• Geomechanics and Engineering
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• v.11 no.2
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• pp.253-267
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• 2016

The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and $K_I$ and $K_{II}$ of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compression-shear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that ${\sigma}_3$ changes linearly with the change of ${\sigma}_1$. And the change rate is related to ${\beta}$, angle between the cracks and ${\sigma}_1$. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.467-476
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• 2004

Because of crack control by steel bars after cracking the material models for reinforced concrete(RC) differ from those for plain concrete(PL). The nonlinear behavior of columns subjected to lateral load was simulated with reasonable accuracy in 3D analysis by applying distinct material models for RC and PL zone subdivided properly on the section. The shear strain is confirmed to develope unstably with ununiform distribution in out-of-plane direction. And this tendency becomes stronger as the thickness of column member increases in out-of-plane direction. If this ununiformity in strain distribution is not taken into consideration the capacity and the deformability of columns in shear dominant failure are overestimated excessively in two dimensional analysis. By introducing equivalent softening model a behavior of columns can be predicted too in two dimensional analysis.

• Structural Engineering and Mechanics
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• v.35 no.1
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• pp.99-117
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• 2010

Beam-column joints are the key structural elements, which dictate the behavior of structures subjected to earthquake loading. Though large experimental work has been conducted in the past, still various issues regarding the post-yield behavior, ductility and failure modes of the joints make it a highly important research topic. This paper presents experimental results obtained for eight beam-column joints of different sizes and configuration under cyclic loads along with the analytical evaluation of their response using a simple and effective analytical procedure based on nonlinear static pushover analysis. It is shown that even the simplified analysis can predict, to a good extent, the behavior of the joints by giving the important information on both strength and ductility of the joints and can even be used for prediction of failure modes. The results for four interior and four exterior joints are presented. One confined and one unconfined joint for each configuration were tested and analyzed. The experimental and analytical results are presented in the form of load-deflection. Analytical plots are compared with envelope of experimentally obtained hysteretic loops for the joints. The behavior of various joints under cyclic loads is carefully examined and presented. It is also shown that the procedure described can be effectively utilized to analytically gather the information on behavior of joints.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.1
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• pp.31-42
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• 2009

Common structural rule (CSR) doesn' t provide any other specific regulations for permanent means of access (PMA) platform structure in a cargo oil tank. The PMA platform is recommended to comply with scantling requirement of local support member. However, it leads to too conservative scantlings compared with actual loads imposed on the platform. This paper proposes a strength assessment procedure for the PMA structure based on a nonlinear ultimate strength. The ultimate strength is evaluated in a sufficiently conservative way. The first linear buckling mode is used as an initial imperfection shape and its magnitude is determined using the definitions of DNV PULS. Since the same imperfection mode as the failure mode of the ultimate limit state is assumed, it can accelerate the failure. Au ultimate strength capacity curve obtained from a series of nonlinear FE analysis is compared with actual stresses calculated by CSR cargo hold analysis.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.1
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• pp.45-56
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• 1990

This study deals with the nonlinear strength analysis of laminated composite cylindrical shells to find the optimum structure of pressure vessel. By applying the F.E.M. using the 8-node degenerated Isoparametric shell element and Total Lagrangian formulation and being adopted Newton-Raphson method with incremental load as a solution scheme. the optimum structure is found from the viewpoint of minimum displacement. As a results of linear analysis on the 9 cases of laminated structure, $[50^{\circ}/-50^{\circ}]$ composition of the shell laminate give the minimum deflection. In case of the nonlinear analysis by applying Quadratic Failure Criteria on laminated combination $[{\theta}^{\circ}/-{\theta}^{\circ}]$, shell laminate structure of ${\theta}=50^{\circ}$ under external uniform pressure was founded as a optimum structure and ${\theta}=50^{\circ}$ for the case of external and axial loading combined.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.309-316
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• 2022

This paper presents nonlinear numerical analysis results which were compared with the tested tensile strengths of CFRP(Carbon Fiber Reinforced Plastic) laminates with 14 different stacking sequences. The composite laminate coupons were cured under an autoclave pressure using resin-impregnated unidirectional tapes. The nonlinearity of the matrix was considered for the analysis, which was obtained from lamina tests. The Hashin failure criteria and progressive failure analysis were used for the nonlinear finite element analysis. The comparison results show that the current approach is acceptable to predict the tensile strengths of the CFRP laminate coupons with various stacking sequences and no damage. However, it is not acceptable to predict the tensile strengths of the laminate specimens with a center hole.

