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Background: Biomechanical research on the lumbar intervertebral disc (IVD) provides valuable information for the diagnosis, treatment, and prevention of related diseases, and has received increasing attention. Using bibliometric methods and visualization techniques, this study investigates for the first time the research status and development trends in this field, with the aim of providing guidance and support for subsequent research.Methods: The Science Citation Index Expanded (SCI-Expanded) within the Web of Science Core Collection (WoSCC) database was used as the data source to select literature published from 2003 to 2022 related to biomechanical research on lumbar IVD. VOSviewer 1.6.19 and CiteSpace 6.2.R2 visualization software, as well as the online analysis platform of literature metrology, were utilized to generate scientific knowledge maps for visual display and data analysis.Results: The United States is the most productive country in this field, with the Ulm University making the largest contribution. Wilke HJ is both the most prolific author and one of the highly cited authors, while Adams MA is the most cited author. Spine, J Biomech, Eur Spine J, Spine J, and Clin Biomech are not only the journals with the highest number of publications, but also highly cited journals. The main research topics in this field include constructing and validating three-dimensional (3D) finite element model (FEM) of lumbar spine, measuring intradiscal pressure, exploring the biomechanical effects and related risk factors of lumbar disc degeneration, studying the mechanical responses to different torque load combinations, and classifying lumbar disc degeneration based on magnetic resonance images (MRI), which are also the hot research themes in recent years.Conclusion: This study systematically reviews the knowledge system and development trends in the field of biomechanics of lumbar IVD, providing valuable references for further research. [ABSTRACT FROM AUTHOR]

Of the 604,485 bridges in the United States, approximately 21% are culverts having a span of 6 m (20 ft) or greater. The load rating of typical bridges presents numerous challenges. Developing load ratings for non-typical structures, such as buried arch-shaped culverts is more complex because of the culverts' unique geometric configuration and their interaction with soil media. This paper proposes an alternative analytical method for load rating in-service reinforced concrete (RC) arch culverts that overcomes the limitations of the widely used elastic frame concept while being straightforward to implement. The proposed analytical method uses two-dimensional finite element models of the arch structure and surrounding soil media. The finite element model was first validated against experimental tests on a full-scale RC arch culvert, subjected to simulated live loads. The validated FE model was used in load rating analysis of 21 RC arch culverts with large fills. It was found that for arch culverts with fills exceeding 2.43 m (8 ft.), the controlling actions are bending moments at the crown and haunch. For culverts with fills greater than 3.05 m (10 ft.), live load effects become negligible. A revised rating formula is proposed for culverts with this characteristic. [ABSTRACT FROM AUTHOR]

NASA's development of new concepts for the Crew Exploration Vehicle Orion presents many similar challenges to those worked in the 1960s during the Apollo programme. However, with improved modelling capabilities, new challenges arise. For example, the use of the commercial code LS-DYNA, although widely used and accepted in the technical community, often involves high-dimensional, time-consuming and computationally intensive simulations. Because of the computational cost, these tools are often used to evaluate specific conditions and are rarely used for statistical analysis. This paper discusses an approach to capture what is learned from a limited number of LS-DYNA simulations to develop models that allow users to conduct interpolation of solutions at a fraction of the computational time. In this approach, response surface models are used to predict the system time responses to a water landing as a function of capsule speed, direction, attitude, water speed and water direction. Furthermore, these models can also be used to ascertain the adequacy of the design in terms of probability measures. This paper presents a description of the LS-DYNA model, a brief summary of the response surface techniques, the analysis of variance approach used in the sensitivity studies, equations used to estimate impact parameters, results showing conditions that might cause injuries and concluding remarks. [ABSTRACT FROM AUTHOR]

In an effort to improve existing two-dimensional (2D) total-strain-based reinforced concrete membrane models, a rational, but highly simplified, smeared bond-slip model was developed. The new model divides a 2D element into bonded and slip regions in the direction perpendicular to the tensile crack orientation. It is essentially a friction model that evaluates maximum frictional stress in a frictional block between the concrete and steel reinforcement. This paper suggests that observed tension stiffening and crack closing behaviors are found to be more complex than the behaviors that existing models are able to represent, particularly under cyclic loading. The proposed model is capable of modeling these behaviors and concrete and steel reinforcement compatibility, including prediction of the crack strains under cyclic loading. The proposed model is validated with cyclic panel test results available in the literature. This paper presents a framework to include smeared bond-slip behavior for 2D total-strain-based models. [ABSTRACT FROM AUTHOR]

In this paper, flexural behavior of horizontally curved prestressed (posttensioned) box bridges is studied by using three-dimensional and refined finite-element modeling and analysis. Bridge length, section geometry, and material properties are the same in all the models, while angle of curvature varies from 0 to 90°. The results of analysis show that in curved bridges, stress distribution is significantly different in comparison to straight bridges. Also, the level of stresses at some locations of section width is considerably high. It is proposed to vary the distribution of the prestressing tendons across section width in order to optimize the bridge capacity. Results show that by proper redistribution of prestressing in section width, significant reduction in resultant stress is possible. [ABSTRACT FROM AUTHOR]

Heat curving is extensively used for fabricating structural steel girders for bridges. Current American Association of State Highway and Transportation Officials (AASHTO) specifications limit usage to Grade 345 steel (F[sub y]=50 ksi), ruling out Grade 485 (F[sub y]=70 ksi) high performance steel (HPS). This paper presents results of a three-dimensional finite-element analysis to assess the applicability of existing AASHTO provisions for HPS 485W sections. The finite-element package NASTRAN was used to conduct the analysis and the model calibrated against experimental data obtained from full-scale tests conducted previously by U.S. Steel Corporation. Comparisons include curvatures, lateral deformations, and residual stresses. The calibrated model was used to predict the performance of an identical HPS girder subjected to the same heat/cool cycles. The three-dimensional analysis predicted smaller curvatures as compared with Grade 250 (F[sub y]=36 ksi) or Grade 345 (F[sub y]=50 ksi) steel. Comparable curvatures could be obtained by using higher temperatures. [ABSTRACT FROM AUTHOR]

