Crashworthy Device Research Articles

A crashworthy device for bridge protection under vessel impact and scour

ABSTRACT For Bridges spanning navigable waterways, scour can amplify damage in the event of a vessel impact. This work investigates the effectiveness of a designed steel crashworthy device in reducing damage to a bridge already affected by scour when subjected to a vessel impact. The findings reveal that the crashworthy device can diminish the peak impact force compared to the bridge system without a steel fender under the same scour conditions. Moreover, the crashworthy device effectively dampens the dynamic response of the bridge during a vessel impact under the same scour conditions. However, with increased scour depth, the impact displacement increases even if a steel fender is used, which may still affect the normal service of the bridge system after collision at a deeper scour depth. Consequently, it is recommended to implement maintenance measures aimed at strengthening and enhancing the horizontal load-carrying capacity of the scoured pile foundation in such cases.

Discretized macro-element method to evaluate the crushing behavior and protective performance of crashworthy devices under ship collisions

For complex and bulky bridge crashworthy devices, accurate finite element (FE) simulation and impact testing both have significant limitations in verifying their protective performance. The simplified single macro-element method has demonstrated its efficiency in assessing ship-bridge collisions, and this study aims to extend the application of this method to the rapid assessment crashworthy devices performance. To accomplish this objective, the accurate determination of the crush curve for the crashworthy device is essential. Furthermore, the single macro-element approach encounters difficulties in accurately capturing the local deformation of a crashworthy device. This study introduced a discretized macro-element (DME) method aimed at rapidly evaluating the crushing behavior and protective performance of crashworthy devices during ship collisions by employing a comprehensive approach that combines experimental, numerical, and analytical techniques. The combination of theoretical analysis and FE simulations indicated that, based on the principles of similarity laws, the crush curve of large crashworthy devices can be deduced through experiments on scaled specimens. By utilizing the derived crush curve for both the ship and crashworthy device, the DME method accurately captured the local deformation of the crashworthy device. The accuracy of the DME method in assessing the performance of crashworthy devices was verified through an illustrative example. A parametric study has demonstrated the potential of the DME method for optimizing the structure of crashworthy device, owing to a significant increase in computational efficiency.

Experimental Investigation of the Dynamic Responses of Thin-Walled and Foam-Filled Steel Tubes Subjected to Repeated Impacts.

In this study, a horizontal impact setup was used to measure the dynamic responses of specimens fixed on a reaction wall and subjected to repeated impacts generated by a large-tonnage impactor. The contact force, deformation process, energy absorption, and other properties of two specimens (a thin-walled steel tube and foam-filled steel tube) were thoroughly investigated. The results demonstrated that the thin-walled tube's properties were consistent with the four-phase and six-phase deformation models and that the foam-filled tube's properties were consistent with the two-phase deformation model. In the early stages of the experiment, the foam-filled and thin-walled tubes were similar in terms of the contact force and energy absorption. However, when the polyurethane (PU) strain reached 0.8, the PU significantly increased the support of the tubes, reduced the contact force (by extending the contact time), and increased the energy absorption capacity by 33.6-43.5%. The crush curves of the specimens were in agreement for cases involving multiple impacts, as well as for one impact with the same impact of kinetic energy. The crush curves can be used to assess the actual performance of crashworthy devices. Furthermore, after repeated impacts, the foam-filled tube exhibited a pseudo-shakedown behavior.

Cumulative-impact method for the assessment of dynamic crush curve of crashworthy devices

Crashworthy devices are integral for protecting bridges from vessel collisions, typically evaluated through finite-element methods. However, experimental verification is challenging owing to the impracticality of using large-scale, high-velocity vessels. In this study, a cumulative-impact method is proposed, which is theoretically and experimentally validated. It uses a small-scale impactor in multiple impacts to determine crashworthy device dynamic crush curve based on energy balance theory. The accuracy of the proposed method depends on the number of impacts and the impact velocity. The relative errors are < 5% for the peak impact force and residual deformation, if the number of impacts is < 5 and the impact velocity is > 3 m/s. A parametric study explores application conditions for the cumulative-impact method through horizontal-impact tests, indicating that small-scale multi-impacts and large-scale single impacts have consistent dynamic crush curves. The proposed method is sufficiently accurate to be used to determine the safety assessment of bridges under vessel collisions.

