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Two continuous lattice steel truss bridges spanning 190 m with subdivided top chord members were constructed on the same design across river Alaknanda at Dugadda and Srinagar, respectively, in Uttarakhand, India. Both bridges were similar in design and geometry having middle span of 110.0 m and two end spans of 40.0 m. Garudchatti bridge at Dugadda was constructed first and opened to traffic, but excessive vibrations and lifting of end supports under live load condition were observed. Construction of Chauras bridge at Srinagar started later, but it collapsed during casting of the deck slab due to buckling of one of its top chord compression members. Failure of Chauras bridge led to the serious concerns in the minds of people and technocrats about the safety of Garudchatti bridge also, because it was constructed using the same design of Chauras bridge. Therefore, it was decided to strengthen and carry out load testing of Garudchatti bridge before reopening to the traffic. In the present work analyses of Garudchatti bridge are presented to identify structurally unsafe members for most severe live loads given in IRC:6-2010 code, and recommendations for strengthening of the critical members. Finite element space frame analyses of the bridge were carried out using STAAD Pro. v8i software to find excessively stressed members beyond their permissible stress limit. The critical compression members were strengthened by welding additional channel sections. RCC anchor blocks were constructed to restrict lifting of end supports under live load. After strengthening, load testing of the bridge was performed to ensure the safety of the bridge. The bridge is now reopened for traffic. In the past a number of bridges have collapsed during load testing. In case of any shortcoming in the design or overloading during load testing, compression members of the truss may suddenly buckle and cause collapse of the bridge. Therefore, it is not advisable to load test steel truss bridges which do not have adequate margin beyond the service load condition. [ABSTRACT FROM AUTHOR]

Cylindrical steel silos are often supported by discrete supports or columns to be able to provide a hopper and to facilitate emptying operations beneath the cylindrical barrel. The simplest mean of support for a light silo is by the use of engaged columns, without the use of unnecessarily expensive ring stiffeners. Such engaged columns gradually introduce the support load into the silo wall by shear, spreading the stresses in circumferential direction. In general, the highest axial compressive stress concentrations can be found in the shell wall in the vicinity of the top of the engaged column, resulting in failure due to excessive yielding and/or local instability. The study aims to identify the optimal combination of dimensions of an engaged column (i.e. the height, the widths in circumferential and radial direction and the thickness) to obtain a failure load as high as possible with as little material in the column as possible. An important condition is the requirement that the columns must withstand a higher load than the silo wall itself. In other words, failure should occur in the vicinity of the terminations of the columns (and not in the column itself). All results and conclusions are based on numerical finite element analyses. [ABSTRACT FROM AUTHOR]

Buckling of flexurally anisotropic composite plates under combined loading is considered. The purpose of the paper is to develop approaches for predicting buckling loads for the plates, basing on buckling analysis results for separate loadings. Theoretical aspects of the problem are explored. The derivatives of the buckling interaction curves are analytically derived. The finite predicting formulae are proposed. The Galerkin-type numerical method for combined loading buckling analysis is developed. The method is based on buckling modes of separate loadings. Numerical examples are discussed. Convergence of the method is shown. Influence of the flexural anisotropy on the buckling behavior is demonstrated. [ABSTRACT FROM AUTHOR]

In this article the effect of delaminations on the load carrying capacity of a large wind turbine blade is studied numerically. For this purpose an 8.65 m long blade section with different initial delaminations in the main spar was subjected to a flapwise dominated bending moment. The model was setup in Abaqus and cohesive elements were chosen for modelling delamination growth. For initial delaminations with a width of 30–50% of the cap width the study showed that delamination close to the surface started to grow in load ranges of normal operation conditions and led to local buckling modes. The local buckling caused high strains and stresses in the surrounding of the delamination, which exceeded the material design properties and therefore should be considered as dangerous. Delaminations placed near the mid-surface of the cap did not have a significant effect on the blade response under normal operation conditions. In the simulations the static load exceeded the design load by more than 40% before delamination growth or cap buckling occurred. It could be concluded that delamination induced near-surface buckling modes have to be considered critical due to an onset of local sublaminate buckling below the design load level. [ABSTRACT FROM AUTHOR]

The vibration behaviors of functionally graded carbon nanotube (FG-CNT) reinforced composite rectangular plates subjected to in-plane loads are studied in this paper. Three types of carbon nanotube (CNT) distributions are researched in this investigation. Reddy’s third-order shear deformation theory (HSDT) is applied to evaluate the displacement fields of the plate. The equation of motion of the structural system is formulated with use of the Hamilton’s principle. The plates investigated in this study are simply-supported on two opposite edges and therefore, in order to solve the coupling set of equations of motion, the state-space Levy method is applied. Based on the Levy solution, the natural frequencies and vibration mode shapes of FG-CNT reinforced composite plates subjected to in-plane loads with different boundary conditions are presented for different thickness-length ratios and aspect ratios. Moreover, the critical in-plane loads for the buckling of different FG-CNT plates are calculated and compared. [ABSTRACT FROM AUTHOR]

