• Geomechanics and Engineering
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• 제16권3호
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• pp.273-284
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• 2018

A detailed understanding of the mechanical behaviors for crushed coal rocks after grouting is a key for construction in the broken zones of mining engineering. In this research, experiments of grouting into the crushed coal rock using independently developed test equipment for solving the problem of sampling of crushed coal rocks have been carried out. The application of uniaxial compression was used to approximately simulate the ground stress in real engineering. In combination with the analysis of crack evolution and failure modes for the grouted specimens, the influences of different crushed degrees of coal rock (CDCR) and solidified grout strength (SGS) on the mechanical behavior of grouted specimens under uniaxial compression were investigated. The research demonstrated that first, the UCS of grouted specimens decreased with the decrease in the CDCR at constant SGS (except for the SGS of 12.3 MPa). However, the UCS of grouted specimens for constant CDCR increased when the SGS increased; optimum solidification strengths for grouts between 19.3 and 23.0 MPa were obtained. The elastic moduli of the grouted specimens with different CDCR generally increased with increasing SGS, and the peak axial strain showed a slightly nonlinear decrease with increasing SGS. The supporting effect of the skeleton structure produced by the solidified grouts was increasingly obvious with increasing CDCR and SGS. The possible evolution of internal cracks for the grouted specimens was classified into three stages: (1) cracks initiating along the interfaces between the coal blocks and solidified grouts; (2) cracks initiating and propagating in coal blocks; and (3) cracks continually propagating successively in the interfaces, the coal blocks, and the solidified grouts near the coal blocks. Finally, after the propagation and coalescence of internal cracks through the entire specimens, there were two main failure modes for the failed grouted specimens. These modes included the inclined shear failure occurring in the more crushed coal rock and the splitting failure occurring in the less crushed coal rock. Both modes were different from the single failure mode along the fissure for the fractured coal rock after grouting solidification. However, compared to the brittle failure of intact coal rock, grouting into the different crushed degree coal rocks resulted in ductile deformation after the peak strength for the grouted specimens was attained.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3199-3210
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• 1996

The buckling and postbuckling behaviors were sutdied analytically and experimentally for stiffened laminated composite panels under compression loading. The panels with I-, blade, -and hat-shapeed stiffeners were investigated. In the analysis, the stiffened panels were anlyzed using the nonlinear finite element method combined with an improved arc-length method. The progressive failure analysis was done by adopting the maximum stress criterion and complete unloading failure model. The effects of the fiber angles were investigated on the buckling and postbuckling behaviors. In the experiment, the web and the lower cap of each stiffener were formed by the continuous lay-up of the skin for cocuring the stiffened panels. Therefore, the separation between stiffener and skin was not found in the junction part even after postbuckling ultimate load and the stiffened panels had excellent postbuckling load carrying capacity. A shadow moire thchnique was used to monitor the out-of-plane deformations of the panels. The piezoelectric films were attached to the panels to get the failure characteristics of the panel. The analytical results on the buckling load, postbuckling ultimate load, and failure pattern showed good agreement with the experimental results.

• Steel and Composite Structures
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• 제21권5호
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• pp.1157-1182
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• 2016

A newly puzzle shape of crestbond rib shear connector is a type of ductile perfobond rib shear connector. This shear connector has some advantages, including relatively easy rebar installation and cutting, as well as the higher shear resistance strength. Thus, this study proposed a newly puzzle shape of crestbond rib with a "${\mho}$" shape, and its shear resistance behaviors and shear strengths were examined using push-out tests. Five main parameters were considered in the push-out specimens to evaluate the effects of shear resistance parameters such as the dimensions of the crestbond rib, transverse rebars in the crestbond dowel, concrete strength, rebar strength, and dowel action on the shear strength. The shear loading test results were used to compare the changes in the shear behaviors, failure modes, and shear strengths. It was found that the concrete strength and number of transverse rebars in the crestbond rib were significantly related to its shear resistance. After the initial bearing resistance behavior of the concrete dowel, a relative slip occurred in all the specimens. However, its rigid behavior to shear loading decreased the ductility of the shear connection. The cross-sectional area of the crestbond rib was also shown to have a minor effect on the shear resistance of the crestbond rib shear connector. The failure mechanism of the crestbond rib shear connector was complex, and included compression, shear, and tension. As a failure mode, a crack was initiated in the middle of the concrete slab in a vertical direction, and propagated with increasing shear load. Then, horizontal cracks occurred and propagated to the front and rear faces of the specimens. Based on the results of this study, a design shear strength equation was proposed and compared with previously suggested equations.

• Geomechanics and Engineering
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• 제24권6호
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• pp.573-588
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• 2021

The interaction of cracks and water significantly affects the fracture mechanism of rocks. In this study, laboratory tests were conducted using sandstone samples containing a single fissure to explore the hydro-mechanical behaviors in the failure process of pre-cracked rocks. The internal crack characteristics were also analyzed using X-ray CT scanning. The results show that the confining pressure has the greatest effect on the mechanical properties (e.g., strengths, elastic modulus, and Poisson's ratio), followed by the fissure inclination and water pressure. At a lower fissure inclination, the confining pressure may control the type main cracks that form, and an increase in the water pressure increases the number of anti-wing cracks and the length of wing cracks and branch cracks. However, the fracture behaviors of samples with a higher fissure inclination are only slightly affected by the confining pressures and water pressures. The effect of fissure inclination on the internal crack area is reduced with the propagation from the fissure tips to the sample ends. The fissure inclination mainly affects the value of permeability but not affect the trend. The impact of pre-existing fissure on permeability is smaller than that of confining pressure and water pressure.

