Axial Force Response Research Articles

Stochastic dynamic analysis of floating bridges exposed to inhomogeneous and irregular waves

As future floating bridges gets longer, the likelihood of significant inhomogeneous wave conditions across them increase. Consequently, a proper assessment of the effects of inhomogeneous wave conditions is needed. In this paper, we present an approach to model inhomogeneous sea states by representing the stochastic process using generalized harmonic decomposition, retaining the coherency inherent in Airy wave theory. The methodology is applied to a concept model of a floating bridge to cross the Bjørnafjord in Norway, which is more than five kilometres wide. The paper emphasizes on frequency-domain simulation, but the required steps to generate time-domain representations are given. To suggest what might be critical considerations in design, the response effects due to some selected conceptual inhomogeneities are highlighted. For varying wave heights alone, it is found that it is likely conservative to approximate the inhomogeneous sea state as homogeneous by assuming the harshest conditions across the full width of the strait. By modulating the mean wave angle of a 100-year swell sea state, a spherical wave front matching the curvature of the bridge girder is found to produce significantly more severe response than the homogeneous reference swell; an increase of 14% of the maximum axial force response is found. Furthermore, a proper treatment of the coherency for swell sea states is found to be crucial, in contrast to typical wind sea conditions.

Evaluation of the effect of the vertical component of an earthquake on the seismic response of container cranes using the shake table test

In this study, the effect of the vertical component of earthquakes on the seismic response of a container crane was investigated by using the shake table test on a 1/20 scale container crane. The effect was investigated by comparing the seismic response of the container crane when subjected to the horizontal component of earthquakes versus the horizontal and vertical components of earthquakes. The seismic responses of the container crane were compared based on acceleration responses, displacements, and internal forces. The main findings of this study are as follows: (1) Vertical acceleration response increased when the vertical and horizontal components of earthquakes were used simultaneously. A maximum increase of 79% was observed for the vertical acceleration response at the trolley-boom girder. The horizontal acceleration response either increased or decreased. The maximum difference was 24% when the container crane was subjected to horizontal component earthquakes versus horizontal and vertical component earthquakes. (2) The horizontal displacements of the container crane increased or decreased under the simultaneous action of the horizontal and vertical components of the earthquakes. The maximum difference was 278% with regard to the derailment of the seaside legs. (3) The internal forces at the top of the lower legs were affected by adding the vertical component of the earthquakes. The maximum difference in the axial force response was 100%, while that of the bending moment was 24%. Therefore, the seismic response of container cranes should be analyzed with and without the vertical component of earthquakes to determine the most extreme case of the seismic response.

High strain rate constitutive and fracture characterization of AA7075-T6 sheet under various stress states

The stress state and strain rate dependent fracture behavior of high strength aluminum sheet, AA7075-T6, is characterized experimentally and numerically. Experiments were performed using shear, hole tension, notch tension, and groove tension specimen geometries at strain rates in the regime 10−2 – 500 s−1. The temperature change on the specimen surface was measured utilizing high speed thermal imaging, while strains were acquired using DIC-based optical measurements. Mild positive rate sensitivity was observed in the flow response for equivalent strains up to approximately 20%, while the flow stress decreased at higher (500 s−1) strain rates as the strain levels increased. An increase in temperature was observed within the gauge region of the specimens during elevated strain rate (500 s−1) tests leading to thermal softening. Positive strain rate sensitivity was observed in the measured axial force response for the hole tension and notch tension specimens. The fracture limits of the AA7075-T6 in the shear, hole tension, and notch specimens decreased between strain rates of 0.01 and 10 s−1, then increased at strain rates between 10 and 500 s−1. A strain rate and temperature dependent Hockett–Sherby (HS-SRT) constitutive model was proposed to capture the dependency of the flow stress on the equivalent plastic strain, strain rate, and temperature. The generalized Drucker-Prager (GDP) fracture model was extended to capture the effect of strain rate on fracture initiation. Numerical simulations of the coupon experiments were then performed to extract the local stress and strain states to calibrate the GDP fracture model across the range of strains considered.

Comparison ofAxial Force Attenuation Characteristics inTwo Different Lower Extremity Anthropomorphic Test Devices.

