• Steel and Composite Structures
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• 제51권4호
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• pp.417-440
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• 2024

Artificial neural networks (ANN) have been the focus of several studies when it comes to evaluating the pile's bearing capacity. Nonetheless, the principal drawbacks of employing this method are the sluggish rate of convergence and the constraints of ANN in locating global minima. The current work aimed to build four ANN-based prediction models enhanced with methods from the black hole algorithm (BHA), league championship algorithm (LCA), shuffled complex evolution (SCE), and symbiotic organisms search (SOS) to estimate the carrying capacity of piles in cold climates. To provide the crucial dataset required to build the model, fifty-eight concrete pile experiments were conducted. The pile geometrical properties, internal friction angle 𝛗 shaft, internal friction angle 𝛗 tip, pile length, pile area, and vertical effective stress were established as the network inputs, and the BHA, LCA, SCE, and SOS-based ANN models were set up to provide the pile bearing capacity as the output. Following a sensitivity analysis to determine the optimal BHA, LCA, SCE, and SOS parameters and a train and test procedure to determine the optimal network architecture or the number of hidden nodes, the best prediction approach was selected. The outcomes show a good agreement between the measured bearing capabilities and the pile bearing capacities forecasted by SCE-MLP. The testing dataset's respective mean square error and coefficient of determination, which are 0.91846 and 391.1539, indicate that using the SCE-MLP approach as a practical, efficient, and highly reliable technique to forecast the pile's bearing capacity is advantageous.

• Steel and Composite Structures
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• 제18권6호
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• pp.1369-1389
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• 2015

In order to investigate the behaviour of lying multi-stud connectors in cable-pylon anchorage zone, twenty-four push-out tests are carried out with different stud numbers and diameters. The effect of concrete block width and tensile force on shear strength is investigated using the developed and verified finite element model. The results show that the shear strength of the lying multi-stud connectors is reduced in comparison with the lying single-stud connector. The reduction increases with the increasing of the number of studs in the vertical direction. The influence of the stud number on the strength reduction of the lying multi-stud connectors is decreased under combined shear and tension loads compared with under pure shear. Yet, due to multi-stud effect, they still can't be ignored. The concrete block width has a non-negligible effect on the shear strength of the lying multi-stud connectors and therefore should be chosen properly when designing push-out specimens. No obvious difference is observed between the strength reductions of the studs with 22 mm and 25 mm diameters. The shear strengths obtained from the tests are compared with those predicted by AASHTO LRFD and Eurocode 4. Eurocode 4 generally gives conservative predictions of the shear strength, while AASHTO LRFD overestimates the shear strength. In addition, the lying multi-stud connectors with the diameters of 22 m and 25 mm both exhibit adequate ductility according to Eurocode 4. An expression of load-slip curve is proposed for the lying multi-stud connectors and shows good agreement with the test results.

• 한국산학기술학회논문지
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• 제18권3호
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• pp.579-585
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• 2017

본 연구는 건축외장재에 케이블을 이용하여 로비공간에 개방성이 확보되고 시공이 간단하여 공사비용을 절감시킬 수 있는 케이블월 시스템을 제안하였다. 제안된 케이블월 시스템은 외장재의 하중을 지탱하기 위해 건축물에 철골구조를 과대하게 설치하는 기존 커튼월 구조와는 다르게 케이블을 철골부재와 철근콘크리트구조로 연결하므로 구조시스템의 단순화와 개방성을 확보할 수 있다. 또한 수직 케이블에 초기장력을 가력 할 경우 케이블접합부에 압축력이 작용되어 유리패널을 효과적으로 가압 고정할 수 있을 뿐만 아니라 풍하중을 효과적으로 구조물에 전달할 수 있게 되었다. 본 연구에서 제안한 케이블월 이론식을 구조해석 프로그램인 MIDAS-GEN에 이용하여 얻어진 해석 값을 구조실험값과 비교한 결과 하중-변형값이 유사한 것으로 나타났으며, 구조실험에 나타난 최대 처짐 값(57.5mm)은 외국 외장재 처짐규준 AAMA(L/60=150mm)보다는 매우 작게 발생되어 제안된 케이블월 시스템을 사용할 경우 구조성능은 충분히 만족하는 것으로 확인되었다.

