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To further improve the load-bearing capability and anti-impact properties of the auxetic structure, a novel enhanced auxetic honeycomb core (NEH) was introduced, and the bending resistance and crashworthiness of this sandwich beam (NEH-SWB) were analyzed through numerical simulation. First, bending tests on sandwich beams under different loading situations revealed that NEH-SWB was more susceptible to impact damage in three-point bending situations than those under four-point bending, and the influence of structural parameters were more pronounced. In addition, the impact of load position and structural parameters on the bending response and deformation pattern of NEH-SWB were investigated. NEH-SWB exhibited superior bending resistance when the punch was located in the S position. Furthermore, increasing the panel thickness and altering the panel thickness configuration both contributed to improving the flexural resistance of NEH-SWBs. At a certain mass, the configuration with T f / T b > 1 exhibited better bending resistance. Meanwhile, increasing both the cell angle (θ) and wall thickness-to-length ratio (t/l) enhanced load-carrying capability and energy absorption of NEH-SWB. Subsequently, further analysis showed that NEH had better bending performance compared to cell structures with reentrant (RH), star-shaped (SSH), and reentrant-star (RSH) honeycombs. Finally, the complex proportion assessment method was employed to examine the significance of structural parameters regarding the flexural behavior of the NEH-SWB. It was concluded that increasing the t/l value could be the best solution to enhance the bending performance of the NEH-SWB. [ABSTRACT FROM AUTHOR]

Bows and stems are often subjected to wave slamming loads. Stiffened plates with curvatures in both longitudinal and transversal directions are the basic members of these structures. As a result, it is important to investigate the lateral ultimate strength of the doubly curved stiffened plates. In this study, the non-linear finite element method (NFEM) is selected to investigate the collapse modes and lateral ultimate strengths of the doubly curved stiffened plates. Additionally, the influences of curvature and geometrical properties on the collapse modes and ultimate strengths of doubly curved stiffened plates are investigated. In the NFEM analysis, a series of numerical simulations, covering different aspect ratios, curvatures, and structural scantlings are performed. Different collapse modes of doubly curved stiffened plates under lateral loading cases are observed. The relationships between the collapse modes and the geometrical properties are then discussed based on the numerical results. Moreover, the results also show that larger curvatures along the stiffeners and stronger stiffeners contribute more to the lateral ultimate strengths. Subsequently, an empirical formula is derived and verified for predicting the lateral ultimate strength of the doubly curved stiffened plates. The results of the empirical formula match well with numerical calculations. [ABSTRACT FROM AUTHOR]

Bows and stems are often subjected to wave slamming loads. Stiffened plates with curvatures in both longitudinal and transversal directions are the basic members of these structures. As a result, it is important to investigate the lateral ultimate strength of the doubly curved stiffened plates. In this study, the non-linear finite element method (NFEM) is selected to investigate the collapse modes and lateral ultimate strengths of the doubly curved stiffened plates. Additionally, the influences of curvature and geometrical properties on the collapse modes and ultimate strengths of doubly curved stiffened plates are investigated. In the NFEM analysis, a series of numerical simulations, covering different aspect ratios, curvatures, and structural scantlings are performed. Different collapse modes of doubly curved stiffened plates under lateral loading cases are observed. The relationships between the collapse modes and the geometrical properties are then discussed based on the numerical results. Moreover, the results also show that larger curvatures along the stiffeners and stronger stiffeners contribute more to the lateral ultimate strengths. Subsequently, an empirical formula is derived and verified for predicting the lateral ultimate strength of the doubly curved stiffened plates. The results of the empirical formula match well with numerical calculations.

