Impact Force Time History Research Articles

Performance of circular CFDST members with external stainless steel tube under transverse impact loading

Abstract This paper presents an experimental and numerical study on the impact performance of circular concrete-filled double skin steel tubular (CFDST) members with external stainless steel tube. Austenitic 304 stainless steel was used for all the test specimens. Taguchi approach was employed for the parametric design of the experimental program. The testing parameters were the impact height, hollowness ratio and axial load level. 18 specimens were tested under transverse impact loading to obtain the failure patterns, the time histories of impact force and mid-span deflection, as well as the strain developments in the stainless steel tube. Finite element (FE) models were then established and verified against the test results, in which the strain rate effects of the stainless steel, the carbon steel and the infilled concrete were considered. The validated FE model was then employed to investigate the whole dynamic response of CFDST members with outer stainless steel tube subjected to impact. The impact resistance of the stainless composite member was also compared with that of the CFDST member with an external carbon steel tube.

Effective Formula for Impact Damping Ratio for Simulation of Earthquake-induced Structural Pounding

Structural pounding during earthquakes may cause substantial damage to colliding structures. The phenomenon is numerically studied using different models of collisions. The aim of the present paper is to propose an effective formula for the impact damping ratio, as a parameter of the impact force model used to study different problems of structural pounding under seismic excitations. Its accuracy has been verified by four various approaches. Firstly, for the case of collisions between two structural elements, the dissipated energy during impact has been compared to the loss of kinetic energy. In the second stage of verifications, the peak impact forces during single collision have been analyzed. Then, the accuracy of different equations have been verified by comparing the impact force time histories for the situation when a concrete ball is dropped on a rigid concrete surface. Finally, pounding between two structures during earthquakes has been studied. The results of the analysis focused on comparison between dissipated and kinetic energy show relatively low errors between calculated and assumed values of the coefficient of restitution when the proposed equation is used. In addition, the results of the comparison between experimentally and numerically determined peak impact forces during single collision confirm the effectiveness of the approach. The same conclusion has been obtained for the whole impact time history for collision between a ball and a rigid surface. Finally, the results of the comparative analysis, conducted for pounding between two structures during an earthquake, confirm the simulation accuracy when the proposed approach is used. The above conclusions indicate that the proposed formula for impact damping ratio, as a parameter of impact force model for simulation of earthquake-induced structural pounding, is very effective and accurate in numerical simulations in the case of different scenarios.

Development of the impact force time-history for determining the responses of bridges subjected to ship collisions

Ship impact force is usually taken as an equivalent static force in current bridge design, which is, however, limited on effectively capturing the dynamic amplification effects. To this end, this work proposes a simplified analytical model for predicting the time-history of ship impact loading on bridges. To validate the FE modeling techniques used in capturing the impact loading, drop hammer impact tests are carried out using scaled steel boxes. Then FE models of 5 typical ships are developed and numerical simulations are conducted to generate the 45 benchmark impact force time-history curves which are used to determine the parameters introduced in the proposed simplified analytical model. The efficiency of the proposed model is evaluated by a case study involving two bridge models, as presented in this paper. It is shown that the proposed simplified analytical model is capable of predicting the time-history of impact loading with sufficient accuracy for ship-bridge collision events when the basic structural frequency of the bridge pier is within 3 Hz. • An analytical model to evaluate the impact loading in a ship-bridge collision occurrence is proposed. • This model is based on 45 numerical impact force time history curves of 5 ships. • FEmodels to capture the impact loads are validated by a group of drophammer impact tests using scaled steel boxes.

Reliability evaluation of secondary support structure in hypothetical drop of reactor core barrel assembly

Dynamic responses of the secondary support structure are investigated to evaluate its structural reliability in a hypothetical drop impact accident of the reactor core barrel assembly in this work. Impact analyses both in still water situation (20 °C) and dynamic water situation (289 °C) are carried out by LS-DYNA. Tensile tests in both temperature cases are conducted for the secondary support structure material (Inconel 690) in order to make the simulation results more accurate with real material properties. Various aspects of structural dynamic responses during impact are analyzed, including distributions of equivalent stress, equivalent plastic strain, and maximum principal stress as well as time histories of impact force, vertical displacement, vertical velocity, and energy. In still water situation, equivalent stress of the secondary support structure exceeds the yield strength due to the higher initial impact velocity and downward base acceleration. But in dynamic water situation, there is no plastic deformation due to the lower initial impact velocity and upward base acceleration. Peak values of the maximum principal stress distributed in the secondary support structure are less than the corresponding ultimate tensile strengths respectively in both analysis cases. Results reveal that both of the secondary support structure and the reactor pressure vessel meet the design criteria of RCC-M Code with respect to stress limits, thus the structural reliability can be ensured in this drop accident.

