• Steel and Composite Structures
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• v.45 no.6
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• pp.797-818
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• 2022

Steel-precast ultra-high-performance concrete (UHPC) composite beams with demountable high-strength friction-grip bolt (HSFGB) shear connectors can be used for accelerated bridge construction (ABC) and achieve excellent structural performance, which is expected to be dismantled and recycled at the end of the service life. However, no investigation focuses on the demountability and reusability of such composite beams, as well as the installation difficulties during construction. To address this issue, this study conducted twelve push-out tests to investigate the effects of assembly condition, bolt grade, bolt-hole clearance, infilling grout and pretension on the crack pattern, failure mode, load-slip/uplift relationship, and the structural performance in terms of ultimate shear strength, friction resistance, shear stiffness and slip capacity. The experimental results demonstrated that the presented composite beams exhibited favorable demountability and reusability, in which no significant reduction in strength (less than 3%) and stiffness (less than 5%), but a slight improvement in ductility was observed for the reassembled specimens. Employing oversized preformed holes could ease the fabrication and installation process, yet led to a considerable degradation in both strength and stiffness. With filling the oversized holes with grout, an effective enhancement of the strength and stiffness can be achieved, while causing a difficulty in the demounting of shear connectors. On the basis of the experimental results, more accurate formulations, which considered the effect of bolt-hole clearance, were proposed to predict the shear strength as well as the load-slip relationship of HSFGBs in steel-precast UHPC composite beams.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.747-756
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• 2008

The purpose of this paper is to investigate the effect of the important parameters on the transfer length during the dynamic flame cutting of tendon experimentally. The considered parameters were strand diameter, concrete cover thickness, stirrup, debonding strand and release method. Ten pretensioned concete beam specimens were cast and tested. Time history curves for the axial strain of tendon were measured by electrical resistance strain gauges mounted on the strands. Experimental results indicated that large dynamic shock effects occurred near cut-end during the sudden release. The prestressing forces are dependent on the parameters above considered. The ratio of residual prestressing forces of 12.7 mm strands is greater than 15.2 mm strands. Using debonding strand and gradual release are more efficient for applying prestressing forces.

• Journal of Ocean Engineering and Technology
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• v.37 no.6
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• pp.273-281
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• 2023

Recently, offshore structures for eco-friendly energy, such as wind and solar power, have been developed to address the problem of insufficient land space; in the case of energy generation, they are designed on a considerable scale. Therefore, the scalability of offshore structures is crucial. The Korea Research Institute of Ships & Ocean Engineering (KRISO) developed multi-linked floating offshore structures composed of floating bodies and connection beams for floating photovoltaic systems. Large-scale floating photovoltaic systems are mainly designed in a manner that expands through the connection between modules and demonstrates a difference in structural response with connection conditions. A fluid-structure coupled analysis was performed for the multi-linked floating offshore structures. First, the wave load acting on the multi-linked offshore floating structures was calculated through wave load analysis for various wave load conditions. The response amplitude operators (RAOs) for the motions and structural response of the unit structure were calculated by performing finite element analysis. The effects of connection conditions were analyzed through comparative studies of RAOs and the response's maximum magnitude and occurrence location. Hence, comparing the cases of a hinge connection affecting heave and pitch motions and a fixed connection, the maximum bending stress of the structure decreased by approximately 2.5 times, while the mooring tension increased by approximately 20%, confirmed to be the largest change in bending stress and mooring tension compared to fixed connection. Therefore, the change in structural response according to connection condition makes it possible to design a higher structural safety of the structural member through the hinge connection in the construction of a large-scale multi-linked floating offshore structure for large-scale photovoltaic systems in which some unit structures are connected. However, considering the tension of the mooring line increases, a safety evaluation of the mooring line must be performed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.875-881
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• 2013

The failure of a bolted joint owing to stress corrosion cracking (SCC) has been considered one of the most important structural integrity issues in a nuclear power plant. In this study, the failure possibility of bolting, which is used to support the steam generator of a pressurized water reactor, owing to SCC and brittle fracture was evaluated in accordance with guidelines proposed by the Electric Power Research Institute, which are called the Reference Flaw Factor method. For this evaluation, first, detailed finite element stress analyses were conducted to obtain the actual nominal stresses of bolting in which either service loads or bolt preloads were considered. Based on these nominal stresses, the structural integrity of bolting was addressed from the viewpoints of SCC and toughness. In addition, the accuracy of the EPRI Reference Flaw Factor for assessing bolting failure was investigated using finite element fracture mechanics analyses.

