• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.26-33
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• 2018

This paper presents experimental and analytical results on flexural behavior of flexural members made of SIFCON. Twelve SIFCON beams were subjected to bending tests and their flexural behavior was evaluated. Experimental variables included steel fiber type, presence of tensile reinforcement, and height of section. The specimens using Type-B steel fibers, which had better pullout resistance than Type-A steel fibers, showed flexural failure behavior without shear failure. The aspect ratio of steel fiber had a great influence on the behavior of SIFCON beams without tensile steel, however the effect on the behavior of SIFCON beams was negligible. In addition, the flexural strength equation for SIFCON was proposed in the study. The mean and standard deviation of the ratios of the predicted value to the experimental value are 1.02 and 0.04, respectively. Therefore, the proposed flexural strength equation can be useful for the design and performance evaluation of SIFCON beam.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.261-270
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• 2006

In this paper, the basic data regarding the application of the MSC (Modular Steel Concrete) beam are presented by comparing the experimental value with the theoretical value, focusing on the bending behavior of the Lip-type MSC beam, which is composed of steel and concrete. Considerable manpower is needed to fabricate the traditional MSC beam, particularly for the tasks of cutting, welding, etc. Because much time is needed to fabricate the traditional SC beam, the prefabrication concept is introduced, easily produce the required size of the SC beam by prefabricating the side module and the lower module, which is made up of a steel sheet. The result indicates that the method of uniting the modules, an d the composition method with concrete, should be improved. The proposed MSC beam can be used as a new structural member by increasing its coherent reinforcement with modules and the composition ratio of steel and concrete through a future study.

• Fire Science and Engineering
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• v.20 no.4 s.64
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• pp.72-76
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• 2006

Polymer/clay nanocomposites have generated considerable interests in the past decade because adding just tiny amount of clay to the polymer matrix could produce a dramatic enhancement in physical, thermal and mechanical properties. Smectite clays, such as montmorillonite (MMT), are of great industrial value because of their high aspect ratio, plate morphology, intercalative capacity, natural abundance and low cost. In this study, PE/MMT nanocomposites were directly prepared by melt intercalating PE and the modified clay. The nanostructure was verified by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their flame retardant properties were measured and discussed by limiting oxygen index (LOI), char yield and smoke mass concentration. And their thermal stabilities were measured by differential thermogravimetric (DTG) and thermogravimetric analysis (TGA). The PE/MMT nanocomposites proved more effective the conventional composites in reinforcement. Two functions in the thermal stability of the PE/MMT nanocomposite, one is the barrier effect to improve the thermal stability, and another is catalysis, leading to a decrease of the thermal stability. The flammability was greatly decreased due to the formation of the clay-enriched protective char during the combustion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.245-251
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• 1999

Carbon fibre reinforced plastic(CFRP) plate is one of the alternative materials for strengthening of reinforced and prestressed concrete members due to excellent strength and light weight. In this paper, the behavior of slabs strengthened with CFRP plate is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear force appear in same position. The failure mode is a peeling-off of the CFRP plate due to flexural-shear crack. This is observed near the loading points with thick plates. Because of this failure mode, thickness of CFRP plates does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When large moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened slab and moment of unstrengthened slab is proposed 1.5-2.0.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.87-94
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• 2013

In recent years, tunnel construction is being increased in order to resolve traffic congestion around urban area, however there are a lot of difficulties due to restrictions such as interference with existing alignment, adjacent structures and cost increase of land acquisition as well as public complaints for negative environmental impacts near the expected tunnel construction site. Therefore, applications of close parallel tunnel have been increasing greatly. But close parallel tunnels cannot guarantee the stability compared with normal parallel tunnel which has enough distance between tunnels. So various methods to strengthen the pillar have been introduced recently, however there is few methods which consider the pillar behaviour in the state of compression. In this paper, the reinforcement methods which reflect the behavior of pillar were reviewed with comparision and analysis by numerical method.

• Geomechanics and Engineering
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• v.22 no.5
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• pp.449-460
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• 2020

The double-lane arrangement model is frequently used in underground coal mines because it is beneficial to improve the mining efficiency of the working face. When the double-lane arrangement is used, the service time of the reserved roadway increases by twice, which causes several difficulties for the maintenance of the roadway. Given the severe non-uniform deformation of the reserved roadway in the Buertai Coal Mine, the stress distribution law in the mining area, the failure characteristics of roadway and the control effect of support resistance (SR) were systematically studied through on-site monitoring, FLAC 3D numerical simulation, mechanical model analysis. The research shows that the deformation and failure of the reserved roadway mainly manifested as asymmetrical roof sag and floor heave in the region behind the working face, and the roof dripping phenomenon occurred in the severe roof sag area. After the coal is mined out, the stress adjustment around goaf will happen to some extent. For example, the magnitude, direction, and confining pressure ratio of the principal stress at different positions will change. Under the influence of high-stress rotation, the plastic zone of the weak surrounding rock is expanded asymmetrically, which finally leads to the asymmetric failure of roadway. The existing roadway support has a limited effect on the control of the stress field and plastic zone, i.e., the anchor cable reinforcement cannot fully control the roadway deformation under given conditions. Based on obtained results, using roadway grouting and advanced hydraulic support during the secondary mining of the panel 22205 is proposed to ensure roadway safety. This study provides a reference for the stability control of roadway with similar geological conditions.

