrete compressive strength on the behavior of columns. In this work, the obtained results indicated that the ductility and capacity of columns were affected by cross section, concrete strength, steel strength, loading eccentricity and slenderness.

Investigations on the Performance Characteristics of Carbon Nano-tubes, Alumina and Titanium Dioxide Based Plasma Sprayed Coatings on AISI 1020 Steel

Vijayanand Palani,Amitesh Kumar,K. R. Vijaya Kumar,P. Kumaran 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.2

The current study deals with the investigation on the performance characteristics of varying composition of coating mixture comprising carbon nano-tube, alumina and titanium dioxide on the thermal spray coating on mild steel. The performance properties, namely tensile and microhardness, were measured for the varying composition of coating mixture based thermal coating on mild steel. Response surface methodology was adopted to access the interdependencies prevailing between various dependent and independent parameters, namely composition of the mixture, tensile and microhardness. Scanning Electron Microscope coupled with elemental mapping were used to show the melting zones features and composition. The experimental results and response graphs indicated that increased weight percentages of carbon nano-tube and TiO2 with an optimal value of alumina at 87.5 percent of total weight showed better performance properties due to better dispersion leading to good bonding suitable for protective coatings. Scanning Electron Microscope images reveal partially melted zones that were restricted to smaller regions, and all particles tend to solidify beginning with a fully molten phase.

Bulging rupture and caustic corrosion of a boiler tube in a thermal power plant

Kim, Y.-S.,Kim, W.-C.,Kim, J.-G. Pergamon 2019 Engineering failure analysis Vol.104 No.-

<P><B>Abstract</B></P> <P>This paper presents a failure analysis of a boiler tube (SA-210 Grade A-1) in a low sulfur waxy residue (LSWR) oil-fired plant. A highly deformed bulged rupture was observed on the outside of the tube, and the steam from the rupture damaged the tube adjacent to the failed tube. Severe thickness reduction was observed on the inner surface, and brown and orange oxides and white scale were present in the failure region. Microstructural examination and hardness tests confirmed that material degradation (voids, microcracks, and decreased hardness) caused by overheating at the failure region had taken place. X-ray diffraction analysis indicated the presence of CaSiO<SUB>2</SUB> and Na<SUB>2</SUB>FeO<SUB>2</SUB>, indicating caustic corrosion. In addition, dimples and striations were observed in scanning electron microscopy fractography results. We therefore concluded that deposits on the interior wall led to overheating, followed by evaporation of the feed water, and then NaOH in the water caused caustic corrosion. Eventually, this corrosion resulted in ductile and fatigue failure arising from internal pressure and thermal fatigue.</P>

An Accurate Analysis for Sandwich Steel Beams with Graded Corrugated Core Under Dynamic Impulse

Asmita Rokaya,김정호 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.5

This paper addresses the dynamic loading characteristics of the shock tube onto sandwich steel beams as an effi cient and accurate alternative to time consuming and complicated fl uid structure interaction using fi nite element modeling. The corrugated sandwich steel beam consists of top and bottom fl at substrates of steel 1018 and corrugated cores of steel 1008. The corrugated core layers are arranged with non-uniform thicknesses thus making sandwich beam graded. This sandwich beam is analogous to a steel beam with web and fl anges. Substrates correspond to fl anges and cores to web. The stress–strain relations of steel 1018 at high strain rates are measured using the split-Hopkinson pressure. Both carbon steels are assumed to follow bilinear strain hardening and strain rate-dependence. The present fi nite element modeling procedure with an improved dynamic impulse loading assumption is validated with a set of shock tube experiments, and it provides excellent correlation based on Russell error estimation with the test results. Four corrugated graded steel core arrangements are taken into account for core design parameters in order to maximize mitigation of blast load eff ects onto the structure. In addition, numerical study of four corrugated steel core placed in a reverse order is done using the validated fi nite element model. The dynamic behavior of the reversed steel core arrangement is compared with the normal core arrangement for defl ections, contact force between support and specimen and plastic energy absorption.