Recent severe ice storms across the United States severely damaged trees resulting in extensive electrical power outages. Furthermore, trees and branches can fall on nearby roads, blocking traffic flow and reducing the safety of drivers. In this study, trees subjected to ice loads were analyzed using the finite element method and Monte Carlo simulation to develop analytical fragility curves. Two-dimensional, fractal trees were constructed with randomly generated geometric and mechanical parameters for four deciduous tree species: Acer saccharum, Tilia americana, Fagus grandifolia, and Quercus alba. Two load case scenarios were considered – with and without the effects of leaves – which were then subjected to varying ice accumulation thicknesses. The resulting fragility curves suggest that leaves have a substantial impact on tree branch damage under ice loads, which is significant because of the increase in unseasonably early ice storms due to climate change. [ABSTRACT FROM AUTHOR]

The remap phase in arbitrary Lagrangian-Eulerian (ALE) hydrodynamics involves the transfer of field quantities defined on a post-Lagrangian mesh to some new mesh, usually generated by a mesh optimization algorithm. This problem is often posed in terms of transporting (or advecting) some state variable from the old mesh to the new mesh over a fictitious time interval. It is imperative that this remap process be monotonic, that is, not generate any new extrema in the field variables. It is well known that the only linear methods that are guaranteed to be monotonic for such problems are first-order accurate; however, much work has been performed in developing non-linear methods, which blend both high and low (first) order solutions to achieve monotonicity and preserve high-order accuracy when the field is sufficiently smooth. In this paper, we present a set of methods for enforcing monotonicity targeting high-order discontinuous Galerkin methods for advection equations in the context of high-order curvilinear ALE hydrodynamics. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

• An overview of determination of fracture toughness from small punch test is given. • A micro-mechanical model given by Gurson is introduced to predict fracture toughness from small punch test. • Verifications are summarized from three high level institutes. The predicted J IC with that from standard fracture toughness tests are in a good agreement. The main tasks of the small punch (SP) technique are to derive standard material properties from a limited amount of material, including strength/toughness, creep and fatigue behaviour etc. The complicated problem of determining fracture toughness poses significant difficulties. Although many methods have been put forward to increase the prediction accuracy, no satisfactory methods are available yet. Recently, the so-called "Local approach" has been introduced to determine ductile fracture from the small punch test by means of a micro-mechanical model introduced by Gurson and modified by Needleman and Tvergaard. By using the observed load-deflection curve from the small punch test, reverse finite element analysis is performed to identify both the material plastic property (σ-ε curve) and the damage parameters of the Gurson model. With these material parameters known, a standard fracture toughness (CT) specimen is simulated by finite element analyses, from which the J- integral and the crack extension can be estimated. A J-R resistance curve can be created by multiple specimens with different load-line-displacements, and the fracture toughness J IC can be determined according to ASTM E 1820-17. In order to verify this new approach, the standard uniaxial test, the small punch tests and the standard fracture toughness tests are needed with the same material. Up to now, only a few of these kinds of experimental verification are available. In this paper, an overview on the existing methods of determination of fracture toughness from small punch test is given, and the "Local approach" for small punch test is addressed. Verifications are summarized from three high level institutes, including MMT in the Czech Republic, JRC Petten in the Netherlands and EPRI in the USA. The predicted J IC with that from standard fracture toughness tests are compared. A good agreement is found and shows that the "Local approach" is capable of predicting fracture toughness from small punch tests. The prediction accuracy by "Local approach" is better than existing methods. Further work is needed as available tests are still limited. [ABSTRACT FROM AUTHOR]

• A splitting resistance equation was proposed for highly prestressed UHPC girders. Ultra-high performance concrete (UHPC) has gained popularity gradually because of its superior mechanical properties, including high compressive and tensile strengths, and exceptional durability. Many researchers have explored the possibility of using long, precast prestressed UHPC girders in buildings and bridges. To do so, the girders generally require a large number of prestressing strands, which causes concern about potential cracking in the end zones at prestress release. Currently, there are no specifications or codes on end zone designs for precast prestressed UHPC girders in the United States. Thus, this paper presents an analytical study that explores highly prestressed UHPC girders' end zone behavior. Finite element analyses were conducted to analyze the end zones of a series of UHPC girders, including one 889-mm-deep and two 813-mm-deep I-girders, and the analysis results were validated with test data. Additional finite element models were developed for other girders with heights of 1,829 mm and 2,743 mm using various reinforcement details. Bursting stress variations in the reinforcement and UHPC were reported based upon the analytical and test results. An equation for splitting resistance attributable to the reinforcement and UHPC was proposed for highly prestressed girders. [ABSTRACT FROM AUTHOR]

In this paper, we present a highly efficient approach for numerically solving the Black–Scholes equation in order to price European and American basket options. Therefore, hardware features of contemporary high performance computer architectures such as non-uniform memory access and hardware-threading are exploited by a hybrid parallelization using MPI and OpenMP which is able to drastically reduce the computing time. In this way, we achieve very good speed-ups and are able to price baskets with up to six underlyings. Our approach is based on a sparse grid discretization with finite elements and makes use of a sophisticated adaption. The resulting linear system is solved by a conjugate gradient method that uses a parallel operator for applying the system matrix implicitly. Since we exploit all levels of the operator's parallelism, we are able to benefit from the compute power of more than 100 cores. Several numerical examples as well as an analysis of the performance for different computer architectures are provided. [ABSTRACT FROM PUBLISHER]

This paper deals with the efficient valuation of American options. We adopt Heston's approach for a model of stochastic volatility, leading to a generalized Black–Scholes equation called Heston's equation. Together with appropriate boundary conditions, this can be formulated as a parabolic boundary value problem with a free boundary, the optimal exercise price of the option. For its efficient numerical solution, we employ, among other multiscale methods, a monotone multigrid method based on linear finite elements in space and display corresponding numerical experiments. [ABSTRACT FROM PUBLISHER]

