• Steel and Composite Structures
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• v.16 no.3
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• pp.253-267
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• 2014

Based on the test on a 1/2.5-scaled model of a two-bay and three-story inner frame composed of reinforced concrete beams and lattice steel reinforced concrete (SRC) irregular section columns under low cyclic reversed loading, the failure process and the features of the frame were observed. The subsequence of plastic hinges of the structure, the load-displacement hysteresis loops and the skeleton curve, load bearing capacity, inter-story drift ratio, ductility, energy dissipation and stiffness degradation were analyzed. The results show that the lattice SRC inner frame is a typical strong column-weak beam structure. The hysteresis loops are spindle-shaped, and the stiffness degradation is insignificant. The elastic-plastic inter-story deformation capacity is high. Compared with the reinforced concrete frame with irregular section columns, the ductility and energy dissipation of the structure are better. The conclusions can be referred to for seismic design of this new kind of structure.

• Journal of the Korean Society for Railway
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• v.10 no.5
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• pp.600-606
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• 2007

3D finite element analyses of a corrugated steel web girder and a steel truss web girder are conducted to investigate the static and dynamic behaviour of the hybrid girders. And the analyses results are compared with those by the equivalent beam theory. The equivalent theory is a theory that all section properties of a truss structure are replaced by section properties of a beam including a shear coefficient. When applying the equivalent beam theory, the shear coefficient of the corrugated steel web girder is estimated as the area ratio of flange section to web section and that of the steel truss web girder is calculated by the equation proposed by Abdel. Static deflections and natural frequencies by 3D finite element analyses and those by the equivalent beam theory are in good agreement.

• Computers and Concrete
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• v.29 no.6
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• pp.393-405
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• 2022

Lightweight concrete is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of lightweight fiber reinforced concrete beams. The main aim of the present study is to investigate the optimum usage of steel fibers in lightweight fiber reinforced concrete (LWFRC). Multi-scale finite element model calibrated with experimental results is developed to study the effect of steel fibers on the mechanical properties of LWFRC beams. To decrease the amount of steel fibers, it is preferred to reinforce only the middle section of the LWFRC beams, where the flexural stresses are higher. For numerical simulation, a multi-scale finite element model was developed. The cement matrix was modeled as homogeneous and uniform material and both steel fibers and lightweight coarse aggregates were randomly distributed within the matrix. Considering more realistic assumptions, the bonding between fibers and cement matrix was considered with the Cohesive Zone Model (CZM) and its parameters were determined using the model update method. Furthermore, conformity of Load-Crack Mouth Opening Displacement (CMOD) curves obtained from numerical modeling and experimental test results of notched beams under center-point loading tests were investigated. Validating the finite element model results with experimental tests, the effects of fibers' volume fraction, and the length of the reinforced middle section, on flexural and residual strengths of LWFRC, were studied. Results indicate that using steel fibers in a specified length of the concrete beam with high flexural stresses, and considerable savings can be achieved in using steel fibers. Reducing the length of the reinforced middle section from 50 to 30 cm in specimens containing 10 kg/m3 of steel fibers, resulting in a considerable decrease of the used steel fibers by four times, whereas only a 7% reduction in bearing capacity was observed. Therefore, determining an appropriate length of the reinforced middle section is an essential parameter in reducing fibers, usage leading to more affordable construction costs.

• Earthquakes and Structures
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• v.16 no.1
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• pp.97-107
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• 2019

The frame structures investigated in this paper is composed of Concrete encased columns with L-shaped steel section and steel beams. The seismic behavior of this structural system is studied through experimental and numerical studies. A 2-bay, 3-story and 1/3 scaled frame specimen is tested under constant axial loading and cyclic lateral loading applied on the column top. The load-displacement hysteretic loops, ductility, energy dissipation, stiffness and strength degradation are investigated. A typical failure mode is observed in the test, and the experimental results show that this type of framed structure exhibit a high strength with good ductility and energy dissipation capacity. Furthermore, finite element analysis software Perform-3D was conducted to simulate the behavior of the frame. The calculating results agreed with the test ones well. Further analysis is conducted to investigate the effects of parameters including concrete strength, column axial compressive force and steel ratio on the seismic performance indexes, such as the elastic stiffness, the maximum strength, the ductility coefficient, the strength and stiffness degradation, and the equivalent viscous damping ratio. It can be concluded that with the axial compression ratio increasing, the load carrying capacity and ductility decreased. The load carrying capacity and ductility increased when increasing the steel ratio. Increasing the concrete grade can improve the ultimate bearing capacity of the structure, but the ductility of structure decreases slightly.

