• Structural Engineering and Mechanics
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• v.56 no.3
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• pp.473-490
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• 2015

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-to-concrete bonded joints. The section analysis that considers the effect of concrete's tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3C
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• pp.113-120
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• 2012

An actual slope failure was analyzed in residual soils at Jinju. Due to rainfall infiltration, the safety factor decreases in the unsaturated layers, since the effective stress and shear strength decrease. In this study, the effective stress is based on suction stress using soil water retention curve. Unsaturated properties were evaluated on soil water retention curve, hydraulic conductivity and shear strength with samples from the site. After infiltration analysis of unsaturated flow under the actual rainfall, the distribution of pore water pressure could be calculated in the slope layers. In the stress field of finite elements, an elastic analysis calculated total stress distribution in the layers and also shear stresses on the slip surface using elastic model. On the slip surface, suction stress and effective stress evaluated the shear strength. As a result, the factor of safety was calculated due to rainfall, which could simulate the actual slope failure. In particular, it was found that the suction stress increases and both the effective stress and the shear strength decrease simultaneously on the slip surface.

• Geomechanics and Engineering
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• v.31 no.5
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• pp.439-452
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• 2022

A forecast of slope behavior during catastrophic events, such as earthquakes is crucial to recognize the risk of slope failure. This paper endeavors to eliminate the significant supposition of predefined slip surfaces in the slope stability analysis, which questions the relevance of simple conventional methods under seismic conditions. To overcome such limitations, a methodology dependent on the slip line hypothesis, which permits an automatic generation of slip surfaces, is embraced to trace the extreme slope face under static and seismic conditions. The effect of earthquakes is considered using the pseudo-static approach. The current outcomes developed from a parametric study endorse a non-linear slope surface as the extreme profile, which is in accordance with the geomorphological aspect of slopes. The proposed methodology is compared with the finite element limit analysis to ensure credibility. Through the design charts obtained from the current investigation, the stability of slopes can be assessed under seismic conditions. It can be observed that the extreme slope profile demands a flat configuration to endure the condition of the limiting equilibrium at a higher level of seismicity. However, a concurrent enhancement in the shear strength of the slope medium suppresses this tendency by offering greater resistance to the seismic inertial forces induced in the medium. Unlike the traditional linear slopes, the extreme slope profiles mostly exhibit a steeper layout over a significant part of the slope height, thus ensuring a more optimized solution to the slope stability problem. Further, the susceptibility of the Longnan slope failure in the Huining-Wudu seismic belt is predicted using the current plasticity approach, which is found to be in close agreement with a case study reported in the literature. Finally, the concept of equivalent single or multi-tiered planar slopes is explored through an example problem, which exhibits the appropriateness of the proposed non-linear slope geometry under actual field conditions.

• Journal of the Korean GEO-environmental Society
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• v.8 no.2
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• pp.11-18
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• 2007

Slope failure triggered by rainfall produces severe effects on the serviceability and stability of railway, Therefore, slope stability problem is one of the major concerns on the operation of railway. In this study, the rainfall conditions triggering slopes failure adjacent to railroads are investigated and the numerical analysis approach in consideration of infiltration and limit equilibrium method based upon multiple slip surfaces are proposed. The rainfall conditions triggering slope failure are as follow: cumulative rainfall is in the range of 150~500 mm, and duration is from 3 to 24 hours. Base upon the rainfall conditions, infiltration analysis and limit equilibrium method for infinite slope condition are carried out. The depth of infinite slope is assumed as 2 m and the multiple slip surfaces modeled with 16.7 cm interval from the bottom slip surface located at the 2 m depth. The assumed bottom slip surface is the location at which factor of safety is converging. The proposed approach shows more reasonable results than the results from the general codes assuming water table at slope surface. In addition, three dimensional plot of cumulative rainfall, rainfall duration, and factor of safety shows that slope stability analysis in consideration of rainfalll must account for cumulative rainfall (rainfall duration).

• Tunnel and Underground Space
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• v.32 no.5
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• pp.312-326
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• 2022

The generalized Hoek-Brown (GHB) criterion, which is recognized as one of the standard failure conditions for rock mass, is specialized for rock engineering applications and covers a wide range of rock mass conditions. Accordingly, many research efforts have been devoted to the incorporation of this criterion into the stability analysis of rock structures. In this study, the slip-line analysis method, which is a kind of elastoplastic analysis method, is combined with the GHB failure criterion to derive analytical equations that can easily calculate the plastic radius and stress distribution in the vicinity of the circular tunnel. In the process of derivation of related formulas, it is assumed that the behavior of rock mass after failure is perfectly plastic and the in-situ stress condition is hydrostatic. In the formulation, it is revealed that the plastic radius can be calculated analytically using the two respective tangential friction angles corresponding to the stress conditions at tunnel wall and elastic-plastic boundary. It is also shown that the plastic radius and stress distribution calculated using the derived analytical equations coincide with the results of Lee & Pietruszczak's numerical method published in 2008. In the latter part of this paper, the influence of the quality of the rock mass on the size of the plastic zone, the stress distribution, and the change of the tangential friction angle was investigated using the derived analytical equations.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.331-338
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• 1999