American option problems under regime-switching model are considered in this paper. The conjectures in [H. Yang, A numerical analysis of American options with regime switching, J. Sci. Comput. 44 (2010), pp. 69–91] about the position of early exercise prices are proved, which generalize the results in [F. Yi, American put option with regime-switching volatility (finite time horizon) – Variational inequality approach, Math. Methods. Appl. Sci. 31 (2008), pp. 1461–1477] by allowing the interest rates to be different in two states. A front-fixing finite element method for the free boundary problems is proposed and implemented. Its stability is established under reasonable assumptions. Numerical results are given to examine the rate of convergence of our method and compare it with the usual finite element method. [ABSTRACT FROM PUBLISHER]

The United States ITER Project Office (USIPO) is responsible for fabrication of the Central Solenoid (CS) for International Thermonuclear Experimental Reactor (ITER). The CS Insert (CSI) project should provide verification of the conductor performance in relevant conditions of temperature, field, currents and mechanical strain. The USIPO will build the CSI that will be tested at the Central Solenoid Model Coil (CSMC) Test Facility at JAEA, Naka, Japan. This paper presents three-dimensional mathematical model of CSI based on the design. Simulations were performed in order to verify structural integrity and compliance with the Japanese High Gas Pressure Safety Law. Numerical simulations lead to the design of the CSI that produced a required strain levels during operation on the superconductor cable, while simultaneously satisfy the ITER magnet structural design criteria. [ABSTRACT FROM PUBLISHER]

The objective of this paper is to provide a modeling and analysis guide that can be used in determining the stress and displacement behaviors of an aircraft nose gear during landing. The paper outlines the modeling and analysis of the nose gear of an aircraft using finite element analysis. The nose gear was first modeled using computer-aided design software and then imported into finite element software. The external forces were determined analytically and the interactions between components were carefully modeled using contact analysis. The tire was modeled using the eye-bar theory. The results obtained in this work are consistent with the Federal Aviation Administration's recommendations for physical testing. [ABSTRACT FROM AUTHOR]

Precast segmental construction of bridges can accelerate construction and minimize the cost of medium span bridges in environmentally sensitive and difficult to access locations. Despite these benefits, the use of precast segmental bridges in seismic regions of the United States remains limited. A main obstacle to their use is concern regarding the seismic response of segment joints. Recent experimental research programs studied the seismic performance of segmental superstructures. However, an estimate of the seismic response of full-scale segmental bridges to real earthquake records remains unknown. This paper presents a segment joint modeling approach and is an important first step toward accurately estimating the seismic response of superstructure segment joints to input ground motions. The approach is a compromise between the detailed and computationally intensive continuum mechanics based finite element approach and a simple approach that models the joints with rotational springs. The approach considers the nonlinear tendon-grout slip response and was validated with data from large-scale experiments. Numerous modeling sensitivity studies were performed and recommendations for implementation in full-scale models are presented. [ABSTRACT FROM AUTHOR]

An asphalt plug joint (APJ) is a type of expansion joint providing quick, easy, and cheap installation along with good surface flatness. However, APJs are known to suffer from premature failure, and their behavior, especially under thermal movement, has not yet been fully established. In this paper, the behavior of a typical APJ subjected to thermal and traffic loads is examined through a series of finite element analyzes employing a temperature-dependent viscoplastic material model. The material parameters are calibrated by using previously published test data, and the model is validated by comparing simulated responses to APJ test data. The developed models are then used to investigate stress and strain distributions, vulnerable locations to cracking failure, and local demands at those locations when a prototype APJ is subjected to various loading and temperature conditions. Sensitivity studies are also conducted to quantify the effect of debonding the bottom of the APJ and loading rate. The model results shed light about APJ response under traffic and thermal loading and provide new, fundamental information that can be used to improve the durability of APJs. For example, the simulation results suggest that intentionally debonding the interface between the gap plate and the APJ is a practical and low cost solution to mitigate the risk of premature APJ failure. [ABSTRACT FROM AUTHOR]

This paper illustrates a procedure to calculate the response of a tethered spherical aerostat to gusts, including the effect of structural nonlinearity and accounting for some of the fluid-structure interaction between the aerostat and tether line. The procedure developed and presented here is based on a full three-dimensional dynamic finite element model, with aerodynamic loads calculated from the relative velocity between a time-varying input airflow and resulting structural velocities. Exact solutions for the static response and a simplified dynamic model, both developed to validate the results of the procedure illustrated in this paper, are also derived and described in detail. The dynamic responses to gusts are compared with the equivalent steady-state solution to assess the approximations of the static solutions. Particular emphasis is placed on the output rotation of the aerostats to quantify disturbances on the pointing stability produced by gusts. [ABSTRACT FROM AUTHOR]

The development of a robust and reliable material model for fabrics used to prevent fan blade-out events in propulsion engines has significant importance in the design of fan-containment systems. Currently, Kevlar is the only fabric approved by the Federal Aviation Administration to be used in fan-containment systems. However, very little work has been done in building a mechanistic-based material behavior model, especially one that can be used to quantify the behavior of Kevlar when subjected to high-velocity projectiles. Experimental static and high strain rate tensile tests have been conducted at Arizona State University to obtain the material properties of Kevlar fabric. In this paper we discuss the development and verification of a constitutive model for dry fabrics for use in an explicit finite-element program. Results from laboratory tests such as tension tests including high-strain rate tests, picture frame shear tests, and friction tests yield most of the material properties needed to define a constitutive model. The material model is incorporated in the LS-DYNA commercial program as a user-defined subroutine. The validation of the model is carried out by numerically simulating actual ballistic tests conducted at NASA-GRC and fan blade out tests conducted at Honeywell Aerospace (Propulsion Engines). [ABSTRACT FROM AUTHOR]

