• Computers and Concrete
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• v.26 no.6
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• pp.587-593
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• 2020

In this study, bond behavior of ordinary concrete and rebars with different diameters and development length was investigated by using Hinged Beam Test (HBT) and Eccentric Pull-Out Test (EPT) comparatively. For this purpose, three different rebar size and development length depending on rebar diameter were chosen as variables. Three specimens were produced for each series of specimens and totally 54 specimens were tested. At the end of the tests it was observed that obtained results for both tests were quite similar. On the other hand, increased bar size, especially for the specimen with 14 mm bar size and 14 development length (lb), caused shear failure of test specimens. This situation infers that when bigger bar size and lb are used in such test, dimensions of test specimens should be chosen bigger and stirrups should be used for producing of test specimens to obtain more adequate result by preventing shear failure. Also, a nonlinear regression analysis was employed between HBT and EPT results. There was a high correlation between the EPT values, lb, rebar diameters and estimated theoretical HBT. In addition, at the end of the study an equation was suggested to estimate bond strength for HBT by using EPT results.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.19-20
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• 2009

Bond of deformed type of GFRP rebar, which has deformations resembles that of ordinary steel rebar, to concrete was investigated experimentally and numerically in this paper. Due to the lower stiffness and strength in shear, surface deformations do not fully works in bond with surrounding concrete. In this paper, the effective surface deformation height of GFRP rebar with ribs was determined based on experimental and numerical results.

• Computers and Concrete
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• v.8 no.4
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• pp.465-472
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• 2011

This paper investigates bond behavior of structural lightweight concrete (SLWC) and ordinary concrete (OC) comparatively using bending test called Standard Belgium Hinged Beam Test (SBHBT). For this purpose the experiments were carried out as three series on 36 beam specimens (12 specimens of SLWC and OC with $20{\phi}$ development length, 12 specimens of SLWC with $25{\phi}$ development length). For each series bond behavior of steel rebars with 8, 10, 12, 14 mm diameters were tested. The results indicate that bond strength of SLWC is considerable lower than OC and $20{\phi}$ development length is insufficient for steel rebars with 12 mm and 14 mm diameters. Therefore development length of SLWC was extended to $25{\phi}$, even if 8 and 10 mm steel rebars provided acceptable bond strength. In this way, bond strength between SLWC and 8 and 10 mm steel rebars was developed. In addition, adequate bond behavior was achieved for 12 mm rebar but the beam in which 14 mm rebar used exceeded their bearing capacity by shear forces before yield stress. This result shows that SBHBT is more convenient for small sized steel rebars.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1193-1198
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• 2001

The glass of Ground Granulated Blast Furnace Slag(GGBFS) was released by the hydroxyl ions during the hydration of the Portland cement. That results in relatively less $Ca(OH)_{2}$ in the concrete replaced with GGBFS than in ordinary portland cement concrete(OPCC). As the quantity of $Ca(OH)_{2}$ is decreased, the rate of carbonation in the concrete replaced GGBFS is faster than OPCC. Therefore, it has been misunderstood that the concrete replaced GGBFS has negative effect on the corrosion of steel by carbonation. Therefore, this study aimed at the relation between carbonation and rebar corrsion in the concrete with GGBFS, measuring air.water permeability, half cell, and corrosion rate by the depth of carbonation.

• 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.46-53
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• 2023

In this paper, we evaluated the flexural performance of three types of reinforced concrete beams (SHCC-RB, SHCC-SB, SHCC-FRP) strengthened with ordinary steel rebar, very high strength (super strength) rebar, and FRP bars together with strain-hardening cement composite (SHCC). For this purpose, a series of beam specimens were manufactured and four-point load bending experiments were performed. As a result of the experiment, all specimens strengthened with SHCC exhibited tightly controlled flexural microcrakcs with the crack width of less than 100 ㎛. This is mostly due to the material properties of SHCC showing tensile strain hardening properties with multiple microcracks under uniaxial tension. The specimen SHCC-FRP showed lower initial cracking moment and yield flexural strength than SHCC-RB, whereas the maximum flexural strength of SHCC-FRP was superior to that of SHCC-RC. This is because the tensile strength of FRP bars is higher than that of ordinary steel reabr. The initial cracking moment of the beam specimen SHCC-SB was similar to that of SHCC-RB, but the yield flexural strength and maximum flexural strength of SHCC-SB were evaluated to be the highest.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.78-81
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• 2003