Design of stiffened panels requires evaluating their behavior under any loading circumstances by considering initial geometric imperfections and the altering effects resulting from eventual material degradation. Both static and dynamic loading scenarios are to be investigated in order to assess safety for buckling strength of these vital structures. In this work, dynamic buckling under in-plane uniform axial compression loading having the form of finite duration pulse is analyzed through nonlinear finite element modeling of the structure. Welding induced defects that consist of initial geometric imperfections modifying the skin plate curvature in the longitudinal direction were incorporated. Material degradation in the heat affected zone was also taken into account. The Budiansky and Roth buckling criterion was employed to predict instability under a given dynamic load pattern. Various profiles including rectangular, triangular, double-triangular and half-sine were considered. The obtained results have shown that both the pulse period and the pulse shape have a drastic effect on the buckling strength. For the considered boundary conditions, pulses having periods that are comparable to two times the period of the first natural mode of vibrations were found to reduce the static buckling strength up to 66% in the elastic regime and 33% in the elastic plastic regime. [ABSTRACT FROM AUTHOR]

We study the stability of thin walled circular cylindrical shells subject to radial pressure loading. Towards this end, we first develop the equations of motion of these shells with predominant radial deflections. We identify additional terms in the shell equations of motion which have mostly been neglected in existing studies and ascertain their importance in predicting the correct static buckling pressure. For finite cylinders, incorporation of these terms results in the best prediction of the static buckling pressure. Furthermore, we also find that the assumed relationships between the in-plane displacements of a generic point and the in-plane displacements of the mid-surface, which change from one shell theory to the other, play a critical role in determining the correct onset of the buckling instability under radial loading. In particular, the Donnell shell theory which is very popular for the study of dynamic problems related to cylindrical shells does not predict the correct buckling pressure. We find that the Flügge–Luré–Byrne theory is best suited for this purpose. Accordingly, the shell equations with the additional terms and the in-plane displacements related as per the Flügge–Luré–Byrne shell theory have been used for the study of parametric instability of a cylinder subject to a uniform radially fluctuating pressure. Stability charts with respect to different combinations of the forcing parameters viz. the static component of the pressure, the amplitude and frequency of the fluctuating component of the pressure have been presented which can serve as design guideline for shells subject to fluctuating radial loads. [ABSTRACT FROM AUTHOR]

The present study is concerned with an analysis of load and frequency interaction effects in the dynamic buckling of sandwich plates and shells with a soft, transversely flexible core. The analysis is based of a general geometrically nonlinear soft-core sandwich model presented and a corresponding extended Galerkin solution strategy presented earlier. In the present study, the formalism is adopted and transformed into an eigenvalue problem. Assuming large transverse average displacements but small amplitudes for the vibration problem, a partially decoupled problem is obtained where in a first step the static buckling and face wrinkling problems can be addressed without consideration of the dynamic problem. In a second step, the dynamic eigenvalue problem can be solved, using the static solution as input parameters. The model is applied in parametric studies on the vibration response of plane and doubly curved sandwich panels with rectangular projection. In all cases, strong interaction effects between the external static preload and the natural frequencies are observed. The development of overall buckling or local face wrinkling instabilities enabled due to the transverse flexibility of the core result in distinct drops of the first natural frequency. [ABSTRACT FROM AUTHOR]

Codes of practice rely on the effective length method to assess the stability of multi-storey frames. The effective length method involves isolating a critical column within a frame and evaluating the rotational and translational stiffness of its end restraints, so that the critical buckling load may be obtained. The non-contradictory complementary information (NCCI) document SN008a (Oppe et al., 2005) to BS EN 1993-1 (BSI, 2005) provides erroneous results in certain situations because it omits the contribution made to the rotational stiffness of the end restraints by columns above and below, and to the translational stiffness of end restraints by other columns in the same storey. Two improvements to the method are proposed in this paper. First, the axial load in adjoining columns is incorporated into the calculation of the effective length. Second, a modification to the effective length ratio is proposed that allows the buckling load of adjacent columns to be considered. The improvements are shown to be effective and consistently provide results within 2% of that computed by structural analysis software, as opposed to the up to 80% discrepancies seen using the NCCI (Oppe et al., 2005). [ABSTRACT FROM AUTHOR]

The Vibration Correlation Technique (VCT) for experimentally nondestructive determination of buckling loads of thin-walled structures is applied to stringer stiffened curved panels manufactured both from aluminum and laminated composite material. The modal behavior of the panels is investigated by exciting the structures using the modal hammer method. Natural frequencies of the panels are recorded as a function of the applied axial compression load. Unlike shell structures which present a non-stable post-buckling behavior, the stringer stiffened panels show a stable post-buckling behavior, enabling the measurement of the natural frequencies up to the actual experimental buckling load. The modal behavior of compressed panels is compared for reference to shells, yielding areas of applicability for VCT to predict efficiently the buckling loads of thin-walled structures. Guidelines are then formulated for the application of the VCT. [ABSTRACT FROM AUTHOR]

The strategy of Reduced Stiffness (or Reduced Energy) Analysis, in which selected energy components are eliminated to account for mode interaction and imperfection-sensitivity in a simplified way, was developed by Croll and co-workers since the early 1980s. This physical interpretation allows the formulation as an eigenvalue problem, in which the eigenvalue (critical load) is a lower bound to experiments and to nonlinear incremental analysis. This paper considers the computational implementation of both reduced stiffness and reduced energy approaches to the buckling of shell structures by means of perturbation techniques and penalty parameter methods. The structural configurations of interest in this work are cylindrical shells with or without a roof. The reduced stiffness approach has been implemented in a special purpose finite element code for shells of revolution, whereas the reduced energy methodology was implemented in a general purpose finite element code. The present results are compared with geometrically nonlinear analysis including geometric imperfections. Achievements and difficulties in extending the methodologies to complex problems in engineering practice are highlighted. [ABSTRACT FROM AUTHOR]

