• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.113-120
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• 2005

The purpose of this study is to investigate the strength and ductility improvement of columns retrofitted by steel-fiber composite plate. Test specimens strengthened by three different materials - steel plate(SP), carbon fiber sheet(CF) and fiber-steel composite plate(CP) - were tested under cyclic lateral load with a constant axial load equal to $20\%$ of the axial compression capacity. The structural capacity of composite plate was good or better than that of other retrofitting materials. Test results from all retrofitted specimens showed that considerably higher retrofitting amount was required for strength enhancement. The ductility of retrofitted columns by composite plate was fairly improved. Also, energy ductility ratio was more effective than displacement ductility ratio for ductility estimation of retrofitted column.

• International Journal of High-Rise Buildings
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• v.9 no.2
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• pp.155-166
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• 2020

To connect exterior reinforced concrete (RC) columns with the steel belt truss, the gusset plates are welded to the steel plates embedded in the RC column. Then, the concrete around an embedded plate is very likely to be damaged by the heat input from a long-time (6 to 48 hours) welding of the embedded and gusset plates at a joint between RC columns and steel belt truss. However, very few studies have assessed the concrete damage caused by the welding heat between embedded and gusset plates, and no clear onsite solution has been found. In this paper, experimental tests have been carried out on 4 full-scale specimen to analyze the effect of long-time (about 6 hours) onsite welding (1-side welding and 3-side welding) between a gusset plate and an embedded plate in high strength concrete with compressive strength of 55 MPa and 80 MPa on RC columns. The effect of the long-time welding heat of embedded and gusset plates, which are used in real high-rise building construction sites, on concrete is analyzed in terms of the following three items: 1) temperature distribution, 2) pattern and characteristics of cracks, and 3) effect of the cracks on the compressive strength of RC column. Based on the experimental results, even though the heat input up to about 150? from the long-time onsite welding on the high-strength concrete column for the joint could result in concrete cracks in a radial form, it is found that the welding cracks have no effect on the axial stiffness and strength of the concrete column.

• Steel and Composite Structures
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• v.39 no.4
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• pp.367-381
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• 2021

Reinforced concrete (RC) columns can be strengthened by direct fastening of steel plates around a column, forming composite actions. This method can increase both the total load bearing area and the concrete confinement stress. To predict the axial load resistance of strengthened RC columns, the equivalent passive confinement stress of the stirrups and the steel jacket should be accurately quantified, which requires the stress in the stirrups and shear force in the connections to be first obtained. In this paper, parameters, i.e., the stress ratio of the stirrups and shear force ratio of steel plate connectors are utilized to quantify the stress of the stirrups and shear force in the connections. A mechanical model for determining the stress ratio of the stirrups and shear force ratio of steel plate connectors is proposed and validated using the experimental results in a previous study. The model is found to be robust. Subsequently, a parametric study is conducted and the optimum stress ratios of the stirrups and the optimum shear force ratios of connectors are proposed for engineering designs.

• Advances in concrete construction
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• v.1 no.2
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• pp.163-185
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• 2013

The use of post-compressed plates (PCP) to strengthen preloaded reinforced concrete (RC) columns is an innovative approach for alleviating the effects of stress-lagging between the original column and the additional steel plates. Experimental and theoretical studies on PCP-strengthened RC columns have been presented in our companion papers. The results have demonstrated the effectiveness of this technique for improving the strength, deformability and ductility of preloaded RC columns when subjected to axial or eccentric compression loading. An original and comprehensive design procedure is presented in this paper to aid engineers in designing this new type of PCP-strengthened RC column and to ensure proper strengthening details for desirable performance. The proposed design procedure consists of five parts: (1) the estimation of the ultimate load capacity of the strengthened column, (2) the design of the initial pre-camber displacement of the steel plate, (3) the design of the vertical spacing of the bolts, (4) the design of the bearing ends of the steel plates, and (5) the calculation of the tightening force of the bolts. A worked example of the design of a PCP-strengthened RC column is shown to demonstrate the application of the proposed design procedure.

• Steel and Composite Structures
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• v.25 no.3
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• pp.287-298
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• 2017

The present study aims to determine the structural response of full scaled rectangular columns under both of vertical and lateral loads using numerical methods. In the study, the composite columns considering full concrete filled circular steel tube (FCFRST) and concrete filled double-skin rectangular steel tube (CFDSRST) section types are numerically modelled using ANSYS software. Vertical and lateral loads are applied to models to assess the structural response of the composite elements. Also similar investigations are done for reinforced concrete rectangular (RCR) columns to compare the results with those of composite elements. The analyses of the systems are statically performed for both linear and nonlinear materials. In linear static analyses, both of vertical and lateral loads are applied to models as only one step. However in nonlinear analyses, while vertical loads are applied to model as only one step, lateral loads are applied to systems as step by step. The displacement and stress changes in some critical nodes and sections and contour diagrams are reported by graphs and figures. At the end of the study, it is demonstrated that the nonlinear models reveal more accurate result then those of linear models. Also, it is highlighted that composite columns provide more and more safety, ductility compared to reinforced concrete column.