Any type of boot or footwear is designed to attenuate and distribute loading to the bottom of the foot. Anthropomorphic test device (ATDs) are used to assess potential countermeasures against these loads. The specific aims of this study were to compare and quantify force attenuation characteristics as a function of input energy for Hybrid-III and Mil-Lx ATD human surrogates. Two lower leg ATD surrogates (Mil-Lx and Hybrid-III) were tested to investigate the influence of a commercially available military boot on lower extremity force response and assess such differences against previously published postmortem human surrogate studies. The testing apparatus impacted the bottom of the foot using a rigid plate at velocities from 2 to 10 m/s. Tests were conducted on each ATD to obtain axial force response with and without boots as a function of input energy. Peak forces ranged from 1 to 16.4kN for the Hybrid-III, and 1 to 8.4kN for the Mil-Lx for similar input conditions. The average force attenuation for the Hybrid-III at upper and lower load cells was 71% (59%-80%) and 70% (58%-78%). The average attenuation for the Mil-Lx at upper and lower load cells was 20% (13%-28%) and 37% (36%-37%), respectively. At the knee load cell, the attenuated peak loads ranged from 62% to 81% for the Hybrid-III and 16% to 30% for the Mil-Lx. Force attenuation characteristics in the booted vs unbooted configuration of the Mil-Lx were significantly different than force attenuation characteristics of the H3 and may better represent in vivo forces during vertical impact injuries, such as IED blasts. Hence for military relevant applications where boots are used, the Mil-Lx may provide a more conservative evaluation of lower extremity protection systems.

Behaviour of vertically loaded steel beams under a travelling fire

As the structural response to a time and space dependent non-uniform temperature field is challenging to manage by code-based design, the behaviour of steel beams exposed to a travelling fire was simulated numerically in this paper. The finite element (FE) models for both thermal and mechanical analyses were validated by two benchmark tests and used to study the effect of uniform and non-uniform thermal exposures and different steel grades on the response of steel beams. The developed five-stage mechanism well characterized the response of the beams exposed to the travelling fire. For the beam in the elastic range, the heating-cooling cycles of gas temperatures induced cyclic axial forces, but the cyclic nature of structural responses was cushioned by material plasticity. For the beams stressed into the plastic range, the repetitions of cycles in axial response created residual deformations that induced catenary action in the beams at lower temperatures. The local heating of the critical sections made the beams more prone to a runaway failure than the uniform heating of the whole beam. Compared to the mild steel beams, the axial force response of the HSS beams showed higher axial compression forces and fluctuated more. The critical temperatures based on the deformation or strength criterion were consistent for the beams with the load ratio of 0.3. However, for designing the beam with the load ratio of 0.5, critical temperature of 350 °C or the strength criteria based on the proportional limit are recommended as the catenary action was activated at low temperatures. These recommendations can be used as a guide for practical design.

Predicting maximum force in SPIF for different materials

Knowing the importance of predicting acting forces during the formation process, our research has conducted 27 Single Point Incremental Forming (SPIF) experiments in hyperboloid format, followed by Finite Element Method (FEM) simulations and regression equations were determined to estimate the maximum axial force in the process. ANOVA analysis of variance was used to determine the significance of material parameters in the maximum axial force response. A multiple linear regression model was constructed to estimate the maximum axial force in the SPIF process. After the experiments, we were able to identify that the maximum axial force increases according to an increase in tool radius, sheet initial thickness, and strength coefficient values, as well as according to the decrease in the strain-hardening exponent. The FEM simulations are in agreement with the experimental values found, and the linear regression model has proven to be efficient to describe results, with R2 of 98.85% and a maximum percentage error of 11.5%.

Finite element analysis of typical fastener type full hall steel tubular scaffolds

Based on fastener type full steel tubular scaffolds of power transmission and transformation project, this paper discusses in detail the establishment process of three-dimensional finite element model, including steel pipes, semi-rigid connections, mass of fasteners and boundary conditions. The stability of scaffold is analyzed and the failure mode of instability and ultimate bearing capacity are calculated. Then the static analysis is carried out to analyze the displacement and axial force response of the scaffold during construction, and finally the measures to strengthen the stability and safety of the scaffolds are given.

