• Journal of the Korean Wood Science and Technology
• /
• v.14 no.2
• /
• pp.3-12
• /
• 1986

The aim of this study is to determine the flexural properties(Modulus of Rupture, Modulus of Elasticity) of Platanus occidentalis L. laminated beams fabricated with 1, 3, 5, 8, 15 lamination and Tension, Compression lamination. The results were as follows: 1. MOR increased with increasing number of lamination in 3, 5, 8, 15-beam and Tension lamination beam. MOR of Compression lamination beam was lower than that of 3-beam, MOR of vertical beam not having Tension or compression lamination was lower than that of horizontal beam, but MOR of vertical beam with tension or compression lamination was same or slightly higher than that of horizontal beam. 2. The allowable working stress showed the same tendency. This stress increased with increasing number of lamination. This value of Tension lamination beam was higher than that of compression lamination beam. 3. MOE of all laminated beams was higher than that of solid beam and Tension lamination beam was higher than that of 3-beam. MOE of Tension lamination beam was higher than that of Compression lamination beam. MOE of all vertical beam was higher than that of horizontal beam except for T-2, T-5, C-3. 4. Most beam failures appeared to begin in tension. These tension failures were classified into Splintering tension, Cross-grained tension, Simple tension, Brittle tension. All test beam failures could be classified into three categories. 1) Tension failure 2) Compression failure 3) Horizontal shear failure.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.1
• /
• pp.225-232
• /
• 2005

The paper presented results of the strength distributions and tension failure behaviors of splices subjected to tension forces. The bolting patterns in the tension splices are regular and staggered patterns in the research. The finite element analyses were carried out to examine the experimental results and evaluated the stress distribution patterns. The yield stresses, maximum tension stresses, stress distribution ratios, and effective net areas were analyzed through the tension experiments.

• Geomechanics and Engineering
• /
• v.11 no.2
• /
• pp.177-195
• /
• 2016

To secure the stability of geotechnical infrastructures and minimize failures during the construction process, a number of support systems have been introduced in the last several decades. In particular, stabilization methods using steel bars have been widely used in the field of geotechnical engineering. Rock bolt system is representative support system using steel bars. Pre-stressing has been applied to enhance reinforcement performance but can be released because of the failure of head or anchor sections. To overcome this deficiency, this paper proposes an innovative support system that can actively reinforce the weak ground along the whole structural element by introducing an active tension bolt containing a spring unit to the middle of the steel bar to increase its reinforcement capacity. In addition, the paper presents the support mechanism of the active tension bolt based on a theoretical study and employs an experimental study to validate the performance of the proposed active tension bolt based on a down-scaled model. To examine the feasibility of the active tension unit in a pillar, the paper considers a pullout test and a small-scale experimental model. The experimental results suggest the active tension bolt to be an effective support system for pillar reinforcement.

• Geomechanics and Engineering
• /
• v.20 no.3
• /
• pp.175-189
• /
• 2020

A set of relatively simple five local shear and tension failure variables is presented and then implemented into a generalized poroelastic hydromechanical numerical model to analyze failure potential and stability of variably saturated geologic media. These five local shear and tension failure variables are formulated from geometrical relationships between the Mohr circle and the Mohr-Coulomb failure criterion superimposed with the tension cutoff, which approximate together the Mohr effective stress failure envelope. Finally, fully coupled groundwater flow and land deformation in two variably saturated geologic media, which are associated with a slope (Case 1) and a tunnel (Case 2), respectively, and their failure potential and stability are simulated using the resultant hydromechanical numerical model. The numerical simulation results of both cases show that shear and tension failure potential and stability of variably saturated geologic media can be analyzed numerically simply and efficiently and even better by using the five local shear and tension failure variables as a set than by using the conventional factors of safety against shear and tension failures only.

