• Structural Engineering and Mechanics
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• v.50 no.2
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• pp.163-180
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• 2014

Inaccurate predictions of effective stiffness for reinforced concrete (RC) columns having plain (undeformed) longitudinal rebars may lead to unsafe performance assessment and strengthening of existing deficient frames. Currently utilized effective stiffness models cover RC columns reinforced with deformed longitudinal rebars. A database of 47 RC columns (33 columns had continuous rebars and the remaining had spliced reinforcement) that were longitudinally reinforced with plain rebars was compiled from literature. The existing effective stiffness equations were found to overestimate the effective stiffness of columns with plain rebars for all levels of axial loads. A new approach that considers the contributions of flexure, shear and bond slip to column deflections prior to yielding was proposed. The new effective stiffness formulations were simplified without loss of generality for columns with and without lap-spliced plain rebars. In addition, the existing stiffness models for the columns with deformed rebars were improved while taking poor bond characteristics of plain rebars into account.

• 건축구조
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• v.19 no.4
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• pp.51-60
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• 2012

In recent years, BIM has been applied to many building projects. However, IFC, which is the core technology of data exchange in BIM, has not been used widely. In particular, IFC has almost never been used to represent rebars in RC structures. This is because the lack of understanding and utilization strategy for data model of IFC on rebars. The purpose of this study is to store and manage the data on rebars using IFC at the schematic design stage. For this, we investigated the data to represent rebars for RC members, such as beam, column, wall, and slab at the schematic design stage. And, we analyzed the data model of IFC on rebars at the schematic design stage. Based on these investigation and analysis on data, we proposed the strategy for utilization of the data model of IFC on rebars. Finally, for verification, we generated a sample IFC file to represent the rebars of a simple RC structure according to the proposed strategy and imported the sample IFC file into the software, which we developed for this study. Based on the results of the import, we concluded that the data on rebars can be stored and managed using the proposed strategy for utilization of the data model of IFC on rebars.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.636-639
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• 2004

Reinforced concrete structures have been used for a long time. However, corrosion problem in reinforcing steel is inevitable, which results in the degradation of performance and the shortening of the life of structures. To overcome such problems, FRP(Fiber Reinforced Polymer) rebars have been developed. Due to their corrosion resistance and their superior mechanical properties, FRP rebars are increasingly applied to concrete structures in other countries. To obtain the composite action between FRP rebars and concrete, sufficient bond between two materials must be secured. But, the behavior of FRP rebars is different from that of steel rebars. Therefore, it is necessary to understand and develop the proper bond mechanism of FRP rebars to use them in concrete structures. This paper presents analytical results to investigate the bond-slip relationship between FRP rebars and concrete based on pull out tests.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.323-326
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• 2005

Uniaxial tension test of Glass Fiber Reinforced Polymer (GFRP) bar reinforced concrete prisms was performed. The objective was to investigate the adequate cover thickness of the GFRP rebars. The tension stiffening effect of GFRP bar reinforced concrete was also studied. The test variables included rebar types (conventional steel rebar and two different GFRP rebars) and cover thicknesses (five different cover thicknesses ranging between 1-3db). Normal strength concrete was used. Cracking patterns on concrete surface and cracking loads were careful1y observed during the direct tensile test. The test results indicated that the adequate cover thickness of the GFRP rebars may even be larger than that of the steel rebars and that the cover thickness of 2db commonly specified for the GFRP rebars may not be large enough. The tension stiffening effect of the GFRP rebars was also quantified and documented from the test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.549-554
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• 2003

In order to overcome the brittle failure of strengthening with FRP-rebars inherent to their brittle properties, two approaches have been attempted. One is to improve the properties like ductile Hybrid FRP Rods, and the other is to develop a ductile strengthening with partially unbonded FRP rebars. Experiments on real size specimen were performed to evaluate the performance of NSM (Near Surface Mounted Strengthening) and SIM (Section Increment Methods) with FRP rebars. This paper discusses the results of the tests on 8 slab specimen in terms of flexural resistance, ductility, and fatigue. They show that NSM or S1M with FRP rebars are very effective measures to strengthen existing RC structures. Above all, strengthening with partially unbonded ductile Hybrid FRP Rods shows sufficient ductility similar to that of properly designed RC structures.

• Journal of the Korea Institute of Building Construction
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• v.10 no.4
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• pp.123-132
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• 2010

Rebar work accounts for approximately 30% of the total construction costs for rebars and concrete. Recently, the high rising prices of rebars have become one of the principle factors of rising construction costs. Therefore, construction companies are putting much effort into loss reduction of rebars. Consequently, in this study, we wished to present loss reduction methods of rebars before the preparation of the placing drawings. To devise such methods, we collected previous case studies and analyzed methods that were applied for loss reduction. As a result of the analysis, we were able to find the following methods for loss reduction of rebars: method of reducing the number of splices at the mat foundation, method of reducing splice length at the internal columns or walls of the underground parking lot, method of reducing cap-ties of internal beams of basement floors excluding perimeter beams, and method of reducing anchorage length at the internal column or wall of the underground parking lot. Based on those analysis results, we presented our own loss reduction methods of rebars. Applying our methods resulted in considerable loss reduction.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.3
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• pp.73-81
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• 2004