Shakedown analysis is a powerful and efficient tool for calculating the safety factors of structures under variable and repeated external quasi-static loads, that can prevent structures from incremental and alternative plasticity collapses. RC slabs in practical engineering applications are usually under long-tern variable and cyclic loads, but their fatigue behavior was rarely reported in the literature, particularly for those governed by the Nielsen yield condition. In this paper, dual static and kinematic shakedown formulations based on displacement-finite elements and conic programming are developed. The resulting optimization problems, characterized by a huge number of variables, are effectively solved. A wide range of practical RC slabs with diverse geometries, loading and boundary conditions are investigated, precisely capturing the collapse modes in terms localized plastic dissipation energy and presenting moment distribution at fatigue state. Strengthening strategies are performed in regions with localized plastic dissipation energy, showing that the load-bearing capacity of such slabs increases significantly while incremental and alternative collapse modes are prevented. • Dual shakedown analysis of reinforced concrete slabs is presented for the first time. • Finite element formulations for pseudo-static and kinematic shakedown analysis with conic programming are described. • Shakedown load factors and collapse modes of various practical RC slabs are reported. • Strengthening strategies are performed and optimal reinforcement layouts are obtained. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to present the formulation and applications of the optimization problem of steel-concrete composite alveolar beams. In addition to presenting the formulation, a comparative analysis of the predominant collapse modes is performed numerically via the finite element method. The optimization program was developed with the GUI platform available in Matlab 2016. Since this is a discrete problem, a Genetic Algorithm (GA) was used to solve the optimization model, implemented with the Matlab optimization toolbox. Numerical examples using finite elements model are presented to validate the solution and analyze its effectiveness, along with an assesment of the predominant collapse modes for a group of 12 beams. The results show that more efficient designs are obtained when optimization tools are applied.

Recent studies on innovative solutions in structural engineering fields highlight the effectiveness of closed-cell aluminum foams as traditional material/architecture core replacement in sandwich structures. This study aims to investigate the mechanical behavior and the collapse modes of innovative sandwich panels with aluminum foam as the core and stainless steel wire mesh-grid as the skins; the manufacturing process was based on the powder compact melting technique. The results of quasi-static three-point bending tests point out the beneficial effects, in terms of mechanical performance, of the reinforcement skin on the sandwiches, compared to the plain foams; this joins by their effectiveness in withstanding thermal and mechanical loads. Moreover, the investigation of the collapse mechanisms of the sandwiches with different thicknesses allows for testing the goodness-of-fit of the experimentally observed collapses with the ones predicted by the failure map from analytical models available in the literature. [ABSTRACT FROM AUTHOR]

This paper presents a study of the stability and collapse modes of a system made up of a masonry arch resting on two piers subject to its own weight. It examines both semicircular arches and three different types of pointed arches commonly found in architecture, namely low-pointed, equilateral, and lancet-pointed arches. The collapse modes characterizing each type of arch-piers systems are then compared by extending the results obtained by the authors in previous work on stand-alone masonry arches of different shapes. The mechanical behavior of these systems is examined via Durand-Claye's method in order to follow the evolution of the stability area and determine the collapse modes of these masonry structures. The method takes into account both the bounded bending capacity of the arch cross section and the limited friction along the joints. Furthermore, the system's safe domain is determined in terms of the limit conditions for arch thickness, pier height and friction coefficient. As expected, arch-piers systems of different shapes exhibit different behaviors at collapse in terms of minimum thickness and collapse modes. [ABSTRACT FROM AUTHOR]

This paper discusses the seismic behavior of reinforced concrete (RC) bridge structures, focusing on the shear–flexure interaction phenomena. The assessment of reinforced concrete bridges under seismic action needs the ability to model the effective non-linear response in order to identify the relevant failure modes of the structure. Existing RC bridges have been conceived according to old engineering practices and codes, lacking the implementation of capacity design principles, and therefore can exhibit premature shear failures with a reduction of available strength and ductility. In particular, recent studies have shown that the shear strength can decrease with the increase of flexural damage after the development of plastic hinges and, in some cases, this can cause unexpected shear failures in the plastic branch with a consequent reduction of ductility. The aim of the research is to implement those phenomena in a finite-element analysis. The proposed model consists of a flexure fiber element coupled with a shear and a rotational slip spring. The model has been implemented in the OpenSEES framework and calibrated against experimental data, showing a good ability to capture the overall response. [ABSTRACT FROM AUTHOR]