Recently, physical properties of concrete containing ternary blended cement were actively researching to develop durability, mobility, and atc. as well as strength increase of concrete. In this study, durability of concrete such as the resistance against chloride ion penetration, rebar corrosion, freeze and thaw, and sulfate were researched for concrete containing ordinary portland cement(OPC) and ternary blended cement(TBC), respectively. For this purpose, concrete specimens containing OPC and TBC, respectively, were made for 37.5% of W/C, and then various durability experiments described above were carried out. As a result, it was observed from the test that concrete containing TBC showed excellent durability than concrete containing OPC.

• Land and Housing Review
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• v.4 no.4
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• pp.371-382
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• 2013

This study performs an experimental investigation to evaluate the behavior of RC flat plate interior joints specimens. Three 60 percent scale Flat Plate interior specimens assemblies representing a portion of a Flat Plate Apartment Structural System subjected to simulated seismic loading (unbalanced moments) under constant axial load were tested, including one specimens with ordinary shear reinforcement and two specimens with folded bend type shear reinforcement. Test results are shown that (1) the design code KBC 2009 is accurate estimate the behavior of specimens. (2) Two types shear reinforcement have a similar structural behavior, but construction work of rebar with folded bend type shear reinforcement is easier than that of ordinary shear reinforcement. (3) In moderate seismic region, RC Flat Plate interior joint with folded bend type shear reinforcement is apply to structural design of Flat Plate.

• Computers and Concrete
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• v.29 no.6
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• pp.407-418
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• 2022

This paper numerically investigates the effect of changes in the mechanical properties (displacement, strain, and stress) of the ultra-high-performance concrete (UHPC) without rebar and the reinforced concrete (RC) using steel re-bars. This reinforced concrete is mostly used in the concrete bridge decks. A mixture of sand, gravel, cement, water, steel fiber, superplasticizer, and micro silica was used to fabricate UHPC specimens. The extended finite element method as used in the ABAQUS software is applied for considering the mechanical properties of UHPC, RC, and ordinary concrete specimens. To calibrate the ABAQUS, some experimental tests have been carried out in the laboratory to measure the direct tensile strength of UHPC by the compressive-to-tensile load converting (CTLC) device. This device contains a concrete specimen and is mounted on a universal tensile testing apparatus. In the experiments, three types of mixed concrete were used for UHPC specimens. The tensile strength of these specimens ranges from 9.24 to 11.4 MPa, which is relatively high compared with ordinary concrete specimens, which have a tensile strength ranging from 2 to 5 MPa. In the experimental tests, the UHPC specimen of size 150×60×190 mm with a central hole of 75 mm (in diameter)×60 mm (in thickness) was specially made in the laboratory, and its direct tensile strength was measured by the CTLC device. However, the numerical simulation results for the tensile strength and failure mechanism of the UHPC were very close to those measured experimentally. From comparing the numerical and experimental results obtained in this study, it has been concluded that UHPC can be effectively used for bridge decks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.134-140
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• 2017

In this study, the flexural behavior of high strength concrete members with different curing condition of 90 MPa of compressive strength was investigated. Experimental parameters included normal and low temperature curing conditions, tensile steel amount and concrete compressive strength. 8 beam members were fabricated and flexural tests were carried out. Crack spacing, load-deflection relation, load-strain relation and ductility index were determined. Experimental results show that as the amount of rebar increases, the number of cracks increases and the crack spacing decreases. The higher the concrete strength, the smaller the number of cracks, but the effect is significantly smaller than the amount of rebar. As a result of comparison with the proposed average crack spacing in the design criteria, the experimental results are slightly larger than the results of the proposed formula, but the proposed formula does not reflect the concrete strength and curing conditions. The ductility index of normal temperature cured members was 3.36~6.74 and the ductility index of low temperature cured members was 1.51~2.82. The behavior of low temperature cured members was found to be lower than that of normal temperature cured members. As a result of comparing the ductility index with the existing studies similar to the experimental members, the ductility index of the high strength concrete member was larger than the ductility index of the ordinary strength concrete of the previous study. Further research is needed to understand more specific results.