Abstract: High strength woven fabrics are ideal candidate materials for use in structural systems where high energy absorption is required. One of the more widely used applications for woven fabrics is in propulsion engine containment systems. In this first part of a two-part paper, details of the experiments to characterize the behavior of dry fabrics including Kevlar® and Zylon® are presented. The experimental program to characterize the behavior of 1420 Denier Kevlar® 49 17×17, 500 Denier Zylon® AS 35×35, and 1500 Denier Zylon® 17×17 are discussed. The primary objective is to use the experimental results in the development of a constitutive model that can be used in an explicit finite element analysis program. These include Tension Tests in both the warp and fill directions of the fabric, Trellising Shear Tests and Friction Tests between fabric layers. The results from these tests provide the basis for development of the constitutive model – relating stresses to strains, characterizing failure and interaction between fabric layers. In addition to these basic material tests, tests on systems built with fabric wraps were also conducted. Ballistic tests of containment wraps subjected to a high velocity projectile were carried out at NASA-Glenn Research Center. While these tests provide a comparison between the energy absorbing characteristics of the three fabrics, they also provide benchmark results to validate the developed finite element methodology discussed in the second part of this paper. [Copyright &y& Elsevier]

This paper introduces a simplified method, known as Henry’s method, for the calculation of distribution factors of the live load moment. Using the simplified method, the live load effects are equally distributed in all beams, including interior and exterior beams. This method has been used in Tennessee for nearly four decades. It offers advantages in simplicity of calculation and flexibility in application. To carefully examine the simplified method, 24 actual bridges of six different types of superstructures were selected for the study. The distribution factors of actual bridges using Henry’s method were compared with the ones from the AASHTO LRFD, the AASHTO standard, and finite-element analysis. In the comparison study, the effects of bridge superstructure types and key parameters that significantly affected the calculation of distribution factors are discussed. Based on the results of the comparison and evaluation, a modified Henry’s method was proposed by introducing modification factors to Henry’s method. With proper modification, the simplified method can be used to determine reasonable and reliable distribution factors of the live load moment. [ABSTRACT FROM AUTHOR]

This first part of a two-part paper on the John A. Roebling suspension bridge (1867) across the Ohio River is an analytical investigation, whereas Part II focuses on the experimental investigation of the bridge. The primary objectives of the investigation are to assess the bridge’s load-carrying capacity and compare this capacity with current standards of safety. Dynamics-based evaluation is used, which requires combining finite-element bridge analysis and field testing. A 3D finite-element model is developed to represent the bridge and to establish its deformed equilibrium configuration due to dead loading. Starting from the deformed configuration, a modal analysis is performed to provide the frequencies and mode shapes. Transverse vibration modes dominate the low-frequency response. It is demonstrated that cable stress stiffening plays an important role in both the static and dynamic responses of the bridge. Inclusion of large deflection behavior is shown to have a limited effect on the member forces and bridge deflections. Parametric studies are performed using the developed finite-element model. The outcome of the investigation is to provide structural information that will assist in the preservation of the historic John A. Roebling suspension bridge, though the developed methodology could be applied to a wide range of cable-supported bridges. [ABSTRACT FROM AUTHOR]

This paper presents the current state of the art of nonlinear analysis of steel-concrete composite structures. The focus is on frame elements, which are computationally faster than continuum finite element models. First, section models are presented, with a review of resultant and fiber models and a discussion of possible practical applications. The presentation of frame elements follows. Models with lumped and distributed inelasticity, as well as models with perfect and partial connections are covered. Rigid and partially restrained joints are then reviewed and discussed at length. A discussion of the analysis of structural walls completes the presentation of the models. Modeling applications to the analysis of composite frames are also presented. This state-of-the-art review focuses on developments that have stemmed from the recently completed National Science Foundation sponsored U.S.-Japan program on composite and hybrid structures. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for the evaluation of the seismic damage in steel moment frame buildings. The rotational capacities, of typical connections of a building in the Los Angeles area, which suffered extensive damage during the Northridge earthquake, were determined using stress triaxiality as an indicator for fracture. The rotational demands of the same connections were obtained from a three-dimensional finite element analysis of the building model. Comparisons of the rotational demands at several locations in the building to the rotational capacities determined by the stress triaxiality analysis showed that fracture of steel moment connections of the building are governed by the triaxiality of stresses. Based on a number of moment connections analyzed, the paper suggests a moment capacity equation for the pre-Northridge welded steel moment connections taking into account the fracture incidence due to stress triaxiality effect. The moment capacity of such connections as dictated by stress triaxiality compared favorably to FEMA-350 requirements. [Copyright &y& Elsevier]

Design, fabrication and erection of industrial steel storage rack systems can nowadays take place at different locations, potentially separated by thousands of kilometers. Consequently, manufacturing engineers need to understand the main code provisions adopted in the country where the rack will be in-service. Frequently, design is carried out in accordance with the European (EU) or United States (US) rack codes, which are the most commonly adopted standards for industrial storage systems. As appraisal of the key differences on structural performance associated with the different code provisions in term of storage performance, a previous study of the Authors was focused on storage pallet racks comprised of bi-symmetric cross-section uprights (vertical members). Now, attention is paid to racks with mono-symmetric uprights, typically influenced by relevant warping effects, which are traditionally neglected by rack provisions and, as a consequence, by manufacturing engineers. The design approaches already considered and compared for bi-symmetric uprights now appear to be inadequate and have been necessarily improved, as suggested by the Authors, including at least the contribution due to the bimoment acting along mono-symmetric uprights. Research outcomes, which are discussed in the paper, are related to a parametric analysis on several racks differing for configurations, geometry of components and degree of rotational stiffness of joints. The associated results regarding the four EU and two US considered alternatives are presented and compared directly to each other to allow for a concrete appraisal of the most relevant differences between the admitted design approaches. In order to highlight the importance of warping effects, which can be evaluated only by means of refined finite element (FE) analysis software, design has been undertaken using also the more traditional FE beam formulation implemented in the commercial analysis packages most frequently used in manufacturing offices. Finally, Appendix A presents a complete design example to be used as benchmark, where all the discussed design options are applied and compared to each other. [ABSTRACT FROM AUTHOR]