In actual marine structures, most stiffened plates are subjected to the combination of in-plane and out-of-plane loads. The influence of lateral loads on stiffened plates' ultimate strengths and collapse modes under combined load cases needs to be further investigated. For this purpose, the authors designed a combined load testing device to apply variable combined loads to stiffened plates, and conducted experiments of three different load cases. In addition, Nonlinear Finite Element Analysis (NFEA) have been performed based on measured initial deflections, which shows the ultimate axial loads and collapse modes match well with experimental results. Numerical models with ISSC recommended initial deflections are also established to investigate the interaction between axial and lateral loads. Results shows that lateral loads cause earlier yielding of the stiffeners. As a result, the out-of-plane constraint to the stiffened plate is weakened, and the global displacement grows significantly as axial load increases. The results of this research can be helpful for understanding lateral loads' influence on the ultimate strengths and collapse modes of stiffened plates under combined load cases, and can provide references for structural designs. • Combined loading experiments have been performed to research the influence of lateral loads on collapse modes of stiffened plates. • A combined loading device which can apply variable lateral loads is designed, and compressed air is used to make lateral loads uniformly distributed and steady. • The results show that global buckling occurs in combined load cases, which results from the yielding of the stiffeners at the endings. • Initial deformation is considered in NFEAs, and the ultimate axial loads and collapse modes match well with the experiments for each load case. • The interaction of lateral loads and axial loads is investigated, and the equation of the ultimate state interaction has been proposed, and the critical lateral loads causing global collapse mode have been derived. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of characterizing the mechanical behaviour and collapse of symmetric circular and pointed masonry arches subject to their own weight. The influence on the arch's collapse features of its shape and thickness, as well as the friction between the arch's voussoirs, is analysed. The safety level of arches is then investigated by suitably reworking in semi-analytical form the graphical method of the stability area proposed by the renowned nineteenth century French scholar, Durand-Claye. According to Durand-Claye's method, the arch is safe if along any given joint both the bending moment and shear force do not exceed the values determined by some given limit condition. The equilibrium conditions corresponding to all possible symmetric collapse modes are individuated. As was expected, pointed and circular arches exhibit different collapse behaviours, in terms of both collapse modes and safe domain. The limit values of arch thickness and friction coefficient are determined and the results obtained consistently compared with those published by Michon in 1857. [ABSTRACT FROM AUTHOR]

Thin-walled single and multi-cell structures are an ongoing topic of interest in the field of crashworthiness, due to their wide range of applications in automotive and aerospace industry as lightweight energy-absorbing structures in crash environments. This work presents a new five-cell cross-section that merges high performance multi-cell and twelve-edge cross-sections from previous research, and compares its performance to four- and nine-cell square cross-sections. Super Folding Element (SFE) theory and Finite Element Analysis (FEA) in LS-DYNA are used to analyze cross-sections and found to have good agreement. The LS-DYNA environment is validated with physical testing. The geometry of the cross-sections is varied in order to find maximal values of the performance parameters specific energy absorption ( SEA ) and crush force efficiency ( CFE ) under stable progressive buckling mode and constraints for manufacturability. The nine- and five-cell cross-sections ultimately out-perform the four-cell cross-section, with the nine-cell having the highest SEA and CFE , though the five-cell design has a significantly lower (47%) mean crush force ( P m ) for only an 11% and 14% loss in SEA and CFE respectively. As a final refinement, the geometry was varied across these two high-performing cross-sections to create equivalent mean crush forces to the four-cell cross-section, which showed the five-cell cross-section to have an improved SEA and better mass efficiency over the nine-cell under a mean crush force constraint. [ABSTRACT FROM AUTHOR]

A comprehensive experimental apparatus for the progressive collapse testing of steel frames has been developed. The apparatus is suited for the testing of planar steel frames to study the load transfer process and the progressive collapse resistance of steel structures under a column removal scenario. In order to simulate a sudden removal of a middle column at the ground storey of the frames, a removable column unit has been designed to allow for an instantaneous knock-out by a pendulum hammer during the test. To avoid the out-of-plane instability of the planar steel frames, an out-of-plane restraining system has been designed and integrated into the test apparatus. Weights simulating the desired gravity loads were attached to the test frame through holding baskets, which were designed to minimize unwanted shaking and ensure that the suspended baskets moved together with the deformed steel frames during the tests. Experimental results showed that the column removal mechanism in the test apparatus was effective. Using this apparatus, the dynamic behaviour of three planer steel frames under a column removal scenario was investigated. Based on the measured deformations and strains, the dynamic response, collapse modes, load transfer path of the steel frames after the removal of the middle bottom column are studied. [ABSTRACT FROM AUTHOR]

