Erosion Criteria Research Articles

Numerical failure analysis of a continuous reinforced concrete bridge under strong earthquakes using multi-scale models

Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional (3D) finite element (FE) model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete (RC) pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundings to the girders and different failure modes to the adjacent piers.

Numerical Simulation of Fragment Separation during Rock Cutting Using a 3D Dynamic Finite Element Analysis Code

To predict fragment separation during rock cutting, previous studies on rock cutting interactions using simulation approaches, experimental tests, and theoretical methods were considered in detail. This study used the numerical code LS-DYNA (3D) to numerically simulate fragment separation. In the simulations, a damage material model and erosion criteria were used for the base rock, and the conical pick was designated a rigid material. The conical pick moved at varying linear speeds to cut the fixed base rock. For a given linear speed of the conical pick, numerical studies were performed for various cutting depths and mechanical properties of rock. The numerical simulation results demonstrated that the cutting forces and sizes of the separated fragments increased significantly with increasing cutting depth, compressive strength, and elastic modulus of the base rock. A strong linear relationship was observed between the mean peak cutting forces obtained from the numerical, theoretical, and experimental studies with correlation coefficients of 0.698, 0.8111, 0.868, and 0.768. The simulation results also showed an exponential relationship between the specific energy and cutting depth and a linear relationship between the specific energy and compressive strength. Overall, LS-DYNA (3D) is effective and reliable for predicting the cutting performance of a conical pick.

Desertification risk assessment and management program

Risk assessment provides the possibility of planning and management to prevent and reduce the risk of desertification. The present study is aimed to assess the hazard and risk of desertification and to develop management programs in the semi-arid western regions of Golestan Province in Iran. Desertification rate was obtained using the Iranian model of desertification potential assessment. Since the rating system was considered for the indicators, data analyses were carried out according to the Mann-Whitney test. The risk of desertification was calculated based on hazard, elements at risk and vulnerability assessment maps. The intensity of desertification was estimated to be medium. Among the factors affecting desertification, agriculture by the weighted average of 3.22 had the highest effect, followed by soil, vegetation, water and wind erosion criteria by weighted averages of 2.45, 2.32, 2.15 and 1.6 respectively. Desertification risk assessment results also showed that about 78% of central and northern parts of the region, with the largest population and residential centers, surface and underground water resources, agriculture and horticulture, is confronted with a high to very high degree of risk. Management plans and control measures, based on risk values were presented in four activities (with two management priorities under critical and non-critical conditions). For the management program with the largest area. Control measures and strategies such as the establishment of halophytic and xerophytic plants, drainage networks, resilient facilities and infrastructure were proposed. Reducing the risk of desertification, could play a crucial role in the sustainable development of drylands and desert ecosystems.

Development of a risk-based multi-criteria approach for watershed prioritization with consideration of soil erosion alleviation (case study of Iran)

The classification of erosion-prone areas is a pre-requisite for providing an efficient watershed management as well as soil conservation. Thus, a practical decision support tool is required to assign priority weights to different related criteria. In this article, 13 effective soil erosion criteria have been used to prioritize different sub-watersheds in Arangeh watershed, Iran. The criteria have been classified in four groups of soil, geomorphology, topography and climate categories. The ranking outcomes of sub-watersheds via Modified Pacific Southwest Inter-Agency Committee method were compared with induced ordered weighted averaging (IOWA) model which considered hierarchy-based attitude and risk-based attitude (RBA) criteria. Copeland aggregation method was also applied as a benchmark for the comparison. Kendall’s Tau, a nonparametric stochastic test, investigated that RBA-based IOWA with fairly optimistic coefficient (α = 0.5) is the most conclusive ranking model because of its highest correlation coefficient which was about 0.9. Finally, the hierarchical clustering method classified sub-catchments. According to the results, four priority groups were identified based on vulnerability of sub-watersheds to soil erosion.