The critical buckling loads of pinned-pinned and cantilever beams are computed using the equations of three-dimensional elasticity rather than typical beam theories. These loads are influenced both by the nature of the assumed displacement field over the beam cross-section and by the inclusion of the terms from the full constitutive tensor. Of special interest are beams that are either anisotropic or auxetic. For anisotropic beams, an increased ratio of longitudinal to shear modulus for cantilevered beams increases the generation of shear buckling rather than flexural buckling. For isotropic auxetic beams, the values of Poisson ratio that define the limit between buckling loads that approach the classical buckling load from above or below are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a method for the determination of the buckling loads of symmetrically laminated composite plates under uniaxial compressive load with explicit consideration of bending–twisting-coupling (BTC). The plates under consideration are assumed to be thin and balanced with a symmetric stacking sequence and consist of layers with ply orientations of {0°/±45°/90°}, but otherwise arbitrary lamination schemes. The characteristic laminate quantities are described in a non-dimensional notation in order to capture all combinations of material and stacking sequences that are physically possible. Plates with rectangular planforms in the framework of Classical Laminate Theory (CLT) under several different sets of boundary conditions are considered, and the buckling problem of such composite laminated plates is solved in an approximate manner by using the classical Rayleigh–Ritz method. Several combinations of the boundary conditions ‘simply supported’ and ‘clamped’ are analyzed, and the obtained results are compared with finite-element simulations for verification purposes. Based on the computed data, two different design equations for sufficiently long plates are developed which allow for a rapid and closed-form analytical assessment of the buckling behavior of symmetrically layered composite plates under explicit consideration of bending–twisting coupling. It is found that the closed-form analytical analysis equations are simple in their application and yet still work with very satisfying accuracy which makes them very suitable for use in practical engineering work. [ABSTRACT FROM AUTHOR]

Nondestructive methods, to calculate the buckling load of imperfection sensitive thin-walled structures, are one of the most important techniques for the validation of new structures and numerical models of large scale aerospace structures. The vibration correlation technique (VCT) allows determining the buckling load for several types of structures without reaching the instability point, but this technique is still under development for thin-walled plates and shells. This paper presents and discusses an experimental and numerical validation of a novel approach, using the vibration correlation technique, for the prediction of realistic buckling loads on unstiffened cylindrical shells loaded in compression. From the experimental point of view, a batch of three composite laminated cylindrical shells are fabricated and loaded in compression up to buckling. An unsymmetric laminate is adopted in order to increase the sensitivity of the test structure to initial geometric imperfections. In order to characterize a relationship with the applied load, the first natural frequency of vibration and mode shape is measured during testing using a 3D laser scanner. The proposed vibration correlation technique allows one to predict the experimental buckling load with a very good approximation, without actually reaching the instability point. Furthermore, a series of numerical models, including non-linear effects such as initial geometric and thickness imperfection, are carried-out in order to characterize the variation of the natural frequencies of vibration with the applied load and compare the results with the experiment findings. Additional experimental tests are currently under development to further validate the proposed approach for metallic and balanced composite structures. [ABSTRACT FROM AUTHOR]

This paper presents a unified Lévy-type solution procedure for the buckling analysis of both thin and thick composite plates under biaxial loads. The plates are simply-supported at two opposite edges, while the two remaining sides are subjected to any combination of simply-supported, clamped and free conditions. The problem is formulated in the context of a variable-kinematic approach, offering the advantage of automatically handling theories of various order. Both layerwise and equivalent single layer theories are considered. The governing equilibrium equations are derived analytically from the Principle of Virtual Displacements (PVD), and are solved exactly referring to the Lévy-type procedure. The accuracy of the predictions is demonstrated by comparison with results available in literature, including exact 3D solutions. A comprehensive set of benchmark results is provided for plates subjected to different loading and boundary conditions and characterized by various width-to-thickness ratios. [ABSTRACT FROM AUTHOR]

Experimental studies and numerical simulations are performed to investigate the structural response of adhesively bonded CFRP cylindrical splice-joint panels subjected to axial compression. Splicer joints used in aerospace composite structures need to sustain the design ultimate loads in the presence of flaws due to manufacturing (debonds), in order to demonstrate compliance with flightworthiness. CFRP cylindrical splice-joint specimens with and without debonds are subjected to compression load. Experimental data reveals that the load-carrying capacity of splicer joint decreases in the presence of debonds. Numerical simulations are carried out in line with experimental observations using finite element analysis. Good correlations with experimental results are obtained both in terms of buckling load capacity and load–displacement responses. Non-destructive methods, pulsed thermography and acoustic emission, are employed to detect and monitor the response of debond respectively. Parametric studies are also performed using finite element analysis to assess the influence of bi-directional loading and the effect of the physical gap provided between basic panels in the splicer joints. [ABSTRACT FROM AUTHOR]

