• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Steel and Composite Structures
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• v.44 no.5
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• pp.651-676
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• 2022

Most of the experimental, theoretical, and numerical studies on the stability of functionally graded composites are deterministic, while there are full of complex interactions of variables with an inherently probabilistic nature, this paper presents a non-intrusive framework to investigate the stochastic nonlinear buckling behaviors of porous functionally graded cylindrical shells exposed to inevitable source-uncertainties. Euler-Lagrange equations are theoretically derived based on the three variable refined shear deformation theory. Closed-form solutions for the shell buckling loads are achieved by solving the deterministic eigenvalue problems. The analytical results are verified with numerical results obtained from finite element analyses that are conducted in the commercial software ABAQUS. The non-intrusive framework is completed by integrating the Monte Carlo simulation with the verified closed-form solutions. The convergence studies are performed to determine the effective pseudorandom draws of the simulation. The accuracy and efficiency of the framework are verified with statistical results that are obtained from the first and second-order perturbation techniques. Eleven cases of individual and compound uncertainties are investigated. Sensitivity analyses are conducted to figure out the five cases that have profound perturbative effects on the shell buckling loads. Complete probability distributions of the first three critical buckling loads are completely presented for each profound uncertainty case. The effects of the shell thickness, volume fraction index, and stochasticity degree on the shell buckling load under compound uncertainties are studied. There is a high probability that the shell has non-unique buckling modes in stochastic environments, which should be known for reliable analysis and design of engineering structures.

• Earthquakes and Structures
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• v.16 no.5
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• pp.589-599
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• 2019

Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be attributed to low post-yield stiffness of core member in a BRB. This paper introduces a multi-core buckling restrained brace. The multi-core term arises from the use of more than one core component with different steel materials, including high-performance steel (HPS-70W) and stainless steel (304L) with high strain hardening properties. Nonlinear dynamic time history analyses were conducted on variety of diagonally braced frames with different heights, in order to compare the seismic performance of regular and multi-core buckling restrained braced frames. The results exhibited that the proposed multi-core buckling restrained braces reduce inter-story and especially residual drift demands in BRBFs. In addition, the results of seismic fragility analysis designated that the probability of exceedance of residual drifts in multi-core buckling restrained braced frames is significantly lower in comparison to standard BRBFs.

• International Journal of High-Rise Buildings
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• v.5 no.3
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• pp.195-203
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• 2016

Shear wall structures have been widely used in high-rise buildings during the past decades, mainly due to their good overall performance, large lateral stiffness, and high load-carrying capacity. However, traditional reinforced concrete wall structures are prone to brittle failure under seismic actions. In order to improve the seismic behavior of traditional shear walls, this paper presents three different metal energy-dissipation shear wall systems, including coupled shear wall with energy-dissipating steel link beams, frame with buckling-restrained steel plate shear wall structure, and coupled shear wall with buckling-restrained steel plate shear wall. Constructional details, experimental studies, and calculation analyses are also introduced in this paper.

• Structural Engineering and Mechanics
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• v.81 no.2
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• pp.179-194
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• 2022

The bending, buckling and free vibration responses of functionally graded material (FGM) beams are investigated semi-analytically by the scaled boundary finite element method (SBFEM) in this paper. In the concepts of the SBFEM, the dimension of computational domain can be reduced by one, therefore only the axial dimension of the beam is discretized using the higher order spectral element, which reduces the amount of calculation and greatly improves the calculation efficiency. The governing equation of FGM beams is derived in detail by the means of the principle of virtual work. Compared with the higher-order beam theory, fewer parameters and simpler control equations are used. And the governing equation is transformed into a first-order ordinary differential equation by introducing intermediate variables. Analytical solutions of the governing equation can be obtained by pade series expansion in the direction of thickness. Numerical example are compared with the numerical solutions provided by the previous researchers to verify the accuracy and applicability of the proposed method. The results show that the proposed formulations can quickly converge to the reference solutions by increasing the order of higher order spectral elements, and high accuracy can be achieved by using a small number of the elements. In addition, the influence of the structural sizes, material properties and boundary conditions on the mechanical behaviors of FG beams subjected to different load types is discussed.