Numerical Modeling of Energy Absorption Behaviour of Aluminium Foam Cored Sandwich Panels with Different Fibre Reinforced Polymer (FRP) Composite Facesheet Skins

Sandwich structures based on Fibre Reinforced Polymer (FRP) facesheet skins bonded with low density aluminium foam core are increasing in use in aerospace and marine industries. These structures are very sensitive to high velocity impact during the service. Therefore, it is necessary to study the energy absorption of the structures to ensure the reliability and safety in use. Experimental investigation of these transient events is expensive and time-consuming, and nowadays the use of numerical approaches is on the increase. Hence, the purpose of this paper is to develop a numerical model of sandwich panels with aluminium foam as a core and Glass, Carbon and Kevlar Fibre Reinforced polymer composite as faceplate, subjected to high velocity impact using ABAQUS/Explicit. The influence of individual elements of the sandwich panel on the energy absorption of the structures subjected to high velocity impact loading was analysed. Selection of suitable constitutive models and erosion criterion for the damage were discussed. The numerical models were validated with experimental data obtained from the scientific literature. Good agreement was obtained between the simulations and the experimental results. The contribution of the face sheet, foam core on the impact behaviour was evaluated by the analysis of the residual velocity, ballistic limit, and damaged area.

Is Risk of Artificial Urethral Sphincter Cuff Erosion Higher in Patients with Penile Prosthesis?

IntroductionFrequently encountered morbidities after prostatectomy include stress urinary incontinence and erectile dysfunction. Patients with severe disease may undergo placement of both a penile prosthesis (PP) and an artificial urethral sphincter (AUS). AimWe hypothesized that concomitant PP may promote AUS cuff erosion by impaired corporal blood flow and/or direct pressure on the cuff. The aim of this study was to compare the rate of AUS cuff erosion in patients with and without a PP. MethodsWe reviewed 366 AUS operations at our tertiary center between 2007 and 2015 with a mean follow-up of 41 months (range 6–104). Included in the analysis were first-time AUS cuff erosions. Patients with recurrent erosions, AUS revisions, and iatrogenic erosions were excluded. In a separate analysis, we analyzed AUS explantations for all causes. Cohorts were compared by demographic information, preoperative characteristics, and rates of erosion and explantation. Main Outcome MeasuresErosion confirmed by cystourethroscopy and explantation of the AUS for all causes. ResultsAmong 366 AUS surgeries at a mean follow-up of 41 months, there were 248 (67.8%) AUS alone cases compared to 118 (32.2%) AUS and PP cases (AUS/PP). Sixty-two patients met exclusion criteria for first-time cuff erosion. Among 304 evaluable AUS patients, we found a significantly higher rate of erosion in the AUS/PP group (11/95, 11.6%) compared to the AUS alone group (9/209, 4.3%, P = .037). When examining explantations for all causes in the entire cohort (n = 366), we observed a significantly higher rate of device removal, (20/118, 17%) in the AUS/PP group compared to the AUS group (23/248, 9.2%, P = .044). ConclusionAUS/PP patients appear to have a higher risk of AUS cuff erosion and explantation compared to men with AUS alone.

Using a mixed DEM/FEM approach to model advanced damage of reinforced concrete under impact

Advanced damage behaviour of reinforced concrete is modelled using a mixed modelling approach, in which concrete is represented through the spherical-type discrete element model, whereas steel reinforcement is modelled by using beam-type finite elements. An original steel-concrete bond model developed and calibrated on pull-out tests is used to ensure transfer of forces between steel and con- crete. The proposed approach is applied to simulate soft and hard-type impacts on RC beams within a very complete modelling framework, thus allowing validating by comparison with experimental data the overall numerical approach developed. Reinforced concrete (RC) structures are widely used as shielding barriers to protect sensitive equipment of industrial facilities such as nuclear power plants. Those protective structures are devised to resist namely impacts of projectiles generated either by natural hazard phe- nomena such as tornados or by human induced events such as a deliberate airplane crash. Because of the extreme severity of such an accidental loading, assessment of the protective structures must go far beyond verification of the resistance to normal operating conditions: it is necessary to investigate the response of the structure until almost its complete failure to assess correctly its ultimate resistance capacity. While continuous approaches such as the finite element method (FEM) are suitable for the nonlinear analysis of structures before failure, they reach their limits when trying to describe macro cracking and fragmentation mechanisms. Even if it is possible to generate discontinu- ities in the standard FEM model by using the element erosion technique proposed by Belytschko and Lin (1) and implemented in most commercial crash codes such as LS-DYNA or ABAQUS Explicit, the numerical precision of the resolution algorithm becomes difficult to control during the advanced fragmentation process due to difficulties of mass and energy conservation and of contact treatment of newly created non-smooth surfaces. Furthermore, numerical results are strongly dependent on the erosion criterion used, which explains why the FEM simulations with activated erosion struggle to produce quantitatively realistic and predictive results in the presence of strong material discontinuities. The discrete element method (DEM) is a powerful alternative to FEM when advanced dam- age states and failure of concrete have to be studied. Indeed, DEM permits very easily the obtaining of realistic macro-crack patterns and material fragments due to its discontinuous

