• Structural Engineering and Mechanics
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• v.72 no.3
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• pp.367-382
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• 2019

This paper presents experimental and analytical investigations on additional fixed-end rotations resulting from the strain penetration of high-strength reinforcement in reinforced concrete (RC) beam-column connections under monotonic loading. The experimental part included the test of 18 interior beam-column connections with straight long steel bars and 24 exterior beam-column connections with hooked and headed steel bars. Rebar strains along the anchorage length were recorded at the yielding and ultimate states. Furthermore, a numerical program was developed to study the effect of strain penetration in beam-column connections. The numerical results showed good agreement with the test results. Finally, 87 simulated specimens were designed with various parameters based on the test specimens. The effect of concrete compressive strength ($f_c$), yield strength ($f_y$), diameter ($d_b$), and anchorage length ($l_{ah}$) of the reinforcement in the beam-column connection was examined through a parametric study. The results indicated that additional fixed-end rotations increased with a decrease in $f_c$ and an increase in $f_y$, $d_b$ and $l_{ah}$. Moreover, the growth rate of additional fixed-end rotations at the yielding state was faster than that at the ultimate state when high-strength steel bars were used.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.697-703
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• 2009

High-strength concrete corbels with varying percentage of steel fibers and two different anchorage types (welding to transverse bar, headed) for the main tension tie were constructed and tested. The results showed that performance in terms of load carrying capacities, stiffness, ductility, and crack width was improved, as the percentage of steel fibers was increased. In addition, the corbel specimens in which headed bars were used as the main tension tie reinforcements showed superior load carrying capacities, stiffness, and ductility compared to the corbel specimens in which the main tension ties were anchored by welding to the transverse bars. From the test results, it is expected that load carrying capacities, durability, and constructibility of high strength concrete corbels would be improved by using steel fibers and headed bars. Experimental results presented in this paper were also compared with various prediction models proposed by researchers and presented in codes. The truss model proposed by Fattuhi provides fairly good predictions for fiber reinforced high-strength concrete corbels.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.77-81
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• 2006

An attempt has been made to measure existing steel stress using magnetoelasticity. A device has been developed and used for the measurement of magnetism in response to the deformation of a steel bar. The proposed technique can be used for the assessment of existing reinforced concrete structures by the measurements of steel stress embedded inside concrete. A traditional technique requires to break the existing steel bar to measure existing strain. However, the proposed technique is developed to measure the stress without damaging the steel bar. A successful application of magnetoelasticity depends on the establishment of relationship between elastic and magnetic response due to loading. To investigate the correlation between the two, steel bars are loaded in tension under uniaxial loading while the magnetic reading is recorded. Based on the test results, equations are suggested to predict stress for steel bars with different diameters.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.785-790
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• 1998

Ground Penetrating Radar (GPR) is a powerful tool with a wide range of applications in the nondestructive testing of concrete. It's useful for the detection of steel bars and delaminations embedded inside concrete, nondestructively. The purpose of this study is to detect a reinforced bar embedded inside concrete and to determine the range of application using GPR. A concrete specimen used for this study has a 25mm diameter steel bar and it's dimensions are 1,000 mm (L)× 1,000 mm(W)×280 mm(D). The advantages and limitations of GPR in these applications for concrete are also discussed.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.1
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• pp.81-87
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• 2008

C-Hook is a kind of conveyer system for transporting steel coil in POSCO. To detect the current position and the trajectory of steel coils in a plant, C-Hooks are tracked by an inspection system based on PLC. The inspection system detects transit of C-Hooks by monitoring a physical contact between steel bars on a C-Hook and the inspection sensors. However, this system is not reliable because of the abrasion, damage and aging. Moreover, the number of distinguishable C-Hooks is limited by the number of combination of steel bars on a C-Hook. It means that more steel bars should be installed for distinguishing the more C-Hooks. Therefore, the conventional system is difficult and expensive to maintain. To overcome these problems, we propose a C-Hook identification system that uses RFID which is a non-contact type identification system, and evaluate its performance and applicability from a new monitoring program that operates along with the conventional system in the real environment of POSCO.

• Steel and Composite Structures
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• v.31 no.3
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• pp.217-232
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• 2019

Modular steel buildings consist of prefabricated room-sized structural units that are manufactured offsite and installed onsite. The inter-module connections must fulfill the assembly construction requirements and soundly transfer the external loads. This work proposes an innovative assembled connection suitable for modular buildings with concrete-filled steel tube columns. The connection uses pretensioned strands and plugin bars to vertically connect the adjacent modular columns. The moment-transferring performance of this inter-module connection was studied through monotonic and cyclic loading tests. The results showed that because of the assembly construction, the connected sections were separated under lateral bending, and the prestressed inter-module connection performed as a weak semirigid connection. The moment strength at the early loading stage originated primarily from the contact bonding mechanism with the infilled concrete, and the postyield strength depended mainly on the tensioned strands. The connection displayed a self-centering-like behavior that the induced deformation was reversed during unloading. The energy dissipation originated primarily from frictional slipping of the plugin bars and steel strands. The moment transferring ability was closely related to the section dimension and the arrangements of the plugin bars and steel strands. A simplified strength calculation and evaluation method was also proposed, and the effectiveness was validated with the test data.