Characterization and Analysis of Extensile Fluidic Artificial Muscles

Extensile fluidic artificial muscles (EFAMs) are soft actuators known for their large ranges of extension, low weight, and blocked forces comparable to those of pneumatic cylinders. EFAMs have yet to be studied in a way that thoroughly focuses on their manufacturing, experimental characterization, and modeling. A fabrication method was developed for production of two EFAMs. The quasi-static axial force response of EFAMs to varying displacement was measured by testing two specimens under isobaric conditions over a pressure range of 103.4–517.1 kPa (15–75 psi) with 103.4 kPa (15 psi) increments. The muscles were characterized by a blocked force of 280 N and a maximum stroke of 98% at 517.1 kPa (75 psi). A force-balance model was used to analyze EFAM response. Prior work employing the force-balance approach used hyper-elastic constitutive models based on polynomial expressions. In this study, these models are validated for EFAMs, and new constitutive models are proposed that better represent the measured stress values of rubber as a function of strain. These constitutive models are compared in terms of accuracy when estimating pressure-dependent stress–strain relationships of the bladder material. The analysis demonstrates that the new hyper-elastic stress models have an error 5% smaller than models previously employed for EFAMs for the same number of coefficients. Finally, the analysis suggests that the new stress functions have smaller errors than the polynomial stress model with the same number of coefficients, guarantee material stability, and are more conservative about the stress values for strains outside of the testing range.

Correlation Effects of Near-Field Seismic Components in Circular Metro Tunnels: A Case Study—Tehran Metro Tunnels

Seismic evaluation of underground structures such as tunnels requires nonlinear dynamic analysis, due to the complex dynamic behavior of soil and the interaction of soil and structure. Simulation of the seismic response of the structure using nonlinear dynamic analysis is possible only with proper acceleration time history. Considering the vertical component of the earthquake (such as near-fault earthquakes) on the site is an important factor to achieve real structural responses. In the current study, soil-tunnel system has been modeled in ABAQUS software, considering Mohr–Coulomb nonlinear model for soil and concrete damage plasticity model for tunnel lining. In order to investigate the effect of seismic components correlation under different combinations of loads on the acceleration, axial force, and maximum shear force in tunnel lining, nonlinear dynamic analysis has been performed under four near-field earthquakes with different horizontal and vertical component ratios, considering 15 load combinations. The results show that increasing the vertical-horizontal component ratio has an insignificant effect on the maximum horizontal acceleration experienced by the tunnel lining. Also, the results of axial forces and shear forces indicate that increasing the ratio of vertical to horizontal components of the earthquake is the most effective factor on the axial force response.

Using model error in response history analysis to evaluate component calibration methods

SummaryThis research is part of a larger effort to better understand and quantify the epistemic model uncertainty in dynamic response‐history simulations. This paper focuses on how calibration methods influence model uncertainty. Structural models in earthquake engineering are typically built up from independently calibrated component models. During component calibration, engineers often use experimental component response under quasi‐static loading to find parameters that minimize the error in structural response under dynamic loading. Since the calibration and the simulation environments are different, if a calibration method wants to provide optimal parameters for simulation, it has to focus on features of the component response that are important from the perspective of global structural behavior. Relevance describes how efficiently a calibration method can focus on such important features. A framework of virtual experiments and a methodology is proposed to evaluate the influence of calibration relevance on model error in simulations. The evaluation is demonstrated through a case study with buckling‐restrained braced frames (BRBF). Two calibration methods are compared in the case study. The first, highly relevant calibration method is based on stiffness and hardening characteristics of braces; the second, less relevant calibration method is based on the axial force response of braces. The highly relevant calibration method consistently identified the preferable parameter sets. In contrast, the less relevant calibration method showed poor to mediocre performance. The framework and methodology presented here are not limited to BRBF. They have the potential to facilitate and systematize the improvement of component‐model calibration methods for any structural system.

Model establishment and response analysis of slope reinforced by frame with prestressed anchors under seismic considering the prestress

Based on the principles of soil dynamics and structural dynamics, a ground motion analysis model of a slope reinforced by a frame with prestressed anchors is established, and the dynamic response of the reinforced slope under horizontal earthquake action is obtained. In this paper, based on the horizontal strip method, the slope height is considered as an influencing factor, and the dynamic analysis model for soil pressure of the slope under earthquake action is developed. When establishing the ground motion analysis model of the reinforced structure, the model was based on the lumped mass method, considering the prestress of the anchors; a frame column is used as a calculation unit to form a concentrated mass string, an anchor is connected with the soil in the form of an elastic support, and prestress is applied to each anchor by a given initial design value. According to the assumed prerequisites proposed above, a structural power control balance equation is established. The axial force response of a prestressed anchor is solved by applying the soil dynamic pressure, prestress and seismic action to the frame structure. The soil pressure distribution characteristics of the reinforced slope system, the displacement response of the reinforcement structure, and the axial force response characteristics of the prestressed anchor can be approximated with this model. The model provides a basis for the seismic design of a slope reinforced by a frame with prestressed anchors.