Safety assessment of Generation Ⅲ nuclear power plant buildings subjected to commercial aircraft crash Part I: FE model establishment and validations

Abstract Investigations of the commercial aircraft impact effect on nuclear island infrastructures have been drawing extensive attention, and this paper aims to perform the safety assessment of Generation Ⅲ nuclear power plant (NPP) buildings subjected to typical commercial aircrafts crash. At present Part I, finite element (FE) models establishment and validations for both the aircrafts and NPP buildings are performed. (i) Airbus A320 and A380 aircrafts are selected as the representative medium and large commercial aircrafts, and the corresponding fine FE models including the skin, beam, fuel and etc. are established. By comparing the numerically derived impact force time-histories with the existing published literatures, the rationality of aircrafts models is verified. (ii) Fine FE model of the Chinese Zhejiang Sanao NPP buildings is established, including the detailed structures and reinforcing arrangement of both the containment and auxiliary buildings. (iii) By numerically reproducing the existing 1/7.5 scaled aircraft model impact tests on steel plate reinforced concrete (SC) panels and assessing the impact process and velocity time-history of aircraft model, as well as the damage and the maximum deflection of SC panels, the applicability of the existing three concrete constitutive models (i.e., K&C, Winfrith and CSC) are evaluated and the superiority of Winfrith model for SC panels under deformable missile impact is verified. The present work can provide beneficial reference for the integral aircraft crash analyses and structural damage assessment in the following two parts of this paper.

Impact Force Identification on Carbon Fibre–Epoxy Honeycomb Composite Panel Based on Local Convex Curve Criterion

Identification of impact force is essential for various engineering applications, such as performance evaluation, design optimisation, noise suppression, and vibration control. There are two categories available for impact force identification, namely, direct measurement and indirect acquisition. For actual engineering structures, direct measurement is often not feasible. Therefore, indirect acquisition, or force identification, is the only means to achieve this goal. Owing to the existence of noise, ill-posedness occurs during the inversion process of force identification, which is the decisive factor for the instability and inaccuracy of this method. The most popular among the existing methods for impact force identification is the Tikhonov regularisation method. The accuracy of this method depends on the determination of the regularisation parameters. This study proposes a new criterion, which is the local convex curve, for the selection of the regularisation parameter. This criterion is compared with the generalised cross validation, L-curve criterion, and other criteria. A carbon fibre–epoxy honeycomb composite panel is selected as the experimental research object, and three indicators, namely, peak relative error, relative error, and correlation coefficient, are used as the evaluation standards. The experimental results indicate that this new criterion can obtain a superior regularisation parameter in comparison with the other seven criteria. This new criterion can realise the accurate reconstruction of the impact force time history and be effective in suppressing the tail disturbance of the reconstructed impact force time history.

Behavior and Design of Bridge Piers Subjected to Heavy Truck Collision

Heavy trucks, such as tractor–semitrailers weighing up to 360 kN, represent a serious collision hazard for unprotected bridge piers. Current specifications recommend designing a bridge pier vulnerable to vehicular impacts for a static force of 2,670 kN applied on the pier at a specified height. However, the impact load delivered by a heavy truck is dynamic and not applied at a single height during the crash process. High-fidelity computational simulation is used to gain insight into how force is delivered to a bridge pier during a crash. The impact force time histories generated during a collision are simplified into a series of triangular pulse functions applied at various heights. Key parameters defining the pulse models are truck weight, approach speed, and pier size. The values of these parameters are derived from numerical regression based on the simulation results. By comparing pier damage modes and deformation profiles, the proposed pulse model is demonstrated to be able to accurately represent the truck impact demands. We have proposed a capacity design philosophy to mitigate the effects of shear failure. We revealed that piers designed according to the proposed philosophy are less likely to fail in shear compared with regular piers. We asserted that together, the simple pulse model and proposed capacity design approach can serve as a basis for future performance-based design provisions for bridge piers subjected to heavy truck impact.

Impact force localization for civil infrastructure using augmented Kalman Filter optimization

Impact forces induced by external object collisions can cause serious damages to civil engineering structures. While accurate and prompt identification of such impact forces is a critical task in structural health monitoring, it is not readily feasible for civil structures because the force measurement is extremely challenging and the force location is unpredictable for full-scale field structures. This study proposes a novel approach for identification of impact force including its location and time history using a small number of multi-metric observations. The method combines an augmented Kalman filter (AKF) and Genetic algorithm for accurate identification of impact force. The location of impact force is statistically determined in the way to minimize the AKF response estimate error at measured locations and then time history of the impact force is accurately constructed by optimizing the error co-variances of AKF using Genetic algorithm. The efficacy of proposed approach is numerically demonstrated using a truss and a plate model considering the presence of modelling error and measurement noises.

