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The concrete-filled steel tube (CFST) columns using high-strength materials have the advantages of small sections and high capacity. However, the high-strength steel tube is susceptible to local buckling which will affect the seismic performance of CFST columns. The experimental study on seismic performance of CFRP confined rectangular CFST columns using high-strength materials indicated that the reinforcement of CFRP improves the bearing capacity and energy dissipation capacity efficiently. Based on the experimental investigation, the refined finite element model (FE model) of the CFRP confined high-strength rectangular CFST column was established in ABAQUS and verified in this paper. Parametric analysis was carried out to learn the influence of important factors such as material strength, width-to-thickness ratio, number of wrapped CFRP layers, and axial compression ratio. By combining the experimental research and parametric analysis, the restoring force model of FRP confined high-strength rectangular CFST column was proposed. The restoring force model could accurately predict the load–displacement curve and provided theoretical support for the design and application of CFRP confined high-strength rectangular CFST column.

This paper presents a study on the fire performance of steel-reinforced concrete-filled steel tubular (SRCFST) columns with square cross-section. The numerical models of SRCFST members, including a heat transfer analysis model and a structural analysis model, are established by ABAQUS to simulate the fire performance. The numerical models are validated against with the experimental data reported previously in terms of temperature field, axial deformation versus time curves, fire resistance and failure modes, and acceptable agreement can be achieved. Sensitivity analyses on contact thermal resistance and transient thermal strain are performed. It can be found that considering transient thermal strain of concrete and thermal resistance across the interface of concrete and steel tube is more realistic and gives accurate assessment for FE models. The fire performances of SRCFST columns, including temperature distributions, the axial deformation-time (Δ-t) curves, axial force distribution and strain are investigated and compared with common CFST columns. The results show that the fire behaviour of SRCFST columns can be further enhanced owing to the embedded profiled steel. Finally, the influences of various parameters on fire resistance, including fire load ratio, material strength, steel tube ratio, profiled steel ratio and slenderness ratio are examined. It is found that a higher profiled steel ratio is more favourable to fire resistance of SRCFST columns assuming the total steel ratio same, and the fire resistance significantly decreases with the increase of fire load ratio and slenderness ratio.

To reveal the projectile failure and fracture modes during high-velocity impact, projectiles made of 35CrMnSi with the same shape but different shell thickness are designed and then the experiments of penetrating high-strength rock target at about 1000 m/s are carried out. The experimental results indicate that all projectiles are completely fractured with petal shaped fragments produced and fail to effectively penetrate the rock target while only the target surface is comminuted. Besides the discussion on projectile material strength failure based on experimental results, projectile structure damage in the form of dynamic plastic buckling failure is also applied and gives a satisfactory explanation for the fracture pattern of petal shaped fragments with three-hinges structures employed. In addition, by taking the failure model of Mott stochastic distribution into account for the projectiles, numerical simulations are carried out to analyze the projectile fracture modes by Autodyn-3D with different discrete forms and exhibit high credibility. Furthermore, the influences of the filling and different impact conditions including velocities, angles of attack (AOA) and incidence angles on the projectile fracture modes are discussed. In general, the experimental results and the adopted numerical method with high credibility are able to reveal the effect of projectile structure damage on fracture modes and can be referred to further study on the projectile fracture during high-velocity penetration.

Isogrid composite lattice cylindrical structure with or without skins which consists of a system of ±ϕ (with respect to the shell axis) helical ribs and circumferential ribs, and has no skins or has skins was studied in a numerical method using ANSYS software, where in this model axial compression and/or pressure loads are applied, to determine the different failure modes which are, failure due to stress exceeds material strength, failure due to local buckling of ribs (crippling), failure due to general buckling of the cylinder and failure due to local buckling skin if the skin is existed. An example was studied to compare the results obtained from the numerical method and other research article.Keywords: FEM, Composite Structures, Isogrid Lattice, Buckling Load

The aim of this work is the numerical assessment of the ultimate behaviour of aluminium alloy beams subjected to non-uniform bending. An extensive numerical analysis has been performed by means of FE code ABAQUS with reference to RHS sections considering different values of the main geometrical and mechanical parameters. In particular, regarding the geometrical parameters the flange slenderness, the flange-to-web slenderness ratio and the moment gradient parameter have been considered. In particular, their influence on the ultimate behaviour of such beams has been investigated by adopting the material constitutive law proposed by Eurocode 9 based on the Ramberg-Osgood model. The investigations concern these parameters considered separately as well as their interaction. The results are herein reported with reference to temper T6 and show the importance of the investigated parameters on the buckling strength and the rotational capacity of aluminium alloy beams. Temper T6 gives rise to a quite low hardening compared to temper T4, which is analysed in a companion paper.

