• Steel and Composite Structures
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• 제13권3호
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• pp.295-308
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• 2012

This paper experimentally investigated the buckling capacity of built-up steel columns mainly, Cruciform Columns (CC) and Side-to-Side (SS) columns fabricated from two Universal Beam (UB) sections. A series of nine experimental tests comprised of three UB sections, three CC sections and three SS sections with different lengths were tested to failure to measure the ultimate axial capacity of each column section. The lengths used for each category of columns were 1.8, 2.0, and 2.2 m with slenderness ratios ranging from 39-105. The measured buckling loads of the tested specimens were compared with the predicted ultimate axial capacity using Eurocode 3, AISC LRFD, and BS 5959-1. It was observed that the failure modes of the specimens included flexural buckling, local buckling and flexural-torsional buckling. The results showed that the ultimate axial capacity of the tested cruciform and side-by-side columns were higher than the code predicted design values by up to 20%, with AISC LRFD design values being the least conservative and the Eurocode 3 design values being the most conservative. This study has concluded that cruciform column and side-to-side welded flange columns using universal beam sections are efficient built-up sections that have larger ultimate axial load capacity, larger stiffness with saving in the weight of steel used compared to its equivalent universal beam counterpart.

• Structural Engineering and Mechanics
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• 제83권5호
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• pp.671-680
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• 2022

The shear capacity of beams is an essential parameter in designing beams carrying shear loads. Precise estimation of the ultimate shear capacity typically requires comprehensive calculation methods. For steel fiber reinforced concrete (SFRC) beams, traditional design methods may not accurately predict the interaction between different parameters affecting ultimate shear capacity. In this study, artificial neural network (ANN) modeling was utilized to predict the ultimate shear capacity of SFRC beams using ten input parameters. The results demonstrated that the ANN with 30 neurons had the best performance based on the values of root mean square error (RMSE) and coefficient of determination (R²) compared to other ANN models with different neurons. Analysis of the ANN model has shown that the clear shear span to depth ratio significantly affects the predicted ultimate shear capacity, followed by the reinforcement steel tensile strength and steel fiber tensile strength. Moreover, a Genetic Algorithm (GA) was used to optimize the ANN model's input parameters, resulting in the least cost for the SFRC beams. Results have shown that SFRC beams' cost increased with the clear span to depth ratio. Increasing the clear span to depth ratio has increased the depth, height, steel, and fiber ratio needed to support the SFRC beams against shear failures. This study approach is considered among the earliest in the field of SFRC.

• 한국전산구조공학회논문집
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• 제22권1호
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• pp.1-13
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• 2009

이 논문에서는 복잡한 기하학적 형상과 비선형 특성들을 보이는 곡선 프리스트레스트 콘크리트(PSC) 사장교의 극한거동을 안정적으로 예측하기 위한 비선형 해법을 제시하였다. PSC 교량 구조물의 비선형 거동 및 극한거동을 예측하기 위한 해법으로서 하중제어법(load control strategy)과 변위제어법(displacement control strategy)을 적용하였다. 콘크리트의 과다한 균열과 재료상태 및 케이블 장력의 급격한 변화로 인해 불평형력(unbalanced load)이 크게 변화하여 이들 두 해법으로 해를 구할 수 없는 경우에 대한 대안으로서 불평형력을 적정한 비율로 감소시키면서 하중제어 법을 적용하여 해를 안정적으로 구해 나가는 불평형력 감쇠(scale-down of the unbalanced load)를 적용한 하중제어법을 제시하였다. PSC 거더교의 극한해석을 수행하여 불평형력 감쇠를 적용한 하중제어법의 정당성을 평가하였다. 또한 곡선 PSC 사장교의 극한해석에 이 논문에서 제시한 비선형 해법을 적용하여 복잡한 비선형성으로 인해 해가 수렴하기 어려운 해석에도 이 해법이 유용함을 확인하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 가을 학술발표회 논문집
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• pp.389-396
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• 1999

In this study compressive and tensile load tests have been performed to investigate reinforcing effect and load transfer mechanism of small diameter piles installed in the foundation soil for the marine suspension bridge. Load tests were carried out on steel plate with diameters of 50cm, 100cm and 150cm varying loads starting from 39 tons up to 314 tons. Small diameter piles were proved to behavior like as friction piles and loads were not transmitted to the bottom of piles. From pull-out tests, the uplift capacity of small diameter piles was largely influenced by reinforcing materials compared to frictional resistance between piles and adjacent soils. The bearing capacity of small diameter piles appeared to be higher than the ultimate bearing capacity evaluated using static formulae. The load carrying capacity of small diameter piles was superior to the bored piles with a similar size. Thus, ultimate bearing capacity estimated from static formulae can provide conservative designs and thereby resulting in economic disadvantages. A further study to accumulate data regarding various soil conditions is recommended for an improved estimation of bearing capacity of piles with small diameter.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.417-430
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• 2017

Ultra high performance concrete (UHPC) has aroused interest around the world owing to superior mechanical and durability properties over conventional concrete. However, the application of UHPC in practice poses difficulties due to its inherent brittleness. UHPC filled in steel tube columns (UHPC-FSTCs) are capable of restricting the brittle failure of non-reinforced UHPC columns and forming a high performance member with enhancement of strength and ductility. Currently, research on UHPC-FSTCs remains very limited and there is relatively little information about the mechanical behavior of these columns. Therefore, this study presents a review of past experimental studies to have a deeper insight into the compressive behavior of UHPC-FSTCs under axial loading on entire section and on concrete core. Based on the test results obtained from Schneider (2006) and Xiong (2012), an analysis was conducted to investigate the influence of the confinement index (${\xi}$) and diameter to steel tube thickness ratio (D/t) on the strength and the ductility in short circular UHPC-FSTCs. Furthermore, the appropriateness of current design codes including EC4, AISC, AIJ and previous analytical models for estimating the ultimate loads of composite columns was also examined by the comparison between the predictions and the test results. Finally, simplified formulae for predicting the ultimate loads in two types of loading pattern were proposed and verified.