• 한국건설순환자원학회논문집
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• 제1권3호
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• pp.211-218
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• 2013

해양환경 조건 중 건습반복환경인 간만대는 구조물내 철근부식이 가장 빨리 일어나는 것으로 알려져 있다. 때문에 부식촉진시험 방법 중 간만대 환경을 재현한 시험방법이 가장 활발하게 진행되어왔다. 그러나 많은 연구들이 부식임계농도 추정이나 염화물침투해석에 집중되어 있는 상황이다. 본 논문에서는 건습반복조건의 환경을 재현하여 구조물내 철근부식촉진시험과 염화물 침투해석을 실시하였다. 배합에 사용된 재료의 종류를 변수로 시험을 실시하였으며, 철근부식모니터링 방법으로 갈바닉 전위측정법과 반전지전위법을 사용하여 철근부식의 유무를 판단하였다. 부식촉진시험결과 각 배합별로 부식기간이 차이가 났으며, 순서는 OPC > FA > BS > 고강도 순으로 나타났다. 부식촉진시험과 동일한 조건으로 FEM 내구성 해석 프로그램인 DuCOM, RCPT 시험을 실시하여 실험결과 값에 대한 타당성을 입증하였다.

• Structural Engineering and Mechanics
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• 제50권6호
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• pp.755-772
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• 2014

A simplistic approach towards evaluation of complete load deflection response of Reinforced Concrete (RC) flexural members under post fire (residual) scenario is presented in this paper. The cross-section of the RC flexural member is divided into a number of sectors. Thermal analysis is performed to determine the temperature distribution across the section, for given fire duration. Temperature-dependent stress-strain curves for concrete and steel are then utilized to perform a moment-curvature analysis. The moment-curvature relationships are obtained for beams exposed to different fire durations. These are then utilized to obtain the load-deflection plots following pushover analysis. Moreover one of the important issues of modeling the initial stiffness giving due consideration to stiffness degradation due to material degradation and thermal cracking has also been addressed in a rational manner. The approach is straightforward and can be easily programmed in spreadsheets. The presented approach has been validated against the experiments, available in literature, on RC beam subjected to different fire durations viz. 1hr, 1.5hrs and 2hrs. Complete load-deflection curves have been obtained and compared with experimentally reported counterparts. The results also show a good match with the results obtained using more complicated approaches such as those involving Finite element (FE) modeling and conducting a transient thermal stress analysis. Further evaluation of the beams during fire (at elevated temperatures) was performed and a comparison of the mechanical behavior of RC beams under post fire and during fire scenarios is made. Detailed formulations, assumptions and step by step approach are reported in the paper. Due to the simplicity and ease of implementation, this approach can be used for evaluation of global performance of fire affected structures.

• Earthquakes and Structures
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• 제15권2호
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• pp.179-191
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• 2018

This study is aimed at investigating the dynamic performance of a composite building structure under seismic ground motions. The building structure is an official fire department building located in southern Taiwan. It is composed of a seven-story reinforced concrete (RC) and an eight-story steel reinforced concrete (SRC) frame. Both frames share a common basement and are separated by expansion joints from the first to the seventh floor. Recorded floor accelerations of the building structure under eight earthquakes occurring during the period from 2011 to 2013 were examined in this paper. It is found that both frames had similar floor acceleration amplifications in the longitudinal direction, while the SRC frame revealed larger response than the RC frame in the transverse direction. Almost invariant and similar fundamental periods under the eight earthquakes in both directions were obtained from their transfer functions. Furthermore, numerical time-history simulations were carried out for the building structure under the most intensive earthquake. It is realized that the seismic response of the composite building was dominated by the first translational mode in each horizontal direction. Higher modes did not significantly contribute to the structural response. The conventional Rayleigh damping model could be appropriately applied to the time-history simulations under bi-directional excitations. Approximate floor acceleration envelopes were obtained with a compound RC and SRC structural model by using the average damping ratios determined from the different structural arrays.

• Nuclear Engineering and Technology
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• 제52권2호
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• pp.381-396
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• 2020

Investigations of the commercial aircraft impact effect on nuclear island infrastructures have been drawing extensive attention, and this paper aims to perform the safety assessment of Generation III nuclear power plant (NPP) buildings subjected to typical commercial aircrafts crash. At present Part I, finite element (FE) models establishment and validations for both the aircrafts and NPP buildings are performed. (i) Airbus A320 and A380 aircrafts are selected as the representative medium and large commercial aircrafts, and the corresponding fine FE models including the skin, beam, fuel and etc. are established. By comparing the numerically derived impact force time-histories with the existing published literatures, the rationality of aircrafts models is verified. (ii) Fine FE model of the Chinese Zhejiang Sanao NPP buildings is established, including the detailed structures and reinforcing arrangement of both the containment and auxiliary buildings. (iii) By numerically reproducing the existing 1/7.5 scaled aircraft model impact tests on steel plate reinforced concrete (SC) panels and assessing the impact process and velocity time-history of aircraft model, as well as the damage and the maximum deflection of SC panels, the applicability of the existing three concrete constitutive models (i.e., K&C, Winfrith and CSC) are evaluated and the superiority of Winfrith model for SC panels under deformable missile impact is verified. The present work can provide beneficial reference for the integral aircraft crash analyses and structural damage assessment in the following two parts of this paper.