This paper deals with the design of an innovative type of bolted junction that shows a high plastic range in the load displacement. The schematization studied and reported in this paper is generally valid for steel structures and can be applied where high ductility is required (for example structures subjected to earthquakes) or statically indeterminate structures. In this case due to the high ductility of the junction there is a redistribution of stress/load in the elements. For this implementation the bolted junction was studied and applied to the arches of a bridge (designed by the University of Brescia). The developed junction described in this paper will solve the problems described above and permit an adjustment of the arch length until a balanced configuration is reached. The design procedure includes a preliminary analytical computation using the most important buckling theories; subsequently it is carried out a numerical analysis which results are validated executing several experimental analyses on a scale model. The final scope is the design of an innovative junction for tubular elements with circular section which permits the modification of the post-buckling curve in order to increase the ductility of the entire junction. The geometric solution studied was verified numerically and experimentally tested on a scale model. The results show a meaningful increase in elastic plastic performance of the junction. Indicatively this innovative geometry increases the elastic plastic behavior on the experimental geometry approximately 2 times when compared with the junction of the tubular elements without the designed junction.

Stability analysis of masonry piers and columns is one of the most frequently treated subjects in the field of structural engineering. This attention is probably due to the challenge to solving the problem including different effects, which play an important role in evaluating the response of eccentrically-loaded columns. In this connection, accurate stability analysis of masonry piers and columns has to take into account the non-linear stress–strain law of masonry in compression, the limited tensile strength, the induced slenderness due to crack formation and geometrical non-linearity. Different theoretical models and numerical approaches were developed in the past to analyze the combined effect of buckling and strength in such structural members. In this paper a numerical method is derived and particularized for the case of clay brick masonry members. After a review of the most widely used analytical models for the compressive behaviour of masonry, the effects of a non-linear constitutive law in compression and cracking were taken into account with suitable moment–curvature curves. The latter were implemented in a simple numerical procedure, and made it possible to calculate the force–displacement curves and safety domains, which account for both strength and stability. The method was finally verified with results derived from non-linear finite element analyses, making it possible to make considerations about the suitability of the method and the related computational effort.

Steel box sections are usually fabricated from flat plates which are welded at the corners. The welding process can introduce residual stresses and geometric imperfections into the sections which can influence their strength. For some thin-walled sections, large periodic geometric imperfections have been observed in manufactured sections. Subsequent investigations have indicated that the imperfections are in fact buckling deformations i.e. the box section has buckled due to welding residual stresses prior to any application of external load. The welding procedure and the behaviour of the box sections under load has been modelled using a finite element analysis that accounts for both geometric and material non-linearities. Tests have been carried out on box sections with a range of width to thickness ratios for the plate elements. Modelling has been shown to give good correlation with the test results. The conditions for buckling to take place as a result of the welding process have been established. A design method has been proposed.

This study deals with the optimum design of composite shells under external pressure with material strength and loss of stability according to the critical mode of imperfections taken as the failure criterion. The problem of optimum design is solved and the critical mode is obtained by nonlinear optimum programming for which the geometric and initial imperfection parameters are treated as variables. Numerical results are obtained for a cylindrical composite shell supported freely at its ends. The effect of shear forces between layers on the load-carrying capacity of the shell is also investigated.

The purpose of this paper is to develop a simple and approximate method with sufficient accuracy for predicting the effect of shearing strains in the middle surface of the walls, which reflect the shear lag phenomenon, on the lateral buckling of thin-walled open member. An energy equation for the lateral buckling has been derived in which the effects of torsion, warping of the member and, especially, the shearing strains in the middle surface of the wall are taken into account. The energy equation can be applied for a prismatic thin-walled member with any kind of open cross-section, for any loading system, and for any end boundary conditions. Some numerical examples by using optimization techniques are given to show the accuracy and applicability of the proposed method here. The results are compared with known results from experiment and finite element method, and good agreement is obtained. Finally, the effect of the shearing strains in the middle surface of the walls on lateral buckling of the thin-walled open member and the effect of the number of Simpson's nodal points taken on optimal values are discussed.