Mapa de aptidão do solo para a aplicação de lodo de esgoto: Bacia dos rios Piracicaba, Capivari e Jundiaí

Considering the technical and economic characteristics of the final disposal of sewage sludge, this paper sought to develop a land feasibility map for sewage sludge (biosolids) application in the watershed of the Piracicaba, Capivari and Jundiai (PCJ) Rivers. The PCJ watershed is located in the States of Sao Paulo and Minas Gerais, and is characterized by large urban areas, important industrial and agricultural areas, and steady population growth. Six restricted classes of soils to receive biosolid applications were considered. The criteria used were susceptibility to erosion, soil type, and restrictive criteria as protected areas, water courses and urban areas. The maps generated have shown that less than 30% of the soil of the PCJ watershed is suitable to biosolids application. Considering only the classes of restriction 0, 1 and 2, it was observed that the areas have great potential for biosolids application: 4,089.3 103 t TS year-1. The sugar cane crop and reforestation areas were considered a priority to receive applications among suitable areas. Suitable reforestation areas cover less than 0.15% of the area of the PCJ watershed, but can be useful for the treatment stations of the west region. The areas covered by sugar cane have an annual sewage sludge reception capacity of 2,582.7 103 t TS.

Numerical study of velocity distribution of fragments caused by explosion of a cylindrical cased charge

This paper presents a study of the velocity distribution of fragments caused by explosion of a cased charge. Available formulas usually predict a uniform fragments velocity at the middle part of the cylinder and only few sources recommend evaluation of a non-uniform velocity distribution. According to few, yet available, experimental results, the latter distribution is more realistic. Three numerical simulation techniques were used in the work described here, to simulate the velocity distribution of a cased cylindrical explosive charge: 2D simulations, 3D simulations and 3D simulations using the SPH method. Additional simulation of a pre-formed fragmentation was also investigated. The failure and erosion criteria of the casing material have been examined in the numerical analyses. The results of the numerical simulations have been verified against reported experimental data, which indicated a non-uniform velocity distribution along the cylinder axis. Overall, there was a good agreement between the 2D, 3D, 3D-SPH methods and the experimental measurements, including the distribution of the lower velocity values near the cylinder edges. Conclusions of this study include characteristics of the velocity distribution and observations regarding advantages and disadvantages of the techniques that were used. It is shown that the velocity distribution can be described by a normalized ‘shape function’, which depends on the casing length-to-diameter ratio. Finally, it is noted that the mass distribution, which has been out of the scope of this study, should be investigated as well.

Physically-sound simulation of low-velocity impact on fiber reinforced laminates

A high-fidelity virtual tool for the numerical simulation of low-velocity impact damage in unidirectional composite laminates is proposed. A continuum material model for the simulation of intraply damage phenomena is implemented in a numerical scheme as a user subroutine of the commercially available Abaqus finite element package. Delaminations are simulated using of cohesive surfaces. The use of structured meshes, aligned with fiber directions allows the physically-sound simulation of matrix cracks parallel to fiber directions, and their interaction with the development of delaminations. The implementation of element erosion criteria and the application of intraply and interlaminar friction allow for the simulation of fiber splits and their entanglement, which in turn results in permanent indentation in the impacted laminate. It is shown that this simulation strategy gives sound results for impact energies bellow and above the Barely Visible Impact Damage threshold, up to laminate perforation conditions.

An effective numerical simulation methodology to predict the impact response of pre-stressed concrete members

This study provides an effective analysis procedure to perform a failure analysis of pre-stressed concrete members subjected to lateral impact loads using the finite element analysis (FEA) program, LS-DYNA. The proposed numerical method includes modeling techniques which define pre-stressing force, concrete constitutive relationship, strain rates, and element erosion criteria. In the FEA model presented in this study, the prestress force is applied by temperature-induced shrinkage in prestressing stands. The stress initialization of concrete to a steady-state condition is completed by using the ‘DYNAMIC_RELAXATION’ option, prior to performing a transient impact analysis. Available experimental data from a beam impact test are used for validation of the proposed methodology. Furthermore, the sensitivity of modeling parameters is examined. It is also shown that the proposed method can be used to predict the response of axially loaded columns for an accidentally applied lateral impact loads, resulting from a car or vessel crash.