A finite element (FE) modelling study on the progressive collapse of steel frames under a sudden column removal scenario is presented. The FE models were developed with refined shell elements using the general purpose FE software package ABAQUS. The FE models were first validated by comparing the predicted responses with the measured results from an experimental study on the progressive collapse of three steel frame specimens. A new bearing capacity-based index was introduced to quantify the robustness of the steel frames. The robustness index takes into account the dynamic effects and the plastic internal force redistribution. By incorporating the experimental results and the numerical simulations, the dynamic amplification factor in the progressive collapse of the steel frames was assessed. The validated FE models were further applied to identify the collapse modes of planar steel frames and evaluate the influences of a range of mechanical and geometrical parameters on the progressive collapse and the robustness. The results showed that, for a column-instability induced progressive collapse mode, the influences of the damping is larger than the influences of the strain rate of material on the robustness. However, for the connection-failure induced progressive collapse mode, the influences of the strain rate is larger than the damping. The type of the steel frame (e.g. weak-beam strong-column or vice versa) and the location of the column removal were both found to play an important role in influencing the critical load and the robustness of steel frames. [ABSTRACT FROM AUTHOR]

This paper discusses the seismic behavior of reinforced concrete (RC) bridge structures, focusing on the shear−flexure interaction phenomena. The assessment of reinforced concrete bridges under seismic action needs the ability to model the effective non-linear response in order to identify the relevant failure modes of the structure. Existing RC bridges have been conceived according to old engineering practices and codes, lacking the implementation of capacity design principles, and therefore can exhibit premature shear failures with a reduction of available strength and ductility. In particular, recent studies have shown that the shear strength can decrease with the increase of flexural damage after the development of plastic hinges and, in some cases, this can cause unexpected shear failures in the plastic branch with a consequent reduction of ductility. The aim of the research is to implement those phenomena in a finite-element analysis. The proposed model consists of a flexure fiber element coupled with a shear and a rotational slip spring. The model has been implemented in the OpenSEES framework and calibrated against experimental data, showing a good ability to capture the overall response.

Thin-walled structures have been widely used in energy absorption and safety applications such as automotive, due to their lightweight and progressive folding modes. This work studies the collapse behavior and energy absorption of corrugated tapered tubes (CTT) under axial crushing numerically. The tested tubular structures were impacted axially with a striker’s mass that is restricted to translational motion along the structures’ axes. The effect of CTT’s geometric features on different performance indicators, namely the initial peak force (PF), mean crushing force (MF), energy absorption (EA) and specific energy absorption (SEA) was studied. The results showed that the amplitude of corrugation is the most influential factor on the force-displacement characteristics of CTTs. Moreover, three deformation modes were found for CTTs, and the development of a mode was mainly influenced by the corrugation’s amplitude and wavelength. In addition, for the tested range of geometric features, the initial peak force was found to be reduced when corrugation is adopted, especially for longer corrugation’s amplitudes and wavelengths. On the other hand, the energy absorption (EA) and specific energy absorption (SEA) were found to be reduced when corrugation is adopted. Finally, it was found that the two most influential geometric factors on the performance indicators of CTT were the corrugation’s amplitude and wall thickness. [ABSTRACT FROM AUTHOR]

Dominant Collapse Mechanisms (DCMs) have been reported to play an important role in collapse capacity of structural systems and the seismic losses consequent to it. Therefore, DCMs of Reinforced Concrete (RC) frames have been studied, in this article, considering Record-To-Record (RTR) and modeling uncertainties. Two sets of RC frames have been designed, in this regard, that share the design assumptions but contain different levels of over-strength. Each set contains 26, 4- to 20-story nonlinearly modeled frames. Initially, Incremental Dynamic Analysis (IDA) was used to identify frames' DCMs. Then, the RTR variability reflected through IDA was combined with spectral shape and pulse effects of the ground motion records. Modeling uncertainties were finally introduced to the study using a response surface based Monte Carlo method. The study results revealed that the degree to which DCMs were affected by the associated uncertainties was a function of the over-strength provided to the frames. This effect is found to be generally important and particularly remarkable for especially detailed ductile structures. [ABSTRACT FROM AUTHOR]

