Papers by Keyword: Buckling

Abstract: The paper deals with the design and development of a new and progressive structural types of footbridges with an external tendon used as a main load bearing member. Main goals of the paper are checking the possibilities of using such structures for many different spatial arrangements and especially identifying the problematic aspects of the design. Using the results of research conducted in previous years, the procedure for finding the optimal shape of the cable was described in detail. For specific examples the process of cable shape optimizations is shown. In the next part the influence of various boundary conditions is discussed. The structures were also checked in terms of ULS and SLS limit states. Particular attention is paid to the buckling analysis of the struts and stress distribution in the deck part. The structures were modeled using FEM software Midas Civil. The models used for basic analysis consist of beam and truss elements. For precise analysis the shell models were used. Finally the dynamic behavior analysis was performed according to SÉTRA methodology. The results and outputs of the research should be used by designers who have to deal with similar structural types and they shall hopefully help to identify the most problematic features.

Abstract: In present paper, a novel two variable shear deformation beam theories are developed and applied to investigate the combined effects of nonlocal stress and strain gradient on the bending and buckling behaviors of nanobeams by using the nonlocal strain gradient theory. The advantage of this theory relies on its two-unknown displacement field as the Euler-Bernoulli beam theory, and it is capable of accurately capturing shear deformation effects, instead of three as in the well-known first shear deformation theory and higher-order shear deformation theory. A shear correction factor is, therefore, not needed. Equations of motion are obtained via Hamilton’s principle. Analytical solutions for the bending and buckling analysis are given for simply supported beams. Efficacy of the proposed model is shown through illustrative examples for bending buckling of nanobeams. The numerical results obtained are compared with those of other higher-order shear deformation beam theory. The results obtained are found to be accurate. Verification studies show that the proposed theory is not only accurate and simple in solving the bending and buckling behaviour of nanobeams, but also comparable with the other shear deformation theories which contain more number of unknowns

Abstract: In this study, a novel numerical method to analyze the bifurcation problemof a rate dependent material using the finite element method is proposed. The consistent stiffness matrix, which is required for a bifurcation analysis using the finite element method, for a rate dependent material is generally hard to compute, therefore, a computational method to calculate the tangent stiffness matrix based on a numerical differential is introduced so that exact bifurcation analyses for the rate dependent material can be conducted. A numerical example of the proposed method is demonstrated, and the adequacy of the proposed method is discussed.

Abstract: This work presents the buckling investigation of embedded orthotropic nanoplates by using a new hyperbolic plate theory and nonlocal small-scale effects. The main advantage of this theory is that, in addition to including the shear deformation effect, the displacement field is modeled with only three unknowns and three governing equation as the case of the classical plate theory (CPT) and which is even less than the first order shear deformation theory (FSDT) and higher-order shear deformation theory (HSDT). A shear correction factor is, therefore, not required. Nonlocal differential constitutive relations of Eringen is employed to investigate effects of small scale on buckling of the rectangular nanoplate. The elastic foundation is modeled as two-parameter Pasternak foundation. The equations of motion of the nonlocal theories are derived and solved via Navier's procedure for all edges simply supported boundary conditions. The proposed theory is compared with other plate theories. Analytical solutions for buckling loads are obtained for single-layered graphene sheets with isotropic and orthotropic properties. The results presented in this study may provide useful guidance for design of orthotropic graphene based nanodevices that make use of the buckling properties of orthotropic nanoplates. Verification studies show that the proposed theory is not only accurate and simple in solving the buckling nanoplates, but also comparable with the other higher-order shear deformation theories which contain more number of unknowns. Keywords: Buckling; orthotropic nanoplates; a simple 3-unknown theory; nonlocal elasticity theory; Pasternak’s foundations. * Corresponding author; Email-tou_abdel@yahoo.com

Abstract: This study was employed to investigate the buckling effect for a single Vf corrugated core. Brief and simple designing method is developed for UHS sandwich structure. This method is based on simplified calculation of slenderness ratio integrated with FEM simulation. Method is developed for studying the local buckling resistance of sandwich structures to optimize the panel dimensions for maximal stiffness. Five different core dimensions were tested (angles of 110-135 ° and height of 35 - 55 mm). Buckling tests were made using two different steel grades; ultra-high-strength (UHS) ARS400 and DC01 mild steel. For comparison, FEM simulations were carried out for the ARS400. The results showed that even 600% higher bending resistance can be achieved for the panel structure using the ultra-high strength steel instead of the low strength counterpart. The comparison showed that the FEM-simulations can be used reliably estimating the buckling effects in UHS panel structures. The difference between the empirical and simulation results was 5.3% in average (S.D. 4.1). In practical tests, best angle and height for the ARS400 was 110 ° and 35 mm respectively. For the DC01, the best dimensions were 125 ° and 35 mm.