In the present study, the buckling behaviour of laminated composite skew plates with different boundary conditions subjected to linearly varying in-plane loads are presented. The skew plate is modelled based on higher order shear deformation theory, which accurately predicts the buckling behaviour for the thick plate. The in-plane stress distribution within the skew plate due to linearly varying in-plane load is equal to the applied in-plane edge load in the pre-buckling range. Using these in-plane stress distributions, the total potential energy functional is formulated. Total potential energy is a function of the total strain energy of skew plate and potential energy due to in-plane stress distributions. The total strain energy of skew plate contains membrane energy, bending energy, additional bending energy due to additional change in curvature and shear energy due to shear deformation, respectively. The total potential energy functionals mapped from physical domain to computational domain over which a set of orthonormal polynomials satisfying the essential boundary conditions is generated by Gram–Schmidt orthogonalization process. Using a Rayleigh-Ritz method in conjunction with Boundary Characteristics Orthonormal Polynomials, the total potential energy functional is converted into sets of algebraic equations. Finally, these algebraic equations are rearranged as a linear eigenvalue problem, which is solved to obtain the critical buckling loads. The numerical results are presented for different skew angles, boundary conditions, length to thickness ratios, aspect ratios and in-plane loadings. It is observed that the critical buckling load increase with the increase of skew angle as well as change in the mode shape at a lower aspect ratio with the increase of skew angle. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to present and discuss failure mechanism, failure mode, as well as plastic deformation of a lattice telecommunication tower obtained during a full-scale pushover test. The manuscript consists of a detailed description of the tested structure and the experimental site. Displacements of particular nodes of the tower are presented as a function of the external load. The main conclusion is that the rigidity of joints between particular elements, which depends on thickness and diameter of connecting flanges and number and quality of bolts, determines the failure mode of the compressed tower legs. In the article, values of axial forces under compression, taken directly from the conducted test, were compared with the standard buckling resistance. On the basis of this comparison, discussion about the effective slenderness factor has been generated, and the proper determination of this coefficient has been proposed. [ABSTRACT FROM AUTHOR]

In this paper the correlation of deformation energy and critical buckling loads is examined. An advanced analysis technique is derived for the investigation of z-section frames typically applied in composite aircraft fuselage. This technique is verified through closed form solutions of z-section columns under quasi-static loading conditions. The method is applied to study the effects of flange width and laminate thickness on the critical failure modes of composite frames. Therein, the focus is on composite structural elements favourable for deformation kinematics in aerospace applications subjected to crash loads. [ABSTRACT FROM AUTHOR]

The paper is devoted to the mathematical modeling of a transverse shearing effect for sandwich beams with sinusoidal corrugated cores. Bending and buckling problems of two sandwich beams are investigated. The core of the first beam is crosswise corrugated, while that of the second one is lengthwise corrugated. Two theoretical models are elaborated for these beams. The influence of the transverse shearing effect on deflections and critical loads of these sandwich beams is presented. Analytical studies have been verified numerically. [ABSTRACT FROM AUTHOR]

An approximate analytical solution of the buckling problem formulated for a composite sandwich cylindrical shell subjected to a uniform external lateral pressure is presented in the paper. Both ends of the shell of finite length are fully clamped. The problem is solved using the Galerkin method. The analytical formula for the critical load has been obtained and verified by comparison with a finite-element solution. Based on this formula buckling analyses of sandwich pipes with different types of core materials normally used in underwater applications have been performed. Applications of the formula to the solutions of design problems have been demonstrated for the clamped–clamped sandwich pipes considering constraints imposed on the value of critical pressure. [ABSTRACT FROM AUTHOR]

A geometrically nonlinear analysis of symmetric variable angle tow (VAT) composite plates under in-plane shear is investigated. The nonlinear von Karman governing differential equations are derived for postbuckling analysis of symmetric VAT plate structures which are subsequently solved using the differential quadrature method. The effect of in-plane extension-shear coupling on the buckling and postbuckling performance of VAT composite plates is investigated. The buckling and postbuckling behaviour of VAT plates under positive and negative shear is studied for different VAT fibre orientations, aspect ratios, combined axial compression and their performance is compared with that of straight fibre composites. It is shown that there can be enhanced shear buckling and postbuckling performance for both displacement-control and load-control and that the underpinning driving mechanics are different for each. [ABSTRACT FROM AUTHOR]

Inelastic behavior of diagonally braced moment resisting frame (DBMRF) dual systems are investigated to determine their yield mechanisms and failure modes, and to quantify the load sharing between the moment frame and the gusset–brace subsystems. An improved performance is sought through new balanced design criteria that will increase a DBMRF system’s ductility, and permit yielding in multiple secondary stages at selected performance levels. The presented balanced design approach is based on a non-dimensional formulation, which addresses both tensile yielding and compressive buckling phases of DBMRF systems and considers the participation of all system constituents. The satisfaction of the proposed balanced design criteria is achieved through parametric studies carried out with high-fidelity three-dimensional finite element (FE) models that are globally and locally validated/verified against experimental data/numerical simulations available in open literature. Using the validated FE models, the collapse behavior of a representative set of DBMRF systems are examined, and the influences of the brace elements’ demand-to-capacity ratios, as well as the gusset plate connection types/sizes on the yield mechanisms and the failure modes are scrutinized. Both pushover and cyclic analyses are carried out; and the overall system ductility and energy dissipation values are investigated for different width-to-height ratios. The responses of system constituents are evaluated using the specified, as well as the expected material properties. The worked examples clearly demonstrate the utility of the proposed balanced design criteria in improving the DBMRF systems’ ductility, and in avoiding premature failure modes. [ABSTRACT FROM AUTHOR]

This paper examines the compressive failure mechanism in edge-to-edge loaded corrugated sandwich panels. The formation of face wrinkles is specifically considered. A detailed finite element model of face sheets and web core of a sandwich panel was developed to provide insight on the failure mechanism. A gradient enhanced continuum damage theory was implemented to capture length effects caused by the material microstructure including formation of damage in the face sheets and core. Distributions of strains in the face sheets determined from finite element analysis (FEA) are compared to experimentally measured strains. The predicted location and orientation of the face wrinkle, as indicated by high values of the second principal strain, agrees well with experimental observations. Load vs. out-of-plane deflection curves obtained from FEA with the gradient enhanced damage material model are compared to those obtained from a linear-elastic material model and experimentally determined curves. The gradient enhanced solution gives qualitatively better agreement with experimental results, although the magnitudes of strains are less than those determined experimentally. [ABSTRACT FROM AUTHOR]

