• Earthquakes and Structures
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• 제10권1호
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• pp.1-23
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• 2016

Steel plate shear walls (SPSWs) have been shown to be efficient lateral force-resisting systems, which are increasingly used in new and retrofit construction. These structural systems are designed with either stiffened and stocky or unstiffened and slender web plates based on disparate structural and economical considerations. Based on some limited reported studies, on the other hand, employment of low yield point (LYP) steel infill plates with extremely low yield strength, and high ductility as well as elongation properties is found to facilitate the design and improve the structural behavior and seismic performance of the SPSW systems. On this basis, this paper reports system-level investigations on the seismic response assessment of multi-story SPSW frames under the action of earthquake ground motions. The effectiveness of the strip model in representing the behaviors of SPSWs with different buckling and yielding properties is primarily verified. Subsequently, the structural and seismic performances of several code-designed and retrofitted SPSW frames with conventional and LYP steel infill plates are investigated through detailed modal and nonlinear time-history analyses. Evaluation of various seismic response parameters including drift, acceleration, base shear and moment, column axial load, and web-plate ductility demands, demonstrates the capabilities of SPSW systems in improving the seismic performance of structures and reveals various advantages of use of LYP steel material in seismic design and retrofit of SPSW systems, in particular, application of LYP steel infill plates of double thickness in seismic retrofit of conventional steel and code-designed SPSW frames.

• Structural Engineering and Mechanics
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• 제84권1호
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• pp.113-127
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• 2022

Steel plate shear walls (SPSWs) are commonly utilized to provide lateral stiffness in high-rise structures. The simplified model is frequently used instead of the fine-scale model in the design of buildings with SPSWs. To predict the lateral strength of steel plate shear walls with diagonal stiffeners (DS-SPSWs), a simplified model is presented, namely the cross brace-strip model (CBSM). The bearing capacity and internal forces of columns for DS-SPSWs are calculated. In addition, a modification coefficient is introduced to account for the shear action of the thin plate. The feasibility of the CBSM is validated by comparing the numerical results with theoretical and experimental results. The numerical results from the CBSM and fine-scale model, which represent the bearing capacity of the DS-SPSW with varied stiffened plate dimensions, are in good accord with the theoretical values. The difference in bearing capacity between the CBSM and the fine-scale model is less than 1.35%. The errors of the bearing capacity from the CBSM are less than 5.67% when compared to the test results of the DS-SPSW. Furthermore, the shear and axial forces of CBSM agree with the results of the fine-scale model and theoretical analysis. As a result, the CBSM, which reflects the contribution of diagonal stiffeners to the lateral resistance of the SPSW as well as the effects on the shear and axial forces of the columns, can significantly improve the design accuracy and efficiency of buildings with DS-SPSWs.

• Structural Engineering and Mechanics
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• 제86권3호
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• pp.385-397
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• 2023

This study presents an experiment and analysis to compare the seismic behavior of full-scale reinforced concrete beam-column joint strengthened by prestressed steel strips, externally bonded steel plate, and CFRP sheets. For experimental investigation, five specimens, including one joint without any retrofitting, one joint retrofitted by externally bonded steel plate, one joint retrofitted by CFRP sheets, and two joints retrofitted by prestressed steel strips, were tested under cyclic-reserve loading. The failure mode, strain response, shear deformation, hysteresis behavior, energy dissipation capacity, stiffness degradation and damage indexes of all specimens were analyzed according to experimental study. It was found that prestressed steel strips, steel plate and CFRP sheets improved shear resistance, energy dissipation capacity, stiffness degradation behavior and reduced the shear deformation of the joint core area, as well as changed the failure pattern of the specimen, which led to the failure mode changed from the combination of flexural failure of beams and shear failure of joints core to the flexural failure of beams. In addition, the beam-column joint retrofitted by steel plate exhibited a high bearing capacity, energy consumption capacity and low damage index compared with the joint strengthened by prestressed steel strip, and the prestressed steel strips reinforced joint showed a high strength, energy dissipation capacity and low shear deformation, stirrups strains and damage index compared to the CFRP reinforced joint, which indicated that the frame joints strengthened with steel plate exhibited the most excellent seismic behavior, followed by the prestressed steel strips.

