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Applicability of the vibration correlation technique (VCT) for nondestructive evaluation of the axial buckling load is considered. Thin-walled cylindrical shells with and without circular cutouts have been produced by adhesive overlap bonding from a sheet of aluminium alloy. Both mid-surface and bond-line imperfections of initial shell geometry have been characterized by a laser scanner. Vibration response of shells under axial compression has been monitored to experimentally determine the variation of the first eigenfrequency as a function of applied load. It is demonstrated that VCT provides reliable estimate of buckling load when structure has been loaded up to at least 60% of the critical load. This applies to uncut structures where global failure mode is governing collapse of the structure. By contrast, a local buckling in the vicinity of a cutout could not be predicted by VCT means. Nevertheless, it has been demonstrated that certain reinforcement around cutout may enable the global failure mode and corresponding reliability of VCT estimation. [ABSTRACT FROM AUTHOR]

The computational methods for solving buckling loads of thin-walled members with open sections are not unique when different concerns are emphasized. In this paper, the buckling loads of thin-walled members in linear-elastic, geometrically nonlinear-elastic, and nonlinear-inelastic behaviors are investigated from the views of mathematical formulation, experiment, and numerical solution. The differential equations and their solutions of linear-elastic and geometrically nonlinear-elastic buckling of thin-walled members with various constraints are derived. Taking structural angle as an example, numerical analysis of elastic and inelastic buckling is carried out via ANSYS. Elastic analyses for linearized buckling and nonlinear buckling are realized using finite elements of beam and shell and are compared with the theoretical results. The effect of modeling of constraints on numerical results is studied when shell element is applied. The factors that influence the inelastic buckling load in numerical solution, such as modeling of constraint, loading pattern, adding rib, scale factor of initial defect, and yield strength of material, are studied. The noteworthy problems and their solutions in numerically buckling analysis of thin-walled member with open section are pointed out. [ABSTRACT FROM AUTHOR]

Buckling of load-carrying column structures is an important design constraint in light-weight structures as it may result in the collapse of an entire structure. When a column is loaded by an axial compressive load equal to its individual critical buckling load, a critically stable equilibrium occurs. When loaded above its critical buckling load, the passive column may buckle. If the actual loading during usage is not fully known, stability becomes highly uncertain. This paper presents an approach to control uncertainty in a slender flat column structure critical to buckling by actively stabilising the structure. The active stabilisation is based on controlling the first buckling mode by controlled counteracting lateral forces. This results in a bearable axial compressive load which can be theoretically almost three times higher than the actual critical buckling load of the considered system. Finally, the sensitivity of the presented system will be discussed for the design of an appropriate controller for stabilising the active column. [ABSTRACT FROM AUTHOR]

Nondestructive methods, to calculate the buckling load of imperfection sensitive thin-walled structures, such as large-scale aerospace structures, are one of the most important techniques for the evaluation of new structures and validation of numerical models. 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 verification of a novel approach using vibration correlation technique for the prediction of realistic buckling loads of unstiffened cylindrical shells loaded under axial compression. Four different test structures were manufactured and loaded up to buckling: two composite laminated cylindrical shells and two stainless steel cylinders. 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. Additional experimental tests and numerical models are currently under development to further validate the proposed approach for composite and metallic conical structures. [ABSTRACT FROM AUTHOR]

Most of the phenomena of various fields of applied sciences are nonlinear problems. Recently, various types of analytical approximate solution techniques were introduced and successfully applied to the nonlinear differential equations. One of the aforementioned techniques is the Homotopy analysis method (HAM). In this study, we applied HAM to find critical buckling load of a column under end load dependent on direction. We obtained the critical buckling loads and compared them with the exact analytic solutions in the literature. [ABSTRACT FROM AUTHOR]

An analytical solution for lateral buckling critical load of leaning-type arch bridge was presented in this paper. New tangential and radial buckling models of the transverse brace between the main and stable arch ribs are established. Based on the Ritz method, the analytical solution for lateral buckling critical load of the leaning-type arch bridge with different central angles of main arch ribs and leaning arch ribs under different boundary conditions is derived for the first time. Comparison between the analytical results and the FEM calculated results shows that the analytical solution presented in this paper is sufficiently accurate. The parametric analysis results show that the lateral buckling critical load of the arch bridge with fixed boundary conditions is about 1.14 to 1.16 times as large as that of the arch bridge with hinged boundary condition. The lateral buckling critical load increases by approximately 31.5% to 41.2% when stable arch ribs are added, and the critical load increases as the inclined angle of stable arch rib increases. The differences in the center angles of the main arch rib and the stable arch rib have little effect on the lateral buckling critical load. [ABSTRACT FROM AUTHOR]