This paper investigates the axial crushing response of concentric expanded metal tubes under impact loading. The study is conducted by means of nonlinear finite element simulations, considering the speed of deformation and the size of the expanded metal cells. In the analysis, two tubes are placed concentrically and then axially crushed with an impact mass at various speed levels. Crushing loaddisplacement responses are analyzed to investigate the influence of the size of the mesh and the impact speed. The results show that specimens with the same mesh sizes increases their crushing length with increasing speed. Finally the main outcome of this investigation is to add to the state of knowledge information concerning the use of expanded metal meshes in impact attenuation devices. [ABSTRACT FROM AUTHOR]

The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches.Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity.The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography.

This paper presents an experimental investigation on the axial crushing of coiled expanded metal tubes subjected to quasi-static compressive loading. The investigation aims at comparing the energy absorption characteristics between tubes fabricated with coiled expanded metal meshes and solid plates. Then, a series of quasistatic axial crushing tests were performed to obtain the structural performance on coiled tubes, and then compare these with round and square solid tubes. Coiled tubes were fabricated using circular and square geometries, as well as various cell orientations. The results showed that cell orientation enhance the energy absorption response of the coiled tubes. Regarding these responses in comparison to those of solid tubes, the results showed that for coiled and solid tubes with the same weight, the energy absorption capacity of the former is much lesser than the latter. [ABSTRACT FROM AUTHOR]

In multi-story buildings, one of the worst collapse types in terms of structural damage and loss of life is the pancake-type collapse, where some or all floors end up lying on top of each other like the layers of a pancake, with the floor contents crushed between them. Mostly observed after strong earthquakes, such collapses are triggered by loss of some or all vertical load bearing elements in some story−often the ground story. Once this occurs, the building part above the lost vertical elements−still intact−starts gaining downward velocity until it meets resistance from below. The ensuing impact forces often lead to collapse progression ending in total collapse. However, there are some examples of buildings in which the columns of an entire story failed and the collapse remained arrested after the subsequent impact. Such cases were observed in the 1995 Kobe earthquake and in the 1985 Mexico City earthquake. There have also been some failed controlled demolition attempts in which the intended total vertical collapse did not occur after letting a building collide with the ground by explosive removal of the vertical load bearing elements in the lowest stories. In an attempt to determine the factors which play the main role in arresting vertical collapse once initiated at the ground level, this paper studies the behavior of vertically falling multi-story building structures impacting a rigid surface representing the ground. A simplified analytical model of the problem is presented. Depending on the structural properties, several possible energy dissipation mechanisms, and−in case the collapse cannot be arrested at impact−collapse modes, are identified. [ABSTRACT FROM AUTHOR]

The crushing behaviors of the buffer devices for the projectile in the high-speed oblique water entry process were investigated numerically. The high-speed water entry tests of the aluminum alloy projectile with a sabot were conducted to study the cavity formation, also used to validate the numerical method. Detailed material parameters of three kinds of foams including expanded polystyrene foam (EPS), closed-cell aluminum foam, and rigid polyurethane foam (PU), and the composite material for the fairings were obtained from a series of statics and dynamics mechanics experiments. Twelve collapse modes of the thin-walled fairings were identified during the oblique water impact. The effects of the length of the fairing, foam type, and water entry angle on these failure modes, and the peak impact acceleration of the projectiles were revealed. The results showed that the load reduction efficiency (LRE) is dependent on both entry angle θ and dimensionless length L F A / D P J . The critical load reduction water entry angle (CLRA) is linearly related to L F A / D P J . Among the three kinds of foam materials, the closed-cell aluminum foam has the best load reduction performance (up to 72.82%) and the widest range of load reduction water entry angles. Meanwhile, the EPS foam makes the projectile withstand the largest impact overload (up to 11.43%). • The collapse modes of the composite fairings are identified and classified during the oblique water entry. • The aluminum foam has the best load reduction performance (up to 72.82%) among the three kinds of foam materials. • The EPS foam-filled buffer device can increase the impact load of the projectile by up to 11.43%. • The critical load reduction water entry angle is linearly related to dimension length L F A / D P J . • The aluminum foam has the widest range of load reduction water entry angles. [ABSTRACT FROM AUTHOR]