• Steel and Composite Structures
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• 제44권6호
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• pp.845-865
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• 2022

In this study, the performance of shear deficient reinforced concrete (RC) beams with rectangular cross-sections, which were externally bonded reinforced (EBR) with high strength CFRP and GFRP strips composite along shear spans, has been experimentally and analytically investigated under vertical load. In the study, the minimum CFRP and GFRP strips width over spacing were considered. The shear beam with turned end to a bending beam was investigated by applying different composite strips. Therefore various arising in each of strength, ductility, rigidity, and energy dissipation capacity were obtained. A total of 12 small-scaled experimental programs have been performed. Beam dimensions have been taken as 100×150×1000 mm. Four beams have been tested as unstrengthened samples. This paper focuses on the effect of minimum CFRP and GFRP strip width on behaviours of RC beams shear-strengthened with full-wrapping, U-wrapping, and U-wrapping+longitudinal bonding strips. Strengthened beams showed significant increments for flexural ductility, energy dissipation, and inelastic performance. The full wrapping strips applied against shear failure have increased the load-carrying capacity of samples 53%-63% interval rate. Although full wrapping is the best strengthening choice, the U-wrapping and U-wrapping+longitudinal strips of both CFRP and GFRP bonding increased the shear capacity by 53%~75% compared to the S2 sample. In terms of ductility, the best result has been obtained by the type of strengthening where the S5 beam was completely GFRP wrapped. The experimental results were also compared with the analytically given by ACI440.2R-17, TBEC-2019 and FIB-2001. Especially in U-wrapped beams, the estimation of FIB was determined to be 81%. The estimates of the other codes are far from meeting the experimental results; therefore, essential improvements should be applied to the codes, especially regarding CFRP and GFRP deformation and approaches for longitudinal strip connections. According to the test results, it is suggested that GFRP, which is at least as effective but cheaper than CFRP, may be preferred for strengthening applications.

• 소성∙가공
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• 제20권3호
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• pp.243-249
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• 2011

In this study, an approach designed to compute high temperature friction coefficients for SCM 435 steel through a pilot hot rolling test and a finite element analysis, is proposed. Single pass pilot hot flat rolling tests with reduction ratios varying from 20 to 40% were carried out at temperatures ranging from 900 to $1200^{\circ}C$. In the proposed approach, the friction coefficient is calculated by comparing the measured strip spread and the roll force with the simulation results. This study showed that the temperature and reduction ratio had a significant influence on the friction coefficient. As both material temperature and reduction ratio become higher, the friction coefficient increases monotonically. This finding is not in agreement with the Ekelund model, which is widely used in the analysis of the hot rolling process. In the present work, the friction coefficient at a reduction ratio of 40% was found to be 1.2 times greater than that at a reduction of 30%. This higher friction coefficient means that an increment of the roll thrust force is expected at the next stand. Therefore, a roll pass designer must understand this phenomenon in order to adjust the reduction ratio at the stands while keeping the driving power, the roll housing structure and the work roll strength within the allowable range.

• 한국분말재료학회지
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• 제3권4호
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• pp.227-232
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• 1996

(i) The development of a metallurgical bond during the spray forming of clad products has offered the possibility of manufacturing large rolls, including those used in hot and cold strip mills. Small rolls are already being produced in Japan. (ii) Technical developments, including the use-of-multi-atomizers have resulted in the elimination of porosity from the internal bore of a sprayed tube. Bimetallic tubing can also be manufactured and the installation of a 4.5 ton tube plant in the USA should provide low operation costs. (iii) Spray forming offers a potentially low cost manufacturing route for superalloy ring/casing components in high strength superalloys. (iv) A large pilot plant has been built for the spray forming of ultra-clean superalloys for turbine disc applications. (v) Using twin-atomizing technology, special steel billets have been spray formed up to 400mm diameter with deposition yields in excess of 90%. (vi) Al/Si alloy extrusion billets with excellent dimensional tolerances are being manufactured for large scale automotive applications. Several new aluminum alloys have also been developed, including high strength, low density and low cocfficient of expansion materials. (vii) New copper alloys have been developed and pilot plants are in operation to produce these alloys once markets have become established.

• Steel and Composite Structures
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• 제12권3호
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• pp.207-230
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• 2012

Nowadays CFRP (Carbon Fiber Reinforced Polymer) became widely used materials for the strengthening and retrofitting of structures. Many experimental and analytical studies are encountered at literature about strengthening beams by using this kind of materials against static loads and cyclic loads such as earthquake or wind loading for investigating their behavior. But authors did not found any study about strengthening of RC beams by using CFRP against low velocity impact and investigating their behavior. For these reasons an experimental study is conducted on totally ten strengthened RC beams. Impact loading is applied on to specimens by using an impact loading system that is designed by authors. Investigated parameters were concrete compression strength and drop height. Two different sets of specimens with different concrete compression strength tested under the impact loading that are applied by dropping constant weight hammer from five different heights. The acceleration arises from the impact loading is measured against time. The change of velocity, displacement and energy are calculated for all specimens. The failure modes of the specimens with normal and high concrete compression strength are observed under the loading of constant weight impact hammer that are dropped from different heights. Impact behaviors of beams are positively affected from the strengthening with CFRP. Measured accelerations, the number of drops up to failure and dissipated energy are increased. Finite element analysis that are made by using ABAQUS software is used for the simulation of experiments, and model gave compatible results with experiments.