Group sparse regularization for impact force identification in time domain

Impact force identification remains a challenging inverse problem, where a small error in structural responses may lead to a large deviation in the actual solution. Recently, sparse regularization has attracted a lot of interest in the field of force identification. However, the standard sparse regularization method for force identification does not consider the intrinsic structure of impact force, i.e., the nonzero elements occur in groups, called group sparsity. In this paper, by exploiting the group sparse structure of impact force time history, we develop a general group sparse regularization method based on minimizing mixed l2,1-norm for the inverse problem of impact force identification. First, the number and size of groups including a complete profile of impact force are determined for penalizing the sum of the l2-norm of groups associated with the pulse profile of impact force. Second, a general group sparse optimization model based on the mixed l2,1-norm penalty for impact force identification is constructed in time domain, leading to a non-smooth convex optimization problem. Third, given the transfer function and the impact response, an accelerated gradient descent method is developed to solve such a group sparse regularization model. Finally, experiments including identification of single and consecutive impact forces are conducted on a clamped-free thin plate to illustrate the effectiveness and applicability of the proposed approach. Experimental results demonstrate that the classical Tikhonov regularization methods can only identify the single impact force from weakly noisy responses; the group sparse regularization method can efficiently identify both single and consecutive impact forces from heavily noisy responses, and has a slightly better improvement of the peak force amplitude than the standard sparse regularization method.

Vibration Analysis of a Single‐Cylinder Reciprocating Compressor considering the Coupling Effects of Torsional Vibration

A piston slap is one of the main vibration sources of the reciprocating machinery. Much work has been done in this field, most of which was based on a constant rotating speed. However, in practice, the speed of a crankshaft may always fluctuate due to the uneven load or excitation. The inertia forces of moving components are much different at the fluctuating rotating speed comparing with that at a constant speed. In this paper, the piston slap and the induced vibration are analyzed based on the instantaneous angular speed measured on a single‐cylinder reciprocating compressor. Firstly, the dynamics of a crank‐connecting rod mechanism is analyzed based on the measured instantaneous angular speed which contains the torsional vibration of the air compressor. The time histories of piston slap impact forces considering and without considering torsional vibration are compared. Then, in order to correlate the piston slap impact with the slap‐induced vibration, the corresponding transfer functions between the middle stroke of the outer surface of the cylinder liner and the excitation points are measured. And the excitation force on the main bearing is also taken into account to bring the simulation closer to the experimental results. The effects of a torsional vibration on the vibration of the cylinder liner are analyzed, and the simulation results show that the torsional vibration is a factor that must be taken into account in the vibration analysis of the single‐cylinder reciprocating compressor.

Low-Velocity Impact Behavior of Interlayer/Intralayer Hybrid Composites Based on Carbon and Glass Non-Crimp Fabric.

Composites have gained wide use in structural applications; however, they are sensitive to impact damage. The use of hybrid composites is an effective way to overcome this deficiency. The effects of various hybrid structures of interlayer and intralayer warp-knitted fabrics with carbon and glass fibers on the low-velocity impact behavior of composite laminates were studied. Drop-weight impact tests were conducted on two types of interlayer, sandwich and intralayer hybrid composite laminates, which were compared with homogenous composite laminates. During low-velocity impact tests, the time histories of impact forces and absorbed energy by laminate were recorded. The failure modes were analyzed using the micro-CT (computed tomography) and C-scan techniques. The results revealed that the hybrid structure played an important role in peak force and the absorbed energy, and that the hybrid interface had an influence on damage modes, whereas the intralayer hybrid composite laminate damage was affected by the impact location. The intralayer hybrid laminate with C:G = 1:1 exhibited better impact resistance compared to the other hybrid structures.

Experimental and Numerical Studies on Concrete Filled Circular Steel Tubular (CFCST) Members Under Impact Loads

This paper presents experimental and numerical studies on the behavior of concrete filled circular steel tubular (CFCST) members under lateral impact loading. Fourteen CFCST member specimens were designed, fabricated and tested using a Drop Hammer Impact Test Machine in a simple double-supported boundary conditions. The main parameters include the outer diameter of CFCST member, the thickness of steel tube and the height of drop hammer. The failure modes, the impact force, the impact force time history curves and the strain time history curves were investigated to evaluate the behavior of CFCST member under an impact load. A finite element analysis (FEA) model of CFCST member under lateral impact loading was established using ABAQUS software, and the accuracy of the proposed model was verified by a comparison with the test results. The response of the specimen under impact loading simulated by FEA model, matches well with the test results.