I investigate the vibration and buckling analysis of functionally graded material (FGM) structures, using a modified 8-node shell element. The properties of FGM vary continuously through the thickness direction according to the volume fraction of constituents defined by sigmoid function. The modified 8-ANS shell element has been employed to study the effect of power law index on dynamic analysis of FGM plates with various boundary conditions and buckling analysis under combined loads, and interaction curves of FGM plates are carried out. To overcome shear and membrane locking problems, the assumed natural strain method is employed. In order to validate and compare the finite element numerical solutions, the reference results of plates based on Navier’s method, the series solutions of sigmoid FGM (S-FGM) plates are compared. Results of the present study show good agreement with the reference results. The solutions of vibration and buckling analysis are numerically illustrated in a number of tables and figures to show the influence of power law index, side-to-thickness ratio, aspect ratio, types of loads, and boundary conditions in FGM structures. This work is relevant to the simulation of wing surfaces, aircrafts, and box structures under various boundary conditions and loadings. [ABSTRACT FROM AUTHOR]

Incremental explosive analysis (IEA) is addressed as an applicable method for performance-based assessment of stiffened and unstiffened cylindrical shells subjected to underwater explosion (UNDEX) loading. In fact, this method is inspired by the incremental dynamic analysis (IDA) which is a known parametric analysis method in the field of earthquake engineering. This paper aims to introduce the application of IEA approach in UNDEX in order to estimate different limit states and deterministic assessment of cylindrical shells, considering the uncertainty of loading conditions. The local, bay, and general buckling modes are defined as limit states for performance calculation. Different standoff distances and depth parameters combining several loading conditions are considered. The explosive loading intensity is specified and scaled in several levels to force the structure through the entire range of its behavior. The results are plotted in terms of a damage measure (DM) versus selected intensity measure (IM). The statistical treatment of the obtained multi-IEA curves is performed to summarize the results in a predictive mode. Finally, the fragility curves as damage probability indicators of shells in UNDEX loading are extracted. Results show that the IEA is a promising method for performance-based assessment of cylindrical shells subjected to UNDEX loading. [ABSTRACT FROM AUTHOR]

We describe a novel technique for restoration of reinforced concrete (RC) structures that have sustained damage during an earthquake. The reinforcement scheme described here is a hybrid seismic retrofitting technique that combines noncompression X-bracing using CF with externally bonded GF sheets to strengthen RC structures that have sustained damage following an earthquake. The GF sheet is used to improve the ductility of columns, and the noncompression CF X-bracing system, which consists of CF bracing and anchors to replace the conventional steel bracing and bolt connections, is used to increase the lateral strength of the framing system. We report seismic restoration capacity, which enables reuse of the damaged RC frames via the hybrid CF X-bracing and GF sheet wrapping system. Cyclic loading tests were carried out to investigate hysteresis of the lateral load-drift relations, as well as the ductility. The GF sheet significantly improved the ductility of columns, resulting in a change in failure mode. The strengthening effect of conventional CF sheets used in columns is not sufficient with respect to lateral strength and stiffness. However, this study results in a significant increase in the strength of the structure due to the use of CF X-bracing and inhibited buckling failure of the bracing. This result can be exploited to develop guidelines for the application of the reinforcement system to restore damaged RC structures. [ABSTRACT FROM AUTHOR]

Analytical solution of the problem of buckling of truncated hemispherical shell of revolution, subjected to tension loading, is obtained. Assumption of membrane prebuckling state is applied, and the range of applicability of this assumption is estimated. The developed algorithm is based on the asymptotic simplification procedure of bifurcation equations. The formula for the bifurcation tension load is derived and compared with the earlier published empirical and numerical results. It is shown that it is sufficiently accurate and can be used in engineering practice. [ABSTRACT FROM AUTHOR]

