• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.259-267
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• 2008

The ultimate strengths of reinforced concrete deep beams are governed by the capacity of the shear resistance mechanism composed of concrete and shear reinforcing bars, and the structural behaviors of the beams are mainly controlled by the mechanical relationships according to the shear span-to-effective depth ratio, flexural reinforcement ratio, load and support conditions, and material properties. In this study, a simple indeterminate strut-tie model reflecting all characteristics of the ultimate strengths and complicated structural behaviors is presented for the design of simply supported reinforced concrete deep beams. In addition, a load distribution ratio, defined as a magnitude of load transferred by a vertical truss mechanism, is proposed to help structural designers perform the design of simply supported reinforced concrete deep beams by using the strut-tie model approaches of current design codes. In the determination of a load distribution ratio, a concept of balanced shear reinforcement ratio requiring a simultaneous failure of inclined concrete strut and vertical steel tie is introduced to ensure the ductile shear failure of reinforced concrete deep beams, and the prime design variables including the shear span-to-effective depth ratio, flexural reinforcement ratio, and compressive strength of concrete influencing the ultimate strength and behavior are reflected upon based on various and numerous numerical analysis results. In the companion paper, the validity of presented model and load distribution ratio was examined by employing them to the evaluation of the ultimate strengths of various simply supported reinforced concrete deep beams tested to failure.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.727-735
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• 2012

Recently, a high-strength strand of 2400 MPa was developed using domestic technologies. In 2011, KS D 7002 was revised to cover the newly developed high-strength strands to support their practical usage. Presently, however, discussions and evaluations are not sufficient on the mechanical properties of the strands and their performance in structural members. Also, there were no detailed reviews on the need to revise the current design code for practical use of the high-strength strands. In this study, flexural behavior of a member with the high-strength strands was estimated through sectional analysis and a review and comparison of the domestic and foreign design codes were conducted considering the analysis results. Also, the need for the revision of the design code was discussed. Such discussion especially focused on the estimation of the stress in strand, which related with various issues such as determination methods for yield point of strands, time-dependent loss of prestressing force, estimation of stress in strand at member failure, and net strain limit for ductile failure of member. The discussion revealed that some parts in the design code need a revision and the further studies are required.

• The Journal of Engineering Geology
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• v.15 no.1
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• pp.9-17
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• 2005

A set of soil samples were picked up from a failed slope formed by rainfall in limestone zone in Jangseong-gun, Jeonnam, Korea, to find out its physical and mechanical characteristics for this study, and variation of safety factor depending on slope inclination was defined by analysing slope stability affected by rainfall. Decomposed limestone soil in the research area is composed of quartz, orthoclase, gibbsite, geothite, etc., with specific gravity of 2.73, and this soil is included in SC by unified soil classification system. Calcium ingredient decreased remarkably during weathering at its mother rock. Coefficient of permeability is 2.56×10/sup -4/ cm/ sec, similar to its value of silty clay. Cohesion decreases remarkably from 3.0 t/ ㎡ to 0.72 t/ ㎡, and Φ value of internal friction angle tends to decrease as it turns to be saturated soil from partial saturated soil in the shear test. To analyze slope stability affected by rainfall, it is reasonable to seek seepage depth with reference to rainfall＊ intensity. In the slope stability analysis, when the seepage depth is the larger, its safety factor is the less, which makes the slope unstable. Comparing with minimum safety factor, 1.5 of cut slope in consideration of the seep-age line, safety factor is found to be satisfactory only when inclination of cut slope of decomposed limestone soil is more than 1：1.2 slope at least considering rainfall. It is also found that decrease of cohesion has great effect on decline of safety factor of slope while partial saturated soil turns to be saturated soil.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.711-717
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• 1999

A multilayer-structure material containing ductile and brittle layer simultaneously was examined and compared with a single layer material using fracture mechanical properties. We found that impact strength of multilayer structure material was considerably higher than single layer's and toughness was enhanced by about two times or higher in similar glass transition temperature($T_g$) region and the same dimension. The superposition principle of impact pulse was used for interpretation of kinetic stress wave as a high-velocity crack proceeds in the plastic. It was understood that the optimum condition of ductile/brittle thickness ratio could be designed in the final toughness enhancement of multilayer.