In the present study, a searching technique for critical slip surface in two dimensional slope stability analysis is proposed. The failure surface generation and analysis has been usually limited to simple geometric shapes. However, more random surfaces need to be examined for some particular ground conditions. For this purpose, random searching technique is developed using genetic algorithm. The generalized limit equilibrium method is employed as the method of stability analysis. Using this technique, the factor of safety is compared with the result by using simplified Bishop's method. In addition, the convergent trend of fitness value is analyzed.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.25-33
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• 1991

The slope stability analysis of Carsington dam is performed, considering the effects of pore water pressure, slip surface configuration, lateral stress and various shear strengths. Without yellow clay layer, the Bowles' and STABR programs were used to find the circular slip surface which has the maximum safety factor. At last using the Morgenstern-Price method, the effects of rainfall and strength of yellow clay were mainly considered in the back analyses after failure. It was found that (1) the potential slip was not predicted in the analysis based on the modified Bishop method without considering the yellow clay layer, and (2) the crllapse of dam had been occurred according to the critical shear strength of the yellow clay and pore water pressure increase.

• Computers and Concrete
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• v.19 no.4
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• pp.375-385
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• 2017

In the present paper experimental and numerical analysis of hook-ended steel fiber reinforced concrete is carried out. The experimental tests are performed on notched beams loaded in 3-point bending using fiber volume fractions up to 1.5%. The numerical analysis of fiber reinforced concrete beams is performed at meso scale. The concrete is discretized with 3D solid finite elements and microplane model is used as a constitutive law. The fibers are modelled by randomly generated 1D truss finite elements, which are connected with concrete matrix by discrete bond-slip relationship. It is demonstrated that the presented approach, which is based on the modelling of concrete matrix using microplane model, able to realistically replicate experimental results. In all investigated cases failure is due to the pull-out of fibers. It is shown that with increase of volume content of fibers the effective bond strength and slip capacity of fibers decreases.

• Steel and Composite Structures
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• v.38 no.5
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• pp.563-582
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• 2021

The present study experimentally and analytically investigated the push-out behaviour of H-shaped steel section embedded in ultrahigh-performance fibre-reinforced concrete (UHPFRC). The effect of significant parameters such as the concrete types, fibre content, embedded steel length, transverse reinforcement ratio and concrete cover on the bond stress, development of bond stress along the embedded length and failure mechanism has been reported. The test results show that the bond slip behaviour of steel-UHPFRC is different from the bond slip behaviour of steel-normal concrete and steel-high strength concrete. The bond-slip curves of steel-normal concrete and steel-high strength concrete exhibit brittle behaviour, and the bond strength decreases rapidly after reaching the peak load, with a residual bond strength of approximately one-half of the peak bond strength. The bond-slip curves of steel-UHPFRC show an obvious ductility, which exhibits a unique displacement pseudoplastic effect. The residual bond strength can still reach from 80% to 90% of the peak bond strength. Compared to steel-normal concrete, the transverse confinement of stirrups has a limited effect on the bond strength in the steel-UHPFRC substrate, but a higher stirrup ratio can improve cracking resistance. The experimental campaign quantifies the local bond stress development and finds that the strain distribution in steel follows an exponential rule along the steel embedded length. Based on the theory of mean bond and local bond stress, the present study proposes empirical approaches to predict the ultimate and residual bond resistance with satisfactory precision. The research findings serve to explain the interface bond mechanism between UHPFRC and steel, which is significant for the design of steel-UHPFRC composite structures and verify the feasibility of eliminating longitudinal rebars and stirrups by using UHPFRC in composite columns.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.749-758
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• 1998

The evaluation of shear stiffness of shear connection in composite bridges with CIP concrete deck is analysed. Shear stiffness of shear connection in full-depth precast concrete deck bridges is obtained from experiments. 3-dimensional finite element analyses of push-out specimen are carried out to investigate the effects of characteristics of filling material strength in shear connection on shear stiffness and local stress distribution. The load-slip relations obtained from the analyses are compared with those of experiments. The equation of initial shear stiffness of shear connection in precast concrete deck bridge is proposed. Linear analyses are performed to evaluate the effects of the shank diameter of shear connector and the strength of mortar on the characteristics of deterioration and failure load obtained by the failure criterions of each material. The failure loads are estimated and compared with test results.