• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.263-271
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• 2005

HPFRCC(High Performance Fiber Reinforced Cementitious Composite) is a class of FRCCs(Fiber Reinforced Cementitious Composites) that exhibit multiple cracking. Multiple cracking leads to improvement in properties such as ductility, toughness, fracture energy, strain hardening, strain capacity, and deformation capacity under tension, compression, and bending. These improved properties of HPFRCCs have triggered unique and versatile structural applications, including damage reduction, damage tolerance, energy absorption, crack distribution, deformation compatibility, and delamination resistance. These mechanical properties of HPFRCCs become different from the kinds and shapes of used fiber, and it is known that the effective size of fiber in macro crack is different from that in micro crack. This paper reports an experimental findings on the mechanical properties of HPFRCCs reinforced with the micro fiber(PP50, PVA100 and PVA200) and macro fiber(PVA660, SF500). Uniaxial compressive tests and three point bending tests are carried out in order to compare with the mechanical properties of HPFRCCs reinforced with micro fibers or hybrid fibers such as compressive strength, ultimate bending stress, toughness, deformation capacity and crack pattern under bending, etc.,

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.7-17
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• 2018

Test bed additional wall combined with PHC-W pile retaining wall has been constructed. To determine the dimensions of test bed additional wall, bending and shear tests of full scale core members of additional wall were tested. Basement additional walls utilizing PHC-W pile retaining wall, which were developed by modifying the cross-section of PHC piles, were classified into the composite additional wall and the non-composite additional wall. Their tests were conducted to obtain bending strength and shear strength of basement additional walls ultilizing PHC-W pile retaining wall. Since bending strengths and shear strengths of the composite additional wall and the non-composite additional wall were similar, it could be confirmed that the non-composite additional wall could be applied instead of the composite additional wall. Full-scale model additional wall was 200 mm thick, thus the thickness of additional wall combined with PHC-W pile retaining wall could be reduced by 100~200 mm.

• Steel and Composite Structures
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• v.29 no.3
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• pp.405-422
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• 2018

In this research, experimental tensile test and manufacturing of carbon nanotube reinforced composite beam (CNTRC) is presented. Also, bending, buckling, and vibration analysis of CNTRC based on various beam theories such as Euler-Bernoulli, Timoshenko and Reddy beams are considered. At first, the experimental tensile tests are carried out for CNTRC and composite beams in order to obtain mechanical properties and then using Hamilton's principle the governing equations of motion are derived for Euler Bernoulli, Timoshenko and Reddy theories. The results have a good agreement with the obtained results by similar researches and it is shown that adding just two percent of carbon nanotubes increases dimensionless fundamental frequency and critical buckling load as well as decreases transverse deflection of composite beams. Also, the influences of different manufacturing processes such as hand layup and industrial methods using vacuum pump on composite properties are investigated. In these composite beams, glass fibers used in an epoxy matrix and for producing CNTRC, CNTs are applied as reinforcement particles. Applying two percent of CNTs leads to increase the mechanical properties and increases natural frequencies and critical buckling load and decreases deflection. The obtained natural frequencies and critical buckling load by theoretical method are higher than other methods, because there are some inevitable errors in industrial and hand layup method. Also, the minimum deflection occurs for theoretical methods, in bending analysis. In this study, Young's and shear modulli as well as density are obtained by experimental test and have not been used from the results of other researches. Then the theoretical analysis such as bending, buckling and vibration are considered by using the obtained mechanical properties of this research.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.49-55
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• 2011

In order to analyze feasibility of replacing a conventional 6-mm Ti bar with a 5-mm bar, a series of rotating bending fatigue tests were carried out on Ti-6Al-4V bars by strengthening the fatigue performance using a special technique called UNSM (Ultrasonic Nanocrystal Surface Modification). The results of S-N curves clearly showed that the performance of the 5-mm titanium specimen was similar to that of the 6-mm specimen when the UNSM treatment was applied. The 5-mm treated specimen converged with small scattering band into the linear line of the non-treated 6-mm one. Below the fatigue life of $10^5$ cycles, the UNSM treatment did not show any significant superiority in the bending stress and fatigue life. However, over the fatigue life of $10^5$ cycles, the effect of UNSM was superior for each fatigue life, and the bending stress became longer and higher than that of the untreated one. In the case of 6-mm Ti-bar with UNSM, the fatigue limit was about 592 MPa, and there was fatigue strength increase of about 30.7% at the fatigue life of $10^4$ cycles compared to the untreated 6-mm bar. Therefore, the compressive residual stress made by the UNSM in Ti-6Al-4V increased the fatigue strength by more than 30%.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.91-101
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• 2004

This study sought to suggest a structural design guide and to investigate the structural performances of the new beam-slab system in order to decrease the height of floors in high-rise steel structure apartments. Experiments were performed to assess the capacity of the new beam-slab system in a steel structure with 9.8-m span, particulary structural material test, pure bending test of composite beam, three-point bending test of composite beam, and bending and shearing tests. Results showed that the suggested composite beam had stable structural behavior when stud connectors were located in the upper flange, and upper bars were calculated normally according to the design of the slab.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.533-541
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• 2010

H-shaped beams, which are constructed between columns, are used widely as slaves in steel structures. The bending moments that occur on both ends of an H-shaped beam, however, are about twice the bending moment that occurs at the center of the H-shaped beam. Because such beam is designed with maximum bending moment, it is deeper and has smaller spaces. To improve these features, if both ends of an H-shaped beam that have maximum bending moments are merely reinforced, the beams could be designed by the bending moment at the center of the H-shaped beam. To analyze the structural performance of the proposed end-reinforced beams (eco-girders). Four specimens were prepared with the following parameters: end-reinforced steel plate, reinforced bars, and reinforced studs and experimental tests of the specimens were performed.