Numerical Investigation on the excavation methods for Large Span Dome in Deep Buried Railway Station

Badaling Great Wall Station, excavated with drilling and blasting method, is the first underground railway station in China. The domeshaped distribution hall is of the maximum span within the entire station and is rare in underground transit projects. To find out an optimal excavation method, the sector method and the ring method are proposed and compared by threedimensional numerical simulation in this paper. The results are as follows: (1) Dome excavated by the modified ring method is of better shape with small and uniform convergence, when compared to the sector method. (2) For the modified ring method, the primary support can be closed in time under the protection of the reserved core rock. Hence, the structure performs well in restraining the surrounding rock from loosening, with larger bending moment and more uniform corresponding axial force response than that induced by the sector method. (3) The modified ring method is recommended for the large span dome. And the reserved core rock plays a beneficial role to support the surrounding rock, which helps to guarantee safety during construction. This research can make guidance for similar projects.

The Hybrid III Upper and Lower Neck Response in Compressive Loading Scenarios With Known Human Injury Outcomes

Objective: Physical biomechanical surrogates are critical for testing the efficacy of injury-mitigating safety strategies. The interpretation of measured Hybrid III neck loads in test scenarios resulting in compressive loading modes would be aided by a further understanding of the correlation between the mechanical responses in the Hybrid III neck and the probability of injury in the human cervical spine. The anthropomorphic test device (ATD) peak upper and lower neck responses were measured during dynamic compressive loading conditions comparable to those of postmortem human subject (PMHS) experiments. The peak ATD response could then be compared to the PMHS injury outcomes.Methods: A Hybrid III 50th percentile ATD head and neck assembly was tested under conditions matching those of male PMHS tests conducted on an inverted drop track. This includes variation in impact plate orientation (4 sagittal plane and 2 frontal plane orientations), impact plate surface friction, and ATD initial head/neck orientation. This unique matched data with known injury outcomes were used to evaluate existing ATD neck injury criteria.Results: The Hybrid III ATD head and neck assembly was found to be robust and repeatable under severe loading conditions. The initial axial force response of the ATD head and neck is very comparable to PMHS experiments up to the point of PMHS cervical column buckle or material failure. An ATD lower neck peak compressive force as low as 6,290 N was associated with an unstable orthopedic cervical injury in a PMHS under equivalent impact conditions. ATD upper neck peak compressive force associated with a 5% probability of unstable cervical orthopedic injury ranged from as low as 3,708 to 3,877 N depending on the initial ATD neck angle.Conclusions: The correlation between peak ATD compressive neck response and PMHS test outcome in the current study resulted in a relationship between axial load and injury probability consistent with the current Hybrid III injury assessment reference values. The results add to the current understanding of cervical injury probability based on ATD neck compressive loading in that it is the only known study, in addition to Mertz et al. (1978), formulated directly from ATD compressive loading scenarios with known human injury outcomes.

The comparison of soil-pile interaction and fixed base support for integral prestressed concrete box-girder bridge

This paper is to investigate the effect of soil-pile interaction for integral prestressed concrete box-girder bridge under low intensity earthquake. The soil-pile interaction was compared to fixed base support to see its effect. In this case study, one integral prestressed concrete box-girder bridge in Selangor, Malaysia had been chosen, that is, Kampung Sawah Bridge. To produce the low seismic loading, the ground response analysis had been conducted to produce three synthetic acceleration time histories loading. For soil-pile interaction, the p-y curves were determined by using LPILE program. The seismic analyses conducted were vibration analysis and nonlinear time history analysis. Free vibration analysis presented the periods and mode shapes of the structure while nonlinear time history analyses presented the maximum displacement at the top of pier and middle of deck and pier and deck forces response. It can be concluded that the soil-pile interaction support gives the longer period compared to fixed base support which almost differ about more than five times higher for the first mode. The displacement soil-pile interaction is higher compared to fixed base support; the increasing of displacement is more at transverse direction event for deck and pier. The all forces response from soil-pile interaction support is higher compared to fixed base support, except the axial force response of pier. Key words: Nonlinear time history, integral concrete box-girder bridge, soil-pile interaction, fixed base.