Numerical simulation of aircraft crash on large-scale LNG storage tank

Abstract The safety of the large-scale LNG (liquid natural gas) storage tank is threatened by the accidental or deliberate aircraft collisions, while the related studies are limited. At present, based on the missile-target interaction method, the dynamic damage and failure of the Chinese Yang Shan pre-stressed LNG storage tank against the impact of the commercial aircraft A320 are assessed numerically. Firstly, the fine FE (finite element) models of LNG storage tank and Airbus A320 aircraft are established with the program HyperMesh, which are validated by comparing with the classic IRIS (Improving the Robustness of Assessment Methodologies for Structures Impacted by Missiles) impact test of deformable missile as well as the modified Riera function, respectively. Then, the whole impact process of A320 aircraft on the LNG storage tank is reproduced with the explicit dynamic analysis program LS-DYNA. The impact force-time history, the deflection of the outer concrete tank, the effective plastic strain of the inner steel tank, et al. are obtained and discussed. Finally, the parametric analyses are performed to study the influences of the impact velocity, angle and position on the dynamic responses of the LNG storage tank. The conclusions are helpful for the design and safety assessment of LNG storage tank subjected to the potential aircraft collision.

Dynamic effects induced by the impact of debris flows on protection barriers

Debris flow is a transient phenomenon that causes large disasters. Retaining systems, whose design is still nowadays a crucial issue, can mitigate this risk. Multiple surges can arise during this phenomenon; thus, an accurate analysis might consider the impact force time histories rather than only its maxima. The aim of this work is to analyze the effects of the interaction between the debris and the barrier during one surging phenomenon. A discrete element model models the granular motion and the interaction between the debris and a rigid open barrier set at the end of the channel. The estimated interaction force time history is then used as input impact force for the dynamic structural analyses of the piles. A total of 12 different structural sections are adopted and the internal forces at the base are critically compared. It results that the first mode vibration period is the parameter that largely affects the behavior of the piles.

3D meso-mechanical modelling of impact response of reinforced concrete beams

An understanding of the response and failure of reinforced concrete structures subjected to impact loadings is of great importance in safety calculations and assessment in civil as well as defence engineering. In this paper, a numerical study is performed on the impact response of reinforced concrete beams by a newly proposed 3D meso-mechanical model together with a recently developed computational dynamic constitutive model for concrete. In the 3D meso-mechanical model, concrete is considered as a three-phase composite material consisting of mortar matrix, coarse aggregates and interfacial transition zone (ITZ layers). The constitutive model for concrete takes into account pressure dependency, shear damage, tensile softening, Lode effect and strain rate effect, etc. It is shown that the numerical results are in good agreement with the experimental observations in terms of time histories of impact force and displacement as well as crack distribution and propagation and that the newly developed 3D meso-mechanical model together with the previously proposed constitutive model for concrete can be used to predict the response and failure of reinforced concrete structures subjected to impact loading.

Mesoscale simulations of the impact resistance performance of rein-forced concrete beams exposed to high temperature

Considering the degradation of the mechanical properties of steel and concrete under high temperature and the strain rate effect of the materials, a mesoscopic numerical analysis model of reinforced concrete beam are proposed based on the meso-structure of concrete. The influences of fire duration time and impact energy on the impact resistance behavior of concrete beams in fire are discussed. In this paper, the failure process of reinforced concrete beam subjected to impact load, the impact force time history, the reaction time of support and the displacement response in the middle span are analyzed. The results show that the mesoscopic numerical model can well simulate the heat transfer process of each components of concrete. With the increase of heating time, the concrete beam under the impact load is more serious, meanwhile the duration of the impact force and the maximum displacement of the span increase, but the impact force peak decreases; with the increase of impact energy, the shear failure of concrete beam is more serious, and the impact force peak increases. The maximum displacement increases linearly with the impact energy.