• Advances in concrete construction
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• v.8 no.3
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• pp.207-215
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• 2019

Application of nanotechnology can be used to tailor made cementitious composites owing to small dimension and physical behaviour of resulting hydration products. Because of high aspect ratio and extremely high strength, carbon nanotubes (CNTs) are perfect reinforcing materials. Hence, there is a great prospect to use CNTs in developing new generation cementitious materials. In the present paper, a parametric study has been conducted on cementitious composites reinforced by two types of multi walled carbon nanotubes (MWCNTs) designated as Type I CNT (10-20 nm outer dia.) and Type II CNT (30-50 nm outer dia.) with various concentrations ranging from 0.1% to 0.5% by weight of cement. To evaluate important properties such as flexural strength, strain to failure, elastic modulus and modulus of toughness of the CNT admixed specimens at different curing periods, flexural bending tests were performed. Results show that composites with Type II CNTs gave more strength as compared to Type I CNTs. The highest increase in strength (flexural and compressive) is of the order of 22% and 33%, respectively, compared to control samples. Modulus of toughness at 28 days showed highest improvement of 265% for Type II 0.3% CNT composites. It is obvious that an optimum percentage of CNT could exists for composites to achieve suitable reinforcement behaviour and desired strength properties. Based on the parametric study, a tentative optimum CNT concentration (0.3% by weight of cement) has been proposed. Scanning electron microscope image shows perfect crack bridging mechanism; several of the CNTs were shown to act as crack arrestors across fine cracks along with some CNTs breakage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.68-75
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• 2021

In this study, the anchoring performance of 57mm headed bars anchored at the external beam-column joint under cyclic loading was evaluated. A total of 6 external beam-column joint test specimens were planned, and anchorage performance was evaluated by setting concrete compressive strength, side covering thickness, lateral reinforcement ratio, and fracture type as major experimental variables. As result of cyclic loading test, it was found that the factors that had the greatest influence on the anchoring capacity of the large-diameter headed bar anchored at the joint were the side cover thickness and the transverse reinforcing bar. It was confirmed that the 57mm large-diameter headed bar anchored at the external beam-column joint showed sufficient anchoring capacity even under cyclic loading.

• Korean Journal of Materials Research
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• v.29 no.11
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• pp.690-696
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• 2019

Geopolymer is an alumina silicate-based ceramic material that has good heat-resistance and fire-resistance; it can be cured at room temperature, and thus its manufacturing process is simple. Geopolymer can be used as a reinforcement or floor finish for high-speed curing applications. In this manuscript, we investigate a high-speed curing geopolymer achieved by adding calcium to augment the curing rate. Metakaolin is used as the main raw material, and aqueous solutions of KOH and $K_2SiO_3$ are used as the activators. As a result of optimizing the high bending strength as a target factor for geopolymers with $SiO_2/Al_2O_3$ ratio of 4.1 ~ 4.8, the optimum ranges of the active agent are found to be $0.1{\leq}K_2O/SiO_2{\leq}0.4$ and $10{\leq}H_2O/K_2O{\leq}32.5$, and the optimum range of the curing accelerator is found to be $$0.82{\leq_-}Ca(OH)_2/Al_2O_3{\leq_-}2.87$$. The maximum flexural strength is found to be 1.35 MPa at $Ca(OH)_2/Al_2O_3=2.82$, $K_2O/SiO_2=0.3$, and $H_2O/K_2O=11.3$. The physical and thermal properties are analyzed to validate the applicability of these materials as industrial insulating parts or repairing finishing materials in construction.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.513-521
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• 2020

In this paper, due to the need for cutting cement-soil group pile composite foundation under the 7-story masonry structure of Zhenghe District and the shield tunnel of Zhengzhou Metro Line 5, a field test was conducted to directly cut cement-soil single pile composite foundation with diameter Ф=500 mm. Research results showed that the load transfer mechanism of composite foundation was not changed before and after shield tunnel cut the pile, and pile body and the soil between piles was still responsible for overburden load. The construction disturbance of shield cutting pile is a complicated mechanical process. The load carried by the original pile body was affected by the disturbance effect of pile cutting construction. Also, the fraction of the load carried by the original pile body was transferred to the soil between the piles and therefore, the bearing capacity of composite foundation was not decreased. Only the fractions of the load carried by pile and the soil between piles were distributed. On-site monitoring results showed that the settlement of pressure-bearing plates produced during shield cutting stage accounted for about 7% of total settlement. After the completion of pile cutting, the settlements of bearing plates generated by shield machine during residual pile composite foundation stage and shield machine tail were far away from residual pile composite foundation stage which accounted for about 15% and 74% of total settlement, respectively. In order to reduce the impact of shield cutting pile construction on the settlement of upper composite foundation, it was recommended to take measures such as optimization of shield construction parameters, radial grouting reinforcement and "clay shock" grouting within the disturbance range of shield cutting pile construction. Before pile cutting, the pile-soil stress ratio n of composite foundation was 2.437. After the shield cut pile is completed, the soil around the lining structure is gradually consolidated and reshaped, and residual pile composite foundation reaches a new state of force balance. This was because the condensation of grouting layer could increase the resistance of remaining pile end and friction resistance of the side of the pile.