There are considered thin periodic plates with moderately large deflections. To take into account the effect of the microstructure on behaviour of these plates the tolerance modelling method is applied, cf. Domagalski and Jędrysiak [2] , Meccanica, 2012. This method makes it possible to derive model equations with constant coefficients involving terms dependent of the microstructure size. The paper contains an computational example of critical load calculations and postbuckling analysis. [ABSTRACT FROM AUTHOR]

The paper studies the influence of internal pressure on circular thin-walled pipes ( D / t > 150 ) subjected to pure bending. Both straight pipes and curved pipes are analysed. Both yield and buckling failures are considered. It is shown that internal pressure decreases the limiting load for yield but increases the limiting load for buckling. The study is mainly FEA-based. A formula to predict critical moment given by linear buckling analysis is proposed. Comments on difference between linear and non-linear analysis results are given. It is shown that a pipe curvature opposite to the bending moment can increase the critical load. It is shown that cylindrical thin-walled shells have an optimal value of internal pressure to which limiting load for yield and critical buckling moment are equal, corresponding to an optimal use of material. [ABSTRACT FROM AUTHOR]

The part 1 [1] of this two-part paper presented an experimental study concerning the web-crippling phenomenon on GFRP pultruded I-shaped profiles and showed that they are very sensitive to transverse compressive loads (lower mechanical properties in the transverse direction) and web-crippling failure. This part 2 reports numerical and analytical results aiming at a better understanding of the web-crippling phenomenon and providing enough data to complement the observations made in the experimental campaign. The scope of these studies was to predict and replicate the behaviour exhibited by the four different GFRP profiles tested (I100, I120, I200 and I400) when subjected to different transverse loading configurations (ETF and ITF) and bearing lengths (varying from 15 to 100 mm). Shell finite element (SFE) models with the Tsai Hill failure criterion were developed in ABAQUS, aiming at simulating the experimental tests performed in part 1. This procedure enabled the comparison of the numerical results with the experimental data, as well as the observation of the stress fields and damage evolution. In general, these models presented good agreement with the test results. An analytical formula was also developed to predict the web-crippling load of GFRP profiles and presented very good agreement with the test results. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to study the effect of I-shape stiffener stiffness on the buckling and post-buckling, up to collapse behavior of stiffened composite panel under the uniform uniaxial compression load. Six stiffened composite panel configurations, which were orthogonally designed with two skin configurations and three I-shape stiffener configurations, were took into account in the experimental investigation. Three specimens for each configuration (18 specimens in total) were manufactured for test. Before tests, the key dimensions of I-stiffener and skin were measured. Furthermore, all the specimens were also inspected visually and detected by the ultrasonic C-scan system. No initial delamination or debonding area was found on all the specimens according to their C-scan images. The experimental results show that the equivalent compression stiffness of I-shape stiffener has great influence on the buckling load and failure mode of stiffened panel, but a little effect on the failure load of stiffened panel. The skin thickness has great impact on the buckling load and the final failure load. [ABSTRACT FROM AUTHOR]

There is evidence that glass fibre reinforced polymer (GFRP) pultruded profiles are particularly susceptible to transverse compressive loads, owing to the much lower mechanical properties in the direction transverse to the pultrusion axis. Although very relevant, the understanding about the web-crippling phenomenon in GFRP pultruded profiles is still very limited, as attested by the lack of information available in design codes and guidelines. This paper reports an experimental study about the web-crippling phenomenon in GFRP pultruded profiles with I-section. The experimental programme included comprehensive material characterization tests (tension, compression, flexure and shear), and full-scale web-crippling tests on four different I-profiles, with heights ranging from 100 mm to 400 mm, thus covering the vast majority of structural profiles currently available in the market. In the web-crippling experiments, two load configurations were tested: interior two flanges (ITF); and end two flanges (ETF). In addition, tests were performed with three different bearing lengths: 15 mm, 50 mm, and 100 mm. The experimental results confirmed the susceptibility of GFRP pultruded profiles to transverse compressive loads, outlining the influence of both the load configuration and the bearing length on the web-crippling phenomenon in terms of strength, stiffness, and failure modes. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are employed to study the instability characteristics of graphyne and its family under compressive loads. The effects of nanosheet side length and aspect ratio on the critical compressive force and critical strain are investigated. It is shown that increasing aspect ratio leads to decreasing the critical compressive force. Besides, the effect of atomic structure on the compressive behavior of nanosheets is explored. It is observed that the zigzag graphynes have larger buckling forces than the armchair graphynes with same geometries. Finally, the buckling behavior of different nanosheets from the graphyne family is studied. It is represented that the nanosheets with more acetylene links have smaller critical compressive forces. [ABSTRACT FROM AUTHOR]