Long-term condition assessment of suspenders under traffic loads based on structural monitoring system: Application to the Tsing Ma Bridge

SUMMARY Structural health monitoring (SHM) system provides an efficient way to the diagnosis and prognosis of critical and large-scale civil infrastructures like long-span bridges. This paper presents a long-term condition assessment approach of suspenders in a cable-suspension bridge under in-service traffic loads based on structural monitoring technique. The traffic loads identified from a monitoring system, including both highway and railway traffic loads, and the finite element model of the bridge are employed to determine the axial force response of the suspender. The stochastic axial force response in the suspender is described by a filtered Poisson process, through which the maximum value distribution of axial forces in its design reference period can be derived using the Poisson Process theory. In this paper, the long-term deterioration process of steel wires in the suspender considers simultaneously the uniform and pitting corrosion and the corrosion fatigue induced by both cyclic loading and environmental attack. Such a stochastic and coupled corrosion fatigue process of steel wires is simulated using the Monte Carlo method, and the time-variant conditions of the suspender are subsequently assessed in a probabilistic way, such as crack depth, number of broken wires, ultimate strength, etc. In particular, two load conditions—the train loads alone and the combination of train load and road traffic load—are examined within this procedure in order to investigate their respective effects on the deterioration. By employing first-order reliability method, the reliability indexes of the suspender under the traffic loads are further estimated in terms of the safety under the extreme traffic load distribution in the design reference period and the serviceability specified in the design specification. The discussions of the life-cycle reliability indexes of the suspender provide guidance to the future decision making related to maintenance and replacement of suspenders, and it may also shed light on the long-term condition assessment of other structural members. Copyright © 2010 John Wiley & Sons, Ltd.

A New Biofidelic Sagittal Plane Surrogate Neck for Head-First Impacts

Objective: To evaluate a prototype sagittal plane surrogate neck model designed to provide a biofidelic response to head-first impacts with a straightened cervical posture. Methods: Published biomechanical studies were used in the design to define the range of motion (ROM) and stiffness in both flexion–extension rotation and axial compression. The neck was tested in a series of head-first impacts on a drop tower to investigate the temporal aspects of the kinetic axial force response for the head and neck. A separate series of flexion–extension tests was conducted in a spinal motion simulator to assess its ROM and bending stiffness. Results: In impacts with a 104 N axial preload, the surrogate head and neck displayed a bimodal response to force development in agreement with published studies of cadaveric head-first impacts. In bending without an axial preload, the neck had an ROM and bending stiffness representative of cadaveric human spines and it included a large neutral zone, but with the incremental addition of axial preload these metrics were somewhat reduced. Conclusions: The model appears suitable for studying the scenario of sagittal plane, aligned column impacts. Further design refinements are required to provide biofidelity in both sagittal bending and head-first impacts using a single level of axial preload. This would be necessary to study impact scenarios where considerable sagittal plane neck rotation occurs at impact. The model has identified some key concepts that must be considered for continued design and improvement of a dedicated dummy neck for head-first impacts.

The influence of viscosity on the strength of an axially strained pendular liquid bridge

Pendular liquid bridges between two relatively moving solid particles (dynamic bridges) occur extensively throughout the powder technology industry, with a typical example being binder granulation. By means of a sensitive linear voltage differential force tranducer, the influence of viscosity on the strength of an axially, periodically strained pendular bridge was investigated where bridge strength is defined as the maximum interparticle force developed during one complete sphere oscillation. The relative importance of the theoretically derived dimensionless groups governing bridge strength is experimentally established for systems exhibiting complete solid—liquid wettability. A simplified solution of dynamic bridge strength based on the superposition of lubrication theory and circular approximation is presented. For a small gap distance with sufficient bridge volume and in the limit of small Reynolds number, a good agreement between the experimental and present theoretical axial force response is observed, indicating the importance of the capillary number Ca in determining pendular bridge strength. The present quasi-static solution is zeroeth-order in Ca and gap distance, and is expected to break down with increasing local inertial effects. Such inertial effects are governed by a modified Bond number. In the limit of low Ca, they lead to an increase in bridge strength due to an added mass effect, whereas in the limit of high Ca, they lead to a reduced, shifted force response due to an insufficient rate of vorticity propagation. Under industrially relevant conditions, the strength of the dynamic bridge was observed to exceed the static by over an order of magnitude. Since a significant number of powder processes such as granulation are not static in nature, viscous interactions between particles should be considered whenever a liquid interstitial phase is present.

Dynamic Loading of Drillpipe During Tripping

Dynamic phenomena when a stand of drillpipe is run into the hole may result in pipe failure, either through exceeding the yield or through kicking the pipe off the slips. Two computer programs based on longitudinal wave propagation have been developed. Results are presented and recommendations are made.