The purpose of this study is to optimize the composition of CSA (calcium sulfoaluminate) cement with sodium silicate (Na2SiO3) and gypsum for binder jetting 3D printing. The preliminary test was carried out with an applicator to decide the proper thickness of one layer before using the 3D printer. A liquid binder was then selected to maintain the shape of the particles. Based on the results, the optimal mixture of dry materials and a liquid activator was derived through various parametric studies. For dry materials, the optimum composition of CSA cement, gypsum, and sand was suggested, and the liquid activator made with sodium silicate solution and VMA (viscosity modified agent) were selected. The setting time with gypsum and sodium silicate was controlled within 30 s. In case of the delayed setting time and the rapid setting mixture, the jetting line was printed thicker or thinner and the accuracy of the printout was degraded. In order to adjust the viscosity of the liquid activator, 10% of the VMA was used in 35% of sodium silicate solution and the viscosity of 200–400 cP was suitable to be sprayed from the nozzle. With this optimal mixture, a prototype of atypical decorative wall was printed, and the compressive strength was measured at about 7 MPa.
The purpose of this study is to investigate the characteristics of fresh concrete and the mechanical properties of hardened concrete with incorporation of amorphous metallic fiber into high strength concrete. Based on the experimental results, the slump decreases as the content of amorphous metallic fiber concrete increases, and it can be ensured that the optimum workability is obtained when 0.3% of concrete volume fraction in mixing is mixed regardless of the length of the steel fiber. In addition, the incorporation of amorphous metallic fiber has a limitation on the enhancement of compressive strength regardless of steel fiber content ratio, but tensile strength and flexural strength increase up to 2 times depending on the increase of the content ratio and length of the steel fiber. The bond stress increased with the increase of the content rate of the steel fiber, but it is considered that the optimum content ratio of amorphous metallic fiber is 0.3 % of volume fraction with regard to the workability and mechanical properties.
Real-time hybrid dynamic test is an economical and efficient method capable of the replacement of the shaking table test. The purpose of this paper is to optimize the control algorithms and the system configuration for the prediction of the structural dynamic behavior with the interaction between a physical substructure and a numerical modeling in the hybrid testing system. FEAPH, nonlinear finite element analysis program for hybrid, was developed with a fixed number of substep iteration method and parallel computational technique in the control algorithms. These algorithms can improve the inefficiency of iterative methods caused by sequential process, so that the computational time can be reduced. Furthermore, the previously used data communication method and the interface between a substructure and an analysis program were simplified in the control system. In order to verify the accuracy of the hybrid system, the dynamic test with steel framed structure was conducted. As the results, the processing time in hybrid test with FEAPH was improved up to 10% rather than with OpenSees. Moreover the testing performance is almost the same trend within a 5% error level.
Advanced foreign countries have performed the fire resistance design of buildings by the alternative performance design methods, which are based on fire engineering theories. However, in the case of South Korea, the process on the alternative fire resistance performance design has only suggested without any applications for real steel structures. This study was performed to evaluate the fire resistance performance of a steel building using the fire resistance performance design program, which was developed in the former research. From this study, it was obtained that the fire resistance design was over designed for the steel building in South Korea.
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