• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.43-52
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• 2015

Constructions of buildings downtown are increasing as much as ever with a strong demand. Top-Down Method is suitable for its advantage in minimizing its disturbance to the neighborhood. Pre-founded when applied to CFT Column on-site welded is required for splicing. To complement the welded built-up square composite Column was developed. Top-down process will be pouring concrete in accordance with a step-by-step process. Thus, Pre-founded Column and cover concrete to determine the stress condition. Therefore, Concrete filled steel square tubular columns encased with precast concrete were studied. Five Centrally loaded Columns were tested to investigate the axial load carrying capacity. we analyzed the strength and behavior of CET Column by Loading conditions and concrete strength, thickness of cover concrete through structure experiments.

• Steel and Composite Structures
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• v.20 no.2
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• pp.251-266
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• 2016

The paper combines two distinct parts. First the behavior of welded headed studs with small diameters of 10 and 13 mm acting as shear connectors (which are not embraced in current standards) is studied. Based on standard push tests the load-slip relationships and strengths are evaluated. While the current standard (Eurocode 4 and AISC) formulas used for such studs give reasonable but too conservative strengths, less conservative and full load-slip rigidities are evaluated and recommended for a subsequent investigation or design. In the second part of the paper the partially encased beams under bending are analyzed. Following former experiments showing rather indistinct role of studs used for shear connection in such beams their role is studied. Numerical model employing ANSYS software is presented and validated using former experimental data. Subsequent parametric studies investigate the longitudinal shear between steel and concrete parts of the beams with respect to friction at the steel and concrete interface and contribution of studs with small diameters required predominantly for assembly stages (concreting). Substantial influence of the friction and effect of concrete confinement was observed with rather less noticeable contribution of the studs. Distribution of the longitudinal shear and its sharing between friction and studs is presented with concluding remarks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.1 no.2
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• pp.141-149
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• 1997

The major objects of this study is to investigate experimentally the strengthening effects and post-failure behavior of reinforced concrete beam-columns with enlarged sections. Tests are carried out to evaluate the influences of axial load intensities, thickness of encased steel plates and reinforcing bars in the grouted parts on the structural behavior of the specimens. The test results show that the amount of reinforcing bars and thickness of steel plate significantly affect on the structural behavior. The ultimate moment capacities of reinforced concrete beam-columns encased with 2mm-thick steel plate are significantly increased to about 10 times of those of unstrengthened specimens.

• Steel and Composite Structures
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• v.14 no.5
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• pp.493-509
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• 2013

Bending behavior of reinforced concrete slabs encased over shallow I-sections at different levels of compression heads were investigated in present study. 1500 mm long I-sections were used to create composite slabs. Compression heads of monolithic experimental members were encased at different levels into the concrete slabs. Shear connections were welded over some of the I-sections. The testing was carried out in accordance with the principles of four-point loading. Results revealed decreasing load bearing and deflection capacities of composite beams with increasing encasement depths into concrete. Mechanical properties of concrete and reinforcing steel were also examined. Resultant stresses calculated for composite beams at failure were found to be less than the yield strength of steel beams. Test results were discussed with regard to shear and slip effect.

• Steel and Composite Structures
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• v.36 no.3
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• pp.261-272
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• 2020

A novel precast concrete-encased steel composite beam, which can be abbreviated as PCES beam, is introduced in this paper. In order to investigate the shear behavior of this PCES beam, a test of eight full-scale PCES beam specimens was carried out, in which the specimens were subjected to positive bending moment or negative bending moment, respectively. The factors which affected the shear behavior, such as the shear span-to-depth aspect ratio and the existence of concrete flange, were taken into account. During the test, the load-deflection curves of the test specimens were recorded, while the crack propagation patterns together with the failure patterns were observed as well. From the test results, it could be concluded that the tested PCES beams could all exhibit ductile shear behavior, and the innovative shear connectors between the precast concrete and cast-in-place concrete, namely the precast concrete transverse diaphragms, were verified to be effective. Then, based on the shear deformation compatibility, a theoretical model for predicting the shear capacity of the proposed PCES beams was put forward and verified to be valid with the good agreement of the shear capacities calculated using the proposed method and those from the experiments. Finally, in order to facilitate the preliminary design in practical applications, a simplified calculation method for predicting the shear capacity of the proposed PCES beams was also put forward and validated using available test results.

