• Structural Engineering and Mechanics
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• 제81권3호
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• pp.281-292
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• 2022

This study aimed to analyze the dynamic punching shear performance of slab-column joints under cyclic loads with the use of double-hooked end (5D) steel fibers. Structural systems such as slab-column joints are widely found in infrastructures. The susceptibility to collapse of such structures when submitted to seismic loads is highly dependent on the structural performance of the slab-column connections. For this reason, the punching capacity of reinforced concrete (RC) structures has been the subject of a great number of studies. Steel fibers are used to achieve a certain degree of ductility under seismic loads. In this context, 5D steel hooked fibers provide high levels of fiber anchoring, tensile strength and ductility. However, only limited research has been carried out on the performance under cyclic loads of concrete structural members containing steel fibers. This study covers this gap with experimental testing of five different full-scale subassemblies of RC slab-column joints: one without punching reinforcement, one with conventional punching reinforcement and three with 5D steel fibers. The subassemblies were tested under cyclic loading, which consisted of applying increasing lateral displacement cycles, such as in seismic situations, with a constant axial load on the column. This set of cycles was repeated for increasing axial loads on the column until failure. The results showed that 5D steel fiber subassemblies: i) had a greater capacity to dissipate energy, ii) improved punching shear strength and stiffness degradation under cyclic loads; and iii) increased cyclic loading capacity.

• Earthquakes and Structures
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• 제22권2호
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• pp.203-218
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• 2022

In this paper, quasi-static tests were carried out on three prefabricated reinforced concrete column-steel beam (RCS) sub-assemblages with floor slabs and one comparison specimen without floor slab. The effects of axial compression and floor slab on the seismic performance were studied, and finite element simulations were conducted using ABAQUS. The results showed that the failure of prefabricated RCS sub-assemblages with floor occurred as a joint beam and column failure mode, while failure of sub-assemblages without floor occurred due to beam plastic hinge formation. Compared to the prefabricated RCS sub-assemblages without floor slab, the overall stiffness of the sub-assemblages with floor slab was between 19.2% and 45.4% higher, and the maximum load bearing capacity increased by 26.8%. However, the equivalent viscosity coefficient was essentially unchanged. When the axial compression ratio increased from 0.24 to 0.36, the hysteretic loops of the sub-assemblages with floor became fuller, and the load bearing capacity, ductility, and energy dissipation capacity increased by 12.1%, 12.9% and 8.9%, respectively. Also, the initial stiffness increased by 10.2%, but the stiffness degradation accelerated. The proportion of column drift caused by beam end plastic bending and column end bending changed from 35% and 46% to 47% and 36%, respectively. Comparative finite element analyses indicated that the numerical simulation outcomes agreed well with the experimental results.

• 대한토목학회논문집
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• 제36권1호
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• pp.31-38
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• 2016

논문에서는 파일형 선박충돌방호공의 주요 에너지 소산기구인 파일의 소성힌지와 선수변형에 대한 변형-에너지곡선을 산정하고 이를 이전 연구에서 개발된 간이 충돌모델에 적용하여 매개변수해석을 수행하였다. 고려된 매개변수는 슬래브의 질량, 파일의 수, 선박의 질량 및 충돌속도였으며 이들 매개변수를 변화시키면서 충돌거동을 분석하였다. 연구결과, 충진강관과 비충진강관의 에너지 소산거동이 차이를 파악했고, 슬래브의 관성질량을 조절하여 방호공의 충돌거동을 변화 시킬 수 있는 것으로 나타났다. 따라서 개발된 간이모델은 기본설계나 최적설계에 이용될 수 있을 것이다.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.114-123
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• 2013