• Journal of the Korean Society of Safety
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• v.20 no.3 s.71
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• pp.188-196
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• 2005

Accident reports from 1991 to 2000 of a steel company were used to analyze which factors induce industrial accidents. The subjects were 8,311 blue-collar workers, who sustained 114 occupational injuries and work on a continuous full-day 3-team 3-shift system of backward rotation(mornings to afternoons to nights). With respect to marital status, the occupational injury rate(OIR) on the married workers was significantly higher compared to unmarried workers. With respect to no, the OIR of those in their early 20s was significantly higher when compared to other age groups. The OIR of highly educated workers showed a reduction when compared with lower educated workers. The OIR of shift workers were significantly higher compared with the daytime workers. The OIR of type of work decreased across the steel manufacturing process, rolling process, machine maintenance section forwarding products section to the field management section. With respect to the block of shift work(morning, afternoon, and night shifts) by the type of work, the OIR of the night shift was higher than those of the morning shift in the steel manufacturing process or forwarding products section. The OIR of the machine maintenance section was slightly higher in the morning shift than those of the night shift. The OIR of the time of day of the shift workers reached a peak between 09:00 and 11:00. The OIR of a slight injury to shift workers decreased across the night, afternoon, to morning shifts whereas the OIR of a serious injury tended to decrease across the night, morning, to afternoon shift. The body parts most commonly injured were the arm and the crus.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.185-186
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• 2021

In Korea, many buildings are built with underground spaces and cast-in-place pile method is mostly applied in the temporary retaining walls for the underground space construction. A H-shaped steel section is generally embedded in the soldier pile in the C.I.P method. In this study, a new and economical section with high strength steel replacing the H-shaped section was proposed and its flexural capacity was evaluated experimentally. The new section is the concrete-filled composite section with pentagonal thin plate and thick flange plate. Test results showed that the proposed section has an excellent flexural strength and ductility.

• Steel and Composite Structures
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• v.15 no.2
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• pp.131-150
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• 2013

This paper presents the experimental results of axially loaded stub columns of slender steel hollow square section (SHS) strengthened with carbon fiber reinforced polymers (CFRP) sheets. 9 specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the CFRP sheet orientation. From the tests, it was observed that two sides would typically buckle outward and the other two sides would buckle inward. A maximum increase of 33% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 100 transversely. Also, stiffness and ductility index (DI) were compared between un-retrofitted specimens and retrofitted specimens. Finally, it was shown that the application of CFRP to slender sections delays local buckling and subsequently results in significant increases in elastic buckling stress. In the last section, a prediction formula of the ultimate strength developed using the experimental results is presented.

• Steel and Composite Structures
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• v.4 no.1
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• pp.49-75
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• 2004

The paper derives, validates and illustrates the application of GBT-based formulae to estimate distortional critical lengths and bifurcation stress resultants in cold-formed steel rack-section columns, beams and beam-columns with arbitrarily inclined mid-stiffeners and four support conditions. After a brief review of the Generalised Beam Theory (GBT) basics, the main concepts and procedures employed to obtain the formulae are addressed. Then, the GBT-based estimates are compared with exact results and, when possible, also with values yielded by formulae due to Lau and Hancock, Hancock and Teng et al. A few remarks on novel aspects of the rack-section beam-column distortional buckling behaviour, unveiled by the GBT-based approach, are also included.

• Structural Engineering and Mechanics
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• v.10 no.5
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• pp.479-489
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• 2000

Based on the stiffness equation of the tapered beam element involving the effects of axial force and shear deformation, numerical investigations are carried out on elastic instability for web-linearly tapered columns with I-section of steel portal frames. Effects of shear deformation on the effective length of the tapered columns with I-section are studied. An efficient approach for determining the effective length of the tapered portal frame columns considering effects of shear deformation is proposed.

• Journal of Korean Society of Steel Construction
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• v.27 no.2
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• pp.219-229
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• 2015

An experimental study was performed for thin-walled rectangular concrete-filled tubular (CFT) columns. The present study mainly focused on evaluation of the axial load-carrying capacity of concrete-filled tubular columns using high-strength steel and slender section. The test parameters were width-to-thickness ratio, concrete strength, steel yield strength, and the use of stiffeners. Five specimens were tested under monotonic axial loading. Although elastic local buckling occurred in the slender-section specimens with high-strength steel, the specimens exhibited considerable post-buckling reserve. The test results also satisfied the predictions of a current design code. The specimens strengthened with vertical stiffeners exhibited improved strength and ductility when compared with the un-stiffened specimens.