Partially concrete encased steel (PE) beams are composite steel beams and concrete elements that present several advantages, such as higher fire resistant, higher flexural capacity, and higher lateral torsional buckling resistant compared to bare steel beams. This paper reports an experimental study of eight PE beams under cyclic loading. The effectiveness of intermediate stiffeners, such as midspan stiffener and plastic hinge zone stiffener, in enhancing composite action and ductility of the PE beams was studied. The ductility performance of PE beams using strengthened beam-to-column connection and weakened beam-to-column connection was also investigated. The test results show that the plastic hinge zone stiffener performed well and has the potential to replace shear connectors. Strengthened and weakened beam-to-column connections can be implemented in PE beams to enhance the ductility of the PE beams; with the details of both strengthened and weakened beam-to-column connections determined by bare steel shape instead of the whole section. In addition, the suggestions to prevent premature failure of weakened beam-to-column connection were provide. [ABSTRACT FROM AUTHOR]

Applied to a hydrogen absorption-desorption cycle, the hydrogen storage bed will experience higher exchange temperatures and variety of mechanical load. Due to the complex structure of the double-layered annulus metal hydride bed and the importance of thermal stress on the failure of a metal hydride bed, the numerical modeling of its hot spot stress was carefully carried out. Moreover, in this paper, an analysis method considering the limit failure mode condition is proposed to deal with the stress analysis in the process of hydrogen absorption and desorption. According to the proposed analysis method, the maximum stress of thermal-structural coupling in the process of hydrogen absorption occurs at about 1/3 along the diameter direction and at the geometric mutation of the connection between the cooling pipe and the main body of the hydrogen storage bed in the process of hydrogen desorption. Apart from that, the hydrogen storage bed is also subjected to thermal-mechanical fatigue by the iterative process of absorption and desorption, and its operating temperature range is in the thermal creep temperature region. Based on the distribution of the stress and temperature, evaluation hot sites were selected and the ASME-NB and ASME-NH codes were used to evaluate fatigue and fatigue creep, respectively. The evaluation showed that the fatigue damage generated during its service life is small, while the creep damage is relatively large and the total damage generated during the service life of the hydrogen storage bed is within the safe range. Aiming at the structure and complex process of a double-layer hydrogen storage bed, creep and fatigue evaluation methods are proposed, various failure modes of hydrogen storage bed are highlighted, and the relationship between process parameters and life is established. [ABSTRACT FROM AUTHOR]

An experimental investigation on deformation shape of a cylindrical shell with internal medium subjected to lateral contact explosion was carried out briefly. Deformation shapes at different covered width of lateral explosive were recovered experimentally. Based on the experimental results, a corresponding analytical approach has been undertaken with rigid plastic hinge theory. In the analytical model, the cylindrical shell is divided into end-to-end rigid square bars. Deformation process of the cylindrical shell is described by using the translations and rotations of all rigid square bars. Expressions of the spring force, buckling moment, and deflection angle between adjacent rigid square bars are conducted theoretically. Given the structure parameters of the cylinder and the type of the lateral explosive charge, deformation processes and shapes are reported and discussed using the analytical approach. A good agreement has been obtained between calculated and experimental results, and thus the analytical approach can be considered as a valuable tool in understanding the deformation mechanism and predicting the deformation shapes of the cylindrical shell with internal medium subjected to lateral contact explosion. Finally, parametric studies are carried out to analyze the effects of deformation shape, including the covered width of the lateral explosive, explosive charge material, and distribution of initial velocity. [ABSTRACT FROM AUTHOR]

This paper presents the behavior of square concrete-filled tubular (CFT) columns with different penetrating gusset plates under axial load. Load transfer mechanism in the CFT columns including load distribution between gusset plate and core concrete and composite action of the gusset plate and steel tube was investigated. Experimental results showed that the axial load can be transferred from the bottom edge, ribs, and the hole of the gusset plate to core concrete through the bearing mechanism. Adding ribs or a hole on the gusset plate can efficiently facilitate load transmission and improve the composite action. Numerical models were established to determine the distribution of axial forces among members in the square CFT column. Then, revised coefficients of elastic modulus for the square CFT column with the gusset plate were proposed. [ABSTRACT FROM AUTHOR]