Approximately 11% of bridges in the United States are categorized as structurally deficient and there is a marked need of more accurately evaluating true structural capacity. Structural Health Monitoring (SHM) systems can provide a timely indication of the need for maintenance, repair, rehabilitation and replacement of bridges and can greatly improve the apportionment and management of limited resources. This paper presents an Automated Ambient Traffic (AAT) approach for determining load rating of bridges monitored by the BECAS SHM system under ambient traffic. The AAT approach was developed through a process integration of truck detection, bridge model calibration, and bridge load rating: (1) the quasi-static bridge strain response and the characteristics of associated trucks are collected; (2) multiple trucks are randomly sampled from a historic Weigh-In-Motion (WIM) database; and (3) for each combination of strain response and truck selection, an Finite Element (FE) model is calibrated and used to calculate a load rating. Sampling strategies were discussed for appropriately quantifying the influence of uncertainties of truck characteristics on the calibration and load rating results. To demonstrate this approach, a sample three-span, five-girder, and two-lane steel girder/concrete deck (I-80) bridge was utilized. A load rating of the I-80 Bridge using the Traditional Known Truck (TKT) approach was performed to provide benchmark results. The results of the calibration and load rating using the AAT approach were derived using three different sampling strategies and compared to those using the TKT approach. The sampling strategy, selecting strain response with a spectrum of higher peak girder strains, associated trucks with a spectrum of higher gross vehicle weights, and two truck events on south and north lanes respectively for a calibration, resulted in the best calibration and load rating results. It was concluded that the AAT approach using the BECAS SHM system is a reliable method for continuously estimating the load carrying capacity of bridges. [ABSTRACT FROM AUTHOR]

In the context of green aviation, as an internationally recognized solution, hydrogen energy is lauded as the "ultimate energy source of the 21st century", with zero emissions at the source. Developed economies with aviation industries, such as Europe and the United States, have announced hydrogen energy aviation development plans successively. The study and development of high-energy hydrogen fuel cells and hydrogen energy power systems have become some of the future aviation research focal points. As a crucial component of hydrogen energy storage and delivery, the design and development of a safe, lightweight, and efficient hydrogen storage structure have drawn increasing consideration. Using a hydrogen-powered Unmanned Aerial Vehicle (UAV) as the subject of this article, the crash characteristics of the UAV's hydrogen storage structure are investigated in detail. The main research findings are summarized as follows: (1) A series of crash characteristics analyses of the hydrogen storage structure of a hydrogen-powered UAV were conducted, and the Finite Element Analysis (FEA) response of the structure under different impact angles, internal pressures, and impact speeds was obtained and analyzed. (2) When the deformation of the hydrogen storage structure exceeds 50 mm, and the strain exceeds 0.8, an initial crack will appear at this part of the hydrogen storage structure. The emergency release valve should respond immediately to release the gas inside the tank to avoid further damage. (3) Impact angle and initial internal pressure are the main factors affecting the formation of initial cracks. [ABSTRACT FROM AUTHOR]

In this study, a full-scale test on the bending performance of concrete sandwich laminated floor slabs with integrated thermal and sound insulation was carried out, and the effects of different reinforcement ratios on the bending performance of concrete sandwich laminated floor slabs were investigated as well as the variation law of the failure modes, characteristic loads, load-mid span deflection, load-rebar strain curves, and anti-slip performance. The results indicate that the concrete sandwich laminated floor slabs present typical bending failure characteristics. According to bending failure characteristics, the damage process can be divided into three stages, i.e., elasticity, cracking, and failure. The bearing capacity significantly increases with the increase in reinforcement ratio. The normal service, yield, and ultimate loads of bearing capacity of the floor slabs with a larger reinforcement ratio increase by 54.55%, 52.94%, and 46.46%, respectively. Moreover, the mid-span deflection decreases significantly with the increase in reinforcement ratio, and the cracking expansion is also delayed. Before cracking, the prefabricated layer and laminated layer can realize load bearing together, and the floor slab is in a state of complete interaction. When the floor slabs reach the ultimate state, the superimposed surface produces a sliding effect, and the floor slab is in a state of partial interaction. The finite element analysis software ABAQUS (with the version number of ABAQUS 2020, the chief creator of David Hibbitt, and the sourced location of the United States) was used to perform nonlinear numerical simulation. The test results accord well with the simulation results, which verifies the correctness of the finite element model. Based on finite element simulation, the influence of post-cast concrete strength on the ultimate load can be ignored. [ABSTRACT FROM AUTHOR]

Abstract: Breakup model is the key area of space debris environment modeling. NASA standard breakup model is currently the most widely used for general-purpose. It is a statistical model found based on space surveillance data and a few ground-based test data. NASA model takes the mass, impact velocity magnitude for input and provides the fragment size, area-to-mass ratio, velocity magnitude distributions for output. A more precise approach for spacecraft disintegration fragment analysis is presented in this paper. This approach is based on hypervelocity impact dynamics and takes the shape, material, internal structure and impact location etc. of spacecraft and impactor, which might greatly affect the fragment distribution, into consideration. The approach is a combination of finite element and particle methods, entitled finite element reconstruction (FER). By reconstructing elements from the particle debris cloud, reliable individual fragments are identified. Fragment distribution is generated with undirected graph conversion and connected component analysis. Ground-based test from literature is introduced for verification. In the simulation satellite targets and impactors are modeled in detail including the shape, material, internal structure and so on. FER output includes the total number of fragments and the mass, size and velocity vector of each fragment. The reported fragment distribution of FER shows good agreement with the test, and has good accuracy for small fragments. [Copyright &y& Elsevier]

Abstract: Recently, a new suite of twelve benchmark problems for adaptive finite element methods (FEM) was published at the US National Institute for Standards and Technology (NIST). These benchmark problems come with exact solutions, and they exhibit all typical difficulties associated with elliptic problems including singularities, steep internal layers, anisotropy, and oscillations. In this paper we solve these benchmark problems using the open source library Hermes (http://hpfem.org). All these results are reproducible—they are part of the Git repository of the open source Hermes project, and the reader can experiment with them by himself/herself. Instructions for this are provided. We hope that authors of other adaptive FEM codes will make their results for these test problems available in a reproducible fashion as well. [Copyright &y& Elsevier]

