• Steel and Composite Structures
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• v.33 no.5
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• pp.755-765
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• 2019

This study examined geometric and physical nonlinear analyses of beams and arches specifically from rolled profiles used in mining and underground constructions. These profiles possess the ability to create plastic hinges owing to their robustness. It was assumed that displacements in beams and arches fabricated from these profiles were comparable with the size of the structure. It also considered changes in the shape of a rod cross-section and the nonlinearities of the structure. The analyses were based on virtual unit moments, effective flexural rigidity of used open sections, and a secant method. The use of the approach led to a solution for the "after-critical" condition in which deformation increased with decreases in loads. The solution was derived for static determinate beams and static indeterminate arches. The results were compared with results obtained in other experimental tests and methods.

• Geomechanics and Engineering
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• v.5 no.1
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• pp.37-55
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• 2013

An important issue in the design of soil-nailing systems, as long-term retaining walls, is to assess their stability during seismic events. As such, this study is aimed at simulating the dynamic behavior and failure pattern of nailed structures using two series of numerical analyses, namely dynamic time history and pseudo-static. These numerical simulations are performed using the Finite Difference Method (FDM). In order to consider the actual response of a soil-nailed structure, nonlinear soil behaviour, soil-structure interaction effects, bending resistance of structural elements and construction sequences have been considered in the analyses. The obtained results revealed the efficiency of both analysis methods in simulating the seismic failure mechanism. The predicted failure pattern consists of two sliding blocks enclosed by three slip surfaces, whereby the bottom nails act as anchors and the other nails hold a semi-rigid soil mass. Moreover, it was realized that an increase in the length of the lowest nails is the most effective method to improve seismic stability of soil-nailed structures. Therefore, it is recommended to first estimate the nails pattern for static condition with the minimum required static safety factor. Then, the required seismic stability can be obtained through an increase in the length of the lowest nails. Moreover, placement of additional long nails among lowest nails in existing nailed structures can be considered as a simple retrofitting technique in seismic prone areas.

• Steel and Composite Structures
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• v.25 no.3
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• pp.287-298
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• 2017

The present study aims to determine the structural response of full scaled rectangular columns under both of vertical and lateral loads using numerical methods. In the study, the composite columns considering full concrete filled circular steel tube (FCFRST) and concrete filled double-skin rectangular steel tube (CFDSRST) section types are numerically modelled using ANSYS software. Vertical and lateral loads are applied to models to assess the structural response of the composite elements. Also similar investigations are done for reinforced concrete rectangular (RCR) columns to compare the results with those of composite elements. The analyses of the systems are statically performed for both linear and nonlinear materials. In linear static analyses, both of vertical and lateral loads are applied to models as only one step. However in nonlinear analyses, while vertical loads are applied to model as only one step, lateral loads are applied to systems as step by step. The displacement and stress changes in some critical nodes and sections and contour diagrams are reported by graphs and figures. At the end of the study, it is demonstrated that the nonlinear models reveal more accurate result then those of linear models. Also, it is highlighted that composite columns provide more and more safety, ductility compared to reinforced concrete column.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.4
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• pp.181-191
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• 2014

This research presents the nonlinear analysis model for reinforced concrete shear wall systems with special boundary elements as proposed by the Korean Building Code (KBC, 2009). In order to verify the analysis model, analytical results were compared with the experimental results obtained from previous studies. Established analytical model was used to perform nonlinear static and dynamic analyses. Analytical results showed that the semi-special shear wall improved significantly the performance in terms of ductility and energy dissipation as expected based on previous test results. Furthermore, nonlinear incremental dynamic analysis was performed using 20 ground motions. Based on computer analytical results, the ordinary shear wall, special shear wall and newly proposed semi-special shear wall systems were evaluated based on the methods in FEMA P965. The results based on the probabilistic approaches accounting for inherent uncertainties showed that the semi-special shear wall systems provide a high capacity/demand (ACMR) ratio owing to their details, which provide enough capacity to sustain large inelastic deformations.

• Computers and Concrete
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• v.6 no.4
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• pp.319-341
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• 2009

A new formulation based on lumped plasticity and inelastic hinges is presented in this paper for nonlinear analysis of Reinforced Concrete (RC) frame structures. Inelastic hinge behaviour is described using the principles of Continuum Damage Mechanics (CDM). Member formulation contains provisions to model stiffness degradation due to cracking of concrete and yielding of reinforcing steel. Depending on its nature, cracking is classified as concentrated or distributed. Concentrated cracking is accounted through a damage variable and its growth is defined based on strain energy principles. Presence of distributed flexural cracks in a member is taken care of by modelling it as non-prismatic. Plasticity theory supported by effective stress concept of CDM is applied to describe the post-yield response. Nonlinear quasi-static analysis is carried out on a RC column and a wide two-storey RC frame to verify the formulation. The column is subjected to constant axial load and monotonic lateral load while the frame is subjected to only lateral load. Computed results are compared with those due to experiments or other numerical methods to validate the performance of the formulation and also to highlight the contribution of distributed cracking on global response.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.2
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• pp.68-73
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• 2000