• Proceedings of the KSR Conference
• /
• 2004.10a
• /
• pp.1390-1395
• /
• 2004

Recently, the load increasement and new regenerative systems of electrified railway system make it a difficult to distinguish between the load current and fault current. The failure of traction system perhaps causes over-current to flow. The high current can collapse other railway systems. If failures of the traction system takes place, the failures are detected and protected lest it should provoke high current flow. The over current from such a traction system failure permit to charge high tension voltage and produces high temperature arc, voltage instability, current cutting, and break down railway systems. The traction system failures detect and the system has to immediately cut off from over-current flow. To isolate the failure, the system can distinguish failure current from current flows. It forces us to adapt such as a new intelligent protection system. The protective system in traction system play a role of detecting and isolating failure points. In this paper, we proposed intelligent algorithm for discriminating normal and abnormal situation instead of the system being operated abnormally.

• Geomechanics and Engineering
• /
• v.16 no.1
• /
• pp.35-47
• /
• 2018

This paper investigates the mechanisms of tunnel spalling and massive tunnel failures using fracture mechanics principles. The study starts with examining the fracture propagation due to tensile and shear failure mechanisms. It was found that, fundamentally, in rock masses with high compressive stresses, tensile fracture propagation is often a stable process which leads to a gradual failure. Shear fracture propagation tends to be an unstable process. Several real case observations of spalling failures and massive shear failures in boreholes, tunnels and underground roadways are shown in the paper. A number of numerical models were used to investigate the fracture mechanisms and extents in the roof/wall of a deep tunnel and in an underground coal mine roadway. The modelling was done using a unique fracture mechanics code FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that both tensile and shear fracturing may occur in the vicinity of an underground opening. Shallow spalling in the tunnel wall is believed to be caused by tensile fracturing from extensional strain although no tensile stress exists there. Massive large scale failure however is most likely to be caused by shear fracturing under high compressive stresses. The observation that tunnel spalling often starts when the hoop stress reaches $0.4^*UCS$ has been explained in this paper by using the extension strain criterion. At this uniaxial compressive stress level, the lateral extensional strain is equivalent to the critical strain under uniaxial tension. Scale effect on UCS commonly believed by many is unlikely the dominant factor in this phenomenon.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2001.10a
• /
• pp.298-303
• /
• 2001

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for a compact tension specimen in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives very much. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

• Journal of Mechanical Science and Technology
• /
• v.17 no.6
• /
• pp.796-804
• /
• 2003

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3$\leq$a/W$\leq$0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K$\_$I/ and $_{4}$ (SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

• Journal of KSNVE
• /
• v.7 no.5
• /
• pp.729-736
• /
• 1997

The subspan oscillation is the most important in bundled transmission lines, which can cause conductor damage and transmission line hardware failures. So it is necessary to analyze the subspan oscillation in details for transmission lines. This paper suggests the basic concept and theoretical analysis method of subspan oscillation for 6 bundle conductor transmission line, which considers wind speed, subspan length and conductor tension. Especially this paper uses a spacer damper model with clamp-arm flexibility and damping characteristics. Theoretical analysis results are proposed.

• Journal of Ocean Engineering and Technology
• /
• v.32 no.5
• /
• pp.297-309
• /
• 2018

After an accident involving mooring link failures in an offloading buoy, verification of the fatigue safety in terms of the out-of-plane bending (OPB) and in-plane bending (IPB) moments has become a key engineering item in the design of various floating offshore units. The mooring links for an 8 MW floating offshore wind turbine were selected for this study. To identify the OPB stiffness (OPB moment versus interlink angle), a numerical simulation model, called the 3-link model, is usually composed of three successive chain links closest to the fairlead or chain hawse. This paper introduces two numerical simulation techniques for the 3-link analyses. The conventional and advanced approaches are both based on the prescribed rotation approach (PRA) and direct tension approach (DTA). Comparisons of the nominal stress distributions, OPB stiffnesses, hotspot stress curves, and stress concentration curves are presented. The multiple link analyses used to identify the tension angle versus interlink angle require the OPB stiffness data from the 3-link analyses. A convergence study was conducted to determine the minimum number of links for a multi-link analysis. It was proven that 10 links were sufficient for the multi-link analysis. The tension angle versus interlink angle relations are presented based on multi-link analyses with 10 links. It was found that the subsequent results varied significantly according to the 3-link analysis techniques.