The eccentric in-plane loading of masonry walls involves complex bending performance that includes second-order effects. In this work, a bidimensional (2D) simplified micro-model for the analysis of this type of failure is developed. An experimental investigation based on 20 tests of full-scale unreinforced masonry walls is performed. The tests are characterised by slenderness and load eccentricity. The analytical methods of Eurocode-6 and ACI-530 are compared with experimental data from the present investigation, other experimental results available in the literature and simulation results from the numerical model.

Fiber‐reinforced plastic (FRP) structural members with open or closed thin‐walled sections are being used as beams and columns for structural applications where buckling is the main consideration in the design. Analytical models for several local buckling modes under axial and shear loading, taking the flange‐web interaction into account, are developed. Experimental data correlating predicted and observed behavior are presented for some commercially available structural shapes. Failure envelopes are developed for box‐ and I‐shape FRP columns and beams. The analytical models presented can be used to predict the behavior of any new pultruted material. The Rayleigh‐Ritz method is used in this work to analyze anisotropic flanges of box and I‐beams. The anisotropy of the material is introduced by ±45° angle‐ply layers introduced recently by pultruted manufacturers to improve the buckling strength of columns as suggested by this investigation.

The paper presents two numerical methods for estimating the experimental critical load and initial imperfection of rectangular plates loaded in edge compression from recordings of load and deflection. The Three Point technique makes use of three sets of such readings to form a system of nonlinear simultaneous equations, the solution of which yields the critical load, initial imperfection, and the constant governing the curvature of the load-deflection curve. The Least Square technique employs the principle of least square curve fitting to calculate these values. Although the techniques were developed primarily for stable bifurcation, it is equally applicable to neutral bifurcation. Both techniques were applied to various experimental results and the calculated values were found to match the recorded values very well.

The strength of aluminum pinned crooked columns has been derived as the basis of a design column curve. The effective length factor concept has then been presented and a value for crooked columns introduced (K c r o o k e d ). This factor can only be numerically determined and has no direct theoretical relation with the classical effective length factor (K e l ) derived from elastic buckling analyses. Many examples have, however, shown that K c r o o k e d is less than K e l and that it is a conservative to base a design on K e l and a column curve derived for pinned crooked columns. It has also been shown that the amount of restraint necessary to compensate the effect of initial imperfection is strongly dependent on the slenderness ratio of the member.

When a metal culvert is buried under a railway or road embankment, large compressive thrusts can develop in the structure as a result of loads from traffic and from the embankment itself. Culverts are liable to elastic buckling failure, because their flexural stiffness is usually low. This technical note reports a study, whose objectives are to: (1) investigate the elastic stability of elliptical tubes: (2) extend the parametric solution, already available for cylindrical tubes, to the behaviour of elliptical tubes. Using a linear finite element analysis for flexible culvert buckling, it is found that the linear buckling strength of an elliptical tube is approximated well by that of a circular tube of the same circumference. Published results for circular tubes buried near the ground surface can also be used for shallow buried elliptical tubes having the same ratio of cover depth to half-span. For non-uniformly loaded circular tubes, maximum hoop force can be used to calculate a conservative factor of safety relative to the critical hoop force for uniformly stressed structures. Both experimental and theoretical researches support the finding that linear buckling is a useful estimate of metal culvert elastic buckling strength. (Author/TRRL)

Analytical procedures are developed for computing the maximum carrying capacity of steel columns subjected to combined axial thrust and lateral load. It is assumed that the columns are permitted to deflect only in the plane of the applied load and that failure is always caused by excessive bending in the same plane. Numerical results are obtained for four types of columns with different loading and support conditions and are presented in the form of interaction curves relating axial thrust, lateral load, and slenderness ratio. The analytically obtained results are compared with the predictions based on an empirical interaction formula and good agreement is observed.