A novel frame-type crashworthy device for protecting bridge piers from vehicle collisions

The development of different types of crashworthy devices that can alleviate the damage of bridge piers under vehicle collisions has attracted the attention of many researchers. However, the existing crashworthy devices often suffer from problems such as high cost, difficulty involved in maintenance, uneconomical expenditure for structural retrofitting after an impact event, etc. This paper develops a novel frame-type crashworthy device using relatively cost-effective steel material. Beam segments with reduced cross-sections are employed to concentrate the plasticity in certain structural components during vehicle collisions, which may facilitate structural repair after impact. Non-linear finite-element (FE) models of a colliding vehicle, of the device and of a protected reinforced concrete (RC) pier column are developed with detailed model validations to assess the effectiveness of the device for pier protection. Numerical results show that the device can absorb a large portion of the impact energy during a vehicle collision and can reduce the magnitude of the impact force and the dynamic response of a protected RC pier column very markedly.

Energy absorption capability of laterally loaded glass/epoxy tubular components containing halloysite nanotubes

The crashworthiness capability of laterally loaded glass/epoxy (GFRE) tubular components containing halloysite nanotubes (HNTs) was explored in this article. GFRE components filled with 0, 1, 2, 3, and 4 weight percent (wt.%) of HNTs were created using wet-wrapping by hand lay-up technique. For the laterally loaded tubes, the crushing load and the energy absorption versus displacement responses were presented. In addition, distortion histories were tracked. The crashworthiness analysis was carried out by evaluating different indicators, i.e., initial crush load [Formula: see text], average crush load ([Formula: see text]), crush load efficiency (CFE), energy absorption (U), and specific absorbed energy (SEA). Two parameters of the Weibull distribution were employed to assess the experimental findings statistically. In addition, mathematical regression models were built to predict the energy absorption indicators. Experimental results demonstrated that an unfilled tube demonstrated the largest CFE of 1.84, while the maximum [Formula: see text] was demonstrated by a tube filled with 2 wt.% of HNTs with a value of 3.70 kN. Additionally, the tube filled with 4 wt.% of HNTs represents the extremes [Formula: see text], U, and SEA with values of 4.26 kN, 128.82 J, and 3.84 J/g, respectively. Due to their improved crashworthiness characteristics, GFRE filled with 4 wt.% of HNTs is suitable for use as a crashworthy device in automobiles.

On crushing behavior of square aluminum/CFRP hybrid structures subjected to quasi-static loading

Metal/composite hybrid thin-walled structures exhibit tremendous merits on the balance design among material costs, weight reduction and mechanical performances. In spite of these advantages, their underlying energy dissipating mechanisms and the influence law of key factors (such as mechanical properties, hybrid ratio, loading angle, etc.) on crushing behavior are still not well illustrated. This study aims to comprehensively explore the crushing deformation characteristics and underlying energy dissipating mechanisms of various square aluminum/CFRP hybrid structures (i.e., aluminum tube internally strengthened with CFRP namely CFRP/AL; aluminum tube externally strengthened with CFRP namely AL/CFRP tubes). Specifically, several axial quasi-static compression tests are performed to compare crushing behavior and performances of between hybrid tubes together with the corresponding net aluminum and CFRP tubes. Experimental results indicate that the total energy absorption of the CFRP/AL hybrid tubes is considerably higher than that of the summation of corresponding individual tubes. Subsequently, finite element models are developed for CFRP/AL hybrid columns to explore the underlying energy-absorbing mechanisms (the contribution of each constituent part on total energy absorption) and the influence law of key factors (mechanical properties, hybrid ratio, loading angle), which cannot be observed from experimental results. Numerical results indicate that the main reasons for the improvement in total energy absorption of CFRP/AL hybrid tubes are the altered deformation pattern of the outer aluminum tube and the significantly increased friction energy. Further, their outer aluminum tube seems to be more likely to generate plastic folding deformation rather than splaying progressive failure mode with increasing initial yield stress. The hybrid ratio and CFRP layer thickness jointly determine the deformation pattern of the CFRP/AL hybrid columns. Finally, it is also found that the load carrying capacity and energy-absorbing characteristics of CFRP/AL hybrid columns gradually reduce with increasing loading angle. The present study is expected to illustrate the potential of such hybrid structure as a crashworthy device and offer some design guidance for application and dissemination.

Comprehensive Crashworthiness Studies of Novel Alternately-Assembled Multi-Frusta Structures for Energy Absorption Applications

In this paper, we propose a new multicellular design of assembled multi-frusta with alternate orientations and varied taper angles for effective energy absorption applications. Extensive crush test experiments, comprehensive finite-element simulations and analytical modeling were carried out to evaluate the energy absorption performance of the newly proposed multicellular assemblies. The performances of these assemblies are calibrated against conventional assembly of uniform tubes. Two aspects of the work were parametrically examined. The first was concerned with the effect of the frusta taper angle, while the second was concerned with the multi-frusta layout on the energy absorption of the proposed multi-frusta assembled structures. The results reveal that the face centered square layout with an appropriately selected taper angle possesses the optimal high specific energy absorption, low peak force, and smooth crushing force curve, which makes it a crashworthy device.

