• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.131-136
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• 2019

Buildability of fresh concrete, a key element of Concrete 3D printing, is the ability to build filaments at a desirable height without excessive deformation or collapse. Buildability is closely related to yield stress, and the higher the yield stress, the better. Also, the shear stress of fresh concrete increases as it hardens over the time after extruded, and consequently the buildability increases. Therefore, in concrete 3D printing, proper time gaps between printed layers (Printing Time Gap, PTG) are required to ensure the buildability of fresh concrete. As the PTG increases, the buildability increases; however, an excessive PTG reduces the bond performance between the printed layers, and the extrudability can be lowered as the printing time increases. In this research, therefore, 3D printing experiments were conducted with the variable of PTG to examine the buildability of 100 MPa-high strength concrete. In addition, a pseudo-layer loading method was applied to simulate the buildability test for 3D concrete printing and its applicability was examined.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.20-26
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• 2014

In this paper, yield stress, tangent modulus and failure strain were varied to ascertain the influence of impact response such as impact force histories and residual energy. And the buckling behavior of FML(Fiber Metal Laminates) were analyzed using numerical method. A number of analyses on FML and aluminum panel were conducted for shear and compression loading to compare the capability of stability. And to evaluate the static performance, static analysis has performed for box beam structure. Low-velocity impact analysis has performed on FML made of aluminum 2024 sheet and glass/epoxy prepreg layers. And the buckling and static performance of FML have been compared to aluminum using the analysis results. For the comparison of structural performance, similar analyses have been carried out on monolithic aluminum 2024 sheets of equivalent weight.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.331-338
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• 2023

Modern bulletproof armor must be light and have excellent penetration resistance to ensure the mobility and safety of soldiers and military vehicles. The ballistic performance of heterogeneous structures of laminated flat plates as bulletproof armor depends on the arrangement of constituent materials for the same weight. In this study, we analyze bulletproof performance according to the stacking sequence of laminated bulletproof armor composed of Kevlar, ultra-high molecular weight polyethylene, and ethylene-vinyl-acetate foam. A ballistic analysis was performed by colliding a 7.62 × 51 mm NATO cartridge's M80 bullet at a speed of 856 m/s with six lamination arrangements with constituent materials thicknesses of 5 mm and 6.5 mm. To evaluate the bulletproof performance, the residual speed and residual energy of the projectile that penetrated the heterogeneous laminated flat plates were measured. Simulation results confirmed that the laminated structure with a stacking sequence of Kevlar, ultra-high molecular weight polyethylene, and ethylene-vinyl-acetate foam had the best bulletproof performance for the same weight.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.9-15
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• 2023

In this study, the lamination performance and strength characteristics of cement-based composite materials according to the laminated specimens manufacturing method were analyzed. As a result of evaluating the buildability according to the layer height, the highest dimensional stability was shown when the layer height was 10 mm in all parts. The mold casting specimen and the printing-Z specimen showed the same compressive strength performance at the age of 28 days. On the other hand, the compressive strength at 28 day of printing-X specimen was the lowest at 71.72 MPa, and 8% lower than that of the mold casting specimen and the printing-Z specimen. The split tensile strength of the laminated specimen may show similar performance to that of the mold casting specimen, but the strength performance may decrease by more than 10% depending on the direction of the layer and the number of layers in the specimen. As a result of the interface analysis of the laminated specimen through X-ray CT analysis, it was confirmed that pores of a certain size were distributed along the interface of the layer.

• Journal of the Korean Society for Railway
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• v.13 no.4
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• pp.440-446
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• 2010

This paper was investigated on the laminated rubber bearing, which mitigates damages of bridges from threat of earthquakes. Laminated rubber bearing can bear large loads for long periods of time and be capable of large deformations during an earthquake. To evaluate seismic isolation with laminated rubber bearing on several earthquake waves, we performed a shaking table test. In this test, deck acceleration was measured by accelerometers and shear force on piers was surveyed by load cells. Furthermore, seismic capacity of isolated systems with laminated rubber bearing was compared with non-isolated systems through shaking table test. The results show that deck acceleration and shear force were relatively reduced by laminated rubber bearing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.6
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• pp.85-92
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• 2010

Recently the earthquake occurrences in Korea are likely to increase. Therefore, the facilities such as bridges and tunnels under the unexpected earthquakes need to be enhanced. Especially most of the subways previously built before 1988 have not been seismically designed, so their seismic safety requirements are required to be inspected and/or reinforced. In this study, the seismic reinforcement using FRP-ductile material layered composites was proposed to reinforce for the subway columns. Material properties of FRP-ductile material layered composites were calculated by laboratory tests considering the laminated conditions of the composites. Numerical simulations were performed using the experimental results of the specimens and the calculated properties of the composites. Seismic performance varied according to the types of composites: ductile material, number of layers, fiber orientations.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.1 s.41
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• pp.43-50
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• 2005

Many highway bridges in Korea need seismic retrofit because only one decade has passed since the seismic design criteria was introduced. For the highway bridges of which bearings are worn and dysfunctional, the validity of seismic retrofit method using laminated rubber bearings was discussed in this study. Real scale RC pier specimens without seismic details were constructed. And then, Pot bearing, Rubber bearing (RB), Lead-rubber bearing (LRB) were applied to these specimens. Through pseudo dynamic test method, dynamic behavior of these RC piers under earthquake was simulated and compared. From the test results, proposed seismic retrofit method was found to be valid.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.2
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• pp.63-72
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• 2004

The purpose of this study is to evaluate seismic performance of reinforced concrete bridge piers supported by laminated rubber bearings. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. Seismic isolator element is developed to predict behaviors of laminated rubber bearings. The proposed numerical method for seismic performance evaluation of reinforced concrete bridge piers supported by laminated rubber bearings is verified by comparison with reliable experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.35-42
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• 2024

This study evaluated the buildability and mechanical properties of 3DP concrete printed in air and underwater environments. Buildability was evaluated by green strength test on fresh concrete and height and deflection immediately and 1 hour after printing. The green compressive strength of the concrete was 5.0 kPa after 30 minutes and 7.9 kPa after 3 hours, an increase of 1.6 times the initial strength. The total height of the laminated parts met the design height regardless of the printing environment. The amount of deflection in air and under water 1 hour after printing was 1 mm and 0.2 mm, respectively, indicating a small amount of deflection under water. The apparent density of the sample appeared in the order of A-M > A-P > UW-P. This is believed to be because a large amount of air is mixed into the concrete during the printing process, and water infiltrates during the underwater printing process. The compressive strength ratio of UW-P/A-P was 0.86 at 1 day, but the compressive strength of the underwater printed concrete was high from 7 days.

• Journal of the Korea Convergence Society
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• v.12 no.1
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• pp.105-110
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• 2021

Radiation shielding of affinity material, which is widely used in medical institutions, is made in sheet form and is mainly applied to apron. Shielding performance is presented based on lead equivalent, and is presented as 0.25-0.50mmPb. In the case of shielding materials where lead is used as the main material, the shielding performance can be adjusted by thickness due to the excellent machinability of lead. However, eco-friendly shielding sheets are difficult to control shielding performance based on thickness criteria as shielding performance varies depending on the content of shielding materials, the properties of polymeric materials that are base materials, and the technical differences in the process. In this study, shielding sheets were manufactured based on thickness to solve these problems and the shielding performance was compared in this study. As a result, it was shown that the laminated structure shielding sheet was more effective.