• 한국재난정보학회 논문집
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• 제9권3호
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• pp.315-323
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• 2013

최근 건설 산업에서 FRP는 재료적 장점으로 RC 구조물의 보강 재료로서 많이 사용되어지고 있다. FRP 외부부착보강은 중량에 비하여 높은 강도 및 강성, 우수한 내구성과 시공성등 여러 가지 장점을 가지는 공법이다. 그러나 외부부착보강은 구조물이 투수성이 낮은 보강재로 밀폐되고 수분이 외부로 배출되지 못함으로 인하여, 장기적인 구조물의 손상을 발생시키는 문제점이 있다. 본 연구에서는 기존의 FRP (Fiber Reinforced Polymer)와 재료적성질은 동등하면서, 투수성을 지녀 콘크리트 구조물의 모체와 부착성 및 내구성능 및 내구성이 우수한 유리섬유 패널(Glass Fiber Composite Pannel )에 대해서 휨 실험을 수행하여 복합소재 스트립의 섬유함량의 변화에 따른 실험변수별 내력증진 및 연성 증진 효과를 비교 분석하였다.

• 한국강구조학회 논문집
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• 제16권4호통권71호
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• pp.479-492
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• 2004

본 연구에서는 강상판의 U리브를 현장에서 상향의 용접자세로 용접이음을 실시할 경우, 용접이음부에는 시공오차에 의한 단차가 발생하고, 응력집중이 발생하기 쉽다. 따라서 본 연구에서는 이면재가 부착된 용접이음부에 대해 응력해석 및 실험을 실시하였다. 이면재가 부착된 U리브 용접이음부의 단차, 루트부 형상, 루트갭 및 이면재의 폭과 두께를 변화시켜 응력해석을 실시한 결과, 단차가 커질수록 응력집중계수는 현저히 증가하였으며, 루트갭도 커질수록 응력집중계수가 증가하는 것을 알 수 있었다. 또한 단차 및 루트갭이 동일한 경우에는 루트부 형상이 직각인 경우보다 반원인 경우에 응력집중계수가 작게 나타났으며, 이면재의 폭 및 두께는 응력집중계수에 그다지 영향을 미치지 않는 것으로 나타났다. 이면재가 부착된 시험편의 피로실험에서는 단차가 커질수록 피로수명이 현저히 저하되었으며 피로균열은 이면재가 부착된 모재측 루트부에서 발생하여 용접비드 표면측으로 전파하였다. 응력해석에서 루트부의 형상이 반원인 경우, 응력집중계수가 작게 나타나므로, 용접조건을 변화시켜 루트부 곡률반경 및 플랭크각을 제어하는 루트부 형상제어법를 개발하였다.

• 한국지반공학회논문집
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• 제24권12호
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• pp.5-12
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• 2008

지반의 지지력을 증가시키는 보강토공법은 일반적으로 산악지대에서 시행되는 건설공사에 쓰여지는데, 보강토 옹벽의 높이가 일반 평지의 성토구조물보다 상당히 높아지며, 성토도로의 시공이나 고속철도 등과 같은 높은 상재하중을 지지하여야 할 경우에는 지반강성을 크게 향상시킬 수 있는 공법의 적용이 요구된다. 또한, 절토공사 현장의 환경문제 및 대지경계 등의 이유로 원지반의 절취량을 최소화 할 수 있는 공법이 지속적으로 요구되고 있으며, 이를 만족하기 위한 많은 공법들이 개발되고 있는 실정이다. 그러나, 일반적인 보강토 옹벽의 경우 옹벽 높이의 $60{\sim}80%$정도에 해당되는 보강재 길이가 요구되어 절토현장에 적용하는데 어려움이 있다. 또한, 근래에 들어 용지경계 확보와 성토구조물의 안정성 확보 등 제한적인 범위에서 적용되던 보강토 옹벽공법이 추가 보강재를 병행, 사용함으로써 절토공사 현장에도 점차 적용되는 사례가 증가하고 있다. 본 연구에서는 보강토 옹벽의 보강재 길이를 줄이는 대선에 쏘일네일링 공법과 같은 사면보강공과 연결하여 충분한 저항력을 확보할 수 있도록 쏘일네일과 강재스트립으로 보강된 복합보 강토옹벽 시스템의 설계 및 시공사례를 소개하고 실제 현장에서 측정된 계측자료를 통해 복합보강토옹벽 시스템의 적용 가능성을 검토하였다.