본 연구는 재생 PET 섬유의 구조보강성능을 규명하기 위한 연구의 일환으로 수행되었다. 재생 PET 섬유의 구조보강성능을 규명하기 위하여 철근 콘크리트 슬래브 부재를 제작하여 휨 성능을 수행하고 기존 합성섬유인 PP 섬유와 합성섬유를 혼입하지 않은 Plain 시편과 비교하였으며, 또한 섬유의 혼입율에 따른 거동을 평가하였다. 실험결과 압축강도는 섬유의 혼입율이 증가할수록 감소하는 것으로 나타났으며 감소 비율은 약 2~7%정도로 나타났다. 휨 실험결과로부터 Plain 시편의 극한성능이 가장 우수한 것으로 나타났으며, 에너지 흡수 능력과 연성지수는 재생 PET 섬유를 0.5% 혼입한 시편이 가장 우수한 것으로 평가되었다. 보 시편에 적용한 경우에는 Plain 시편에 비해 연성능력 뿐 아니라 극한성능도 증가되는 것으로 나타났으나 슬래브 시편의 경우 연성능력은 증가되나 극한성능이 감소하는 것을 확인 할 수 있어 보 시편에 비해 상대적으로 보강효과가 적게 나타나고 있다. 따라서 슬래브 구조물에 적용할 경우에는 배합과 혼입량을 적절히 사용해야 할 것으로 사료된다.

• Steel and Composite Structures
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• 제49권1호
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• pp.81-89
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• 2023

A simplified calculation method of natural vibration characteristics of high-speed railway multi-span bridge-longitudinal ballastless track system is proposed. The rail, track slab, base slab, main beam, bearing, pier, cap and pile foundation are taken into account, and the multi-span longitudinal ballastless track-beam-bearing-pier-cap-pile foundation integrated model (MBTIM) is established. The energy equation of each component of the MBTIM based on Timoshenko beam theory is constructed. Using the improved Fourier series, and the Rayleigh-Ritz method and Hamilton principle are combined to obtain the extremum of the total energy function. The simplified calculation formula of the natural vibration frequency of the MBTIM under the influence of vertical and longitudinal vibration is derived and verified by numerical methods. The influence law of the natural vibration frequency of the MBTIM is analyzed considering and not considering the participation of each component of the MBTIM, the damage of the track interlayer component and the stiffness change of each layer component. The results show that the error between the calculation results of the formula and the numerical method in this paper is less than 3%, which verifies the correctness of the method in this paper. The high-order frequency of the MBTIM is significantly affected considering the track, bridge pier, pile soil and pile cap, while considering the influence of pile cap on the low-order and high-order frequency of the MBTIM is large. The influence of component damage such as void beneath slab, mortar debonding and fastener failure on each order frequency of the MBTIM is basically the same, and the influence of component damage less than 10m on the first fourteen order frequency of the MBTIM is small. The bending stiffness of track slab and rail has no obvious influence on the natural frequency of the MBTIM, and the bending stiffness of main beam has influence on the natural frequency of the MBTIM. The bending stiffness of pier and base slab only has obvious influence on the high-order frequency of the MBTIM. The natural vibration characteristics of the MBTIM play an important guiding role in the safety analysis of high-speed train running, the damage detection of track-bridge structure and the seismic design of railway bridge.

• Earthquakes and Structures
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• 제9권6호
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• pp.1193-1219
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• 2015

The purpose of this study is to evaluate the seismic performance of high-rise reinforced concrete (RC) box-type wall structures commonly used for most residential buildings in Korea. For this purpose, an analytical model was calibrated with the results of the earthquake simulation tests on a 1:5 scale 10-story distorted model. This calibrated model was then transformed to a true model. The performance of the true model in terms of the stiffness, strength, and damage distribution through inelastic energy dissipation was observed with reference to the earthquake simulation test results. The model showed high overstrength factors ranging from 3 to 4. The existence of slab in this box-type wall system changed the main resistance mode in the wall from bending moment to tension/compression coupled moment through membrane actions, and increased the overall resistance capacity by about 25~35%, in comparison with the common design practice of neglecting the slab's existence. The flexibility of foundation, which is also commonly neglected in the engineering design, contributes to 30~50% of the roof drift in the stiff direction containing many walls. The possibility of concrete spalling and reinforcement buckling and fracture under the maximum considered earthquake (MCE) in Korea appears to be very low when compared with the case of the 2010 Concepcion, Chile earthquake.

