• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.5 s.51
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• pp.85-97
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• 2006

Capacity design is to guarantee ductile failure of whole bridge system by preventing brittle failure of columns and any other structural elements until the columns develope fully enough plastic deformation capacity. This concept has been explicitly regulated in most bridge design specifications of foreign countries except the current Korea Bridge Design Specifications. In the capacity design, the transformed shear force from flexural overstrength of reinforced concrete column is used as the design lateral shear force for shear design of columns and design of footings and piles. Different calculating methods are adopted by the design specifications, since the variability of material strength and construction circumstances of the local regions should be considered. This paper proposed material overstrength factors by investigating 3,407 reinforcing bar data and 5,405 concrete compressive strength data collected in Korean construction sites. It also proposed calculating procedures for flexural overstrength of reinforced concrete columns using the material overstrength. Finally, overstrength factor was proposed as 1.5 by investigating 1,500 column section data from moment-curvature analysis using the material overstrength.

• KIEAE Journal
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• v.15 no.1
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• pp.139-146
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• 2015

This is an experimental study on the engineering characteristics of perforated reinforced concrete beams with shells. In the material matter of this study, the water cement ratio put 60%, the ratio of substitution of oyster shells to fine aggregate 30%. And in the structural matter, the form of opening put circle and square, the size of opening as the radius and the length of it changed from one to three times of the beam depth with a change presence and absence of reinforced steel around opening. All thirteen reinforced concrete beam tests composed one standard beam and twelve six beams with the circle and square opening were tested in shear strength under two points loading and compared and analyzed the characteristics of test beams under the same conditions one another. The results of the study showed as followed. 1) The initial crack load value of the opening test beams is similar the standard beam but the maximum load value decreased with increase in proportion of the opening size, in the square opening than the circle opening and in the absence than the presence of reinforced steel. 2) As the difference between the circle opening and the square opening beams is represented 2.17~9.8% in the maximum load value and the load capacity of the square opening suddenly decrease than it of the circle opening, it is judged because of the shortage of concrete section, the concentration of the stress in the corner of the square opening and material influence of shell substitution. 3) The failure figure such as the pattern of the crack and so on is represented brittle failure as the opening size is the bigger and the ratio of substitution is higher because of the lack material properties.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.143-153
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• 2003

New strengthening method based on Near Surface Mounted technique (NSM) is suggested, which can overcome the brittle nature of failure inherent to those reinforced concrete beams strengthened with FRP composite materials. The suggested technique secures ductile failure of reinforced concrete beams by having the strengthening Hybrid FRP rebars unbonded in parts. Experiments were performed in order to compare structural behaviors of strengthened beams with and without unbending along the Hybrid FRP rebars. Test results showed that only those beams strengthened by partially unbonded NSM failed in ductile manner. Theoretical expressions were derived for the minimum unbonded length of Hybrid FRP rebars with which ultimate strength of the reinforced concrete beam with partially unbonded NSM could be reached. The suggested partially unbonded NSM technique is expected to significantly improve the structural behavior of the strengthened beam with FRP composite materials.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.149-154
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• 2012

The size and distribution of welding residual stress and welding deformation in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, non-destructive technique using laser electronic speckle pattern interferometry, plate of welding specimen according to the external load on the entire behavior of residual stress are presented measurement techniques. Once, welding specimen force tensile loading, using electronic speckle pattern interferometry is measured. welding specimen of base metal and weld zone measure strain from measured result, this using measure elastic modulus. In this study, electronic speckle pattern interferometry use weld zone and base metal parts of the strain differences using were presented in residual stress calculated value, This residual stress value were calculated by numerical calculation. Consequently, weld zone of modulus high approximately 3.7 fold beside base metal and this measured approximately 8.46 MPa.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.179-190
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• 1998

Shear failure of reinforced concrete (RC) beams is serious problem due to sudden brittle failure and many experimental results proved that size effect in shear strength of RC beams is an important feature of reinforced concrete members. As the sizes of RC beams very large, experiments sometimes become very difficult so that empirical design formula or the experimental data on shear strength of RC beams could not be obtained. Then the numerical analyses for size effect on shear strength of RC beams become very important. In this study, finite-element technique of reinforced concrete is employed of shear analysis of RC beams without web reinforcement and the size effects in shear strength are numerically analyzed. The influencing factors to the size effect in the shear strength of RC beams are extensively analyzed and compared with those by major shear strength equations including several standard specifications.

• Coupled systems mechanics
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• v.2 no.4
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• pp.329-348
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• 2013

This study aims at observing the coupling behaviours between suspended ceilings and partition walls in terms of their global seismic performance using full-scale shake table tests. The suspended ceilings with planar dimensions of $6.0m{\times}3.6m$ were tested with two types of panels: acoustic lay-in and metal clip-on panels. They were further categorized as seismic-braced, seismic-unbraced, and non-seismic installations. Also, two configurations of 2.7 m high partition wall specimens, with C-shape and I-shape in the plane layouts, were tested. In total, seven ceiling-partition-coupling (CPC) specimens were tested utilizing a unidirectional seismic simulator. The test results indicate that the damage patterns of the tested CPC systems included failure of the ceiling grids, shearing-off of the wall top railing, and, most destructively, numerous partial detachments and falling of the ceiling panels. The loss of panels was mostly concentrated near the center of the tested partition wall. The testing results also confirmed that the failure mode of the non-seismic CPC systems was brittle: The whole system would collapse suddenly all at once when the magnitude of the inputs hit the capacity threshold, rather than displaying progressive damage. Overall, the seismic capacity of the unbraced and braced CPC systems could be up to 1.23 g and 2.67 g, respectively; these accelerations were both achieved at the base of the partition wall. Nonetheless, for practical applications, it is noteworthy that the three-dimensional nature of seismic excitations and the size effect of the ceiling area are parameters that exacerbate the CPC's seismic response so that their actual capacity may be dramatically decreased, leading to important losses even in moderate seismic events.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.723-738
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• 2017

