Failure mechanism analysis under compression loading of unidirectional carbon/epoxy composites using micromechanical modelling

A nonlinear formulation capable of accurately and efficiently predicting the nonlinear response of an axially restrained prismatic beam-column with initial geometric imperfections (i.e., initial curvature and connection eccentricities) and nonlinear temperature-dependent end connections under elevated temperatures is presented. The proposed model includes the effects of (1) an arbitrary thermal gradient along both the span and cross section of the member and (2) the nonlinear behavior and any stiffness and strength degradations of the beam-column material. However, high-temperature creep and shear deflection effects are not taken into consideration. The proposed model is generic allowing the implementation of any thermal regime and the use of any stress-strain-temperature curves of the beam-column material. The stress-strain-temperature curves of the material can be either theoretical or experimental providing a more realistic approach to the structural response of beam-columns subjected to different fire conditions. Two comprehensive examples are presented and discussed in detail showing the effectiveness and accuracy of the proposed iterative method on the nonlinear large-deflection behavior of slender prismatic beam-columns under high temperatures, including the combined effects of initial imperfections, end restraints, and nonlinear end connections.

ABSTRACTSteel products which have various characteristic (e.g. high ductility, high yield stress, low yield stress and high weldability) are used as main structures by diversification of demanded application, and technology for steel manufacturing has developed. Because steel square tubular member is processed by cold‐forming and welding in the process of manufacturing, residual stress will exist in the products. Moreover, due to the cold‐forming process, geometrical initial imperfection, i.e., global and local, will exist. These initial imperfection are still remained even so the technology for steel manufacturing is developed. However, effect of the initial imperfection on elasto‐plastic behaviour of square hollow section columns under compressive axial force with bending moment is not clarified. In this paper, firstly, the effect of individual initial imperfection (e.g. initial global imperfection, initial local imperfection or residual stress) on elasto‐plastic performance is investigated independently; comparison between the experimental results are shown. It is shown that initial local imperfection has a significant impact on elasto‐plastic performance. Secondly, the effect of composite initial imperfections is investigated. The amplitude of the local imperfection is the most influential initial imperfection on the deformation capacity of the column, and the deformation capacity decreased with an increase of the amplitude of local imperfection. Validation of the numerical simulation were also performed and recommend values of imperfections are shown.

The two failure modes of shell structure, dynamic instability and intensive destruction, have no distinct boundary on their structural performance; they are fuzzy and are difficult to determine problems. By using the comprehensive evaluation method in fuzzy mathematics and taking the initial imperfection of the structure into consideration, this paper, taking Kiewitt spherical shell as an example, made parameter impact analysis to the structure, and investigated the influence of span ratios, the initial geometric imperfections and bar cross-section of the structure under earthquake failure mode. Ensuring the relations between a variety of response factors of the structure and fuzzy failure modes, the paper established a power failure mode shell structure of fuzzy comprehensive evaluation model and evaluation method, and described the application of the method in the discrimination of failure mode on Kiewitt monolayer Shell with initial defect; the consequences showed that this method can solve the problem of failure mode identification better with more realistic facts and possesses higher accuracy.

Concrete-filled steel tubes subjected to axial compression: Life-cycle based performance

Computational micromechanics model for the analysis of fiber kinking in unidirectional fiber-reinforced polymers

Modular steel scaffolds are commonly used as supporting scaffolds in building construction, and traditionally, the load carrying capacities of these scaffolds are obtained from limited full-scale tests with little rational design. Structural failure of these scaffolds occurs from time to time due to inadequate design, poor installation and over-loads on sites. In general, multi-storey modular steel scaffolds are very slender structures which exhibit significant non-linear behaviour. Hence, secondary moments due to both <TEX>$P-{\delta}$</TEX> and <TEX>$P-{\Delta}$</TEX> effects should be properly accounted for in the non-linear analyses. Moreover, while the structural behaviour of these scaffolds is known to be very sensitive to the types and the magnitudes of restraints provided from attached members and supports, yet it is always difficult to quantify these restraints in either test or practical conditions. The problem is further complicated due to the presence of initial geometrical imperfections in the scaffolds, including both member out-of-straightness and storey out-of-plumbness, and hence, initial geometrical imperfections should be carefully incorporated. This paper presents an extensive numerical study on three different approaches in analyzing and designing multi-storey modular steel scaffolds, namely, a) Eigenmode Imperfection Approach, b) Notional Load Approach, and c) Critical Load Approach. It should be noted that the three approaches adopt different ways to allow for the non-linear behaviour of the scaffolds in the presence of initial geometrical imperfections. Moreover, their suitability and accuracy in predicting the structural behaviour of modular steel scaffolds are discussed and compared thoroughly. The study aims to develop a simplified and yet reliable design approach for safe prediction on the load carrying capacities of multi-storey modular steel scaffolds, so that engineers can ensure safe and effective use of these scaffolds in building construction.