• Journal of Korean Society of Steel Construction
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• v.22 no.1
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• pp.67-74
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• 2010

The cases of collapse of greenhouses in rural areas have been increasing due to the unexpected heavy snow load. Studies on how to prevent the collapse of greenhouses are rare, however, and the damages are repeated annually. This studysuggests two reinforcing methods: the use of ahigh-strength tapered module, and the addition of a pre-tension tie. The high-strength tapered section is installed where the bending moment is maximum. The design of a plastic greenhouse is controlled by its strength rather than its deflection. The shape of a greenhouse resembles that of an arch system, but its actual structural behavior is the frame behavior, because it is non-continually composed of a curved element (a beam) and vertical elements (columns). This system is too weak and slender to resist a vertical load, because an external load is resisted by the moment rather than by axial force. In this study, a new method, the installation of a temporary tie at the junction of the arch and the column only during snow accumulation, is proposed. The tie changes the action of the greenhouse frame to an arch action. The arch action is more effective when the pre-tension force is applied in the tie, which results in a very strong temporary structural system during snowfall. As a result of using this high-strength tapered section, the combined strength ratio of what? decreased from 10% to 30%. In the case of the additional reinforcement with a tie, it was reduced by half.

• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.41-49
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• 2011

A long-span (more than 8m) plastic greenhouse is currently being used in farms due to its magnified benefits, such as the convenience of the farming equipment used, and the land usage efficiency. In this study, the reinforcing effects of the use of a pretension tie were shown. In a previous study, tests for a 6.5m single-span-type greenhouse announced by Rural Development Administration were carried out. The tests of symmetric and eccentrics now loading by the sun and wind were conducted for the 10.2m span with a ${\phi}48.1{\times}2.1$ section in this study, after which the load-deflection relationship was compared for the cases of reinforcement with a tie and without a tie. The results of the symmetric snow loading test showed that the strength increased by 68~93% in the case of the specimen with a tied arch. The failure mode of the specimen without a tie tended to be that with a sway failure mechanism, and that of the reinforcement specimens with a tie tended to be that with an arch buckling mechanism. The results of the eccentric snow loading test showed that the strength of the specimen with a tie increased by 10~20% compared to that of the specimen without a tie. For the failure mode of the latter, a combined failure mechanism was adapted, although the failure mode of the tied specimens tended to be that with an arch buckling mechanism.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.353-364
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• 2011

In a previous research performed by the authors, the allowable compressive stress coefficient (K) in pretensioned members with rectangular section at transfer was proposed based on strength design theory. In this study, a subsequent research of an enormous analysis was performed to determine the K factor for Tee and inverted Tee section members, considering the effect of section height (h), section type, amount of tendons ($A_{ps}$), and eccentricity ratio (e/h). Based on the analysis results, the allowable compressive stress coefficients (K) for Tee and inverted Tee section members at transfer were derived, which limit the maximum allowable stresses as 80% and 70% of the compressive strengths at the time of release for Tee section and inverted Tee section, respectively. And these were larger than the allowable stresses specified in domestic and other international codes. In order to verify the proposed equations, they were compared to the test results available in literature and other codes, which showed that the allowable stresses in domestic and international codes are unconservative for the cases with low eccentricity ratios while conservative for those with high eccentricity ratios. The proposed equations, however, estimate the allowable stresses of the Tee and inverted Tee section members reasonably close to test results.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.105-127
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• 1999

Application of the soil nailing method is continuously extended in maintaining stable excavations and slopes. Occasionally, however, ground anchor support system may not be used because of space limitations in urban excavation sites nearby the existing structures. In this case, soil nailing system with relatively short length of nails could be efficiently adopted as an alternative method. The general soil nailing support system, however, may result in excessive deformations particularly in an excavation zone of the existing weak subsoils. Pretensioning the soil nails then, could play important roles in reducing deformations mainly in an upper part of the nailed-soil excavation system as well as improving local stability. In the present study, the analytical procedure and design technique are proposed to evaluate maximum pretension force and stability of the pretensioned soil nailing system. Also proposed are techniques to determine the required thickness of a shotcrete facing and to estimate probability of a failure against the punching shear. The predicted results are compared with the limited measurements obtained from the excavation site constructed by using the pretensioned soil nails. Based on the proposed procedure and technique, effects of the radius of a influence circle and dilatancy angle on the thickness of a shotcrete facing, bonded length and safety factors are analyzed. In addition, effects of the reduction of deformations expected by pretensioning of the soil nails are examined in detail throughout an illustrative example and FLAC$^{2D}$ program analysis.s.