• Computers and Concrete
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• v.30 no.4
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• pp.277-287
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• 2022

Due to the scarcity of extortionate experimental data, fatigue failure of the reinforced concrete (RC) element might be achieved economically adopting nonlinear finite element (FE) analysis as an alternative approach. However, conventional implicit dynamic analysis is expensive, quasi-static method overlooks interaction effects and inertia, direct cyclic analysis computes stabilized responses. Apart from this, explicit dynamic analysis may provide a numerical operating system for factual long-term responses. The study explores the fatigue behavior based on a simplified explicit dynamic solution employing nonlinear time domain analysis. Among fourteen RC beams, one beam is selected to validate under static loading, one under fatigue with the experimental study and other twelve to check the detail fatigue behavior. The SWOT (Strength, Weakness, Opportunities, Threats) analysis has been carried out to pinpoint the detail scenario in the adoption of numerical approach as an alternative to the experimental study. Excellent agreement of FE and experimental results is seen. The 3D nonlinear RC beam model at service fatigue limits is truthful to be used as an expedient contrivance to envisage the precise fatigue behavior. The simplified analysis approach for RC beam under fatigue offers savings in computation to predict responses providing acceptable accuracy rather than the complicated laboratory investigation. At higher frequency, the flexural failure occurs a bit earlier gradually compared to the repeated loading case of lower frequency. The deflection increases by 6%-10% at the end of first cycle for beams with increasing frequency of cyclic loading. However, at the end of fatigue loading, greater deflection occur earlier for higher load range because of more rapid stiffness degradation. For higher frequency, a slight boost in concrete compressive strains at an initial stage of loading has been seen indicating somewhat stepper increment. Stiffness degradation in larger loading cycle at same duration escalates the upsurge of the rate of strain in case of higher frequency.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.383-390
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• 2008

A Precast Prefabricated Bridge Column using steel tube and prestressing bar was proposed for the application of precast method on substructure. A column specimen designed by the proposed bridge column system was made and performed a quasi-static test. The failure mode appeared to be a flexural failure and there is no damage on column segment connection. And it is good use of the self-centering ability by prestressing force. Test results showed that a column specimen satisfy the earthquake specification, and the structural stability was verified. Nonlinear finite element analysis was performed and compared with the test results. Force-displacement relation and location of crack from the analysis results were compared with the test results and it agreed well. The quantitative analysis was also performed by a parametric study using this modeling technique.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.1
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• pp.47-57
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• 2024

Recently, in newly constructed apartment buildings, the exterior wall structures have been characterized by thinness, having various openings, and a significantly low reinforcement ratio. In this study, a nonlinear finite element analysis was performed to investigate the crack damage characteristics of the exterior wall structure. The limited analysis models for a 10-story exterior wall were constructed based on the prototype apartment building, and nonlinear static analysis (push-over analysis) was performed. Based on the finite element (FE) analysis model, the parametric study was conducted to investigate the effects of various design parameters on the strength and crack width of the exterior walls. As the parameters, the vertical reinforcement ratio and horizontal reinforcement ratio of the wall, as well as the uniformly distributed longitudinal reinforcement ratio and shear reinforcement ratio of the connection beam, were addressed. The analysis results showed that the strength and deformation capacity of the prototype exterior walls were limited by the failure of the connection beam prior to the flexural yielding of the walls. Thus, the increase of wall reinforcement limitedly affected the failure modes, peak strengths, and crack damages. On the other hand, when the reinforcement ratio of the connection beams was increased, the peak strength was increased due to the increase in the load-carrying capacity of the connection beams. Further, the crack damage index decreased as the reinforcement ratio of the connection beam increased. In particular, it was more effective to increase the uniformly distributed longitudinal reinforcement ratio in the connection beams to decrease the crack damage of the coupling beams, regardless of the type of the prototype exterior walls.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.3
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• pp.161-168
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• 2018

Pohang earthquake occurred on November 15, 2017, with a magnitude of 5.4. The damage of the structure caused by the Pohang earthquake was the most significant in 4-story piloti-type buildings, where the damage patterns were different according to the location of columns and walls at the first story. One building with a staircase at a corner shows shear failure at columns, and Another building with a staircase in the middle shows no failure or shear failure at staircase walls. Therefore, two different piloti-type buildings were selected; one has a staircase at a corner and another has in the middle, and the seismic behavior of the buildings were examined by nonlinear dynamic analysis applying a ground motion measured at Pohang. Analytical model well simulated the actual behavior of the piloti-type buildings during the earthquake. Analysis results showed that walls have an insufficient shear strength wherever the location of the staircase is and columns with insufficient transverse reinforcement could be failed when the staircase is located at a corner. Conclusively, structural engineers should design columns and walls in piloti-type buildings to possess sufficient capacity according to the location of staircase.