In this paper, the nonlinear post-buckling analysis of imperfect two-dimensional quasicrystal cylindrical shells is performed. The nonlinear governing equations are established by considering initial geometric imperfection, higher-order shear deformation theory and phonon-phason fields coupling effect. The load-shortening curves and buckling modes are obtained by the Galerkin’s method. Numerical results are compared with the existing results and excellent agreements are obtained. Effects of geometrical parameters, initial imperfection and phonon-phason fields coupling effect on the critical load and imperfection sensitivity of two-dimensional quasicrystal cylindrical shells are discussed in detail.

Precast prestressed concrete beams present camber after prestressing and early-age imperfections like initial sweep and rotations. Because there have been many reported cases of collapse with this type of element when supported only by bearing pads and during transport, its nonlinear behavior must be understood for a possible improvement in safety during handling and erection. From this observation, it should be pointed out that there have been no analytical studies on the nonlinear response of the problems. Also, no analytical solution accounts for the initial rotation of the elements on stability analysis. Thus, the purpose of the present research is to present nonlinear solutions for prestressed concrete beams resting on elastomeric bearing pads as well as truck and trailer during transport while considering initial imperfections and camber. The equations are obtained by using the Rayleigh-Ritz variational method. From the results, the nonlinear study demonstrates that the problem is highly sensitive to initial imperfections due to the unstable trajectory after peak load. The most critical imperfection for rollover of beams is the initial rotation, compared with initial camber and initial sweep. However, all misalignments influenced the maximum load. Furthermore, the proposed formulation can determine the nonlinear rollover behavior combining all these factors.

An automated, energy-based, finite-difference procedure for the elastic collapse of rectangular plates and panels

A Homogenization Scheme for Nonlinear Viscoelastic Behaviors of Particulate Reinforced Composites

Assessment of the ultimate strength of stiffened panels of ships considering uncertainties in geometrical aspects: Finite element approach and simplified formula

In this paper, the nonlinear static and free vibration analysis of Euler-Bernoulli composite beam model reinforced by functionally graded single-walled carbon nanotubes (FG-SWCNTs) with initial geometrical imperfection under uniformly distributed load using finite element method (FEM) is investigated. The governing equations of equilibrium are derived by the Hamilton's principle and von Karman type nonlinear strain-displacement relationships are employed. Also the influences of various loadings, amplitude of the waviness, UD, USFG, and SFG distributions of carbon nanotube (CNT) and different boundary conditions on the dimensionless transverse displacements and nonlinear frequency ratio are presented. It is seen that with increasing load, the displacement of USFG beam under force loads is more than for the other states. Moreover it can be seen that the nonlinear to linear natural frequency ratio decreases with increasing aspect ratio (h/L) for UD, USFG and SFG beam. Also, it is shown that at the specified value of (h/L), the natural frequency ratio increases with the increasing the values amplitude of waviness while the dimensionless nonlinear to linear maximum deflection decreases. Moreover, with considering the amplitude of waviness, the stiffness of Euler-Bernoulli beam model reinforced by FG-CNT increases. It is concluded that the R parameter increases with increasing of volume fraction while the rate of this parameter decreases. Thus one can be obtained the optimum value of FG-CNT volume fraction to prevent from resonance phenomenon.

EDITORIAL

A novel type of angle steel buckling‐restrained brace (ABRB) has been developed for easier control on initial geometric imperfection in the core, more design flexibility in the buckling restraining mechanism and easier assembly work. The steel core is composed of four angle steels to form a non‐welded cruciform shape restrained by two external angle steels, which are welded longitudinally to form an external tube. Component test was conducted on seven ABRB specimens under uniaxial quasi‐static cyclic loading. The test results reveal that the consistency between the actual and design behavior of ABRB can be well achieved without the effect of weld in the core. The ABRBs with proper details exhibited stable cyclic behavior and satisfactory cumulative plastic ductility capacity, so that they can serve as effective hysteretic dampers. However, compression–flexure failure at the steel core projection was found to be the primary failure mode for the ABRBs with hinge connections even though the cross‐section of the core projection was reinforced two times that of the yielding segment. The failure mechanism is further discussed by investigating the Nu– Mu correlation curve. It is found that the bending moment response developed in the core projection induced by end rotation was the main cause for such a failure mode, and it is suggested that core projection should be kept within elastic stage under the possible maximum axial load and bending moment response. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Investigation of the Lateraltorsional Buckling Behaviour of Engineered Wood I-Joists with Varying End Conditions