• Geomechanics and Engineering
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• 제28권2호
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• pp.197-207
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• 2022

The seismic holding behaviors of plate anchor embedded into submerged coarse-grained soils were investigated considering different anchor inclinations. The limit equilibrium method and the Pseudo-Dynamic Approach (PDA) were employed to calculate the inertia force of the soils within the failure rupture. In addition, assuming the permeability of coarse-grained soils was sufficiently large, the coefficient of hydrodynamic force applied on the inclined plate anchor is obtained through adopting the exact potential flow theory. Therefore, the seismic holding resistance was calculated as the combination of the inertia force and the hydrodynamic force within the failure rupture. The failure rupture can be developed due to the uplift loads, which was assumed to be an arc of a circle perpendicular to the anchor and inclines at (π/4 - φ/2). Then, the derived analytical solutions were evaluated by comparing the static breakout factor N_γ to the published experimental and analytical results. The influences of soil and wave properties on the plate anchor holding behavior are reported. Finally, the dynamic anchor holding coefficients N_γd, were reported to illustrate the anchor holding behaviors. Results show that the soil accelerations in x and z directions were both nonlinear. The amplifications of soil accelerations were more severe at lower normalized frequencies (ωH/V) compared to higher normalized frequencies. The coefficient of hydrodynamic force, C, of the plate anchor was found to be almost constant with anchor inclinations. Finally, the seismic anchor holding coefficient oscillated with the oscillation of the inertia force on the plate anchor.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.738-741
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• 2004

This study is concerning on modeling to predict the flexural behaviors of FRP-confined concrete structural members. For compressive behaviors of confined concrete by FRP jackets, the hypoelasticity-based constitutive law of concrete has been presented under the basis of three-dimensional stress states. The strength enhancement of concrete wrapped by FRP jackets has been determined by the failure surface of concrete in tri-axial states, and its corresponding peak strain is computed by the strain enhancement factor. The behavior of FRP jackets has been modeled using the mechanics of orthotropic laminated composite materials in two-dimensional stress states. To be based on the three-dimensional constitutive laws, an algorithm for the prediction of flexural bending behaviors of FRP-confined concrete structural member has been presented.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.61-64
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• 2004

The strength characteristics as well as deformation behaviors of honeycomb sandwich composite (HSC) structures were investigated under bending in consideration of various failure modes such as skin layer yielding, interface-delamination, core shear deformation and local buckling. Deformation behaviors of honeycomb sandwich plates were observed with various types of aluminum honeycomb core and skin layer. Their finite-element analysis simulation with a real model of honeycomb core was performed to analyze stresses and deformation behaviors of honeycomb sandwich plates. Its results were very comparable to the experimental ones. Consequently, the increase in skin layer thickness and in cell size of honeycomb core had dominant effects on the strength and deformation behaviors of honeycomb sandwich composites.

• 산업기술연구
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• 제17권
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• pp.213-218
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• 1997

This study is concerned with characteristics of bending collapse of aluminum members with multi-cell section. Aluminum is light so it is compatible of being used for vehicle structures members. Bending collpase behaviors of aluminum members with multi-cell section are very complex and tension failure mode are occured in experiment. In this paper, the aluminum members are modeled to be able to represent the tension failure mode and, characteristics of bending collapse of aluminum members with multi-cell section by experimental method are compared with the results of PAM-CRASH.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.935-940
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• 2002

This paper presents the failure mode on Headed Bars and prediction of tensile capacity, which is governed by concrete cone failure. 17 different plate types, three different concrete strengths and three different welding types of specimens were simulated. Static tensile load was applied Headed Bars were manufactured in different areas, and their shape and thickness are based on ASTM 970-98. Calculation of embedment length in concrete is conducted based on CSA 23.3-94, and static tensile load was applied. Tested pullout capacities were compared to the values determined using current design methods such as ACI-349 and CCD method.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.537-542
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• 1999

The design methodologies for carbon fiber sheet(CFS) strengthening of RC structures are not well established yet because the structural behavior of strengthened RC structures is more complex than that of unstrengthened ones. Even though the research for the methods using CFS has beed studied, the strengthening effects and structural behaviors of strengthened structures are not systematized yet. The purpose of this study is to carry out the experimental studies on three kinds of half scale RC slab bridges and to investigate the behavior of RC slab bridges from the experimental results. Typical flexural failure occurs in the non-strengthening slab like general RC slab bridges, and also the flexural failure occurs in the all area strengthened slab with sudden rip-off failure of strengthening material by punching shear. For the case of strip type strengthened slab, flexural failure occurs, with rip-off of second strip at the base of loading point. Strengthening effect on the slab using CFS is that the strength is increased upto 7~15 percent and the crack pattern is changed.