Behaviors of concrete filled square steel tubes confined by carbon fiber sheets (CFS) under compression and cyclic loads

Park, Jai Woo,Hong, Young Kyun,Choi, Sung Mo 국제구조공학회 2010 Steel and Composite Structures, An International J Vol.10 No.2

The existing CFT columns present the deterioration in confining effect after the yield of steel tube, local buckling and the deterioration in load capacity. If lateral load such as earthquake load is applied to CFT columns, strong shearing force and moment are generated at the lower part of the columns and local buckling appears at the column. In this study, axial compression test and beam-column test were conducted for existing CFT square column specimens and those reinforced with carbon fiber sheets (CFS). The variables for axial compression test were width-thickness ratio and the number of CFS layers and those for beam-column test were concrete strength and the number of CFS layers. The results of the compression test showed that local buckling was delayed and maximum load capacity improved slightly as the number of layers increased. The specimens?ductility capacity improved due to the additional confinement by carbon fiber sheets which delayed local buckling. In the beam-column test, maximum load capacity improved slightly as the number of CFS layers increased. However, ductility capacity improved greatly as the increased number of CFS layers delayed the local buckling at the lower part of the columns. It was observed that the CFT structure reinforced with carbon fiber sheets controlled the local buckling at columns and thus improved seismic performance. Consequently, it was deduced that the confinement of CFT columns by carbon fiber sheets suggested in this study would be widely used for reinforcing CFT columns.

Endochronic simulation for the response of 1020 carbon steel tubes under symmetric and unsymmetric cyclic bending with or without external pressure

Kuo-Long Lee,Chien-Min Hsu,Chao-Yu Hung 국제구조공학회 2008 Steel and Composite Structures, An International J Vol.8 No.2

This paper presents the theoretical simulation of the response of 1020 carbon steel tubes subjected to symmetric and unsymmetric cyclic bending with or without external pressure by using the endochronic theory. Experimental data of 1020 carbon steel tubes tested by Corona and Kyriakides (1991) were used for evaluating the theoretical simulation. Several cases were considered in this study, they were symmetric bending without external pressure, symmetric bending with external pressure, unsymmetric bending without external pressure, and unsymmetric bending with external pressure. The responses of the moment-curvature, ovalization-curvature and ovalization-number of cycles with or without external pressure were discussed. It has been shown that the theoretical simulations of the responses correlate well with the experimental data.

Axial impact behavior of confined concrete filled square steel tubes using fiber reinforced polymer

Yitian Zhang,Bo Shan,Thomas H.K. Kang,Yan Xiao 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.2

Existing research on confined concrete filled steel tubular (CCFT) columns has been mainly focused on static or cyclic loading. In this paper, square section CCFT and CFT columns were tested under both static and impact loading, using a 10,000 kN capacity compression test machine and a drop weight testing equipment. Research parameters included bonded and unbonded fiber reinforced polymer (FRP) wraps, with carbon, basalt and glass FRPs (or CFRP, BFRP, and GFRP), respectively. Time history curves for impact force and steel strain observed are discussed in detail. Experimental results show that the failure modes of specimens under impact testing were characterized by local buckling of the steel tube and cracking at the corners, for both CCFT and CFT columns, similar to those under static loading. For both static and impact loading, the FRP wraps could improve the behavior and increase the loading capacity. To analyze the dynamic behavior of the composite columns, a finite element, FE, model was established in LS-DYNA. A simplified method that is compared favorably with test results is also proposed to predict the impact load capacity of square CCFT columns.

