• Steel and Composite Structures
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• v.16 no.1
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• pp.97-114
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• 2014

This paper deals with a study on ultimate strength behaviour of eccentrically loaded CFT columns with and without shear connectors. Thirty specimens are subjected to experimental investigation under eccentric loading condition. P-M curves are generated for all the test specimens and critical eccentricities are evaluated. Three different D/t ratios such as 21, 25 and 29 and L/D ratios varying from 5 to 20 are considered as experimental parameters. Six specimens of bare steel tubes as reference specimens, twelve specimens of CFT columns without shear connectors and twelve specimens of CFT columns with shear connectors, in total thirty specimens are tested. The P-M values at the ultimate failure load of experimental study are found to be well agreed with the results of the proposed P-M interaction model. The load-deflection and load-strain behaviour of the experimental column specimens are presented. The behaviour of the CFT columns with and without shear connectors is compared. Experimental results indicate that the percentage increase in load carrying capacity of CFT columns with shear connectors compared to the ordinary CFT columns is found to be insignificant with a value ranging from 6% to 13%. However, the ductility factor of columns with shear connectors exhibit higher values than that of the CFT columns without shear connectors. This paper presents the proposed P-M interaction model and experimental results under varying parameters such as D/t and L/D ratios.

• Fire Science and Engineering
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• v.24 no.6
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• pp.104-111
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• 2010

The strength of steel in a concrete filled steel tube (CFT) is reduced in a fire, but the concrete filled structurally ensures the fire resistance due to its high thermal capacity. This research analyzed the fire resistance performance due to the variances of concrete strength filled inside of steel tube and the load ratios, which can influence on the fire resistance of CFT. As $280{\times}280{\times}6$ CFT columns with the concrete strengths of 24 MPa and 40 MPa and the axial load ratios of 0.9, 0.6, and 0.2 in accordance with KS F 2257-1 and 7 were heated with loading to examine the fire resistance performance, the fire resistance used to 24 MPa concrete showed 27, 113, and 180 minutes according to the axial load ratios, 0.9, 0.6, and 0.2 respectively. In case of 40 MPa concrete, the fire resistance were turned out to be 19 and 28 minutes for the axial load ratios, 0.9 and 0.6 respectively. The results of fire resistance with 40 MPa concrete showed the much lower fire resistance performance than those of 24 MPa concrete. In case of 40 MPa, the fire resistance performance was not increased significantly according to the axial load ratio than that of 24 MPa. The main reason why the higher concrete strength showed lower fire resistance than that of lower guessed the internal stress had the concrete strength weak.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.589-596
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• 2002

In this study, static pile load tests with load transfer measurement were accomplished in the field. Yield pile capacity (or ultimate pile capacity) determined by load-settlement-time relationship was determined and axial load transfer behavior was analyzed. In the test for the four test piles were behaved as end bearing pile but ratios of skin friction to total pile capacity were 27%∼33%.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2010.04a
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• pp.371-376
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• 2010

The strength of steel material in a concrete filled steel tube (CFT) is reduced in fire, but the filled interior concrete structurally ensures the fire resistance due to its high thermal capacity. More, the contractibility of CFT is excellent since it can be constructed without form work. This research analyzed the interior concrete strength and deformation characteristics, which are the influence factors of the fire resistance of CFT, in proportion to the axial load ratio. The fire resistance performance according to changes of the axial load ratio showed great fluctuation. As $280{\times}280{\times}6$ CFT columns with the concrete strengths of 24 MPa and 40 MPa and the axial load ratios of 0.9, 0.6, and 0.2 in accordance with KS F 2257-1 and 7 were heated with loading to examine the fire resistance performance, the 24 MPa concrete exhibited the fire resistance time as 27, 113, and 180 minutes for the axial load ratios, 0.9, 0.6, and 0.2 respectively. In case of 40 MPa concrete, the fire resistance time were turned out to be 19 and 28 minutes for the axial load ratios, 0.9 and 0.6 respectively. The results of 40 MPa concrete showed the much lower fire resistance performance when comparing with those of 24 MPa concrete. The fire resistance performance was not increased significantly when the axial load ratio was reduced. Therefore, the deceased fire resistance performance of high strength concrete is assumed to be caused by the internal pressure increase upon the heat application.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.167-172
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• 1992

To analyze the effects compressive strength of concrete and longitudinal steel ratio on second-order moment of columns, 30tied rein reinforced concrete columns with hinged ends were tested. The 80mm square cross section was used and the amount of eccentricity was 24mm. The compressive strengths of column specimens with slenderness ratios of 10, 60, and 100were 250, 648 and 880kg/$\textrm{cm}^2$, and the longitudinal steel ratios were 1.98%(4-D6) and 3.95%(8-D6). The ratio of ultimate load capacity to that of short column with the same eccentricity (Pu/Pn) was much decreased at high slenderness ratio with increasing the compressive strength of concrete. And the lateral displacement of slender column at the ultimate load was decreased as the strength was increased. These are due to that at high slenderness ratio the load capacity and behavior of column are affected by flexural rigidity. And, it was also found that with increasing steel ratio, the value of Pu/Pn and the lateral displacement at the ultimate load were larger for the same slenderness ratio.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.33 no.9
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• pp.355-363
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• 1984

