• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.3-11
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• 2002

A moment-curvature relationship to simulate the behavior of reinforced concrete (RC) columns under cyclic loading is introduced. Unlike previous moment-curvature models and the layered section approach, the unposed model takes into account the bond-slip effect by using a monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The pinching enact caused by axial force is considered with an assumption that the absorbing energy corresponding to any deformation level maintains constant regardless of the magnitude of applied axial force. The advantages of the proposed model, comparing tn layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures.. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed mood.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.2
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• pp.151-161
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• 1998

In this study, an attempt is made to apply the concept of fuzzy-bayesian theory to the integrity assessment of RC highway bridge, and uncertainty states are represented in terms of fuzzy sets which define several linguistic variables such as "very good", "good", "average", "poor", "very poor", etc. Especially, the concept of fuzzy conditional probability aids to derive a new reliability analysis which includes the subjective assessment of engineers without introducing any additional correction factors. The fuzzy concept are also used as reliability indexes for the condition assessment based on the proposed models, the proposed fuzzy theory-based approach with the results of visual inspection and extensive field load tests are applied to the integrity assessment of a new RC highway bridge, namely, Jichok bridge.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.4
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• pp.90-97
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• 1997

Field inspections and laboratory tests for 31 agricultural reservoirs in Kyungki province were performed to provide basic data for maintenance and rehabilitation of agricultural reservoirs and to evaluate structural degradation of agricultural reservoirs Results of the study are as follows : 1) From survey's results of embankments, signs of settlement and lateral movement are appeared in 17 reservoirs. Crest settlement of 20~80cm, downstream settlement of 10~90cm, and 20~160cm lateral movement of embankments are detected from settlement and movement analysis of 17 reservoirs. Crest and downstream settlements and lateral movement are greatly occurred in 20 ~ 40 years after embankment construction. 2) About 39% of total reservoirs shows seepage problems occurred in the lower part of berm and retaining wall located between embankment and spillway. Probability of seepage problems is higher at retaining wall than others. 3) Concrete strength estimated by Schmidt hammer in structures of reservoirs is a range of 100~l50kgf/$cm^2$ and average deviation of concrete strength is about l0kgf/$cm^2$. Strength difference$({\delta}S)$ between compressive strength estimated by Schmidt hammer and uniaxial compressive strength of concrete core is about $\pm$100kgf/$cm^2$. This difference is due to absence or presence of reinforced bar in concrete core, variable length of concrete core and limitation of Schmidt hammer. 4) About 68% of total reservoirs shows leaching, 58% alkali-aggregate reaction and 71 % abrasion/frost. Leaching, alkali-aggregate reaction and abrasion/frost occurred in most reservoirs when passed 10 years after construction of structure parts.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.29-36
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• 1987

In most of the structural members with initial cracks, the strength tends to decrease as the member size increases. This phenomenon is known as size effect. Among the structural materials of glass, metal or concrete, etc., concrete represents the size effect even without initial crack. According to the previous size effect law, the concrete member of very large size can resist little stress. Actually, however, even the large size member can resist some stress if there is no initial notch. This means that the fracture mechanism of very small or very large size member follows strength criterion, but the medium size member follows non-linear fracture mechanics (NLFM). In this study, the empirical models which are derived based on nonlinear fracture mechanics are proposed according to the regression analysis with the existing test data of large size specimens for uni-axial compression test, splitting tensile test and shear test of reinforced concrete beams.

• Structural Engineering and Mechanics
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• v.82 no.2
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• pp.173-189
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• 2022

This study presents an experimental and numerically study about the effects of fiber reinforcement ratio on the behavior of concrete-filled steel tubes (CFST) under dynamic impact loading. In literature have examined the behavior of GFRP and FRP wrapped strengthened CFST elements impact loads. However, since the direction of potential impact force isn't too exact, there is always the probability of not being matched the impact force of the area where the reinforced. Therefore, instead of the fiber textile wrapping method which strengthens only a particular area of CFST element, we used fiber-added concrete-filled elements which allow strengthening the whole element. Thus, the effect of fiber-addition in concrete on the behavior of CFST elements under impact loads was examined. To do so, six simply supported CFST beams were constructed with none fiber, 2% fiber and 10% fiber reinforcement ratio on the concrete part of the CFST beam. CFST beams were examined under two different impact loads (75 kg and 225 kg). The impactors hit the beam from a 2000 mm free fall during the experimental study. Numerical models of the specimens were created using ABAQUS finite element software and validated with experimental data. The obtained results such as; mid-span displacement, acceleration, failure modes and energies from experimental and numerical studies were compared and discussed. Furthermore, the Von Misses stress distribution of the CFST beams with different ratio of fiber reinforcements were investigated numerically. To sum up, there is an optimum amount limit of the fiber reinforcement on CFST beams. Up to this limit, the fiber reinforcement increases the structural performances of the beam, beyond that limit the fiber reinforcement decreases the performances of the CFST beam under transverse impact loadings.