• Transactions of Materials Processing
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• v.30 no.2
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• pp.91-98
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• 2021

The present study deals with the microstructure and mechanical properties of 700 MPa-grade high-strength seismic resistant reinforced steel bars fabricated by various TempCore process conditions. For the steel bars, in the surface region tempered martensite was formed by water cooling and subsequent self-tempering during TempCore process, while in the center region there was ferrite-pearlite or bainite microstructure. The steel bar fabricated by the highest water flow and the lowest equalizing temperature had the highest hardness in all regions due to the relatively fine microstructure of tempered martensite and bainite. In addition, the steel bar having finer microstructures as well as the high fraction of tempered martensite in the surface region showed the highest yield and tensile strengths. The presence of vanadium precipitates and the high fraction of ferrite contributed to the improvement of seismic resistance such as high tensile-to-yield strength ratio and high uniform elongation.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.1-10
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• 2014

In this study, out-of-plane flexural test was performed to analyze behavior properties for a beam specimen which imitated a structure with connection member between reinforced concrete and steel plate concrete part. Tie bars between a upper and a lower steel plate, and tie wide flange shapes between upper and lower ribs were designed to prevent the steel plate or the ribs from breakaway in the connection of the specimen. As a result of the test, ductile failure behavior of the specimen and the functionality of the tie members were conformed as originally intended. Also, tension tests were performed to evaluate the design appropriateness of two specimens produced to anchor and connect mechanically #14 bars. The two test results showed that the anchorage connection system behaves in elastic limit during the main bars yielded, and the integrity of the designed system was verified.

• Structural Engineering and Mechanics
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• v.83 no.4
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• pp.415-433
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• 2022

Eighteen (18) (120×300×2200 mm) beams were prepared and tested to evaluate the shear strength of Glass Fiber Reinforced Concrete (GFRC) beams with no shear reinforcement, and evaluate the effectiveness of various innovative strengthening systems to increase the shear capacity of the GFRC beams. The test variables are the amount of discrete glass fiber (0.0, 0.6, and 1.2% by volume of concrete) and the type of longitudinal reinforcement bars (steel or GFRP), the strengthening systems (externally bonded (EB) sheet, side near-surface mounted (SNSM) bars, or the two together), strengthening material (GFRP or steel) links, different configurations of NSM GFRP bars (side bonded links, full wrapped stirrups, side C-shaped stirrups, and side bent bars), link spacing, link inclination angle, and the number of bent bars. The experimental results showed that adding the discrete glass fiber to the concrete by 0.6%, and 1.2% enhanced the shear strength by 18.5% and 28%, respectively in addition to enhancing the ductility. The results testified the efficiency of different strengthening systems, where it is enhanced the shear capacity by a ratio of 28.4% to 120%, and that is a significant improvement. Providing SNSM bent bars with strips as a new strengthening technique exhibited better shear performance in terms of crack propagation, and improved shear capacity and ductility compared to other strengthening techniques. Based on the experimental shear behavior, an analytical study, which allows the estimation of the shear capacity of the strengthened beams, was proposed, the results of the experimental and analytical study were comparable by a ratio of 0.91 to 1.15.

• Steel and Composite Structures
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• v.39 no.5
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• pp.583-598
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• 2021

The composite steel reinforced concrete (SRC) columns have been widely used in Structural Engineering due to their good performances. Many studies have been done on the SRC columns' performances, but they focused on the ordinary types with conventional configurations and materials. In this study, nine new types of steel reinforced lightweight aggregate concrete (SRLAC) short columns with cross-shaped (+shaped and X-shaped) steel section were tested under monotonically axial compressive load; the studied parameters included steel section ratio, steel section configuration, ties spacing, lightweight aggregate concrete (LWAC) strength, and longitudinal bars ratio. From the results, it could be found that the specimens with larger ties ratio, concrete strength, longitudinal bars ratio, and steel section ratio achieved great strength and stiffness due to the excellent interaction between the concrete and steel. The well-confined concrete core could strengthen the steel section. The ductility and toughness of the specimens were influenced by the LWAC strength, steel section ratio, and longitudinal bars ratio; in addition, larger ties ratio with smaller LWAC strength led to better ductility and toughness. The load transfer between concrete and steel section largely depends on the LWAC strength, and the ultimate strength of the new types of SRLAC short columns could be approximately predicted, referring to the codes' formulas of ordinary types of steel reinforced concrete (SRC) columns. Among the used codes, the BS-5400-05 led to the most conservative results.