As bridge conditions in the United States continue to deteriorate, rapid bridge replacement procedures are needed. Decked precast prestressed concrete (DPPC) girders are used for rapid bridge construction because the bridge deck is precast with the girders eliminating the need for a cast-in-place slab. One of the concerns with using DPPC girders as a bridge construction option is the durability of the longitudinal joints between girders. The objectives of this paper were to propose a method to use a spring element modeling procedure for representing welded steel connector assemblies between adjacent girders in DPPC girder bridges, perform a preliminary study of bridge perfornlance under multiple loading scenarios and bridge configurations, and discuss model flexibility for accommodating future field data for model verification. The spring elements have potential to represent the contribution of joint grout materials by altering the spring stiffness. [ABSTRACT FROM AUTHOR]

With the use of probabilistic and risk-based methods by industry it is often necessary to estimate and input values for the reliability of inspection methods typically in terms of probability of detection (POD). In many cases this has been based on expert judgement. In recent years a more structured approach has developed using multi-parameter POD models. POD models have been around since the early 1990s. Inspection reliability has featured recently in a number of important legal cases, which has focused attention on the factors affecting reliability and approaches used to estimate reliability in practical circumstances. This paper will review the development of models for POD in Europe and the USA in the last decade and the current state-of-the-art in inspection reliability modelling by ESR Technology and others. Examples will include models for composite inspection developed for the European Space Agency and a specific model-based and simulator ‘POD Generator’ approach developed in the offshore industry through the HOIS joint industry project. This allows the POD for corrosion mapping and radiography inspections to be estimated and parametric studies undertaken to estimate the reliability of commercial inspection equipment in real situations. Other model-based approaches will be assessed. These include model-assisted POD approaches developed in the US aerospace industry, use of transfer functions to extend hit/miss and â versus a POD trial data to new applications, simulated POD trials, the addition of POD modules to established 3D and CAD inspection models and the use of NDT simulators. There are analogies now for POD modelling for NDT methods to the use of finite element analysis for stress analysis. In the early 1990s, FE analysis was treated with some suspicion and normal practice was to carry out expensive large-scale component tests. Nowadays, FE analysis is widely accepted and large-scale testing is carried out as the exception to validate the FE models. The use of model-assisted and model-derived methods to derive POD data has gained significant acceptance and arguably is becoming the preferred method to generate POD values, with POD trials providing model validation. Empirical methods developed in NNDTC to correct POD data for human and environmental effects are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of a full-scale load test and a 3D finite element analysis on a two-tier, 5m high, geosynthetic reinforced segmental retaining wall (GR-SRW) subjected to a surcharge load aiming at investigating the response of the GR-SRW to various levels of surcharge load. The results of the load test at working stress condition revealed that the GR-SRW''s response to the test load was well within the serviceability limits, and that the currently available design guideline tends to over-estimate the surcharge load-induced reinforcement forces. The predicted results for the surcharge load well in excess of the test load indicated that the surcharge load-induced reinforcement strains exponentially decrease with depth, showing a good agreement in qualitative terms with that assumed in the FHWA design guideline. The predicted wall deformation at the allowable bearing pressure of 200kPa was within the serviceability level demonstrating an excellent load carrying capacity of the GR-SRW. Design implications and the findings from this study are discussed. [Copyright &y& Elsevier]

The current paper describes a simple and yet comprehensive lumped-parameter model (LPM) for simulating the National Highway Traffic Safety Administration (NHTSA) sideimpact safety tests for passenger vehicles. The LPM includes new lumped masses, not previously reported in a single multibody model, for key vehicle side-structure systems identified with the help of an energy-based study conducted using explicit finite element analysis of two passenger vehicles. In addition to the vehicle side structure, lumped masses for the NHTSA side-impact barrier and 'rest of vehicle', the latter implying the mass of the vehicle minus the combined mass of the side-structure subsystems considered in the LPM, have been incorporated so that the total mass of the system corresponds to that of an actual vehicle-barrier system in a NHTSA side-impact test (Lateral Impact New Car Assessment Program (LINCAP) or FMVSS 214). The lumped masses are interconnected with elastic-plastic springs. A unique feature of the present model is the inclusion of two lumped side-impact dummies for obtaining predictions of the front and rear (thoracic trauma index (TTI)). The validity of the present LPM is established by performing LS-DYNA-based LINCAP simulations of two realworld vehicles, namely the Dodge Neon and Dodge Intrepid, and obtaining a reasonably good correlation of the computed structural and occupant responses as well as TTI (front and rear) with the corresponding test results reported by the NHTSA. [ABSTRACT FROM AUTHOR]

The present paper is a summary of the R&D results obtained through SSC SR-1446 project sponsored by Ship Structure Committee together with Alcan Marine, France, and Lloyd's Register Educational Trust, UK. It is recognized that the use of ultimate limit state (ULS) design method in addition to more conventional structural design standards will help make possible to move high-speed vessels to open-ocean transiting of large high-speed vessels, which is what the US Navy is certainly trying to do. The aim of the project is to investigate the collapse characteristics of aluminum stiffened plate structures used for marine applications by mechanical testing, together with nonlinear finite element analysis (FEA). Fabrication-related initial imperfections significantly affect the ULS behavior, and thus it is of vital importance to identify the features of initial imperfections prior to ULS computations. In the present study, a statistical database of fabrication- related initial imperfectionson welded aluminum stiffened plate structures is also developed. The database and insights developed will be useful for design and building of welded aluminum high-speed oceangoing vessel structures. [ABSTRACT FROM AUTHOR]

A probabilistic fatigue assessment methodology for riveted railway bridges is presented. The methodology is applied to a typical, short-span, riveted U.K. railway bridge under historical and present day train loading. On the loading side, the problem is randomized through dynamic amplification and traffic volume; on the resistance side, the S-N curves and the cumulative damage model are treated probabilistically. Model uncertainty is represented by the ratio between actual and calculated stresses, the latter obtained through finite element analysis. Annual response spectra for a fatigue-critical connection are developed through Monte Carlo simulation, which show that there is a continual and accelerating increase in the mean stress range experienced by the connection with time. S-N curves proposed in United States and United Kingdom codes are used in combination with Miner’s rule, to estimate the remaining fatigue life of the connection for different target failure probabilities. Parametric studies revealed that fatigue life estimates exhibit the highest sensitivity to detail classification, to S-N predictions in the region of high endurances, and to model uncertainty. This highlights the importance of field monitoring for old bridges approaching the end of their useful life. [ABSTRACT FROM AUTHOR]