Numerical evaluation of novel crashworthy devices for protection of RC piers subjected to vessel impact

The protection of bridge piers crossing navigation channels from the collisions of passing vessels is a critical issue nowadays, as vessel collision upon bridge piers has become one of the major threats to the safety of waterway bridges. This paper aims to develop a novel cost-effective crashworthy device, and to assess the effectiveness of the proposed device for protection of reinforcement concrete (RC) pier columns from vessel impact. The proposed protective device is comprised of a series of steel beams arranged in a frame-type manner with I-shaped cross-sections, where beam segments with reduced cross-sections are used to limit the plastic mechanism within certain structural components. The energy-dissipation capacity of the proposed device and its effectiveness for pier protection are thoroughly assessed by numerical approaches using general-purpose finite-element (FE) programs, where a barge is employed as the impacting vessel. Detailed non-linear FE models of the barge–device–pier system are developed and validated, and a parametric study is then conducted using the validated FE models with consideration of several important design parameters including barge impact velocity and geometric dimensions of the device. The numerical results show that the proposed device can absorb a large portion of impact energy during an impact event, which significantly reduces the magnitudes of impact forces transmitted to a protected RC pier column and attenuates the damage occurred to both the pier column and the impacting barge vessel. It is also found that the plastic deformation of the device can be effectively limited within the section-reduced beam segments whilst the remaining part remains elastic during impact, which would greatly facilitate the restoration of a damaged device after an impact event.

Numerical evaluation of a novel crashworthy device for pier protection from barge impact

Bridges located in navigation waterways are susceptible to ship impact due to the large ship transportation volume nowadays. The development of effective energy-dissipation devices which can protect bridges from ship impact has drawn much attention in recent years. As a result, many different types of protective structures such as composite crashworthy devices have been developed, analyzed and applied in bridge engineering. However, such protective structures are often extremely costly and were difficult to repair after an impact event. This paper aims to develop a novel crashworthy device with a steel-frame configuration of potentially low production cost and to numerically evaluate its mechanical behavior to quantify its energy-dissipation capacity. The strategy of using reduced cross-sections for certain steel beams in the device is proposed to limit plastic mechanisms within certain structural components whilst ensuring that others remain elastic during impact. The effectiveness of this strategy is numerically evaluated based on the assumption that the reduced cross-sections are rigidly connected to form a continuous beam model. The proposed strategy would greatly facilitate the restoration process of such devices after an impact event by replacing only those structural components where plastic deformations have occurred.

Multi-objective optimisation of a honeycomb-filled composite energy absorber for subway vehicles

To meet the requirements of passive safety protection during vehicle collision, a honeycomb-filled composite energy absorber (HFCEA) was designed in this study. A finite element model was established and effectively verified using experimental data. To evaluate the effects of the outer tube thickness, diaphragm thickness and honeycomb strength on the specific energy absorption (SEA) and the undulation of the plateau force (UPF), a polynomial response surface method was employed. To optimise the crash performance of the structure, i.e. to maximise the SEA and minimise the UPF, a multi-objective particle swarm optimisation was performed. A critical honeycomb strength was determined, beyond which the composite structure loses its weight efficiency. The UPF could be significantly reduced by increasing the honeycomb strength and reducing the outer tube thickness. This shows that the proposed composite structure can serve as an excellent crashworthy device for railway vehicles.

Experimental Study on the Performance of a Crashworthy Device for the Monopile Offshore Wind Turbine against Ship Impact

In the present work, a crashworthy device for a monopile offshore wind turbine has been proposed, which consists of the inner two-layer rubber torus and the outer thin steel shell. The performance of the crashworthy device against ship impact has been investigated experimentally. Based on the prototype of a 4 MW monopile wind turbine in the East China Sea, the scale ratio of the test model has been designed to be 1/50. The test ship model has been simplified as a “rigid car” equipped with a high-frequency force sensor in the front, which is available for changing the ship mass with different weights. The ship-impact velocity can be accurately controlled by a motion platform driven by a direct current machine. The effect of the key design parameters of the crashworthy device on its anti-impact performance has been tested and compared under typical ship impact cases. The results indicate that the crashworthy device can effectively reduce both the ship impact force and the top nacelle acceleration, and the physical mechanism that has been clarified. The outer thin steel shell can significantly use its structural deformation to absorb the ship impact energy, which is beneficial for reducing the structural damage of the offshore wind turbine (OWT)’s tower. The inner rubber torus can effectively prolong the ship impact duration, which is available for smoothing the impact force. Finally, the porous design for the outer steel shell of the crashworthy device has been proposed and tested.