Ballistic Impact: A Comparative Case Study Using Lagrangian Method with Erosion Criterion and SPH

The ballistic simulation attempted in this work is among the most difficult as both the projectile and the target experience significant deformations. Traditionally these simulations have been performed using a Lagrangian approach, i.e. a deformable mesh with large mesh deformations. There are three often used techniques when studying ballistic problems with the Lagrangian method: remeshing (generally not available for 3D hexahedra meshes), the 'pilot hole' technique and material erosion. Because these techniques imply element removal, in order to allow the calculation to continue, the Lagrangian method lacks a physical basis. Moreover, no general guidance exists for selecting one of the three techniques mentioned before. The Smoothed Particle Hydrodynamic method as implemented in the commercial code LS-DYNA has been used in this paper to solve the problem of the impact between different caliber projectiles and various types of metal targets. The results are compared to those produced by dynamic analysis using conventional finite element methods with material erosion as implemented in LS-DYNA.

Litter decomposition rates of green manure as affected by soil erosion, transport and deposition processes, and the implications for the soil carbon balance of a rainfed olive grove under a dry Mediterranean climate

Soil erosion by water promotes the distribution of soil organic carbon (SOC) and nutrients within the landscape. Moreover, soil redistribution may have a large impact on litter decomposition dynamics. There is a current lack of information about the role of soil erosion in the SOC balance of sloping agricultural fields because its magnitude and direction depend on the dominant horizontal and vertical C fluxes at the different landform (eroding, transport and depositional) positions within the hillslope. Therefore, the significance of these lateral fluxes in the local C balance has to be assessed when interactions with vertical C fluxes (e.g., litter decay) are also taken into account. An experiment was designed to increase our understanding of the role of different phases of the soil erosion process in litter decomposition and the resulting impact on the soil C balance of a rain-fed olive grove under a dry Mediterranean climate, in which two or three high intensity-low frequency rainfall events are responsible for the majority of the annual soil erosion. To accomplish this, four replicate plots were installed at three different landform positions, according to erosion criteria (eroding, transport and depositional sites), and two litter types (Avena sativa L. or Vicia sativa L.) with contrasting initial litter chemistry (high C:N, low C:N) were deployed in the middle of the summer season, before the expected occurrence of rainfall events in the experimental area. Two successive rainfall events led to pronounced patterns of erosion and associated processes of soil transport and deposition, accounting for 99% of total soil loss in the experimental area and leading to the burial of most of the litterbags located at the depositional positions. The results indicate that soil erosion (lateral movement and soil mixing) may be an important mechanism of litter decomposition, as litter mass loss rates were related closely to the amount of soil infiltrated/deposited within the litterbags for both litter types, decay rates at depositional sites being about three-fold higher than at eroding and transport sites. Our results also indicate that soil mobilisation by erosion has significant impacts on C dynamics, causing lateral and vertical fluxes of C similar in magnitude to those induced by changes in land use or management. According to our estimates, soil C losses driven by land-use change could be compensated after 20 years of green manure incorporation in this rainfed Mediterranean olive grove.

철근콘크리트 건물의 폭발하중에 의한 연쇄붕괴 해석을 위한 침식 기준

In this paper, reference erosion criteria value suitable for progressive collapse analysis of RC structure due to blast load is proposed. Erosion is fundamentally a numerical technique to overcome the problems such as large numerical errors or abrupt termination of analysis and previous study has been suggested value for blast analysis. But concrete has different stress-strain curve according to strain rate. Consequently, the erosion criteria for the realistic progressive collapse simulation were suggested by comparing experiment results and numerical analysis results. Finally, the real progressive collapse of Oklahoma Federal Building was analyzed by using the median value of two values. And as a result, the analysis result is the actual collapse of the well described.

Mild steel plates impacted by hard projectiles

The evaluation of ballistic resistance of steel targets is important due to its direct application to the safety of defense protective structures such as bunkers for military personnel, shelters for arms and explosives as well as safety of nuclear containment against missile impact. Experiments on penetration of 23mm hard projectiles into mild steel plates were performed for 500mm square plates with 30, 50, 60, and 150mm total thicknesses. Results for ballistic limits obtained from existing empirical and analytical relations are compared with those from experiments. In addition, numerical simulations to predict the experimental results were made. Erosion (cell removal) criteria were established in order to realize simulation. Effect of the erosion strain value for which cells are removed on the prediction of penetration into steel plates was investigated. The numerical results show that erosion strain value has a significant effect on the prediction of perforation into steel plates.