• Earthquakes and Structures
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• 제18권1호
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• pp.113-127
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• 2020

In this study, the behavior of external beam-column joints reinforced by plain and deformed bars with non-seismic reinforcement details is investigated and compared. The beam-column joints represented in this study include a benchmark specimen by seismic details in accordance with ACI 318M-11 requirements and four other deficient specimens. The main defects of the non-seismic beam-column joints included use of plain bar, absence of transverse steel hoops, and the anchorage condition of longitudinal reinforcements. The experimental results indicate that using of plain bars in non-seismic beam-column joints has significantly affected the failure modes. The main failure mode of the non-seismic beam-column joints reinforced by deformed bars was the accumulation of shear cracks in the joint region, while the failure mode of the non-seismic beam-column joints reinforced by plain bars was deep cracks at the joint face and intersection of beam and column and there was only miner diagonal shear cracking at the joint region. In the other way, use of plain bars for reinforcing concrete can cause the behavior of the substructure to be controlled by slip of the beam longitudinal bars. The experimental results show that the ductility of non-seismic beam-column joints reinforced by plain bars has not decreased compared to the beam-column joints reinforced by deformed bars due to lack of mechanical interlock between plain bars and concrete. Also it can be seen a little increase in ductility of substructure due to existence of hooks at the end of the development length of the bars.

• Steel and Composite Structures
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• 제35권4호
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• pp.475-494
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• 2020

Presented are experimental results from 24 full-scale push test specimens to study the behaviour of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. The tests use a single-sided horizontal push test setup and are divided into two series. First series contained shear loading only and the second had normal load besides shear load. Four parameters are studied: the effect of wire mesh position and number of its layers, placing a reinforcing bar at the bottom flange of the deck, normal load and its position, and shear stud layout. The results indicate that positioning mesh on top of the deck flange or 30 mm from top of the concrete slab does not affect the stud's strength and ductility. Thus, existing industry practice of locating the mesh at a nominal cover from top of the concrete slab and Eurocode 4 requirement of placing mesh 30 mm below the stud's head are both acceptable. Double mesh layer resulted in 17% increase in stud strength for push tests with single stud per rib. Placing a T16 bar at the bottom of the deck rib did not affect shear stud behaviour. The normal load resulted in 40% and 23% increase in stud strength for single and double studs per rib. Use of studs only in the middle three ribs out of five increased the strength by 23% compared to the layout with studs in first four ribs. Eurocode 4 and Johnson and Yuan equations predicted well the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic experimental load. These equations highly under-estimated the stud capacity, by about 40-50%, for tests with normal load. AISC 360-16 generally over-estimated the stud capacity, except for single stud/rib push tests with normal load. Nellinger equations precisely predicted the stud resistance for push tests with normal load, with ratio of experimental over predicted load as 0.99 and coefficient of variation of about 8%. But, Nellinger method over-estimated the stud capacity by about 20% in push tests with single studs without normal load.

• 한국건설순환자원학회논문집
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• 제6권3호
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• pp.153-159
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• 2018

지하구조물에 주로 발생하는 탄산화는 콘크리트 내부의 공극수의 pH감소에 따라 부식을 유발할 수 있으므로 많은 연구가 진행되고 있다. 그러나 이산화탄소로부터 표면을 보호하는 간단한 표면 보수방법을 통하여 구조물의 내구수명의 연장이 가능하다. 기존의 결정론적 유지관리 기법과는 다르게, 확률론적 유지관리 기법에서는 내구수명의 변동성이 고려될 수 있으나 정규분포만 다루고 있다. 본 연구에서는 정규분포 이외에 로그분포를 고려할 수 있는 수명-확률분포를 유도하였으며, 이를 기초로 다양한 수명-확률분포 함수를 고려한 보수비 산정기법을 제안하였다. 제안된 기법은 초기의 내구수명 분포 또는 보수재를 통하여 연장된 내구수명 분포가 정규 또는 로그분포를 가질 경우 목표내구수명의 연장에 따라 확률론적 기법을 통하여 보수비를 평가할 수 있다. 보수를 통한 내구수명이 로그분포를 가질 경우 효과적으로 보수비를 감소시킬 수 있으며, 장기 실험 또는 실태조사를 통하여 내구수명 분포가 정의될 수 있다면 더욱 합리적인 유지관리 계획을 수립할 수 있을 것으로 판단된다.