Evaluation of composite crashworthy device for pier protection against barge impact

Barge impact is a potential hazard to bridge piers located in navigation waterways. Pier protection against barge impact is of vital importance and thus protective structures of different types are currently extensively used in bridge designs. Glass fiber reinforced plastic (GFRP) is a kind of composite that has been widely used in the design of crashworthy devices for many bridges in China. However, many questions regarding the mechanical properties of this composite remain to be answered. In this paper, a series of material property experiments, i.e. tension, compression, bending and shear experiments, are conducted using GFRP samples, based on which the GFRP material parameters are determined. A quasi-static crushing experiment using a scaled composite cylinder is conducted to investigate the failure mechanism of GFRP, epoxy resin and polyurethane foams which comprise the composite section. In addition, a numerical model of the scaled composite cylinder is developed and validated using experimental results. The validated numerical model is then used to evaluate the effectiveness of a full-scale cylindrical crashworthy device with composite section subjected to barge impact.

Optimization of honeycomb strength assignment for a composite energy-absorbing structure

This study proposes a new composite structure to promote energy absorption capability of railway vehicles by integrating characteristics of a thin-walled steel structure and aluminum honeycomb fillers. Non-linear explicit code LS_DYNA3D(971) was utilized in building detailed finite element models, which were also validated by previous test data. Considering the expensive selling price, complicated fabricating technology and low production rate of high strength honeycomb, honeycombs with appropriate strength should be selected to fill in the steel structure. Therefore, scientific sampling points were chosen from the design space using Box-Behnken design method. Analysis of variance was performed in order to explore the effects of distributed honeycomb strength in four levels on crashworthiness indicators. Response surface methodology (RSM) was well applied to perform both parametric analysis and multiobjective optimization for searching the optimal configurations. Here, two different criterion were conducted in optimization process by adopting desirability approach. It was find that the composite structure with high strength honeycombs in level-1 and level-2 and relatively low strength honeycombs in level-3 and level-4 are preferable for use. Comparing with the empty steel structure, the optimal EA capacity is promoted by 35.32% in criterion 1 and 34.35% in criterion 2, being able to bear the condition with crashing speed of 36 km/h and impacting mass of 55.3 t. It illustrates that the new composite structures can be recommended as excellent crashworthy devices.

Impact protection of bridge piers against rockfall

The Dujiangyan-Wenchuan highway serves as a vital passage to and from the region severely damaged by the 5.12 Wenchuan Earthquake in China. Chediguan Bridge is located on the highway and spans the Minjiang River. During the earthquake, the bridge was severely destroyed by rockfalls. Although the bridge was subsequently rebuilt and opened to traffic on May 12, 2009, it was destroyed again on July 25, 2009 by rock avalanches that had been located perilously high on the right bank of the Minjiang River, and caused deaths, casualties, and roads being cut off. A subsequent investigation revealed multiple perilous rocky areas on the massif along the Minjiang river bank, indicating an extremely high risk of another rockfall hazard, which could, again, lead to damage to the bridge and a further disastrous outcome. To mitigate the rockfall hazard to the bridge, a new flexible, energy-dissipating crashworthy device for bridge piers is developed to withstand the impact of rockfall. Numerical simulations using nonlinear finite element analysis was carried out to simulate the rockfall impact process on bridge piers. The following influencing factors during the impact process were taken into account: material nonlinearity, geometric nonlinearity, as well as contact nonlinearity. The results show that the new protective structure of bridge piers can effectively buffer rockfall impacts and significantly improve the anti-impact capability of the bridge piers.

Novel Crashworthy Device for Pier Protection from Barge Impact

Barge impact is a potential hazard for bridge piers located in navigation waterways. Protective structures of different types, for example, dolphin structures, artificial islands, and guiding structures, have been widely used in bridge designs against barge impact. However, such structures often imply high cost and suffer from difficulties in installation as well as maintenance challenges. This paper aims to devise and investigate a new type of crashworthy device which is comprised of vertically supported impact cap connected to the bridge pier using a series of steel beams in a frame‐type arrangement. This sacrificial steel structure is designed to form plastic hinges for energy dissipation whilst limiting the force transmitted to the protected pier. The dynamic analysis of the proposed crashworthy device subjected to barge impact is conducted using a simplified impact model previously developed by the authors. The parametric studies in this paper show that the proposed device has a large energy dissipation capacity and that the magnitude of impact force transmitted to the bridge pier can be dramatically reduced. In addition, an optimization model is proposed in this paper to achieve the cost‐optimized design of the crashworthy device for a given impact scenario with constraints as per the prescribed design requirements.

