• Earthquakes and Structures
• /
• v.25 no.1
• /
• pp.57-67
• /
• 2023

The buckling of longitudinal reinforcements under seismic loading accelerates the degradation of the bearing capacity of reinforced concrete columns. The traditional hysteretic constitutive model of reinforcement, which does not consider buckling, usually overestimates the seismic performance of pier columns. Subsequent researchers have also proposed many models including the buckling effects. However, the accuracy of these hysteretic constitutive models proposed for simulating the buckling behavior is inadequate. In this study, based on their works, the influence of historical events on buckling is considered, the path of the re-tensioning phase is corrected by adjusting the boundary lines, and the positions of the onset buckling point and compressive buckling path during each buckling deformation are corrected by introducing correction parameters and a boundary line. A modified hysteretic constitutive model is obtained, that can more accurately reflect the buckling behavior of reinforcements. Finally, a series of hysteresis tests of reinforcements with different slenderness ratios were then conducted. The experimental results verify the effectiveness of the proposed modified model. Indicating that the modified model can more accurately simulate the equivalent stress-strain relationship of the buckling reinforcement segment.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.27 no.5
• /
• pp.139-146
• /
• 2023

In this study, compressive strength and adhesion strength were measured as repair materials to evaluate the mechanical and electrical properties of compression and shear specimens with self-sensing repair materials. As a result of the experiment, the strength improvement rate of the compression test specimen was higher than the section enlargement area ratio, but the shear test specimen did not show an improvement in strength as much as the section enlargement area ratio. Compression experiments under load showed high correlation between FCR-Strain and FCR-Stress, confirming self-sensing performance. However, the shear test did not show as much correlation as the compression test. Accordingly, it is judged that the self-sensing repair material is suitable for the compression member on which the compression load acts in the building.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.1316-1323
• /
• 2005

Most tunnel lining material which has been used in the domestic is a concrete. But many problems as the construction period, the cost, and the crack occurrence for the design, construction, and management were happened in the concrete lining. For this reason, many research institutes like the Korea Highway Corporation recognize the necessity of an alternate material development and grow on the interest for that. So in this study, the behaviour characteristics for the application of the Corrugated Steel Plate Lining in cut-and-cover tunnel are evaluated as several conditions for the backfill height, the cutting slope, and the relative density of backfill soil are changed. In addition, through using that conditions, CHBDC(2000, Canadian Highway Bridge Design Code) is evaluated if it could be applied to the design by comparing with the numerical analysis results. As the behaviour characteristics of the Corrugated Steel Plate Lining by CHBDC and the static numerical analysis are analyzed, both the methods show the same linear increases of the compressive stress according to the increase of the backfill height. The CHBDC of the dead load condition has very similar tendency by comparing with the result of the static numerical analysis.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.41 no.2
• /
• pp.101-111
• /
• 2021

Two different types of shear-friction tests were classified by external loadings and referred to as a push-off and a pull-off test. In a pull-off test, a tension force is applied in the transverse direction of the test specimen to produce a shear stress at the shear plane. This paper presents a method to evaluate shear transfer strengths of uncracked pull-off specimens. The method is based on the compression field theory and different constitutive laws are applied in some ways to gain accurate shear strengths considering softening effects of concrete struts based on Modified Compression Field Theory (MCFT) and Softened Truss Model (STM). The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with the predicted values. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked pull-off test specimens. A shear strength evaluation formula considering the effective compressive strength of a concrete strut was proposed, and the applicability of the proposed formula was verified by comparing with the experimental results in the literature.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.1
• /
• pp.39-48
• /
• 2015

Reinforced concrete (RC) structures strengthened with FRP materials would cause the loss of the reinforcing effect and the sudden failure of the structure due to the debonding of FRP. The debonding fracture strength of the FRP-strengthened concrete structures has been evaluated using the same strength method as applied in RC structures based on the debonding strain of FRP. However, the values of the FRP debonding strain are different according to design guidelines. Thus, this study carried out an experimental study on RC beams reinforced with GFRP and evaluated the debonding fracture strength of the strengthened beams from each design guideline. Since the debonding failure occurs prior to reaching the ultimate value of concrete compressive strain, this study accounts for the nonlinear stress distribution of concrete. This study also proposed equations that can evaluate the debonding strength of GFRP-strengthened RC beams with similar safety to the ultimate flexural strength of non-strengthened RC beams.