Integral abutment bridges are often a preferred bridge type for moderate spans throughout the United States. However, design methods and construction details vary from state to state. Variations between states are noted in the methods employed to accommodate deformations in the piles. The significance of these differences was evaluated through a finite-element study. The effects of backfill properties and soil restraint on piles were evaluated with regard to bridge distortions and maximum moment realized in the piles. Results show that bridge expansion is predominantly affected by backfill conditions, whereas contraction is influenced by pile restraint conditions. Pile moments are minimized when denser backfill and lower pile restraint are provided. The influence of abutment soil-structure spring modeling assumptions is addressed. Models were calibrated to the reference bridge at Orange-Wendell, Mass, which has been instrumented and data collected for 4 years. [ABSTRACT FROM AUTHOR]

NASA's effort to develop a large payload, high altitude, long-duration balloon, the ultralong duration balloon, focuses on a pumpkin shape superpressure design. It has been observed that a pumpkin balloon may be unable to pressurize into the desired cyclically symmetric equilibrium configuration, settling into a distorted, undesired state instead. Hoop stress considerations in the pumpkin design lead to choosing the lowest possible bulge radius, whereas robust deployment is favored by a large bulge radius. Mechanical locking may be a contributing factor in the formation of undesired equilibria. Long term success of the pumpkin balloon for NASA requires a thorough understanding of the phenomenon of multiple stable equilibria. This paper uses the notion of stability to classify balloon designs. When we applied our finite element model to a balloon based on the NASA Phase IV-A pumpkin design, we found the fully inflated/fully deployed strained equilibrium float configuration was unstable. To demonstrate our approach for exploring the stability of constant bulge radius designs and their sensitivity to parameter changes we carry out a number of parametric studies. We focus on analytical studies, but we also compare our results with flight data whenever possible. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we consider a free boundary problem which arises in the pricing of an American call option. The free boundary represents the optimal exercise price as a function of time before a maturity date. We are developing a parameter estimation technique to obtain both the optimal exercise curve of an American call option and its price. For the numerical solution of a forward problem, a time marching finite element method is adopted. Numerical experiment shows the convergence property of the approximation scheme. [Copyright &y& Elsevier]

Abstract: Unlined reinforced concrete shear walls are often used as ‘tertiary boundaries’ in the United States Department of Energy (DOE) to house dangerous gases. An unanticipated event, such as an earthquake, may cause gases stored inside the walls to disperse into the environment resulting in excess pollution. To address this concern, in this paper, a methodology to numerically predict the gas leakage rate through these shear walls under lateral loading conditions is proposed. This methodology involves finite element and flow rate analysis. Strain distributions are obtained from the finite element analysis, and then used to simulate the crack characteristics on the concrete specimen. The flow rate through the damaged concrete specimen is then estimated using flow rate formulas available from the literature. Results from an experimental specimen are used to evaluate the methodology, and particularly its robustness in the flow rate estimation. [Copyright &y& Elsevier]

Modern numerical software packages have potential as development tools for research and educational purposes. One such package is FEMLAB® , a finite element based environment with a user-defined, flexible equation solver. This paper describes the implementation and use of a vector Helmholtz solver in FEMLAB® for educational purposes. [ABSTRACT FROM AUTHOR]

Piping elbows under bending are vulnerable to cracking at the crown. Hence it is necessary to estimate the crack driving force. This paper presents a closed form expression for the plastic J-integral for axially through-wall cracked, long radius elbows under opening bending moment. The equation is derived, based on a large number of finite element analyses covering a wide range of geometries. The non-linear finite element analyses were performed using WARP3D software and accounted for geometric and material non-linearity. The material was assumed to follow the Ramberg–Osgood law with a wide range of strain hardening exponent (n=2,3,5,7 and 10). [Copyright &y& Elsevier]

Presents a study which considered the retirement of land from agricultural production as a means of reducing the volume of subsurface drainage generated in the Western San Joaquin Valley, California. Conflict between food production and ecosystem health echoes; Conceptual model of land retirement; Characteristics of deforming finite element (DFE) model; Assumptions in DFE transect model.

Model building codes and standards in the United States find their bases in a probabilistic model of glass load resistance (LR). In general, architectural flat glass design predicated on these model building codes and standards is restricted to rectangular glass lites continuously supported along one, two, three, or four sides. When a design professional wishes to use glass with an odd shape (i.e., a nonrectangular shape), design procedures in the model building codes and standards regress to a maximum stress approach. A maximum stress approach to design represents a much different philosophy than does the probabilistic approach. When compared to the probabilistic approach, designs based upon a value of maximum allowable stress may result in much less efficient design. Therefore, the need exists for a design approach for odd-shaped glass lites that has a probabilistic basis for glass load resistance. The primary analysis tools available to engineers today are based on the finite-element method and can be applied to a wide range of different glass lite geometries. The authors developed a nonlinear finite-element model and applied the glass failure prediction model (GFPM) to the nonlinear finite-element model output to determine probability of breakage for combinations of selected flat odd-shaped glass lite geometries and loads. The authors compared the LR of the odd-shaped glass lites to the LR of flat glass lites with the LR of rectangular glass lites having the smallest dimensions so that they would encompass the odd-shaped lites. The authors also compared the maximum principal stresses determined for the flat odd-shaped glass lites (loaded with a pressure equal to the LR of the flat odd-shaped glass lites) from the nonlinear finite-element model to recommended values of maximum allowable stress from model building codes and standards. [ABSTRACT FROM AUTHOR]