DDVS 기법을 활용한 일반 구조용 탄소강관 및 강재 파이프 서포트 영상기반 변위계측

설동현,김홍진,신승훈,김구연,신경재 대한건축학회지회연합회 2019 대한건축학회연합논문집 Vol.21 No.1

Applicability of vision-based dynamic displacement measurement system was evaluated to measure displacement caused by buckling under load on pipe. In order to analyze the accuracy according to the height of pipes, the height of carbon steel tubes for general structural purposes and Steel pipe supports is set to 0.5m from 2m to 4m. Dynamic Displacement Vision System (DDVS) method is used for vision-based displacement measurement and ROI (Region Of Interest) is set to track to solve the problem that the target deviates from ROI when displacement occurs. The displacement obtained by DDVS method is compared with the displacement measurement results of LVDT (The Linear Variable Differential Transformer) which is the contact displacement sensor. In addition, the displacement obtained by DDVS method is combined with load data from the data logger to form load-displacement relationship. The load-displacement relationship is compared with load-displacement relationship by obtained LVDT. The square of the correlation coefficient (R^2) was used as the method of analyzing the error, and there is very little error regardless of the height of error. 본 연구에서는 파이프에 하중 재하 시 좌굴에 의해 발생하는 변위를 계측하기 위해 영상기반 변위계측 시스템의 적용성을 평가하였다. 하중 재하 방식으로는 UTM에서 액추에이터의 변위를 일정시간 간격으로 조절하여 하중을 가하는 방식을 사용하였으며, 높이에 따른 정확도 비교 분석을 위해, 일반 구조용 탄소 강관과 강재 파이프 서포트의 높이를 2m부터 4m까지 0.5m 간격으로 설정하였다. 영상기반 변위계측을 위해 DDVS (Dynamic Displacement Vision System) 기법을 활용하였으며, 변위 발생 시 타겟이 ROI (Region Of Interest)를 벗어나는 문제를 해결하기 위해 ROI를 추적하도록 설정하였다. 영상기반 변위계측 결과는 기존의 접촉식 센서인 LVDT (The Linear Variable Differential Transformer)의 변위계측 결과를 비교하여 그 오차를 분석하였다. 또한 영상기반 계측변위는 데이터로거로부터 수집된 하중으로부터 하중-변위 관계 데이터를 형성하여 LVDT로부터 수집된 하중-변위 데이터와 비교하여 오차를 분석하였다. DDVS 오차를 분석하는 방법으로 상관계수의 제곱 값 (R^2)을 적용하였으며, 모든 높이에서 상관계수의 제곱 값 (R^2)이 1에 가까워 오차가 매우 적게 발생하였다.

뿜칠두께와 CFRP Re-Bar 내부 배치에 따른 콘크리트충전 각형강관 기둥의 내화성능 평가

한슬기 ( Han Seul-gi ),다시뎀베렐너럽바담 ( Dashdemberel Norovbadam ),김선희 ( Kim Sun-hee ),최성모 ( Choi Sung-mo ) 한국복합신소재구조학회 2022 복합신소재구조학회논문집 Vol.13 No.5

콘크리트 충전강관은 국부좌굴을 방지하고 내화성이 향상되기 때문에 건설현장에서 많이 적용되며 휨성능을 향상시키기 위해 강관 내부에 철근을 보강하여 사용한다. 그러나 철근은 부식되며 내구성이 저하되기 때문에 이를 대신할 소재에 대한 연구가 진행되고 있다. 탄소섬유보강근은 철근에 비해 경량이며 고강도와 내부식성이 우수하다는 이점이 있다. 그러나 임계온도가 250℃로 철근의 임계온도인 538℃에 비해 현저히 낮기 때문에 내화피복이 필요하다. 따라서 열전달해석을 통해 탄소섬유보강근을 사용하였을 때 온도분포를 확인하고 P-M상관도를 도출하여 적용 가능여부를 확인하고자 한다. 해석결과 내화성능을 확보하기 위해 콘크리트 피복두께 40mm, 뿜칠내화피복재 30mm를 적용하거나 콘크리트 피복두께 60mm, 뿜칠내화피복재 20mm를 적용하면 3시간 내화성능을 만족하는 것으로 평가되었다. Concrete filled steel tubes are often used at construction sites to prevent local buckling and improve fire resistance, and reinforcement is used inside the steel pipes to improve moment performance. However, as reinforcing bars corrode and become less durable, research is underway on alternative materials. Carbon fiber reinforcing bars are lighter than reinforcing bars and have advantages of high strength and corrosion resistance. However, since the critical temperature is 250℃, which is significantly lower than the critical temperature of 538℃, fireproof coating is required. Therefore, when carbon fiber reinforcement is used through heat transfer analysis, the temperature distribution is confirmed, and the P-M curve is derived to confirm the applicability. As a result of the analysis, it was evaluated that the fire resistance for 3 h is satisfied by applying 40 mm of concrete cover thickness, 30 mm of spray-applied fire resistive material, 60 mm of concrete cover thickness, and 20 mm of spray-applied fire resistive material.

Structural behavior of CFRP strengthened concrete-filled steel tubes columns under axial compression loads

박재우,최성모 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.5

This paper presents the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened CFT (concrete-filled steel tubes) columns under axial loads. Circular and square specimens were selected to investigate the retrofitting effects of CFRP sheet on CFT columns. Test parameters are cross section of CFT, D/t (B/t) ratios, and the number of CFRP layers. The load and ductility capacities were evaluated for each specimen. Structural behavior comparisons of circular and rectangular section will be represented in the experimental result discussion section. Finally, ultimate load formula of CFRP strengthened CFT will be proposed to calculate the ultimate strength of CFRP strengthened circular CFT. The prediction values are in good agreement with the test results obtained in this study and in the literature.