FRP reinforcing bars(rebars) are produced through a variety of manufacturing process includes pultrusion, and filament winding and braiding etc. Each manufacturing method produces a different surface condition of FRP rebar. The surface properties of FRP rebar is an important property for mechanical bond with concrete. Current methods of providing surface deformation to FRP rebars include helical wrapping, surfaces and coating and rib molding. The problem with the helical wrapping method is that it can not provide enough surface deformation for good bond and it can be easily sheard off from the FRP rebars. Sand coating and rib molding provide surface deformation only to the outer FRP skins. Therefore, FRP rebar has about 60% of bond strength of steel rebar. The main objective was to evaluate the bond properties of FRP rebar after environmental exposure. Five types of FRP rebar includes CFRP ISO, GFRP Aslan, AFRP Technora CFRP(Korea), and GFRP(Korea) rebars performed direct bond tests. Also, FRP rebar bond specimens were subjected to exposure conditions including alkaline solution, acid solution, salt solution and deionized water etc. According to bond test results, CFRP(Korea) and CFRP(Korea) rebars were found to have better bond strength with concrete than previous FRP rebars. Also, FRP(Korea) rebar had more than about 70% in bond strength of steel rebar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.157-164
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• 2006

This paper presents the durability characteristics of commercially available CFRP rebars under various environmental conditions. Two types of GFRP rebars were tested by using an accelerated aging method. A total of 264 rebar specimens were conditioned up to 132 days in the moisture, chloride. alkaline, and freeze-thaw environmental conditions. The durability characteristics of conditioned rebars were obtained by comparing the tensile strength, horizontal shear strength, and elastic modulus between the unconditioned and conditioned GFRP rebars. The test results indicated that the mechanical properties of GFRP were significantly reduced after conditioning. Long-term degradation of GFRP rebars was also estimated using the results of a short-term durability test.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.570-576
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• 2018

In reinforced concrete structures, the joints of ordinary rebars are usually lap joints, which are bound by binding wires with rebars, and mechanical joints by couplers. In domestic design standards (concrete design code), welded lap joints are restricted for ordinary rebars, but overseas standards allow welded lap joints of ordinary rebars through pre-heating. This study investigated the domestic and international standards/criteria and evaluated the fracture strength by performing the tensile test on the lap welded joint of SD400 grade rebars, which is used the most in the construction sites. The weld length of the specimen for weld lap joints is based on the minimum weld length (8d) given in the KS standard (KS B ISO 17660-1). According to AWS D1.4, the preheating temperature was set to $150^{\circ}C$ for D19 and below, and $260^{\circ}C$ for D22 and above. In the test results, the tensile strength of rebars with welded lap joints exceeded the required strength (125% of the yield strength) according to the concrete design code. To analyze the effect of preheating, the tensile strength of the welded rebars after preheating was not significantly different from that of the welded rebars without preheating. The carbon equivalent content (Ceq) of the rebars used in the test was 0.45% or less. Under AWS D1.4, no preheating is required if the carbon equivalent is less than 0.45%. All specimens with a welded lap length of 8d failed by a bar fracture. The effect of preheating was confirmed to be insignificant due to the low carbon equivalent of the rebar.

• Computers and Concrete
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• v.31 no.6
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• pp.513-525
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• 2023

This research presents the experimental and theoretical evaluations on circular steel-fiber-reinforced-concrete (SFRC) columns reinforced by glass-fiber-reinforced-polymer (GFRP) rebar under the axial compressive loading. Test programs were designed to investigate and compare the effect of different parameters on the structural behavior of columns by performing tests. Theses variables included conventional concrete (CC), fiber concrete (FC), steel/GFRP longitudinal rebars, and transversal rebars configurations. A total of 16 specimens were constructed and categorized into four groups in terms of different rebar-concrete configurations, including GFRP-rebar-reinforced-CC columns (GRCC), GFRP-rebar-reinforced-FC columns (GRFC), steel-rebar-reinforced-CC columns (SRCC) and steel-rebar- reinforced-FC columns (SRFC). Experimental observations displayed that failure modes and cracking patterns of four groups of columns were similar, especially in pre-peak branches of load-deflection curves. Although the average ultimate axial load of columns with longitudinal GFRP rebars was obtained by 17.9% less than the average ultimate axial load of columns with longitudinal steel rebars, the average axial ductility index (DI) of them was gained by 10.2% higher than their counterpart columns. Adding steel fibers (SFs) into concrete led to the increases of 7.7% and 6.7% of the axial peak load and the DI of columns than their counterpart columns with CC. The volumetric ratio had greater efficiency on peak loads and DIs of columns than the type of transversal reinforcement. A simple analytical equation was proposed to predict the axial compressive capacity of columns by considering the axial involvement of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop rebar. There was a good correlation between test results and predictions of the proposed equation.