The effect of fluctuating discharge from Glen Canyon Dam on downstream sandbars is of significant concern to dam operators, environmentalists, and the public. In this contribution, the observations of seepage-related erosion caused by fluctuations in dam discharge are presented. A finite-element model embracing Biot's coupled stress–pore water pressure theory is used to study seepage-induced slope failures of sandbars in the Grand Canyon. In addition, a simple model based on seepage parallel to slope in an infinite, homogeneous, cohesionless soil was used to determine the limiting stable seepage slope. In this paper, it is shown that this limiting stable seepage slope becomes a predefined failure plane. Sand deposited above this stable seepage slope will eventually fail along the predefined plane from gravitational forces, high pore-water pressure and seepage forces. Field data from an instrumented sandbar in the Grand Canyon subjected to the fluctuating discharge from Glen Canyon Dam are compared with the predictions from the simple model, the finite-element model, and conventional slope-stability analyses. [ABSTRACT FROM AUTHOR]

Architectural glazing designers in the United States and many other parts of the world use prescriptive methods to determine the load resistance (LR) of glazing and glazing constructions in buildings based on a probabilistic theory of glass strength. This theory is known as the glass failure prediction model (GFPM). The GFPM relates the probability of breakage to surface stress magnitude induced by lateral uniform loads acting on the glass as well as the duration of stress. Glass design charts in US model building codes and standards use a nonlinear finite difference model developed during the early 1980s as the basis to determine surface stresses induced by lateral loads. The primary analysis tools available to engineers today are based on the finite-element method and not on the finite difference method. The authors developed a nonlinear finite-element model and applied the GFPM to the nonlinear finite-element model output to determine the probability of breakage for selected glass lite geometry and load combinations. The results of their analyses compare favorably with values in model building codes and standards. This model will facilitate architectural glazing designers when they must design glazing for fenestrations that charts in model building codes and standards currently do not address. [ABSTRACT FROM AUTHOR]

Typical ASME Section XI subcritical cracking analyses assume an idealized flaw shape driven by stress intensity factors developed for semi-elliptical shaped flaws. Recent advanced finite element analyses (AFEA) conducted by both the United States Nuclear Regulatory Commission (U.S.NRC) and the nuclear industry for long circumferential indications found in the pressurizer nozzle dissimilar metal welds at the Wolf Creek power plant suggest that the semi-elliptical flaw assumption may be overly conservative in some cases. The AFEA methodology that was developed allowed the progression of a planar flaw subjected to typical stress corrosion cracking (SCC)-type growth laws by calculating stress intensity factors at every nodal point along the crack front, and incrementally advancing the crack front in a more natural manner. Typically, crack growth analyses increment the semielliptical flaw by considering only the stress intensity factor at the deepest and surface locations along the crack front, while keeping the flaw shape semi-elliptical. In this paper, a brief background to the AFEA methodology and the analyses conducted in the Wolf Creek effort will be discussed. In addition, the predicted behavior of surface cracks under normal operating conditions (plus welding residual stress) using AFEA will be investigated and compared with the semi-elliptical assumption. Conclusions on the observation of when semi-elliptical flaw assumptions are appropriate will be made. These observations will add insight into the conservatism of using an idealized flaw shape assumption. [ABSTRACT FROM AUTHOR]

In engineering practice, it is generally accepted that most of components are subjected to multiaxial stress‐strain state. To analyse this complicated loading state, different types of specimens of 2A12 (2124 in the United States) aluminium alloy were tested under multiaxial loading conditions and a new multiaxial fatigue analysis method for the state of three‐dimensional stress and strain is proposed. Elastic‐plastic finite element method (FEM) and a proposed vector computing method are used to describe the loading state at the critical point of specimen, by which the parameter ΓT is calculated at the new defined subcritical plane to consider the effect of additional cyclic hardening. Meanwhile, the principal equivalent strain is still calculated at the traditional critical plane. The new damage parameter is composed of different process parameters, by which the dynamic path of strain state, including loading environments and material properties, are fully considered in one loading cycle. According to experimental verifications with 2A12 aluminium alloy, the results show that the proposed method shows satisfactory, accurate, and reliable results for multiaxial fatigue life prediction in the state of three‐dimensional stress and strain. [ABSTRACT FROM AUTHOR]

Featured Application: This study is mainly aimed at the difficulty of welding hidden welds of the overlapped K-joints in engineering, and strengthening the grouting concrete in the chord to compensate for this defect. Furthermore, it can provide a technical reference for optimizing construction technology. The K-joints can be popularized and applied in civil engineering, hydraulic engineering, and even the military field in steel structures, bridge structures and airport terminals. Due to the insufficient radial stiffness of the steel tube, the cracking of the weld and the plastic deformation of the string often occur under the cyclic loading of the hollow section pipe joint. In order to avoid such a failure, the overlapped K-joints were strengthened by pouring different concrete into the chords. Furthermore, to explore the detailed effect of filling different concrete in a chord on the hysteretic behavior of the overlapped K-joints, six full-scale specimens were fabricated by two forms, which included the circular chord and braces, the square chord and circular braces, and the low cyclic loading tests, which were carried out. The failure modes, hysteretic curves and skeleton curves of the joints were obtained, and the bearing capacity, ductility and energy dissipation of the joints were evaluated quantitatively. The results showed that plastic failure occurs on the surface of the chord of the joints without filling concrete, while the failure mode of the joints filled with concrete in the chords was the tensile failure of the chords at the weld of the brace toe, and the compressive braces had a certain buckling deformation; The strengthening measures of concrete filled with chord can effectively improve the mechanical properties of the K-joints, the delay of the plastic deformation of the chord, and improve the bearing capacity of the K-joints. Contrarily, the ductility coefficient and the energy dissipation ratio of K-joints decreased with the concrete filled in the chord. The hysteretic behavior of the K-joints with a circular chord and brace was slightly better than that of the K-joints with a square chord and circular brace, and the hysteretic behavior of the K-joints strengthened with fly ash concrete, which was better than that of the K-joints strengthened with ordinary concrete. The results of ANSYS (a large general finite element analysis software developed by ANSYS Company in the United States) analysis agreed well with the experimental results. [ABSTRACT FROM AUTHOR]