철근콘크리트 부재의 폭발해석을 위한 침식 기준

Erosion is fundamentally a numerical technique to overcome the problems such as large numerical errors or abrupt termination of analysis which are associated with the excessive element distortions in finite element analysis. In this paper, erosion was utilized to represent cracks and failures in the reinforced concrete structures subjected to blast or impact loads. The erosion criteria for the realistic blast simulation were suggested by comparing experiment results and numerical analysis results. Instantaneous effective strain of 0.1 was proposed as a reference erosion criteria value to show the closest failure shape to the blast experiments of reinforced concrete beams and slabs.

Defining Erosion Limit for Concrete

Numerical simulation is usually used for predicting the response of concrete and fiber reinforced concrete structures to blast or impact loads. Depending on both charge weight and standoff distance, blast loads can cause fracture and spalling of concrete. In order to numerically reproduce these effects, an erosion model can be used to remove from the calculation the elements that have reached certain criteria. This erosion model represents a numerical tool to avoid great distortion of Lagrange meshes. For this reason, its application to the simulation of a physical phenomenon requires the calibration with experimental results. A review of different erosion criteria and limits used by different authors to simulate concrete under blast loads is presented in this paper. Some application examples and comparisons with experimental results are developed to show the effect of erosion limit on damage results and the dependence on the materials properties, mesh size and scaled distance.

Derivation of a representative piping resistance parameter based on random field modelling of erosion paths

The piping mechanism is a dangerous failure mechanism for dikes and other flood protection structures in the world. A dike fails due to piping in case a head difference causes a water flow below the dike that, in case the flow is strong enough, causes the soil particles to erode. The progressing erosion ultimately results in the collapse of the dike. The grain size d 70 (determining piping resistance) is highly variable in space. The resistance of a dike stretch with respect to piping is not determined by the smallest value of d 70 in the sand layer that is susceptible to piping but by the largest d 70 in the erosion path (d 70,mech). The ultimate goal of this paper is to find the relation between (measured) point variability of d 70, which follows from collected samples, and the ‘mechanism variability’ d 70,mech, which follows from an analysis of erosion paths. Based on this relation, a new representative design value of d 70 can be derived. The spatial variability in d 70 is modelled with random field simulations. A model is developed that captures the formation of an erosion path in a generated d 70 random field, using an erosion criterion which combines the representative grain size d 70 and groundwater flow velocity near the tip of the backward developing erosion path. The model captures the search for the weakest path under flow influence. By applying the model to multiple random field realisations and to various assumed scales of fluctuation of d 70, the distribution of d 70,mech is obtained for various scales of fluctuation. The main outcome of the new model is that the smaller the scale of fluctuation, the larger the characteristic value of d 70,mech, whereas smaller characteristic values may be found for larger scales of fluctuation. This has some important implications for the design of dikes with respect to piping. If a detailed analysis shows a small scale of fluctuation of d 70, a larger representative design value of d 70 may be used, based on the distribution of d 70,mech. Hence, this may result in significant smaller dike (or berm) designs and lower dike construction costs.

OP0132 Validation of the 2010 ACR/EULAR classification criteria for rheumatoid arthritis in the very early arthritis community-based (VERA) cohort: Slight improvement after excluding erosion criterion

BackgroundTo validate the ACR/EULAR criteria by comparison with the 1987 ACR criteria for RA, in an independent community-based very early arthritis cohort (VErA).MethodsVErA cohort was community-based recruited and conservatively treated...

Impact modeling of foam cored sandwich plates with ductile or brittle faceplates

This paper reports numerical results of low velocity impact on open-face sandwich plates with an impactor of 2.65kg mass hitting with 6.7m/s velocity. The numerical simulation is done using 3D finite element models in LS-DYNA. The sandwich plates used for the present work have a core made of commercial aluminum alloy foam (Alporas) with faceplates made of either ductile aluminum (Al) or brittle carbon fiber reinforced plastic (CFRP). Selection of suitable constitutive models and erosion criterion for the failure analysis is investigated. A simplified analytical model for the peak load prediction under punch-through failure mode is presented. Numerically predicted contact force versus time, energy absorbed versus time along with the failure modes are compared with the experimental measurements and observations. Within experimental scatter, there is a good agreement between the numerical predictions and experimental measurements. Further more, the analytically predicted peak load values are in excellent agreement with the experimental measurements.