Rock is a heterogeneous material, which introduces complexity in the analysis of rock slopes, since both the existing discontinuities within the rock mass and the intact rock contribute to the degradation of strength. Rock failure is often catastrophic due to the brittle nature of the material, involving the sliding along structural planes and the fracturing of rock bridge. This paper proposes an advanced discretization method of rock mass based on block theory. An in-house software, GeoSMA-3D, has been developed to generate the discrete fracture network (DFN) model, considering both measured and artificial joints. Measured joints are obtained from the photogrammetry analysis on the excavation face. Statistical tools then facilitate to derive artificial joints within the rock mass. Key blocks are searched to provide guidance on potential reinforcement measures. The discretized blocky system is subsequently implemented into a discontinuous deformation analysis (DDA) code. Strength reduction technique is employed to analyze the stability of the slope, where the factor of safety can be obtained once excessive deformation of slope profile is observed. The combined analysis approach also provides the failure mode, which can be used to guide the choice of strengthening strategy if needed. Finally, an illustrated example is presented for the analysis of a rock slope of 20 m height inclined at $60^{\circ}$ using combined GeoSMA-3D and DDA calculation.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.949-960
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• 2002

Flat plate structures under lateral load are susceptible to punching shear failure of the slab-column connection. To prevent such brittle failure, strength and ductility of the connection should be ensured. However, due to complexity in the behavior and difficulty in simulating the actual load and boundary conditions of the flat plate system, it is not easy to obtain reliable data regarding to the strength and ductility from the previous experimental studies. In the present study, a numerical study was performed for interior connections of continuous flat plate. For the purpose, a computer program for nonlinear FE analyses was developed, and the validity was verified by comparisons with the existing experimental results. Through the parametric studies, the variations of bending moment, shear, and torsional moment around the connection were investigated. Based on the findings of the numerical studies, the aspects which need to be improved in current design methods were discussed. The results of the present study will be used for developing a design method for the flat plate-column connection in the companion paper.

• Magazine of the Korea Concrete Institute
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• v.8 no.3
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• pp.177-185
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• 1996

Four types of experiments were performed to check the similitude of member behavior between prototype and 1 /10 scale models : (1) Test of slender columns with P-$\Delta$ effect, (2) Test of short columns with and without confinement steel, (3) Test of simple beams without stirrups, and (4) 'T-beam test. Based on the results of experiments, the conclusions were made as follows : (1) The P-$\Delta$ effect of slender columns can be almost exactly represented by 1/10 scale model. (2) The effect of confinement on short columns by the hoop steel can be also roughly simulated by 1/10 scale model. (3) The failure modes of simple beams without stirrups are brittle shear failures in prototype whereas those of 1/10 scale models are the ductile yielding of tension steel followed by large diagonal tension cracking and compressive concrete failure. (4) The behaviors of prototype and 1/10 scale model in T-beams appear very similar.

• The Journal of Korean Academy of Prosthodontics
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• v.28 no.2
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• pp.147-163
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• 1990

Although dental porcelain demonstrates lasting esthetic results, it suffers from inherent brittle fractures. Various techniques and materials for intraoral porcelain repair has been suggested. This study investigated the in vitro shear strength of three porcelain repair systems according to aspects of the porcelain fractures. The purpose of this study was to evaluate the shear bond strength of three porcelain repair systems(All-bond, Clearfil, Scotchprime) according to fractured surface of porcelain - fused - to - metal restorations. For this study specimens were divided into five groups : group 1 represented fracture occurred at body porcelain layer, group 2 represented fracture occurred at opaque porcelain layer, group 3 represented fracture including 1/3 of metal exposure, group 4 represented fracture including 2/3 of metal exposure, and group 5 represented all metal surface was exposed. Specimens were stored in double deionized water(24Hr, $37^{\circ}C$) and thermocycling was performed(24Hr, 1080cycles), and subjected to a shear force parallel to the repair resin and porcelain interface by use of an University Testing Machine. The results of this study were obtained as follows : 1. In group 1 and 2, bond strength was relatively high, and bond strength showing reducing tendency as exposure of metal was increased. 2. In group 1, bond strength was relatively high, and no significant differences in porcelain repair system. 3. In group 2, 3 and 4, All-bond and Clearfil provided significantly higher bond strength than scotchprime. 4. In group 5, bond strength was the lowest among all groups and especially in case if Scotchprime. 5. Cohesive failure was observed in group 1 and 2, adhesive failure was observed in group 5, and cohesive / adhesive failures were observed in group 3 and 4.