Highlights: [•] GBT formulation to perform first-order elastoplastic analyses of thin-walled members. [•] Applicable to members exhibiting arbitrary local/distortional/global deformation patterns. [•] Numerical results concerning the three steel beams presented and discussed in detail. [•] Mechanical insight and numerical efficiency provided by the GBT modal nature illustrated. [•] Accuracy of the GBT-based results assessed through comparisons with SFEA values. [ABSTRACT FROM AUTHOR]

Abstract: Sandwich structures have been widely employed to build lightweight components having good mechanical properties and energy absorbing capacity, especially in the transport industry. The aim of this paper was the analysis of static and low-velocity impact response of two typologies of aluminium honeycomb sandwich structures with different cell size. The static bending tests produced various collapse modes for panels with the same nominal size, depending on the support span distance and on the honeycomb cell size. Simplified collapse models were applied to explain the experimental observations and a good agreement between predicted and experimental limit loads was achieved. Low-velocity impact tests were, also, performed on the two typologies of aluminium honeycomb sandwiches and a theoretical approach, based on the energy balance model, has been applied to investigate their impact behaviour. The failure mode and damage of the honeycomb panels have been investigated using the 3D Computed Tomography. [Copyright &y& Elsevier]

The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity. The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography. [ABSTRACT FROM AUTHOR]

Abstract: Nonlinear finite element analysis is used to investigate the quasi-static axial collapse response of cylindrical tubes which are externally stiffened by multiple identical rings. The rings divide the long tube into a series of short thin-walled tubes. It is assumed that the size and shape of integral stiffeners are controlled through a machining process. The effects of various geometric parameters such as wall thickness, ring spacing, ring thickness and width on the collapse response, crush force and energy absorption of monolithic, integrally stiffened steel tubes are studied and used as a general framework for a design optimization study. Through design and analysis of computer experiments, global metamodels are developed for the mean crush force and energy absorption, using the radial basis function approximation technique. Using both single- and multi-objective design optimization formulations, optimum designs for different response characteristics are found. The crush mode in the form of progressive collapse or buckling is found to heavily depend on the ratio of stiffener spacing to stiffener height as well as the ratio of wall thickness to stiffener thickness. The optimization results show the viability of externally stiffened tubes as efficient energy absorbers. [Copyright &y& Elsevier]

Abstract: In this paper, experimental investigation of two new structural design solutions with the aim of improving crashworthiness characteristics of cylindrical metal tubes is performed. In the first design method, a rigid steel ring is press-fitted on top of circular aluminum tubes. When this arrangement of dissipating energy is subjected to axial compression, the rigid ring is driven into the cylindrical tube and expands its top area; then, plastic folds start shaping along the rest of the tube length as the compression of the structure continues. In the second design method, wide grooves are cut from the outer surface of steel thick-walled circular tubes. In fact, this method converts thick-walled tubes into several thin-walled tubes of shorter length, being assembled together coaxially. When this energy absorbing device is subjected to axial compression, plastic deformation occurs within the space of each wide groove, and thick portions control and stabilize collapsing of the whole structure. In the present study, several specimens of each developed design methods with various geometric parameters are prepared and compressed quasi-statistically. Also, some ordinary tubes of the same size of these specimens are compressed axially to investigate efficiency of the presented structural solutions in energy absorption applications. Experimental results show the significant efficiency of the presented design methods in improving crashworthiness characteristics and collapse modes of circular tubes under axial loading. [Copyright &y& Elsevier]