• Composites Research
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• v.13 no.3
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• pp.9-20
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• 2000

Free vibration characteristics of a cantilevered laminated composite beam with multiple non-propagating transverse open cracks are investigated. In the present analysis a special ply-angle distribution referred to as asymmetric stiffness configuration inducing the elastic coupling between chord-wise bending and extension is considered. The multiple open cracks are modelled as equivalent rotational springs whose spring constants are calculated based on the fracture mechanics of composite material structures. Governing equations of a composite beam with open cracks are derived via Hamilton's Principle and Timoshenko beam theory encompassing transverse shear and rotary inertia effect is adopted. The effects of various parameters such as the ply angle, fiber volume fraction, crack numbers, crack positions and crack depthes on the free vibration characteristics of the beam with multiple cracks are highlighted. The numerical results show that the existence of the multiple cracks in an anisotropic composite beam affects the free vibration characteristics in a more complex fashion compared with the beam with a single crack.

• Explosives and Blasting
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• v.28 no.1
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• pp.1-10
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• 2010

In blasting for lighting, fatigue behaviors of pillars such as destruction and deformation may occur due to blasting vibration and flyrock, which may cause collapses of cavities. This study aims to identify dynamic behavior of pillars to maintain efficient safety of cavities in large drafts. when they collide with flyrocks under blasting for the excavation. For the purpose, we compared ground vibration around pillar when flyrock collided with the pillar and that when explosive blast happened for the excavation. we conducted fragmentation analysis of the flyrock and compared impact vibration obtained from empirical equation with ground vibration obtained from regression analysis of real vibration data. also we compared those with results analyzed from numerical analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.53-62
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• 1992

Material can be degraded by using it for a long service under the high temperature and pressure circumstances, Therefore, material degradation can affect the strength of mechanical structures. At present, the life prediction of the degraded structures is considered as an important technical problem. In this paper, the degraded 21/4Cr-lMo steel is the material used for about 10 years around 400.deg. C in an oil refinery plant. The recovered one was prepared out of the above degraded steel by heat treatment for one hour at 650.deg. C. The degradation effect was investigated through the tension test, Hardness test and Charpy impact test. On the smooth surface material, the fatigue crack initiation, growth and coalescence stages of the distributed small cracks were investigated with photographs, and the crack length and density were measured. The measuring results were analyzed by quantative and statistical methods.

• Journal of Korean Society of Steel Construction
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• v.11 no.4 s.41
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• pp.339-350
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• 1999

In this study, blowholes, a kind of solid defects, were intentionally introduced in transverse butt-welded joints which are widely used for the connection of main members in steel structures to evaluate the fatigue characteristics of these joints with blowholes according to the difference of the size and shape of blowholes, and a series of tests were performed. Static test results proved that the static strength of these joints with blowholes was not affected by their size and shape. From the fatigue test results on these joints with blowholes, the size and shape of blowholes inside the weld metals were strongly affected in fatigue strength, and we suggested the relationship between fatigue strength and their size and shape quantitatively. Also, Using the relationship of fatigue crack growth rate and stress intensity factor range, the fatigue life of transverse butt-welded joints with blowholes can be estimated properly.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.1
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• pp.10-18
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• 1996

This study verified the relationship between fracture mechanics parameters and X-ray parameters for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation test were carried out and X-ray diffraction technique was applied to fatigue fractured surface. The change in X-ray parameters(residual stress, half-value breadth) according to the depth of fatigue fractured surface were investigated. The depth of maximum plastic zone, $w_y$, were determined on the basis of the distribution of the half-value breadth for normalized SS41 steel and that of the residual stress for M.E.F. dual phase steel. $K_{max}$ could be estimated by the measurement of $w_y$.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.77-85
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• 2015

This paper describes the development of force limiting device(FLD). The FLD could induce compressive yield before occurring elastic buckling for slender member under compressive load. Therefore, it might prevent reduction of load carrying capacity by elastic buckling and the structures with the devices would behave stable. A new type of FLD reduced cross area is proposed in this study different to existing studies like as out of plane type, slit type and folded plate type. The parameters of specimens are depth, width and number of cutting. The structural capacity and characteristics of proposed types were verified by experiment and FEM analysis. The FLD of cutting type is efficient in compressive member.