This paper addresses the analysis and design of fuzzy control systems for a class of complex nonlinear systems. Firstly, the nonlinear system is represented by Takagi-Sugeno(TS) fuzzy model and the global controller is constructed by compensating each linear model in the rule of TS fuzzy model. The design of conventional TS fuzzy-model-based controller is composed of two processes. One is to determine the static state feedback gain of each local model and the other is to validate the stability of the designed fuzzy controller. In this paper, we propose an alternative methods for the design of TS fuzzy-model-based controller. The design scheme is based on the extension of conventional optimal control theory to the design of TS fuzzy-model-based controller. By using the proposed method, the design and stability analysis of the TS fuzzy model-based controller is reduced to the problem of finding the solution of a set of algebraic Riccati equations. And we use the recently developed interior point method to find the solution of AREs, where AREs are recast as the LMI formulation. A numerical simulation example is given to show the effectiveness and feasibiltiy of the proposed fuzzy controller design method.

• Earthquakes and Structures
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• v.22 no.2
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• pp.169-184
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• 2022

The importance of seismicity in developing countries and the strengthening of buildings is a topic of major importance. Therefore, the study of several solutions with the development of new technologies is of great importance to investigate the damage on retrofitted structures by using probabilistic methods. The Federal Emergency Management Agency considers three types of performance levels by considering different scenarios, intensity and duration. The selection and scaling of ground motions mainly depends on the aim of the study. Intensity-based assessments are the most common and compute the response of buildings for a specified seismic intensity. Assessments based on scenarios estimate the response of buildings to different earthquake scenarios. A risk-based assessment is considered as one of the most effective. This research represents a practical method for developing countries where exists many active faults, tall buildings and lack of good implementable approaches. Therefore, to achieve the main goal, two high-rise steel buildings have been modeled and assessed. The contribution of buckling-restrained braces in the elastic design of both buildings is firstly verified. In the nonlinear static range, both buildings presented repairable damage at the central top part and some life safety hinges at the bottom. The nonlinear incremental dynamic analysis was applied by 15 representative/scaled accelerograms to obtain levels of performance and fragility curves. The results shown that by using probabilistic methods, it is possible to estimate the probability of collapse of retrofitted buildings by buckling-restrained braces and tuned mass dampers, which are practical retrofitting options to protect existing structures against earthquakes.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.297-305
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• 2002

As advanced earthquake analysis/design methods such as the nonlinear static analysis are developed, it is required to estimate precisely the cyclic behavior of reinforced concrete members that is characterized by strength, deformability, and capacity of energy dissipation. However, currently, estimation of energy dissipation depends on empirical equations that are not sufficiently accurate, or experiment and sophisticated numerical analysis which are difficult to use in practice. In the present study, nonlinear finite element analysis was performed to investigate the behavioral characteristics of flexure-dominant RC members under cyclic load. The effects of axial force, arrangement of reinforcing bars, and reinforcement ratio on the cyclic behavior were studied. Based on the investigation, a simplified method to estimate the capacity of energy dissipation was proposed, and it was verified by the comparison with the finite element analyses and experiments. The proposed method can estimate the energy dissipation of RC members more precisely than currently used empirical equations, and it is easily applicable in practice.

• Special Issue of the Society of Naval Architects of Korea
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• 2011.09a
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• pp.51-54
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• 2011

This paper presents methods for design and strength analysis of lifting lugs utilized in assembling, erection, and turning over of ship structures. Lifting lugs are designed in accordance with ASME BTH-1-2008; Design of Below-the-Hook Lifting Devices. Experimental tests for fillet welded joints were conducted to design weld size of lifting lugs and under-structures. The nonlinear finite element method, using MSC.Marc software, is employed for limit state assessment of lifting lugs in static loading conditions. The analysis considers nonlinearities in material properties and contact between lifting lug and pin.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.9-12
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• 2004

Coupling beams subject to cyclic loads exhibit different behavioral characteristics and energy dissipation capacity varying with re-bar layouts. In the present study, nonlinear analysis method was developed using analogous truss model. Using the numerical method, parametric studies were performed to investigate the behavioral characteristics and the energy dissipation mechanism of coupling beams with various re-bar layouts subject to cyclic loading. Based on the investigation, a simple and practical method for evaluating the energy dissipation capacity of coupling beams was developed and verified by experiments. The proposed method accurately predicted the dissipated energy during cyclic loading addressing design parameters such as re-bar layouts, re-bar ratio, and deformation. The proposed method can be easily applied to nonlinear static and dynamic methods for seismic analysis and design.