• Journal of the Korea Institute of Building Construction
• /
• v.15 no.1
• /
• pp.25-33
• /
• 2015

In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.2 no.2
• /
• pp.128-136
• /
• 2014

It is known that the best way to recycle fly ash is to use in concrete. It is impossible to bury in the ground this fly ash recently, so it is trying to use high volume fly ash concrete. Nevertheless, recent main research topics are focused in the part of material only. However, it is necessary to perform the researches about elasticity modulus, stress-strain relationship and structural behavior. Therefore, in this paper, 18 test members were manufactured with 3 test variables, namely fly ash replacement ratio 0, 35, 50%, concrete compressive strength 20, 40, 60MPa and 2 tensile steel ratio. 18 test members were tested for flexural behavior. From the test results, there were no differences between 35, 50% high volume fly ash cement concrete and ordinary concrete without fly ash (FA=0%). In order to evaluate the HVFAC flexural behavior, Analytical model was proposed and the computer program was developed. There were no differences between test results and analysis results. So, the proposed analytical model was reasonable.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.313-316
• /
• 2008

Corrosion of steel in the reinforced concrete structures is one of the main reason of degradation. It causes that lifetime of structures is shortened and maintenance cost is increased. And it also causes degradation of structures like bridges which are under repeated load. So, many research have been performed about FRP rebar. But there are few research about FRP rebar under fatigue. This study is to examine flexural characteristic of concrete beam reinforced with FRP(CFRP, GFRP) rebar under static and fatigue for considering the application. The specimens that used in this study are designed by ACI 440.1R-06 and reinforced with CFRP(CR) or GFRP(GR) overly. In the result of static bending test, all specimens were failed at compression phase. In fatigue test, the fatigue stress level was 60%, 70% or 80% of the static bending strength. Most of the specimens seemed to be compressive failure, but CR-60 and CR-70 specimens were failed with rupturing of tension bar.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.3
• /
• pp.143-149
• /
• 2019

In this study, a U-shape composite beam was developed to be effectively used for a steel parking lot which is 8m or lower in height. When the U-shape composite beam was applied to a steel parking lot, essential considerations were story-height and long-span. In addition, due to the mixed structural system with reinforced concrete and steel material, the U-shape composite beam needed to have a structural integrity and reliable performance over demand capacity. The main objective of this study was to investigate the performance of the structure consisting of the reinforced concrete (RC) slab and U-shape beam. A U-shape composite beam generally used at a parking lot served as a control specimen. Four specimens were tested under four-point bending. To calculate theoretical values, strain gauges were attached to rebar, steel plate, and concrete surface in the middle of the specimens. As the results, initial yielding strength of the control specimen occurred at the bottom of the U-shaped steel. After yielding, the specimen reached the maximum strength and the RC slab concrete was finally failed by concrete crush due to compressive stress. The structural performance such as flexural strength and ductility of the specimen with the increased beam depth was significantly improved in comparison with the control specimen. Furthermore, the design of the U-shape composite beam with the consideration of flexural strength and ductility was effective since the structural performance by a negative loading was relatively decreased but the ductile behavior was evidently improved.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.2
• /
• pp.267-278
• /
• 2003

Artificial neural networks are efficient computing techniques that are widely used to solve complex problems in many fields. In this study, in order to predict tunnel-induced ground movements, Tunnel Behavior Prediction System (TBPS) was developed by using these artificial neural networks model, based on a Held instrumentation database (i.e. crown settlement, convergence, axial force of rock bolt, compressive and shear stress of shotcrete, stress of concrete lining etc.) obtained from 193 location data of 31 different tunnel sites where works are completed. The study and test of the network were performed by Back Propagation Algorithm which is known as a systematic technique for studying the multi-layer artificial neural network. The tunnel behaviors predicted by TBPS were compared with monitored data in the tunnel sites and numerical analysis results. This study showed that the values obtained from TBPS were within allowable limits. It is concluded that this system can effectively estimate the tunnel ground movements and can also be used f3r tunneling feasibility study, and basic and detailed design and construction of tunnel.