• Journal of Korean Society of Steel Construction
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• v.25 no.2
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• pp.209-222
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• 2013

Eccentric axial loading test was performed for concrete-encased columns using 800MPa steel and 100MPa concrete. To maximize the contribution of the high-strength steel, L-shaped steel sections were placed at four corners, and connected to each other by lattices, links, or battens. Compared to a H-section of the same area, the moment-arm and strain of the L-sections are increased. Also, the corner L-sections provide good lateral confinement to concrete core. The test results showed that the peak strength and effective flexural stiffness of the L-section columns were increased by more than 1.4 times those of the H-section column.

• Computers and Concrete
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• v.31 no.3
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• pp.253-265
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• 2023

In this research, the gene expression programming (GEP) technique was employed to provide a new model for predicting the maximum loading capacity of concrete-encased steel (CES) columns. This model was developed based on 96 CES column specimens available in the literature. The six main parameters used in the model were the compressive strength of concrete (f_c), yield stress of structural steel (f_ys), yield stress of steel rebar (f_yr), and cross-sectional areas of concrete, structural steel, and steel rebar (A_c, A_s and A_r respectively). The performance of the prediction model for the ultimate load-carrying capacity was investigated using different statistical indicators such as root mean square error (RMSE), correlation coefficient (R), mean absolute error (MAE), and relative square error (RSE), the corresponding values of which for the proposed model were 620.28, 0.99, 411.8, and 0.01, respectively. Here, the predictions of the model and those of available codes including ACI ITG, AS 3600, CSA-A23, EN 1994, JGJ 138, and NZS 3101 were compared for further model assessment. The obtained results showed that the proposed model had the highest correlation with the experimental data and the lowest error. In addition, to see if the developed model matched engineering realities and corresponded to the previously developed models, a parametric study and sensitivity analysis were carried out. The sensitivity analysis results indicated that the concrete cross-sectional area (A_c) has the greatest effect on the model, while parameter (f_yr) has a negligible effect.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.31-42
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• 2014

In this paper, concrete-filled steel tubular columns encased with precast reinforced concrete were studied. Four eccentrically loaded columns and a concentrically loaded column were tested to investigate the axial load-carrying capacity. The test parameters were the use of fiber reinforcement for cover concrete, eccentricity, column length, and lateral reinforcement. The maximum axial loads of the specimens agreed with the nominal strengths predicted by KBC 2009. However, in some specimens, the load carrying capacity quickly decreased after the peak strength due to spalling of the cover concrete.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.747-757
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• 2004

With steel and concrete composite beams, the incomplete interaction between the steel and the concrete slab leads to an appreciable increase in beam deflections. Moreover, encased composite beams using a deep deck plate or hollow-core PC slabs are critical to deflection due to their inherent geometry. In this paper, by using the calculation tools that were developed for a previous study on the deflection of encased composite beams considering the slip effects and load-slip curve, the shear bond stress and additional deflection induced due to interface slip of the encased composite beam are presented. It was found that the slip effects significantly contribute to the encased composite beam deflections and result in stiffness reduction of up to 30% compared to that of full shear interaction beams. The predicted results were compared with the measurement of 18 specimens tested in this study, and comparisons show a high degree of accuracy, within 6%.

• Steel and Composite Structures
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• v.52 no.2
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• pp.121-134
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• 2024

To investigate the compressive behavior of partially encased recycled aggregate concrete (PERAC) stub columns after exposed to elevated temperatures, 22 specimens were tested. The maximum temperature suffered, the replacement ratio of recycled coarse aggregate (RCA), the endurance time and the spacing between links were considered as the main parameters. It was found that the failure mode of post-heated PERAC columns generally matched that of traditional partially encased composite (PEC) columns, but the flange of specimens appeared premature buckling after undergoing the temperature of 400℃ and above. Additionally, the ultimate strength and ductility of the specimens deteriorated with the elevated temperatures and extended heating time. When 400℃< T ≤ 600℃, the strength reduction range is the largest, about 11% ~ 17%. The higher the replacement ratio of RCA, the lower the ultimate strength of specimens. At the temperature of 600℃, the ultimate strength of specimens with the RCA replacement ratio of 50% and 100% is 0.94 and 0.91 times than that of specimens without RCA, respectively. But the specimen with 50% replacement ratio of RCA showed the best ductility performance. And the bearing capacity and ductility of PERAC stub columns were changed for the better due to the application of links. When the RCA replacement ratio is 100%, the ultimate strength of specimens with the link spacing of 100 mm and 50 mm increased 14% and 25% than that of the specimen without links, respectively. Based on the results above, a formula for calculating the ultimate strength of PERAC stub columns after exposure to high temperatures was proposed.