Morphing aircraft aim to increase the performance of aircraft over multiple flight conditions, by enabling shape changes in flight in order to optimise their aerodynamic properties for the current conditions. The skin of a morphing aircraft is a critical component. It must be compliant in degrees of freedom that are required for actuation, to minimise the actuation loads. However, it must also carry structural loads, and therefore be stiff in load bearing degrees of freedom. This leads to a requirement for extremely anisotropic material systems. A common solution is the use of a corrugated panel. However, previous work on corrugations has not addressed the problem of compressive buckling loads. This work analyses the performance of corrugated panels under buckling loads, and optimises corrugation patterns for the objectives of weight, buckling performance, and actuation compliance. Simplified analytical models that derive properties equivalent to conventional plates are used to obtain approximate estimates of the buckling loads. Furthermore a new mode of buckling, that occurs entirely in-plane and is unique to panels with extreme anisotropy is analysed. The simple models allow optimisation to be performed, and both a single-objective and a multi-objective approach are demonstrated. The results are compared to Finite Element Analysis. [ABSTRACT FROM AUTHOR]

This present work aims to investigate the effect of debonds on the structural performance of adhesively bonded curved carbon fiber reinforced plastic (CFRP) panels under compressive loading environment. Representative curved panels are fabricated with a quasi-isotropic lay-up. Two types of specimens are prepared for the studies, one without debonds and the other with debonds of specified size, artificially introduced within the lap region. Pulsed thermography non-destructive technique is employed for the detection of debonds on the specimens. A set of experiments are conducted with displacement, strain and acoustic emission sensors to ascertain the performance of adhesively bonded joints under compression loading. Computational analyses are carried out using commercial finite element code MSC/NASTRAN to reproduce the experimental behavior and to aid in understanding the effect of closed debonds on the bonded joints. The computational model predictions are in good agreement with experimental observations. The effects of location of debond and panel curvatures are studied computationally incorporating debonds of different sizes. It is observed that debond location along the specimen length has significant effect and the buckling load reduces when the panel curvature increases for the same debond size. [ABSTRACT FROM AUTHOR]

The importance of taking into account geometric imperfections for cylindrical and conical thin-walled structures prone to buckling had been already recognized by the first authors dealing with new formulations. Nowadays, the analysts still use empirically based lower-bound methods such as the NASA SP-8007 guideline to calculate the required knock-down factors (KDFs), which does include important mechanical properties of laminated composite materials, such as the stacking sequence. New design approaches that allow taking full advantage of composite materials are required. The single perturbation load approach (SPLA), a new deterministic approach first proposed by Hühne, will be investigated with unstiffened composite conical structures varying the geometry, lamina and layup. The SPLA׳s capability for predicting KDF is compared with the NASA approach. The SPLA was applied to the geometrically perfect structures and to the structure with geometric imperfections of two types, mid-surface imperfections and thickness imperfections. The study contributes to the European Union (EU) project DESICOS, whose aim is to develop less conservative design guidelines for imperfection sensitive thin-walled structures. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of geometric nonlinearity and temperature field on the in-plane elastic behaviour and buckling of crown-pinned circular steel arches that is subjected to a uniform radial load. Differential equations of equilibrium are derived based on the principle of stationary potential energy, and analytic solutions for the linear and nonlinear behaviour and buckling loads are derived. It is found that the nonlinearities have significant influences on the in-plane behaviour and buckling of crown-pinned arches. The nonlinear bending actions produced by the uniform radial load in crown-pinned arches are substantial, while the linear bending actions are equal to zero for three-pinned arches and are small for one-pinned arches. The nonlinear buckling loads are much lower than their linear counterparts. It is also found that the uniform temperature field influences the nonlinear elastic behaviour and buckling of crown-pinned arches, while it has no effects on the linear internal actions of three-pinned arches and small effects on those of one-pinned arches. As temperature increases, radial displacements decrease while the nonlinear buckling loads increases. It is further found that crown-pinned arches can buckle only in a symmetric mode, but not in an antisymmetric mode. Comparisons with the finite element results show that the analytical solutions derived in this paper are quite accurate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Compressive tests on glass columns with rectangular, T and X cross-sections. [•] Stability analyses including elastic torsional and local buckling. [•] Buckling strength of single panels depends very much on the slenderness. [•] Local and torsional buckling effects reduce the bearing capacity of T and X columns. [Copyright &y& Elsevier]

Abstract: Fire safety has become an important part in structural design due to the ever increasing loss of properties and lives during fires. Conventionally the fire rating of load bearing wall systems made of Light gauge Steel Frames (LSF) is determined using fire tests based on the standard time–temperature curve in ISO834 (ISO 834-1, 1999 [1]). However, modern commercial and residential buildings make use of thermoplastic materials, which mean considerably high fuel loads. Hence a detailed fire research study into the fire performance of LSF walls was undertaken using realistic design fire curves developed based on Eurocode parametric (ENV 1991-1-2, 2002 [2]) and Barnett's BFD (Barnett, 2002 [3]) curves using both full scale fire tests and numerical studies. It included LSF walls without cavity insulation, and the recently developed externally insulated composite panel system. This paper presents the details of finite element models developed to simulate the full scale fire tests of LSF wall panels under realistic design fires. Finite element models of LSF walls exposed to realistic design fires were developed, and analysed under both transient and steady state fire conditions using the measured stud time–temperature curves. Transient state analyses were performed to simulate fire test conditions while steady state analyses were performed to obtain the load ratio versus time and failure temperature curves of LSF walls. Details of the developed finite element models and the results including the axial deformation and lateral deflection versus time curves, and the stud failure modes and times are presented in this paper. Comparison with fire test results demonstrate the ability of developed finite element models to predict the performance and fire resistance ratings of LSF walls under realistic design fires. [Copyright &y& Elsevier]