• Magazine of the Korean Society of Agricultural Engineers
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• v.24 no.4
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• pp.92-98
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• 1982

The major objective of this study was to investigate the heat resistance of epoxy resin mortar. For this purpose, these tests of compressive and bending strength were accomp- olished with various heating temperature (40˚C, 60˚C, 80˚C, 100˚C, 120˚C), and with various mixing ratio (1: 2, 1: 4, 1: 6, 1: 8, 1:10, 1:12, 1:14). The exprimental resin was to be Epi-Bis type epoxy resin, which is widely used as construction materials. The results obtained are summarized as follows; 1. The variations of color tone started to begin at 60˚C, and it has come out very heavy at 120˚C. It was assumed that the decrement of weight resulted from carbonization were about 0.22% at 100˚C, and about 0.34% at 120˚C. 2. The compressive and bending strength were increased with temperature rise up to 80˚C, but these were made rapid decrease when the given temperature was over. And so, the mean decrement of compressive and bending strength at 120˚C reached up to 35.5% and 26.4%, respectively. 3. The regression equation between compressive and bending strength for epoxy resin mortar under heat exposure were obtained as follows; od=0. 371oc+39. 23 (r=0. 986) And the estimated value of bending strength was corresponded to about 37 percent in comparing with that of the compressive strength. 4. Consquently, the heat resistance temperature of epoxy resin mortar was to be around 80˚C, and it was generally very low values. But it was regarded that the epoxy resin mortar will not be difficult with materials of civil engineering works and agricultural structures.

• Computers and Concrete
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• v.24 no.1
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• pp.73-83
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• 2019

Concrete reinforced with fiber reinforced polymer (FRP) bars (FRP-RC) has attracted a significant amount of research attention in the last three decades. A limited number of studies, however, have investigated the effect of bond slip on the performance of FRP-RC columns under eccentric loading. Based on previous experimental study, a finite-element model of eccentrically loaded FRP-RC columns was established in this study. The bondslip behavior was modeled by inserting spring elements between FRP bars and concrete. The improved Bertero-Popov-Eligehausen (BPE) bond slip model with the results of existing FRP-RC pullout tests was introduced. The effect of bond slip on the entire compression-bending process of FRP-RC columns was investigated parametrically. The results show that the initial stiffness of bond slip is the most sensitive parameter affecting the compression-bending performance of columns. The peak bond stress and the corresponding peak slip produce a small effect on the maximum loading capacity of columns. The bondslip softening has little effect on the compression-bending performance of columns. The sectional analysis revealed that, as the load eccentricity and the FRP bar diameter increase, the reducing effect of bond slip on the flexural capacity becomes more obvious. With regard to bond slip, the axial-force-bending-moment (P-M) interaction diagrams of columns with different FRP bar diameters show consistent trends. It can be concluded from this study that for columns reinforced with large diameter FRP bars, the flexural capacity of columns at low axial load levels will be seriously overestimated if the bond slip is not considered.

• Coupled systems mechanics
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• v.10 no.6
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• pp.509-520
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• 2021

Fiber-reinforced concrete (FRC) is a composite material where small fibers made from steel or polypropylene or similar material are embedded into concrete matrix. In a material model each constituent should be adequately described, especially the interface between the matrix and fibers that is determined with the 'bond-slip' law. 'Bond-slip' law describes relation between the force in a fiber and its displacement. Bond-slip relation is usually obtained from tension laboratory experiments where a fiber is pulled out from a matrix (concrete) block. However, theoretically bond-slip relation could be determined from bending experiments since in bending the fibers in FRC get pulled-out from the concrete matrix. We have performed specially designed laboratory experiments of three-point beam bending with an intention of using experimental data for determination of material parameters. In addition, we have formulated simple layered model for description of the behavior of beams in the three-point bending test. It is not possible to use this 'forward' beam model for extraction of material parameters so an inverse model has been devised. This model is a basis for formulation of an inverse model that could be used for parameter extraction from laboratory tests. The key assumption in the developed inverse solution procedure is that some values in the formulation are known and comprised in the experimental data. The procedure includes measured data and its derivative, the formulation is nonlinear and solution is obtained from an iterative procedure. The proposed method is numerically validated in the example at the end of the paper and it is demonstrated that material parameters could be successfully recovered from measured data.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.481-488
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• 1999

Recently a removable soil nail is demanded due to problems beyond of economical and engineering purpose. In this study controlled displacement and controlled force field pull-out tests are carried out 7 times in order to evaluate short-term and long-term pull-out characteristics of the removable soil nail. For evaluating application of removable soil nailing system, bending tests of removable soil nails and tensile tests of fixed sockets are carried out. In the removable soil nailing system, the predicted horizontal displacements from FLAC-2D are also compared with the field measurements occurred in stepwise excavation. And approach for the stability analysis of removable soil nailing system after removed is proposed.