• Steel and Composite Structures
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• v.6 no.4
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• pp.285-302
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• 2006

This paper describes the design and behaviour of cold-formed stainless steel slender circular hollow section columns. The columns were compressed between fixed ends at different column lengths. The investigation focused on large diameter-to-plate thickness (D/t) ratio ranged from 100 to 200. An accurate finite element model has been developed. The initial local and overall geometric imperfections have been included in the finite element model. The material nonlinearity of the cold-formed stainless steel sections was incorporated in the model. The column strengths, load-shortening curves as well as failure modes were predicted using the finite element model. The nonlinear finite element model was verified against test results. An extensive parametric study was carried out to study the effects of cross-section geometries on the strength and behaviour of stainless steel slender circular hollow section columns with large D/t ratio. The column strengths predicted from the parametric study were compared with the design strengths calculated using the American Specification, Australian/New Zealand Standard and European Code for cold-formed stainless steel structures. It is shown that the design strengths obtained using the Australian/New Zealand and European specifications are generally unconservative for the cold-formed stainless steel slender circular hollow section columns, while the American Specification is generally quite conservative. Therefore, design equation was proposed in this study.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.643-650
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• 2012

The limitation of the yield strength in reinforced concrete columns is given for the effective use of high-strength steel bar, because very high-strength steel bar does not yield while concrete fails in compression. In order to overcome this limitation, it is required to increase peak strain of the concrete. The objective of this study is to examine the confinement effect of plate type lateral reinforcement in reinforced concrete columns. From this experimental study, the reinforced concrete columns confined by plate type carbon fiber sheets showed higher compressive strength and peak concrete strain comparing to the unconfined columns. The confinement effect is higher when cross-sectional type is a circular one than a square one. Moreover, the confinement effect was also higher for circular type confinement. Based on this study, high-strength steel bars with strength exceeding 800 MPa can be effectively used for reinforced concrete columns confined by plate type lateral reinforcements.

• Steel and Composite Structures
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• v.41 no.5
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• pp.747-759
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• 2021

Built-up Double-I (BD-I) columns have been commonly used for mid-rise steel-frame structures in Iran. These columns consist of two hot rolled IPE sections which are connected by two cover plates and fillet welds. Until 2017, BD-I columns were employed in intermediate moment resisting frames (MRF) using welded flange plate (WFP) connections. To evaluate the seismic behavior of the connections, four samples were made and tested based on cyclic loading according to AISC 341-16. It was concluded that typical samples cannot satisfy the seismic provisions related to intermediate MRFs. In contrast, the proposed connections retrofitted with two-part external diaphragms were able to satisfy not only the seismic requirements related to intermediate MRFs but also those related to special MRFs according to AISC. The numerical modeling of these samples was performed using ABAQUS finite element software. This study compared the hysteresis moment-rotation curves, plastic strains, and behavior modes in both experimental samples and numerical models.

• Journal of the Korea Institute of Building Construction
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• v.13 no.3
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• pp.272-281
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• 2013

Concrete filled tube (CFT) columns, which consist of a steel tube filled with concrete, combine the benefits of the two materials. The steel tube provides a confining pressure to the concrete, while the local buckling of steel plate can be prevented by the concrete core. CFT columns also have a high fire resistance due to the heat storage effect of concrete under fire. For this reason, it is possible to develop CFT columns without fire protection measures. CFT columns without fire protection have many advantages, including quality control, cost reduction, better space efficiency and a shorter construction period. Due to these advantages, studies on the development of CFT columns without fire protection measures have been performed. However, CFT columns lose their bearing capacity under fire because the steel tube is exposed to the outside. As a result, the structure is collapsed, causing significant damage. In this research, we made a CFT column using high strength concrete (100 MPa) and high strength steel (800 MPa). We use steel fiber and nylon fiber with concrete to provide fire resistance. We perform the fresh concrete experiment and investigate the fire resistance of the CFT column (${\Box}400{\times}400{\times}15{\times}3000mm$) under loading. To investigate the effect of steel fiber on increasing fire resistance, we compare the fire resistance time according to the steel fiber. Through the test, it was found that the CFT specimen with steel fiber had better fire resistance performance than other cases.

• Steel and Composite Structures
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• v.19 no.5
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• pp.1299-1319
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• 2015

This paper presents a detailed parametric study, conducted using finite element tools to cover a range of several geometric and material parameters, on the behaviour of thin-walled partially encased composite (PEC) columns. The PEC columns studied herein are composed of thin-walled built-up H-shaped steel sections with concrete infill cast between the flanges. Transverse links are provided between the opposing flanges to improve resistance to local buckling. The parametric study is confined to eccentrically-loaded columns subjected to major axis bending only. The parameters that were varied include the overall column slenderness ratio (L/d), load eccentricity ratio (e/d), link spacing-to-depth ratio (s/d), flange plate slenderness ratio (b/t) and concrete compressive strength ($f_{cu}$). The overall column slenderness ratio was chosen to be the primary variable with values of 5, 10 and 15. Other parameters were varied within each case of L/d ratio. The effects of the selected parameters on the behaviour of PEC columns were studied with respect to the failure mode, peak axial load, axial load versus average axial strain response, axial load versus lateral displacement response, moment versus lateral displacement behaviour and the axial load-moment interaction diagram. The results of the parametric study are presented in the paper and the influences of each of the parameters investigated are discussed.