• Steel and Composite Structures
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• 제32권5호
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• pp.583-594
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• 2019

In recent years, composite concrete-filled steel tubular (CFST) members have been widely utilized in framed building structures like beams, columns, and beam-columns since they have significant advantages such as reducing construction time, improving the seismic performance, and possessing high ductility, strength, and energy absorbing capacity. This paper presents a new composite joint - the composite CFST beam-column joint in which the CFST member is used as the beam. The main components of the proposed composite joint are steel H-beams, CFST beams welded with the steel H-column, and a reinforced concrete slab. The steel H-beams and CFST beams are connected with the concrete slab using shear connectors to ensure composite action between them. The structural performance of the proposed composite joint was evaluated through an experimental investigation. A three-dimensional (3D) finite element (FE) model was developed to simulate this composite joint using the ABAQUS/Explicit software, and the accuracy of the FE model was verified with the relevant experimental results. In addition, a number of parametric studies were made to examine the effects of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab on the proposed joint performance.

• Steel and Composite Structures
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• 제43권2호
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• pp.229-240
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• 2022

The main objective of this work is presenting a mathematical model for the concrete slab with fiber reinforced polymer (FRP) layer under the impact load. Impacts are assumed to occur normally over the top slab and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The structure is assumed viscoelastic based on Kelvin-Voigt model. Based on the sinusoidal shear deformation theory (SSDT), energy method and Hamilton's principle, the motion equations are derived. Applying DQM, the dynamic deflection and contact force of the structure is calculated numerically so that the effects of mass, velocity and height of impactor, boundary conditions, FRP layer, structural damping and geometrical parameters of structure are shown on the dynamic deflection and contact force of system. Results show that considering structural damping leads to lower dynamic deflection and contact force. In addition, increasing the impact velocity of impactor yields to increases in the maximum contact force and deflection while the contact duration is decreased. The result shows that the contact force and the central deflection of the structure decreases and the contact time decreases with assuming FRP layer.

• Geomechanics and Engineering
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• 제37권1호
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• pp.1-8
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• 2024

Buckling failure is one of the classical types of catastrophic landslides developing on inclination-paralleled rock slopes, which is mainly governed by its self-weight, earthquake and ground water. However, nearly none of the existing studies fully consider the influence of slope self-weight, earthquake and ground water on the mechanical model of buckling failure. In this paper, based on energy equilibrium principle and elastoplastic slab theory, a thorough mechanical analysis on bucking slopes has been carried out. Furthermore, an analytical solution for slip bucking failure of rock slopes has been proposed, which fully considers the effect of slope self-weight, seismic force and hydrostatic pressure. Finally, the methodology is used to conduct comparative analysis with other analytical solutions for three practical buckling studies. The results show that the proposed approach is capable of providing a more accurate and reasonable evaluation for stability of rock slopes with potential buckling failure.

• Steel and Composite Structures
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• 제37권1호
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• pp.15-26
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• 2020

The top-and-seat angles with double web angles are commonly used in the design of beam-to-column joints in Asian and North American countries. The seismic behavior analysis of these joints with large cross-section size of beam and column (often connected by four or more bolts) is a challenge due to the effects from the relatively larger size of stiffened angles and the composite action from the adjacent concrete slab. This paper presents an experimental investigation on the seismic performance of exterior composite beam-to-column joints with stiffened angles under cyclic loading. Four full-scale composite joints with different configuration (only one specimen contain top angle in concrete slab) were designed and tested. The joint specimens were designed by considering the effects of top angles, longitudinal reinforcement bars and arrangement of bolts. The behavior of the joints was carefully investigated, in terms of the failure modes, slippage, backbone curves, strength degradation, and energy dissipation abilities. It was found that the slippage between top-and-seat angles and beam flange, web angle and beam web led to a notable pinching effect, in addition, the ability of the energy dissipation was significantly reduced. The effect of anchored beams on the behavior of the joints was limited due to premature failure in concrete, the concrete slab that closes to the column flange and upper flange of beam plays an significant role when the joint subjected to the sagging moment. It is demonstrated that the ductility of the joints was significantly improved by the staggered bolts and welded longitudinal reinforcement bars.