Numerical analysis of collision between a tractor-trailer and bridge pier

Accidents involving collisions of heavy-duty trucks with highway bridge piers occurred occasionally, in which the bridge piers might be subjected to severe damage, and cause the collapse of the superstructure due to the loss of axial loading capacity. The existing researches are mostly concentrated on the light- or medium-duty trucks. This article mainly concerns about the collisions between the heavy-duty trucks (e.g. tractor-trailer) and bridge piers as well as the evaluation of the impact force. First, by modifying the finite element model of Ford F800 single-unit truck, which was developed by National Crash Analysis Center, the finite element model of a tractor-trailer is established. Then, the full-scale tractor-trailer crash test on concrete-filled steel pier jointly conducted by Texas Transportation Institute, Federal Highway Administration, and Texas Department of Transportation is numerically simulated. The impact process is well reproduced and the established model is validated by comparison of the impact force. It indicates that the tractor-trailer impact force time history consists of two or three peaks and the corresponding causes are revealed. Furthermore, the parametric influences on the impact force are discussed, including the diameter and cross section shape of the pier, cargo weight, impact velocity, relative impact position, and vehicle type. Finally, the finite element model of an actual reinforced concrete highway bridge pier is established, and the impact force and lateral displacement of the pier subjected to the impact of the tractor-trailer are numerically derived and discussed.

Dynamic behaviour of axially-loaded RC columns under horizontal impact loading

This paper presents an experimental study undertaken for investigating the dynamic responses of axially-loaded reinforced concrete (RC) columns under horizontal impact loading. A total of 15 square RC columns, categorised by three different types of cross-section dimensions, were tested using horizontal impact facilities. The test specimens had fixed boundary condition at their bottoms. The impact load was realised by a test truck and applied at the top position of the RC column. Three main parameters, namely the slenderness ratio, the impact weight and the impact velocity, are considered in the study. Based on the experimental results, the crack pattern, impact force, deformation, strain development and energy dissipation are discussed. Through the recording of the relative movement between hammer and specimen, the repeated process of contact and separation was observed. Compared with that of the conventional drop weight impact test, the impact force-time history curves obtained from the horizontal impact test show more fluctuationat the stabilisation stage, because the existence of gravitational acceleration of drop hammer and larger velocity in drop weight impact test accelerates the repeated process of contact and separation between the hammer and specimen. As the input impact energy increases, the flexure-controlled failure of column was observed, which is characterised by the yielding of tensile reinforcement and the spalling of concrete cover. The experimental results presented herein provide benchmark data for the further research study of RC columns subjected to horizontal impact forces. The equivalent static force calculated by empirical formula of AASHTO is adopted to compare with the experimental results, which indicates that the empirical equation only related to the impact weight and velocity could overestimate the equivalent static force that would leads to too conservative impact-resistance structural design.

Experimental research on impact loading characteristics by full-scale airplane impacting on concrete target

To investigate the impact loading characteristic during an airplane impacting process, an experiment of a full-scale airplane impacting on a movable concrete target was carried out, using a rocket slid propulsion facility. In the experiment, an on-off signal measurement system was used to monitor the airplane’s impacting velocity; the total impacting process as well as the fragment dispersion of the airplane’s wreckage were recorded by a high-speed photography system. Moreover, five accelerometers were installed on the reverse side of the target to measure its acceleration, from which the impact force-time history can be obtained. Moreover, two storage airborne accelerometers were placed on the airplane’s tail to measure the acceleration history of the airplane, from which both the crushing force-time history and the crushing force distribution along the fuselage can be obtained. It is found that the measured impact force-time history is in good agreement with that calculated using the modified Riera impact loading model. This verifies the reliability of using the modified Riera model to predict the impact force acting on the target during the airplane impacting process, and the value of the correction coefficient α in the Riera model can also be determined. In addition, it is observed that, except at the initial moment, the ratio of the crushing impulse to the impacting one remains roughly a constant, which makes it possible to further simplify the Riera model by getting rid of the crushing force distribution curve.

Numerical simulation of GLARE 4A fiber-metal laminates subjected to ballistic impact

This article deals with the evaluation of the ballistic resistance of GLARE 4A fiber-metal laminates subjected to high velocity impact by a cylindrical projectile. Important impact variables such as the ballistic limit, the impact load and the absorbed energy time histories are predicted using the ANSYS LS-DYNA software. The simultaneous existence of various impact damage mechanisms, which is unique in fiber-metal laminates, is demonstrated using the numerical results. Each of the mechanisms absorbs a part of the initial impact energy and contributes to the high ballistic impact resistance the materials. With reference to the considered GLARE 4A panels, the behavior of the transient impact load is analyzed and useful conclusions are drawn. It is found that the maximum impact load is applied at the beginning of ballistic impacts, during the initial local indentation of the panels under the projectile. It is substantially higher than the following peak values of the impact force time history. It is revealed that during the beginning of ballistic impacts, the impulse of the collision increases as the thickness of the panels is increased. The work done by the impact load during the local indentation stage is also an increasing function of the panels’ thickness.