Four test pieces with different steel plate center-to-center distances and reinforcement ratios are subjected to low-cycle repeat quasistatic loading to optimize properties as failure mode, hysteretic curve, skeleton curve, energy dissipation parameters, strength parameters, and seismic performance of high-strength concrete low-rise shear walls. The embedded steel plates are shown to effectively restrict wall crack propagation, enhance the overall steel ratio, and improve the failure mode of the wall while reducing the degree of brittle failure. Under the same conditions, increasing the spacing between the steel plates in the steel plate concrete shear wall can effectively preserve the horizontal bearing capacity of the shear wall under an ultimate load. The embedded steel plates perform better than concealed bracing in delaying stiffness degeneration in the low-rise shear walls, thus safeguarding their long-term bearing capacity. The results presented here may provide a workable basis for shear wall design optimization. [ABSTRACT FROM AUTHOR]

Ship-to-shore (STS) container gantry cranes, used at terminals for loading and unloading containers from a ship, are an important part of harbor structures. The size and weight of modern STS container cranes are increasing to satisfy the demand for bigger ships. This is expected to result in more lateral load when excited by seismic motions. The existing Korean STS container cranes did not behave properly during several recent moderate earthquakes in South Korea. Typical Korean STS container cranes must be checked for the earthquake-resistant capacity. In this research, two nonlinear static analyses procedures, also known as pushover analyses, commonly used for seismic design of buildings, namely, capacity spectrum method and equivalent linearization method, are comprehensively studied to check their suitability for studying seismic behavior of STS cranes. Results obtained by these two nonlinear static analysis methods are then compared with the results obtained by nonlinear time-history analyses of the STS cranes by exciting them with nine recorded earthquake time histories around worldwide. The behaviors of the cranes are analyzed in terms of the total base shear, drift, and base uplift. The comparisons indicate that the nonlinear static methods can be appropriate for estimating the total base shear and drift of the portal frame of a container crane. The pushover analyses also provide information on performance levels as defined in ASCE/SEI 41-13, of a typical Korean STS container crane. Furthermore, it is observed that the uplift response of the crane is strongly influenced by the duration of an earthquake. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of a cylinder with material attributes that vary arbitrarily in the radial direction under non-uniformly distributed normal and tangential pressures. A stress and displacement solution method for plane strain on a radial heterogeneous cylinder with inner and outer surfaces subjected to uneven normal and tangential pressures under two types of contact conditions (i.e., complete contact and smooth contact) is proposed based on the theory of elastic mechanics. In addition, a group of linear equations is derived, through which the analytical solution of a radial heterogeneous cylinder under a non-uniform load can be obtained. The validity of the analytical solution is verified by comparing it with the results of a numerical simulation. This research shows that the solution is more convenient and universal than traditional methods and can provide a theoretical basis for the stress state analysis, stability evaluation, and structure design of heterogeneous cylindrical structures, all of which have great significance in practical engineering. [ABSTRACT FROM AUTHOR]

Dynamic characteristics of a flexible hub-beam system with a tip mass under gravity loads are investigated. The slope angle of the centroid line of the beam is utilized to describe its motion. Hamilton’s principle is used to derive the equations of motion and their boundary conditions. By using Lagrange’s equations, spatially discretized equations based on assumed mode method are derived, and the equations of motion are expressed in nondimensional matrix form. The incremental harmonic balance (IHB) method is used to solve for periodic responses of a high-dimensional model of the rotating hub-beam system with a tip mass for which convergence is reached. A frequency equation is derived giving the relationship between the nondimensional natural frequencies and three nondimensional parameters, that is, the rotating angular velocity, the tip mass, and the hub radius ratio. A comparative study is performed for nonlinear frequency responses of the system with a tip mass under different values of tip masses and damping ratios. [ABSTRACT FROM AUTHOR]

A full-scale test model with a distinct loading system is developed to analyze the dynamic change process of ballast beds under cyclic longitudinal reciprocated loading. The test analysis methodology accounts for the service performance, longitudinal resistances, and evolution trend of ballast beds under long-term loading. The analysis shows that the ballast resistance-displacement curves under cyclic loading are a set of closed hysteretic curves, indicating obvious energy consumption. In particular, a granular ballast bed is subject to cyclic softening during the cyclic process and the ballast longitudinal resistances degenerate obviously. More particularly, the cyclic softening of a granular ballast bed is dependent on the dynamic disturbance amplitude—the higher the dynamic disturbance amplitude, the more severe the cyclic softening will become. Moreover, this methodology contributes to forming a foundation for an in-depth understanding of the dynamic service performance of ballast CWR tracks and of the stress deformation mechanism of continuously welded rail tracks. [ABSTRACT FROM AUTHOR]