This paper investigates a new and efficient design method to encourage axisymmetric collapsing mode in tubes with higher length than the critical length to collapse in concertina mode when subjected to axial compression. In this innovative design method, wide circumferential grooves are cut from the outer surface of the tube at some determined areas along tube length. When this structure is subjected to axial compression, folds are shaped within the space of these grooves. In fact, this method divides a long tube without the potential of collapsing in axisymmetric mode into several tubes of shorter length, being assembled together coaxially, with the potential to collapse in axisymmetric mode. In the present study, several numerical simulations using LS-DYNA finite element explicit code are performed to study the energy absorption characteristics of this structure under quasi-static compression and to determine the effect of various geometric parameters on its collapsing modes of deformation. In order to verify these numerical results, some experimental tests are performed. An analytical model to predict mean crush force of the new shock absorber is also developed in the present study. Through experimental, numerical and analytical studies, major parameters in design are identified, and typical modes of deformation that may occur during axial compression of tubes with wide external grooves are characterised. Also, load-displacement history and deformation mechanism of the structure under axial compression are described. It has been shown that with consideration of design parameters, characterised in this paper, cutting wide external grooves along circular metal tube length can significantly improve their energy absorption characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Quasi-static and dynamic axial crushing tests were performed on thin-walled square tubes and spot-welded top-hat sections made of high-strength steel grade DP800. The dynamic tests were conducted at velocities up to 15m/s with an impacting mass of 600kg in order to assess the crush behaviour, the deformation force and the energy absorption. Typical collapse modes developed in the sections and the associated energy absorbing characteristics were examined and compared with previous studies on high-strength steel. A significant difference was observed between the quasi-static and the dynamic crushing tests in terms of the deformation force and impact energy absorption. As this difference is attributed to strain-rate and inertia effects, material tensile tests at elevated strain rates have been carried out. A comparison is made with analytical methods and the response was under-predicted. In addition, numerical simulations of the axial crushing of the thin-walled sections were performed and comparisons with the experimental results were satisfactory. The validated numerical model was used to study the energy absorption capacity of thin-walled sections with variations in the yield strength, sheet thickness, flange width and spot-weld spacing. Structural effectiveness differences have been captured through simulations between spot-welded top-hat sections made of mild steel and high-strength steel. [Copyright &y& Elsevier]

Abstract: The control of the plastic flow mechanism during axial collapse of metallic hollow cylinders is of particular interest in the present work for the absorbed energy. Hence, an experimental methodology is developed during which some different tubular structures are loaded under compressive quasi-static strain rate. These structures of various geometrical parameters η = R m/t and λ = R m/L (R m: mean radius, L: initial length and t: thickness of tube) are made either from copper or aluminum considered as an energy dissipating system. At this point, the effects of both parameters on the mean collapse load and absorbed energy are appropriately studied. The role of η ratio, which has been largely investigated previously, is studied again. Moreover, it is found that the λ ratio has a non-negligible influence on the deformation mode for a given η. It is well known that the absorbed energy is influenced by the deformation mechanism, i.e., for the axisymmetric mode, the related absorbed energy becomes more important than that of the diamond fold mechanism for a given cylinder. Accordingly, to maximize the absorbed energy, two different structural solutions, namely fixed-ends and subdivided structure, are developed for encouraging the axisymmetric mode. It is convenient to consider the classical axial collapse situation (noted as free-ends) as a comparison reference. In this work, it is recognized that the subdivided solution is relatively the best solution. As a result, the absorbed energy increases up to 21% in comparison with the free-ends situation for copper tubes. [Copyright &y& Elsevier]

Appropriate seismic assessment of reinforced concrete bridges is an important challenge in structural engineering in consideration of the number and relevance of bridges built without applying advanced codes of practice and of the strategic role of transportation networks in modern economy. This paper focuses on some relevant aspects of the damage development and collapse modes of hollow piers, as commonly designed in the past. The following aspects have been considered: absence of confinement, inadequate shear strength, shifting of the critical section, insufficient length of lap splices. A series of experimental tests has been designed and performed; the capacity of predicting appropriate results of formulations recommended in codes of practice or proposed in recent research documents has been checked comparing experimental and analytical results. [ABSTRACT FROM AUTHOR]