An ideal and an approximate eauivalent circuits of a face-mounted PZT piezoelectric transformer were introduced from the equivalent circuit taking into account the mechanical loss of a PZT piezoelectric disk vibrator. And several expressions for the resonant frequencies and for the voltage ratios were derived from the approximate circuit of the transformer. From the experiments on the vltage ratios regarding the frequency variation without load and on the load variation at resonant frequency, it was found that the voltage ratio increased with the increase of load resistance and decreased sharply with the slight deviation from the resonant frequency, and that no-load voltage ratio at the resonant frequency was proportional to the product of the mechanical quality factor and the square of the electromechanical coupling factor of the vibrator.

• Earthquakes and Structures
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• v.24 no.5
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• pp.365-375
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• 2023

Energy dissipation systems increase the energy dissipation capacity of buildings considerably. In this study, the effect of dampers on a typical 10-storey reinforced concrete structure with a ductile moment-resisting frame was investigated. In this context, 5 different models were created according to the calculation of the slip load and the positions of the dampers in the structure. Nonlinear time-history analyzes using 11 different earthquake acceleration records were performed on the models using the ETABS program. As a result of the analyses, storey displacements, energy dissipation ratios, drift ratios, storey accelerations, storey shears, and hysteretic curves of the dampers on the first and last storey and overturning moments are presented. In the study, it was determined that friction dampers increased the energy dissipation capacities of all models. In addition, it has been determined that positioning the dampers in the outer region of the structures and taking the base shear as a basis in the slip load calculation will be more effective.

• Wind and Structures
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• v.36 no.3
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• pp.149-160
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• 2023

Lightness and flexibility of membrane roofs make them very sensitive to any external load. One of the most important parameters that controls their behavior, especially under wind load is the sag/span ratio of edge cables. Based on the value of the pretension force in the edge cables and the horizontal projection of the actual area covered by the membrane, an optimized design range of cable sag/span ratios has been determined through carrying on several membrane form-finding analyses. Fully coupled fluid structure dynamic analyses of these membrane roofs are performed under wind load with several conditions using the CFD method. Through investigating the numerical results of these analyses, the behavior of membrane roofs with cables sag/span ratios selected from the previously determined optimized design range has been evaluated.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.958-964
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• 2001

It is difficult to apply a conventional selection guide for diffusers when the diffuser is installed in a perimeter zone, because the ADPI(Air Diffusion Performance Index) vs. T/L(Throw/Length) curve listed in conventional guide does not consider the perimetric heating load. The objective of this study is to evaluate the effect of the perimetric heating load on the ADPI and to propose a selection guide for proper diffuser when perimetric heating load exists. The velocity and temperature distributions and the ADPI value are obtained numerically with various heat load ratios and air flow rates. The ADPI values by numerical result were compared with existing experimental data to verify the method for evaluation of ADPI proposed in present study. In case of a high side wall diffuser, the ADPI decreased with increases of the flow rate on every heat load ratio of present study except 0.75. Also, the ADPI vs. T/L curves have been proposed for the heat load ratios of 0.25, 0.5, 0.75 to guarantee comport thermal environment when diffusers are installed in perimeter zone.

• Steel and Composite Structures
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• v.47 no.6
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• pp.709-728
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• 2023

Experimental and analytical studies were conducted to clarify the influencing mechanisms of the longitudinal reinforcement on performance of axially loaded Reinforced Concrete-Filled Steel Tube (R-CFST) short columns. The longitudinal reinforcement ratio was set as parameter, and 10 R-CFST specimens with five different ratios and three Concrete-Filled Steel Tube (CFST) specimens for comparison were prepared and tested. Based on the test results, the failure modes, load transfer responses, peak load, stiffness, yield to strength ratio, ductility, fracture toughness, composite efficiency and stress state of steel tube were theoretically analyzed. To further examine, analytical investigations were then performed, material model for concrete core was proposed and verified against the test, and thereafter 36 model specimens with four different wall-thickness of steel tube, coupling with nine reinforcement ratios, were simulated. Finally, considering the experimental and analytical results, the prediction equations for ultimate load bearing capacity of R-CFSTs were modified from the equations of CFSTs given in codes, and a new equation which embeds the effect of reinforcement was proposed, and equations were validated against experimental data. The results indicate that longitudinal reinforcement significantly impacts the behavior of R-CFST as steel tube does; the proposed analytical model is effective and reasonable; proper ratios of longitudinal reinforcement enable the R-CFSTs obtain better balance between the performance and the construction cost, and the range for the proper ratios is recommended between 1.0% and 3.0%, regardless of wall-thickness of steel tube; the proposed equation is recommended for more accurate and stable prediction of the strength of R-CFSTs.