Abstract: Mechanical behavior of lithium-ion battery modules is investigated by conducting tensile tests of the module components, constrained compression tests of dry module representative volume element (RVE) specimens, and a constrained punch test of a small-scale dry module specimen. The results of tensile tests of the module components are used to characterize the tensile behavior of module specimens. The results in-plane constrained compression tests of module RVE specimens indicate that the load carrying capacity is characterized by the buckling of the module components and the final densification of the module components, and the nominal stress-strain curves appear to be independent of the specimen height. The results of different compressive nominal stress-strain curves in the in-plane and out-of-plane directions indicate the module RVE specimens are anisotropic. The results of a buckling analysis of the module RVE specimens under in-plane constrained compression are in agreement with the experimental results. The module RVE specimen is dominated by the buckling of the aluminum heat dissipater sheet under in-plane constrained compression. Finally, the results of a constrained punch test of a module specimen are in agreement with those of the corresponding finite element analyses based on a macroscopic homogenized foam material model. [Copyright &y& Elsevier]

Abstract: A solution is proposed to the buckling problem formulated for a rectangular sandwich plate having all the edges fully clamped (CCCC plate) and subjected to a uniaxial compressive loading. The analysis of the out-of-plane deformation of the buckled plate is based on the equations of the first order shear deformation theory (FSDT). Galerkin method has been employed to solve the problem. Variations of the plate deflection and angles of rotation between the unloaded edges have been approximated using the solution to the bending problem for the shear deformable beam with clamped ends. The approximation of these variables between the loaded edges has been performed using trigonometry series. The solution to the problem is reduced to the calculation of the eigenvector of corresponding homogeneous system of linear equations and determination of its least component. Verification of the solution obtained has been performed using finite-element analysis. [Copyright &y& Elsevier]

Abstract: Shells are thin-walled structures whose stability and performance is governed by geometrical buckling. The buckling stability of shell structures has been investigated through numerous analytical and experimental studies. In an experimental investigation, it is quite important to determine the accurate buckling load of the structure as the critical load is usually masked by failure owing to large deformations as well as the effects of initial imperfections. On this basis, the main objective of this study is to evaluate the applicability of the Southwell, Massey, Modified, and Meck plotting methods in predicting the accurate critical buckling loads of conical shell structures with various geometrical properties. To this end, the buckling loads of several test specimens are determined through application of the aforementioned plotting methods as well as consideration of the test data for strain and displacement deformation variables, and compared with numerical and analytical predictions. Based on the findings of this study, agreement between the extrapolated and numerical as well as analytical results for buckling loads of the considered conical shell specimens is quite satisfactory, which is in turn indicative of applicability of the extrapolation techniques in experimental determination of buckling loads of shell structures. [Copyright &y& Elsevier]

Abstract: Weld-induced geometric imperfections have been reported to have especially detrimental effects on the buckling resistance of shells under hydrostatic pressure. The effect of circumferential imperfections caused by continuous welding on the joined areas between the curved panel edges of the cylindrical and conical shells of steel storage tanks with fixed conical roofs is the most important case in this context. The present paper discusses 12 laboratory specimens in three groups, labeled SP200 (S=Specimen, P=Perfect, 200=height (mm) and radius of Cylinder), SP250 (S=Specimen, P=Perfect, 250=height (mm) and radius of Cylinder) and SP300 (S=Specimen, P=Perfect, 300=height (mm) and radius of Cylinder) loaded under uniform hydrostatic pressure. The samples were modified to include circumferential imperfections at the junctions between the curved edges of the panels of the cylindrical and conical shells, with amplitudes of 2t, 4t and 8t in depth (where t is the thickness of the conical or cylindrical shell). The results of testing under different codes are compared. This study shows that geometrical imperfections at different ratios of t/R (where R the radius of the tanks) may have decreasing, neutral or increasing effects on buckling resistance and can result in softening or stiffening behaviors of the shells. [Copyright &y& Elsevier]

Abstract: A new solution for analyzing of the symmetrical composite plate having two parallel edges simply supported and the remaining parallel edges being clamped (SS–C–SS–C plate) subjected to linear-varying in-plane loads is presented. Levy series are used to represent the displacement field of the plate and a numerical procedure is developed based upon finite-difference method. Convergence study is carried out as well. The proposed method has been validated for both isotropic and composite plates with various aspect ratios and load parameters through numerical examples. [Copyright &y& Elsevier]

Abstract: A continuum based approach is presented for buckling analysis of single layer graphene sheets with skew shape. The straight-sided quadrilateral graphene field is mapped into a square domain in the computational space using a four-node graphene element. Then, the governing equations and boundary conditions of the graphene are transformed from the physical domain into a square computational domain by using the geometric transformation. Some numerical examples related to buckling loads of skew shaped graphene are presented for different geometric parameters. Results related to buckling loads of the single layer graphene with skew shape have been presented which can serve as benchmark solutions for future investigations. [Copyright &y& Elsevier]

Abstract: A series of finite element analyses are conducted to investigate the influence of boundary conditions and geometry of the model on the predicted collapse behaviour of stiffened panels. Periodic and symmetric boundary conditions in the longitudinal direction are used to calculate the ultimate strength of stiffened panels under combined biaxial thrust and lateral pressure. The calculated ultimate strength of stiffened panels are compared with those by different FEM (finite element method) code and are assessed. The periodic boundary condition in the longitudinal direction for two spans or bays model provides an appropriate modelling to a continuous stiffened panel and can consider both odd and even number of half waves and thus, is considered to introduce the smaller model uncertainty for the analysis of a continuous stiffened panel. [Copyright &y& Elsevier]