• Earthquakes and Structures
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• v.22 no.5
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• pp.503-515
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• 2022

This paper presents the development of seismic fragility curves for a precast reinforced concrete bridge instrumented with a structural health monitoring (SHM) system. The bridge is located near an active seismic fault in the Dominican Republic (DR) and provides the only access to several local communities in the aftermath of a potential damaging earthquake; moreover, the sample bridge was designed with outdated building codes and uses structural detailing not adequate for structures in seismic regions. The bridge was instrumented with an SHM system to extract information about its state of structural integrity and estimate its seismic performance. The data obtained from the SHM system is integrated with structural models to develop a set of fragility curves to be used as a quantitative measure of the expected damage; the fragility curves provide an estimate of the probability that the structure will exceed different damage limit states as a function of an earthquake intensity measure. To obtain the fragility curves a digital twin of the bridge is developed combining a computational finite element model and the information extracted from the SHM system. The digital twin is used as a response prediction tool that minimizes modeling uncertainty, significantly improving the predicting capability of the model and the accuracy of the fragility curves. The digital twin was used to perform a nonlinear incremental dynamic analysis (IDA) with selected ground motions that are consistent with the seismic fault and site characteristics. The fragility curves show that for the maximum expected acceleration (with a 2% probability of exceedance in 50 years) the structure has a 62% probability of undergoing extensive damage. This is the first study presenting fragility curves for civil infrastructure in the DR and the proposed methodology can be extended to other structures to support disaster mitigation and post-disaster decision-making strategies.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.180-187
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• 1998

In this paper the attention is focused on the modeling of reinforced concrete(R/C) wall structures to check effectiveness and reliability of elasto-plastic analysis. A relatively simple and reliable wall model is investigated, which is suitable to be efficiently incorporated in a practical pushover analysis of R/C wall structural systems. Two types of analogous frames have been examined to the stress analysis of shear walls. One analogous frame is similar to the widely used wide-column model, the second analogous frame also is called truss model which includes vertical edge column and braces. Further studies are needed to apply to nonlinear seismic analysis of building structure with R/C shear walls.

• Computers and Concrete
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• v.26 no.2
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• pp.137-150
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• 2020

In this paper, the bending behavior of single-walled carbon nanotube-reinforced composite (CNTRC) laminated plates is studied using various shear deformation plate theories. Several types of reinforcement material distributions, a uniform distribution (UD) and three functionally graded distributions (FG), are inspected. A generalized higher-order deformation plate theory is utilized to derive the field equations of the CNTRC laminated plates where an analytical technique based on Navier's series is utilized to solve the static problem for simply-supported boundary conditions. A detailed numerical analysis is carried out to examine the influence of carbon nanotube volume fraction, laminated composite structure, side-to-thickness, and aspect ratios on stresses and deflection of the CNTRC laminated plates.

• Structural Engineering and Mechanics
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• v.39 no.2
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• pp.207-221
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• 2011

This paper aims to study the behavior of short reinforced concrete columns confined with external glass Fiber Reinforced Polymers (GFRP) sheets under eccentric loads. The experimental part of the study was achieved by testing 9 specimens under eccentric compression. Three eccentricity ratios corresponding to e/t = 0, 0.10, 0.50 in one direction of the column were used. Specimens were divided into three groups. The first group was the control one without confinement. The second group was fully wrapped with GFRP laminates before loading. The third group was wrapped under loading after reaching 75% of failure loads of the control specimens. The third group was investigated in order to represent the practical case of strengthening a loaded column with FRP laminates. All specimens were loaded until failure. The results show that GFRP laminates enhances both failure load and ductility response of eccentrically loaded column. Moreover, the study also illustrates the effect of confinement on the first crack load, lateral deformation, strain in reinforcement and failure pattern. Based on the analysis of the experimental results, a simple model has been proposed to predict the improvement of load carrying capacity under different eccentricity ratios. The predicted equation takes into consideration the eccentricity to cross section depth ratio, the ultimate strength of GFRP, the thickness of wrapping laminate, and the time of wrapping (before loading and under loading). A good correlation was obtained between experimental and analytical results.

• Computers and Concrete
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• v.18 no.1
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• pp.53-68
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• 2016

In this study, an investigation is made from the statics and economic aspects of the possibility of using the composite material ferrocement on the surfaces of squat cylindrical grain silos. For this purpose, the geometry of two model silos, each of height 5 m and diameter 5 m and 12.5 m, was designed. Five different reinforced plates of 10 and 20 mm thickness were produced to research the most suitable ferrocement plates to be used on the surface of these silos. Most durable reinforcement type for covering the silo surface was determined by pressure and bending tests. Grade 30 and Grade 55 steel plates were also considered for use in covering steel-coated silos. In the statics analysis performed with SAP2000, the least plate thicknesses needed for silos surfaced with Grade 30 and Grade 55 steel were found to be 6.20 mm and 4.70 mm respectively for silos of diameter 5 m, and 6.70 mm and 5.00 mm for silos of diameter 12.5 m. In the economic analysis, it was found that 20 mm thick Type 4 (with a wire diameter of 0.30 mm and a mesh aperture of $2mm{\times}2mm$ square type) reinforced ferrocement surfacing material was 5.6-6.1 times more economical than Grade 30 steel surfacing material and 4.4-4.7 times more economical than using Grade 55 steel. These results show that ferrocement can be used in place of steel from the point of view both of statics and economy.