The similitude criteria of stiffened plates subjected to combined longitudinal compression and lateral pressure are explored based on the collapse modes. The proposed approaches assume the plate, overall, beam-column, web and torsional slenderness would domain the collapse modes. Apart from these ratios, a non-dimensional parameter of lateral pressure is used for designing the magnitude of lateral pressure acting on the scale models for experiments in the laboratory. Meanwhile, the scaling factors of lateral pressure are proposed based on the thin-walled beam theory, which is used to verify the validation of the dimensionless parameter of lateral pressure. The similitude of the full-scale prototype and scale models are verified by the normalized ultimate stress. In view of the numerical results, the similitude criteria could give a reasonable design of scale models under the combined loads. (1) The similitude criteria of stiffened plates subjected to combined longitudinal compression and lateral pressure are presented. (2) Four kinds of typical collapse modes (Overall, Beam-column, Tripping and Web) are selected to verify the similitude criteria. (3) The scaling factors of lateral pressure are proposed based on the thin-walled beam theory, which is used to verify the validation of the dimensionless parameter of lateral pressure. (4) The minimum number of stiffened plate unit are explored in the four typical collapse modes, which could maintain the ultimate strength and save space. [ABSTRACT FROM AUTHOR]

[Display omitted] • The 3D-Printing bio-inspired structures are presented. • Analytical solutions of compression are described based on functional relationship. • Mechanical properties are analyzed in terms of experiment, simulation and analysis. Numerous complex structures with excellent mechanical properties have been created to adapt to impact conditions and these bio-inspired structures play a significant role in applications of protective engineering in the future. In this paper, the three-dimensional finite element models of the normal honeycomb structure, the concave honeycomb structure, the inclined column honeycomb structure and the imitational peanut shell structure are developed. Quasi-static crushing experiments, explicit dynamic simulation analysis and theoretical analysis are carried out to validate their availability, whose results verify the impact stability and specific energy absorption of the models. The results demonstrate ICHS can lead to the higher specific energy absorption. According to the comparison between NHS, CHS, ICHS and IPSS, it is found that the carrying capacity of ICHS increases by 82%, 73.4% and 9.6%, and the stiffness increases by 600.1%, 73.2% and 24.9%, respectively. Moreover, from the perspective of the overall collapse modes, the deformation of ICHS is the most stable. [ABSTRACT FROM AUTHOR]

Aluminium honeycomb sandwich panels are an interesting lightweight structural solution for several applications such as marine structures, aerospace, automotive and aeronautics. In many of these applications, in-service conditions produce fatigue loadings: as a result, safer use of aluminium honeycomb sandwich structures requires a deep knowledge of their fatigue response, which was seldom studied in previous literature. The aim of the current study is to evaluate the fatigue response of aluminium honeycomb sandwich panels subjected to three-point bending loading conditions. The experimental investigation was performed on a commercial aluminium honeycomb sandwich structure with an overall thickness of 11 mm. A preliminary static analysis was performed both under three and four point bending conditions. The static tests allowed the identification of the static bending strength and the absence of a significant strain rate influence. Crashworthiness parameters were evaluated and a slight better performance was found under four point bending. The combination of static tests with Computed Tomography analysis resulted in the observation of the phenomena involved in static bending response of aluminium honeycomb sandwich structures, which are mainly dependent on cell walls buckling. Fatigue tests were conducted under three-point bending conditions. The influence of boundary conditions on fatigue life and on collapse modes were investigated by considering different supports spans. For one condition the S-N curve was obtained and its equation was compared to literature results. Two different collapse mechanisms were observed depending on the supports span: for larger supports span a fracture of the tensioned skin was observed, whereas lower supports span produced core shear. The former mode differed significantly from static failure with the same boundary conditions. In both cases, failure occurred suddenly and this should be taken into consideration in industrial applications. An analytical model was applied to predict fatigue collapse modes and limit loads. A fatigue failure map describing the relationship between supports span, collapse modes and fatigue limit loads was obtained, in order to provide a quantitative tool for aluminium honeycomb sandwich structures design. The fatigue failure map was able to accurately predict the experimental results. • Fatigue bending response of aluminium honeycomb sandwich structures. • Collapse modes variation with boundary conditions under fatigue bending. • Effect of boundary conditions on fatigue response. • Analysis of the failure mechanisms by means of 3D Computed Tomography. • Prediction model for fatigue collapse modes. [ABSTRACT FROM AUTHOR]