Abstract: Compressive response and energy absorption of a composite honeycomb is studied. The base material is a circular cell hexagonally packed thin-wall polycarbonate honeycomb. Polydimethylsiloxane (PDMS) elastomer is used as the filler material. Filled honeycomb specimens are quasi-statically loaded under controlled displacement along an inplane direction. Synergistic energy absorption in the filled specimen is observed, as its load response is much greater than the sum of the individual load responses of unfilled honeycomb and the filler material, respectively. Analysis of the crush response is conducted using two methods: (a) Digital image correlation (DIC) to monitor strains and displacement fields in the sample during initial stages of loading and in the vicinity of first failure. (b) Finite element (FE) modeling of the filled honeycomb using the ABAQUS/Explicit finite element code, accounting for the hyperelastic compression response of the PDMS filler. The smeared crack approach (SCA) is implemented in the honeycomb to simulate the longitudinal tearing of the cell wall and to subsequently capture the localization failure in the model. Good agreement between experiment and analysis is reported. [Copyright &y& Elsevier]

Highlights: [•] Critical review of design methods for slender RC panels under eccentric axial load. [•] Experimental campaign on cracked and uncracked centrally reinforced panels. [•] Improved capacity prediction using a computational model with lumped plasticity. [•] Testing and calculations combined with a Design Assisted by Testing (DAT) approach. [•] Novel and more efficient design capacity curve derived using the DAT procedure. [Copyright &y& Elsevier]

Abstract: Some of the knock-down factors applied in design of rocket launcher structures are based on design recommendations which rely on lower-bound curves from experimental data. The best known example is the NASA guideline SP 8007, published in 1965 and revised in 1968, which is applied for cylindrical structures in the space industry. This guideline is based on test data, computational methods and resources from the 1930–1960's. At that time the application of less empirical methods for the design of actual cylindrical shells could not count with the current computational power, and the available methods led to quite large discrepancies between experiments and test observations. Significant improvement on the available analyses approaches and manufacturing techniques since 1960's have not been taken into account in design processes using the NASA SP-8007, and many authors have recognized that for the current standards this guideline is leading to conservative structures. Another aspect for attention regarding application of the NASA SP-8007 for composite shells is that it does not consider the laminate stacking sequence. Moreover, physical observations regarding how does the imperfection sensitivity of unstiffened cylindrical shells change with the presence of an induced geometric imperfection have also suggested that the current applied design rules are too conservative. This conservativeness is confirmed by many tests carried out recently. This study presents an overview of the problem and a detailed description of the physical observations regarding the buckling mechanism of the thin shells under consideration. It is discussed how these observations can be used for less conservative, laminate dependent, knock-down factors accounting for geometric imperfections. The single perturbation load approach is studied in detail and a physically based definition for the minimum perturbation load (P1) is given, paving the way for the development of semi-analytical methods to calculate this minimum perturbation load. [Copyright &y& Elsevier]

Abstract: In the present paper, a three-dimensional elasticity approach is employed to investigate buckling of heterogeneous functionally graded plates under biaxial compression, shear, tension-compression, and shear-compression load conditions. In this regard, a formulation that employs a full compatible three-dimensional Hermitian element with 168 degrees of freedom and guarantees continuity of the strain and stress components is used. It is known that all of the available famous commercial finite element softwares and the proposed series solutions satisfy continuity conditions of the displacement rather than the stress components. Buckling occurrence is detected based on checking both the instability onset and equilibrium criteria. Results are extracted based on a Galerkin-type orthogonality. Therefore, they are more accurate than those obtained based on the traditional Ritz method. The presented three-dimensional finite element analysis and the extracted results are quite new. A vast variety of results including results of biaxial compression, compression-tension, shear, and shear-compression load cases is considered and discussed in detail. [Copyright &y& Elsevier]

Abstract: This paper analytically investigates the mechanism of compressive strength reduction of composite laminated plates due to impact damage in quasi-isotropic laminates. Simplified mechanistic models are proposed. Explicit form solutions including the upper and lower bounds of applied load against end-shortening are derived for the local post-buckling stage by using the numerically derived load vs. end-shortening relationship of a square plate whose circular portion is allowed to deflect like a plate with circular damage. Based on the solution, explicit expressions of the average energy release rate for self-similar delamination growth are also given for the applied load as a function of the dimensions of the plate and the circular damage. Through the solutions we can roughly estimate the failure load due to delamination instability. The meaning of low CAI strength is discussed through the present solution and previous CAI experiments. [Copyright &y& Elsevier]

Abstract: In this paper, instability of a thick through-the-thickness functionally graded material (FGM) rectangular plates under the practical cases of thermal and mechanical loading conditions is analyzed. Uniform shear, uniform uni-axial or biaxial compression/tension, uniform temperature rise, heat conduction across the thickness, and combined cases are considered. For thermal buckling and combined cases in thermal field, temperature dependency of the properties is also taken into account. The four-variable refined plate theory with parabolic distribution of shear strains through-the-thickness is implemented to establish the governing equilibrium and stability equations. Only the clamped type of boundary conditions is considered after the proof of bifurcation type buckling existence. The resulted equations are uncoupled in a reasonable manner. The multi-term Galerkin method is used to derive the critical buckling loads/temperatures and buckled shapes of the plate under various loading conditions. [Copyright &y& Elsevier]

Highlights: [•] A fixed shallow arch was used to study the equilibrium path of the bistable strut. [•] The virtual work principle was adopted to establish nonlinear equilibrium equations. [•] The critical load for symmetric snap-through buckling was obtained. [•] The post-buckling behavior of the arch was also investigated. [Copyright &y& Elsevier]