Optimization and application of a crashworthy device for the monopile offshore wind turbine against ship impact

The risk of offshore wind turbines collision with ships is on the rise during the service period with the increase of offshore wind farms and ship routings. In order to minimize the damage of offshore wind turbines caused by ship impact, a crashworthy device, which contains a rubber blanket and outer steel shell, is proposed. The rubber hardness and the rubber and steel shell thicknesses of the crashworthy device are optimized by comparing the collision-force and nacelle acceleration using LS-DYNA explicit code. The main reason for lessening the maximum collision-force and nacelle acceleration is that the rubber blanket could absorb a portion of ship energy by using its own structure deformation. Therefore, an optimal crashworthy device for the monopile offshore wind turbine, meeting the weight constraint, is suggested and implemented in various impact scenarios. The obvious effects of crashworthy devices are a decrease of the maximum collision-force and nacelle acceleration, especially for ships with smaller initial kinetic energy. The damage area of plastic strain for foundations is reduced to zero when crashworthy devices are used in the analysis scenarios. This paper may be useful in anti-impact design of offshore wind turbines.

A study on ship impacting a flexible crashworthy device for protecting bridge pier

As the accident of a vessel impacting a bridge pier will cause serious disaster, such as destroyed bridge, sinking ship and polluting environment, the technology and method to protect bridge pier from ship collision have been widely investigated recently. Due to the huge kinetic energy of large-tonnage ship and the short time duration in the collision, the studies involve impact mechanics. A developed flexible crashworthy device has been developed to protect bridges, which consists of an outer steel-periphery, an inner steel-periphery and the rubber coating SWRCs(soft elements) installed between them. When the SWRC crashworthy device is installed, the collision duration under low impact force is prolonged due to its high compliance, which results in the ship having enough time to turn its navigation direction and most of the remainder kinetic energy being carried off by the turned away ship. Consequently, both impact forces on the ship and on the bridge pier decrease markedly. This is the key reason as to why the SWRC crashworthy device can avoid the destruction of both the bridge and the ship. Based on our results of theoretical studies and numerical simulations, the present paper will propose an experiment-adopted a real ship to impact a flexible crashworthy device. The collision test has been performed 12 times with different speed, carrying capacity, and impact angle of the ship. After the experiments, the ship, flexible crashworthy device and the pier are not damaged. The experiments show that the flexible crashworthy device can turn away the impact ship, so that the ship moves along the outer part of the device, which reduces the ship impact force on the bridge pier obviously. It not only protects bridges but also avoids the damage to ships.

On the Impact Force and Energy Transformation in Ship-Bridge Collisions

Taking ship-bridge collision as an example, how the wave propagation and the dynamic behavior of materials influence the impact force and energy transformation are studied from the impact dynamics viewpoint. By using a new flexible, energy-dissipating crashworthy device developed by the authors, both the impact force and energy transformed can be markedly reduced, which is much conductive to protect both bridge and ship.

In situ testing on a new crashworthy device against ship-mitre gate collision

The mitre gate has been widely used in ship locks. However, apart from the normal operational loads, the gate is subjected to unexpected incidents, including sudden loads such as collision of the ship. Due to the fact that this kind ofstructure is widely used in a variety of ship locks and holds great promise for future applications, the safety of the structure has received widespread attention. Nowadays, traditional steel fenders are widely used as crashworthy devices in most mitre gates. In order to improve the crashworthiness of the structure, a new crashworthy device made from rubber composite against ship-mitre gate collision is developed instead of traditional steel fenders. In situ testing on this new fender is performed in order to investigate the crashworthiness of the fender. A real ship is used to crash against the gate in the ship lock to create a structural vibration in the test. The dynamic responses of the gate with steel and the new fender are detected so as to compare the effects of the different collision protection systems used in the gate. The test results show that the vibration amplitude changes greatly between gates with steel and the new fender. The structural maximal acceleration and strain responses all decrease when the gate installs the new fender. Based on the in situ vibration test conducted, the installation of a new fender as collision protection device is proven to be an effective method to make the gate in the ship lock safer.