Abstract: The unused reserves of metal and manufacturing techniques of forgings and hardening of products promoting minimization and stabilization of deformation and a buckling of gear details are revealed. Need of rationing of size of a hardenability of steel, a regulation of speed of cooling of forgings after hot stamping and application of isothermal annealing as preliminary heat treatment is established. The rational scheme of laying and technology of low-temperature cementation of pinion gears providing the minimum change of the geometrical sizes of details in chemical and thermal processes is offered.

Abstract: The loss of vertical structures stability is always a very dangerous phenomenon. It is almost impossible to predict it, because it develops very quickly, avalanche-like. One solution to this problem is to increase the cross section of the compressible elements. However, this solution leads to a significant increase in weight and load on the underlying structures. It is necessary to be able to accurately determine the critical force of F_cr for various forms of compressible elements and schemes of fastening. The article presents the solution of the problem of fiberglass rods stability by the energy method in the form of Tymoshenko-Ritz, which is reduced to the problem of determining eigenvalues in the algebraic theory of matrices. In the MatLab software complex, the value of the critical load F_cr is obtained by numerical method with different stiffness and pinning schemes.

Abstract: Pitting corrosion often leads to the creation of small holes in steel tubular member of platform structures when a protective coating is damaged. A single pit on slender compression element can cause a significant reduction in the buckling capacity of the member. Euler formula is no longer applicable for determining the critical buckling load when cutout presence on the member. This research was conducted to numerically study the effect of a circular hole on the buckling capacity of slender steel tubular member. A variation on hole positions was at 0.125 L, 0.25 L, 0.375 L, and 0.5 L, where L is the length of the member. The hole was taken to be 0.5 pipe diameter. Two nonlinear geometric 3D Finite Element models were developed to analyzed the member critical buckling load: (a) buckling analysis, where the problem was formulated as eigenvalue problem based on the nonlinear incremental equilibrium equations, and (b) nonlinear analysis, where the nonlinear equilibrium equations were developed and solved by several schemes to get the load – deflection curve. For the both models, the tubular member was discretized into: (a) shell elements, and (b) solid elements. The numerical results were verified by experimental investigation. The results showed that: (a) the presence of cutout reduced the buckling load significantly, (b) the reduction ranging from 3% to 10% depending on the hole positions, (c) the maximum reduction occurs when the hole position was in the middle of the member length, (d) compared to experimental results, the critical buckling load obtained from buckling analysis deviated 1~4% while those of nonlinear analysis deviated 1~5%, (e) the buckling mode corresponded with member bent away to opposite side of the cutout position.

Abstract: Buckling-restrained braces (BRBs), which were first applied in 1989 in Japan, are now widely used worldwide as ductile seismic-proof members in seismic zones, such as those in Japan, USA, Taiwan, China, Turkey, and New Zealand. Although the design procedures of BRBs and their applications are described in the design codes and recommendations of several countries, they do not necessarily cover all the required aspects. Moreover, various new types of BRBs are still under investigation by many researchers. In this paper, the early history of BRB research and development and state-of-the-art views on the items required to design BRBs for obtaining stable hysteresis are briefly overviewed. This is followed by a summary of various representative application concepts and up-to-date investigations.

Abstract: In the present study, buckling of eccentrically loaded nanobeams in which the load is not applied at the centroid of cross section, has been studied. Eringen’s Nonlocal Elasticity Theory has been used in the formulation of governing equation of motion of the nanobeam. Simply supported and free boundary conditions for nanobeam have been taken consideration. The effect of nonlocal parameter, eccentricity of the load, nanobeam length on the buckling deflection and critical buckling load on nanobeam have been investigated. Present results can be useful in the design of nano-structures.