• Structural Engineering and Mechanics
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• 제51권5호
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• pp.847-866
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• 2014

This paper describes a formulation to predict optimum post-tensioning forces and cable dimensioning for self-anchored cable-stayed suspension bridges. The analysis is developed with respect to both dead and live load configurations, taking into account design constrains concerning serviceability and ultimate limit states. In particular, under dead loads, the analysis is developed with the purpose to calculate the post-tensioning cable forces to achieve minimum deflections for both girder and pylons. Moreover, under live loads, for each cable elements, the lowest required cross-section area is determined, which verifies prescriptions, under ultimate or serviceability limit states, on maximum allowable stresses and bridge deflections. The final configuration is obtained by means of an iterative procedure, which leads to a progressive definition of the stay, hanger and main cable characteristics, concerning both post-tensioning cable stresses and cross-sections. The design procedure is developed in the framework of a FE modeling, by using a refined formulation of the bridge components, taking into account of geometric nonlinearities involved in the bridge components. The results demonstrate that the proposed method can be easily utilized to predict the cable dimensioning also in the framework of long span bridge structures, in which typically more complexities are expected in view of the large number of variables involved in the design analysis.

• Nuclear Engineering and Technology
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• 제45권4호
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• pp.469-476
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• 2013

In a postulated severe core damage accident in a PHWR, multiple failures of core cooling systems may lead to the collapse of pressure tubes and calandria tubes, which may ultimately relocate inside the calandria vessel forming a terminal debris bed. The debris bed, which may reach high temperatures due to the decay heat, is cooled by the moderator in the calandria. With time, the moderator is evaporated and after some time, a hot dry debris bed is formed. The debris bed transfers heat to the calandria vault water which acts as the ultimate heat sink. However, the questions remain: how long would the vault water be an ultimate heat sink, and what would be the failure mode of the calandria vessel if the heat sink capability of the reactor vault water is lost? In the present study, a numerical analysis is performed to evaluate the thermal loads and the stresses in the calandria vessel following the above accident scenario. The heat transfer from the molten corium pool to the surrounding is assumed to be by a combination of radiation, conduction, and convection from the calandria vessel wall to the vault water. From the temperature distribution in the vessel wall, the transient thermal loads have been evaluated. The strain rate and the vessel failure have been evaluated for the above scenario.

• Steel and Composite Structures
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• 제38권3호
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• pp.319-336
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• 2021

To achieve a rational detail of the girder-abutment joints in composite integral bridges, and validate the performance of the joints with perfobond connectors, this paper proposes two innovative types of I-shaped steel girder-concrete abutment joints with perfobond connectors intended for the most of bearing capacity and the convenience of concrete pouring. The major difference between the two joints is the presence of the top flange inside the abutments. Two scaled models were investigated with tests and finite element method, and the damage mechanism was revealed. Results show that the joints meet design requirements no matter the top flange exists or not. Compared to the joint without top flange, the initial stiffness of the one with top flange is higher by 7%, and the strength is higher by 50%. The moment decreases linearly in both types of the joints. At design loads, perfobond connectors take about 70% and 50% of the external moment with and without top flange respectively, while at ultimate loads, perfobond connectors take 53% and 26% of the external moment respectively. The ultimate strengths of the reduced sections are suggested to be taken as the bending strengths of the joints.

• Earthquakes and Structures
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• 제22권3호
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• pp.319-330
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• 2022

Retrofit of soft-story buildings due to seismic loads using Gap-Inclined-Brace (GIB) system is considered a new retrofit technique that aims to maintain both strength and stiffness of structure. In addition, it provides more ductility and less P-delta effect, and subsequently better performance is observed. In this paper, the effect of the eccentricity between GIB and the retrofitted column due to installation on the efficiency of the retrofitting system is studied. In addition, a modification in the determination method of GIB properties is introduced to reduce the eccentricity effect. Also, the effect of GIB system on the seismic response of mid-rise buildings with different heights considering soft-story at various heights has been studied. A numerical model is developed to study the impact of such system on the response of retrofitted soft-story buildings under the action of seismic loads. To achieve that goal, this model is used to perform a numerical investigation, by considering five case study scenarios represent several locations of soft-story of two mid-rise reinforced concrete buildings. At first, Non-linear static pushover analysis was carried out to develop the capacity curves for case studies. Then, Non-linear time history analyses using ten earthquake records with five peak ground accelerations is performed for each case study scenario before and after retrofitting with GIB. The results show that large GIB eccentricity reduce the ultimate lateral resistance and deformation capacity of the retrofitting system. Moreover, the higher the retrofitted building, the more deformation capacity is observed but without significant increase in ultimate lateral resistance.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.255-258
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• 2005

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally bonded prestressed CFRP (Carbon Fiber Reinforced Polymer) strips. A total of 7 specimens have been manufactured of which specimens strengthened with bonded CFRP strips considering the level of prestress as experimental variable, and a specimen with simply bonded CFRP strips. The following phenomena have been observed through the experimental results. The specimen with simply bonded CFRP strips failed below 50$\%$ of its tensile strength due to premature debonding. On the other hand, all the specimens strengthened with prestressed CFRP strips showed sufficient strengthening performance up to the ultimate rupture load of the CFRP strips. Also, it was observed that the cracking loads and yield loads of the strengthened beams were increased proportionally to the prestress level, but the maximum loads were nearly equal regardless of the prestress level.