• Advances in Computational Design
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• v.3 no.1
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• pp.17-34
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• 2018

Tall buildings are categorized as important structures because of the large number of occupants and high construction costs. The choice of competent lateral load resisting systems in tall buildings is of crucial importance. Bracing systems have long been an economic and effective method for resisting lateral loads in steel structures. However, there are some potential adverse aspects to bracing systems such as the limitations they inflict on architectural plans, uplift forces and poor performances in compression. in order to eliminate the mentioned problems and for cost optimization, in this paper, six 20-story steel buildings and frames with different types of bracing, i.e., conventional, mega-scale and buckling-restrained bracing (BRB) were analyzed. Linear and modal push-over analyses were carried out. The results pointed out that Mega-Scale Bracing (MSB) system has significant superiority over the conventional bracing type. The MSB system is 25% more economic. Some other advantages of MSB include: up to 63% less drift ratio, up to 38% better performance in lateral displacement, up to 100% stiffer stories, and about 50% smaller uplift forces. Moreover, MSB equipped with BRB attests even a better seismic behavior in the aforementioned parameters.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.347-354
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• 2012

In this study, the equations of torsional and warping constants of a I-shaped plate girder with sine corrugated web are suggested. Because of geometric characteristics of the section, a I-shaped plate girder with corrugated web shows high out-of-plane stiffness, shear strength, and torsional stiffness. Torsional constant and warping constant definitely affect lateral-torsional buckling loads. Therefore, exact estimation of the sectional properties is quite important. But, it is difficult to estimate these properties by former methods. So, this study was focused on suggestion of the rational equations to calculate torsional and warping constants. In order to investigate the effects of geometric characteristics of sine-corrugated webs on torsional stiffness and warping torsional constant, finite element analyses for pure torsional behavior and warping torsional behavior of I-shaped plate girders were performed. By regression analyses of the analytical results, rational equations of the torsional constant and warping constant were suggested. Suggested equations for the properties were validated based on the analytical results of lateral-torsional buckling of simply supported I-shaped plate girder. By suggested equations, torsional and warping constants of I-shaped plate girders with a sine-corrugated web can be rationally estimated and more exact lateral-torsional buckling load can be simply calculated.

• Structural Engineering and Mechanics
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• v.91 no.3
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• pp.325-334
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• 2024

This paper deals with the dynamic buckling behavior of truncated conical shells composed of carbon nanotube composites, an important area of study in view of their very wide engineering applications in aerospace industries. In this regard, the effective material properties of the nanocomposite have been computed using the Mori-Tanaka model, which has already been established for such analyses. The motion equations ruling the structure's behavior are derived using first order shear deformation theory, Hamilton's principle, and energy method. This will provide adequate background information on its dynamic response. In an effort to probe the dynamic instability region of the structure, differential quadrature method combined with Bolotin's method will be adopted to tackle the resulting motion equations, which enables efficient and accurate analysis. This work considers the effect of various parameters in the geometrical parameters and the volume fraction of CNTs on the structure's DIR. Specifically, it became clear that increasing the volume fraction of CNTs shifted the frequency range of the DIR to higher values, indicating the significant role of nanocomposite composition regarding structure stability.

• Structural Engineering and Mechanics
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• v.90 no.3
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• pp.313-323
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• 2024

Most of existing buildings in Mexico City are made of reinforced concrete (RC), however, it has been shown that they are very susceptible to narrow-band long duration ground motions. In recent years, the use of dual systems composed by Buckling Restrained Braces (BRB) has increased due to its high energy dissipation capacity under reversible cyclical loads. Therefore, in this work the behavior of RC buildings with BRB is studied in order to know their performance, specifically, the energy distribution through height and response transformation factors between the RC and simplified systems are estimated. For this propose, seven RC buildings with different heights were designed according to the Mexico City Seismic Design Provisions (MCSDP), in addition, equivalent single degree of freedom (SDOF) systems were obtained. Incremental dynamic analyses on the buildings under 30 narrow-band ground motions in order to compute the relationship between normalized hysteretic energy, maximum inter-story drift and roof displacement demands were performed. The results shown that the entire structural frames participate in energy dissipation and their distribution is independent of the global ductility. The results let propose energy distribution equations through height. Finally, response transformation factors between the SDOF and multi degree of freedom (MDOF) systems were developed aimed to propose a new energy-based approach of BRB reinforced concrete buildings.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1445-1453
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• 2009

The dropper supports the contact wire and is attached using thimbles and various types of dropper clips on the catenary. Consequently droppers are subject to mechanical loads from friction and buckling during the passage of pantographs. If such mechanical loads occur repeatedly with every passing pantograph, it is possible that the dropper wire will break due to fatigue. In order to investigate failure causes for the high speed line dropper, theoretical analyses and experiments have been carried out. In this paper, mathematical formulas are derived for the prediction of the dropper static load. The measured values in the experiment agree well with the theoretical predictions. And, we performed measurement for the variation of forces on the dropper. To analyze the cause analysis on fracture of dropper wire, we have conducted experiment such as fatigue test of new products, SEM(Scanning Electron Microscope) and EDX(Energy Dispersive X-ray) of fractured specimens in the field. Finally, we also measured the vertical displacements when a pantograph moved at 300km/h under the Korean high speed overhead line.