• Journal of the Korean Wood Science and Technology
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• v.49 no.4
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• pp.336-359
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• 2021

In this study, hybrid CLT research and development trends were analyzed to improve the low rolling shear strength of CLT, a large wooden panel used in high-rise wooden buildings. Through this, basic data that can be used in research and development directions for localization of CLT were prepared. As a way to improve the low rolling shear strength, the use of hardwood lamina, the change of the lamina arrangement angle, and the use of structural composite materials are mainly used. Rolling shear strength and shear modulus of hardwood lamina are more than twice as high as softwood lamina. It confirmed that hardwoods can be used and unused species can be used. Rolling shear strength 1.5 times, shear modulus 8.3 times, bending stiffness 4.1 times improved according to the change of the layer arrangement angle, and the CLT strength was confirmed by reducing the layer arrangement angle. Structural wood-based materials have been improved by up to 1.35 times MOR, 1.5 times MOE, and 1.59 times rolling shear strength when used as laminas. Block shear strength between the layer materials was also secured by 7.0 N/mm², which is the standard for block shear strength. Through the results of previous studies, it was confirmed that the strength performance was improved when a structural wood based materials having a flexural performance of MOE 7.0 GPa and MOR 40.0 MPa or more was used. This was determined based on the strength of layered materials in structural wood-based materials. The optimal method for improving rolling shear strength is judged to be the most advantageous application of structural wood based materials with strength values according to existing specifications. However, additional research is needed on the orientation of CLT lamina arrangement according to the fiber arrangement of structural wood-based materials, and the block shear strength between lamina materials.

• Journal of the Korean Wood Science and Technology
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• v.43 no.4
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• pp.446-455
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• 2015

Based on comparative studies on standards and grading procedures of machine graded lumber in Korea and other countries, this study proposed a procedure of determining the grade classification and design strengths of domestic machine graded lumber. Differences between machine stress rated lumber and E-rated laminations were detailed in order to clarify the need for the procedure improvement. To this improvement the use of average MOE requirement for grading was introduced instead of the fixed minimum MOE requirement which is currently used in the Korean standards. It was found that the fixed minimum MOE requirement method was easier for an inspector to grade but, less efficient as a strength predictor than the average MOE requirement method. The advantage of average MOE requirement method is statistically MOR-MOE regression-based MOR prediction and highly efficient in quality control though it requires a computer-aided operation system in an initial setup. A major weakness of the current Korean grading system was found that different strength characteristics depending on wood species were not reflected on the grade classification and the tabulated allowable design stress. The proposed procedures were developed taking advantages of respective merits of both methods and based on MOR-MOE regression analysis. Through this procedure, the grades of machine stress rated lumber should be revised to become interchangeable with E-rated lamination, which would be beneficial to the cost competitiveness of domestic machine graded lumber and glued laminated timber industry.

• KIEAE Journal
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• v.8 no.3
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• pp.77-83
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• 2008

The effective mixture of structural laminated timber and other materials is expected to extend the potentials of building structures because of the potentials to realize high performance in structural safety. The classical joint types using drift pin and bolts are occurred local failures due to the small bearing area. In result, new joints using H shaped steel were suggested in this research. The objective of this study is to evaluate elasto-plastic behaviors by strengthening types of wood frames with new joints connecting structural laminated timber with H shaped steel. A total of five specimens of about one-second scale were tested. Specimens had columns with 1,050 height and $84mm{\times}100mm$ section, and a beams with 1,950mm length and $130mm{\times}100mm$ section. Also, the specimens were stiffened by brace, hwang-toh brick, and autoclaved lightweight concrete. The results of the test showed that the specimen stiffened with autoclaved lightweight concrete was characterized by fairly good strength and stiffness than those of the other specimens. Initial stiffness of H-2.0D-NS specimen with 2 times inserting length of beam height showed 1.33 times than that of H-1.5D-NS specimen. However, the strength of H-2.0D-NS specimen has not improved too much than H-1.5D-NS specimen.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.22 no.1
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• pp.43-56
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• 2012

Wireless sensor networks consist of numerous small-sized nodes equipped with limited computing power and storage as well as energy-limited disposable batteries. In this networks, nodes are deployed in a large given area and communicate with each other in short distances via wireless links. For energy efficient networks, dynamic clustering protocol is an effective technique to achieve prolonged network lifetime, scalability, and load balancing which are known as important requirements. this technique has a characteristic that sensing data which gathered by many nodes are aggregated by cluster head node. In the case of cluster head node is exposed by attacker, there is no guarantee of safe and stable network. Therefore, for secure communications in such a sensor network, it is important to be able to encrypt the messages transmitted by sensor nodes. Especially, cluster based sensor networks that are designed for energy efficient, strongly recommended suitable key management and authentication methods to guarantee optimal stability. To achieve secured network, we propose a key management scheme which is appropriate for hierarchical sensor networks. Proposed scheme is based on polynomial key pool pre-distribution scheme, and sustain a stable network through key authentication process.