In order to investigate the aerostatic instability mode and underlying failure mechanism of the new suspension bridge with double main spans, a corresponding program based on aerostatic load increment and two-iteration scheme was developed with considering the effects of aerostatic and geometric nonlinearity. Three double-main-span suspension bridges were taken as a case study to analyze the full range of aerostatic instability with different initial attack angles. Results show that there are two aerostatic instability modes for the double-main-span suspension bridge, one of which is the bilateral antisymmetric instability mode and the other is the single-span instability mode. The critical aerostatic velocity corresponds to the instability mode that occurs first, which is dependent on structural dynamic properties and initial attack angles. In addition, mechanism of the two aerostatic instability modes was discussed in detail. [ABSTRACT FROM AUTHOR]

During countersunk hole machining, defects like geometrical deviation of the chamfer angle and delamination are easily introduced into the structure. To investigate the influences of geometrical deviation on delamination propagation around the countersunk hole during assembly, a progressive damage model (PDM) combining cohesive element was proposed and validated. Numerical analyses were then carried out to study delamination propagation behavior under the influences of geometrical parameters including delamination factor, chamfer angle, and location of delamination. The results show that when delamination appears at the transition area of the countersunk hole, the load causing the delamination evolution is much smaller than other cases. [ABSTRACT FROM AUTHOR]

This article presents an analytical study for forced vibration of a cylindrical shell which is composed of a functionally graded piezoelectric material (FGPM). The cylindrical shell is assumed to have two-constituent material distributions through the thickness of the structure, and material properties of the cylindrical shell are assumed to vary according to a power-law distribution in terms of the volume fractions for constituent materials, the exact solution for the forced vibration problem is presented. Numerical results are presented to show the effect of electric excitation, thermal load, mechanical load and volume exponent on the static and force vibration of the FGPM cylindrical shell. The goal of this investigation is to optimize the FGPM cylindrical shell in engineering, also the present solution can be used in the forced vibration analysis of cylindrical smart elements. [ABSTRACT FROM AUTHOR]

The thermo-mechanical nonlinear vibrations and stability of a hinged-hinged axially moving beam, additionally supported by a nonlinear spring-mass support are examined via two numerical techniques. The system is subjected to a transverse harmonic excitation force as well as a thermal loading. Hamilton's principle is employed to derive the equations of motion; it is discretized into a multi-degree-freedom system by means of the Galerkin method. The steady state resonant response of the system for both cases with and without an internal resonance between the first two modes is examined via the pseudo-arclength continuation technique. In the second method, direct time integration is employed to construct bifurcation diagrams of Poincaré maps of the system. [ABSTRACT FROM AUTHOR]

This paper presents a new semi-analytical solution for the Timoshenko beam subjected to a moving load in case of a nonlinear medium underneath. The finite series of distributed moving loads harmonically varying in time is considered as a representation of a moving train. The solution for vibrations is obtained by using the Adomian's decomposition combined with the Fourier transform and a wavelet-based procedure for its computation. The adapted approximating method uses wavelet filters of Coiflet type that appeared a very effective tool for vibration analysis in a few earlier papers. The developed approach provides solutions for both transverse displacement and angular rotation of the beam, which allows parametric analysis of the investigated dynamic system to be conducted in an efficient manner. The aim of this article is to present an effective method of approximation for the analysis of complex dynamic nonlinear models related to the moving load problems. [ABSTRACT FROM AUTHOR]

An experimental and numerical analysis of the response of laminated composite plates under high-velocity impact loads of soft body gelatine projectiles (artificial birds) is presented. The plates are exposed to tensile and compressive preloads before impact in order to cover realistic loading conditions of representative aeronautic structures under foreign object impact. The modelling methodology for the composite material, delamination interfaces, impact projectile, and preload using the commercial finite element code Abaqus are presented in detail. Finally, the influence of prestress and of different delamination modelling approaches on the impact response is discussed and a comparison to experimental test data is given. Tensile and compressive preloading was found to have an influence on the damage pattern. Although this general behaviour could be predicted well by the simulations, further numerical challenges for improved bird strike simulation accuracy are highlighted. [ABSTRACT FROM AUTHOR]