Analysis of tapered and cylindrical piles under blast loading

PurposeThe purpose of this paper is to present a probabilistic assessment and verify the effectiveness of seismic improvement schemes against earthquake, blast and progressive collapse. The probabilistic analysis is performed by taking into account the uncertainties in loading such as planar configuration and amplitude of the blast loading. A standard Monte Carlo (MC) simulation method is employed to generate various concepts of the uncertain parameters within the problem. For a given concept, various local dynamic analyses are performed within a certain range of distance, in order to quantify and locate the damage induced by impact wave on structural elements. In the next step, a limit state analysis is performed in order to investigate whether a progressive collapse mechanism forms under the acting loads or not.Design/methodology/approach( | ) and ( | ) are blast fragility and seismic fragility, respectively; ( ) and ( ) are annual occurrence rate of earthquake and blast, respectively. The purpose of the current study is to calculate for the primary structure as well as the retrofitted structure. Annual occurrence rate of earthquake can be calculated by using probability seismic hazard analysis for the site of interest, where the structure is located. In this paper, blast fragility and seismic fragility are defined rather differently; in other words, seismic fragility is defined as the probability of structural collapse given a specified level of seismic intensity whereas blast fragility is defined as the probability of collapse given that a significant blast event takes place. Both blast and earthquake loading conditions involve the activation of energy dissipation mechanism and, as a consequence, both can be resisted employing ductility enhancing techniques, such as column wrapping or jacketing and steel bracing.FindingsThe current paper aims to present a probabilistic assessment of progressive collapse under blast and earthquake loads. Non-dependent and incompatible events are considered to obtain a general rate of collapse. Finally, probabilistic collapse rate was obtained for a moment frame before and after modifying with convergent steel brace (CBF). The purpose of doing so is to investigate whether seismic improvement schemes can reduce collapse risk of different critical events or not.Originality/valueObjective of the present work is to present a methodology for calculating the annual risk of collapse for a civil structure subjected to both seismic and blast loads, using a bi-hazard approach. Given that a blast event takes place, the probability of progressive collapse is calculated using a MC simulation procedure. The simulation procedure implements an efficient non-linear limit state analysis, formulated and solved as a linear programming problem. The probability of collapse caused by an earthquake event can be calculated by integrating the seismic fragility of the structure and the seismic hazard for the site.

Fluid-Structure Interaction Analysis Using Finite Element Methods for IRWST of Reactor Building

Cold spray is a rapidly developing coating technology for depositing materials in the solid state. In this deposition process, the spray particles are accelerated to a high velocity by a high-speed gas flow, and then form a dense and high quality coating due to plastic deformation of particles impinged upon the solid surface of substrate. 2D and 3D modelling of particle impacting behaviours in cold spray deposition process by using ABAQUS/Explicit was conducted for four couples of materials (i.e. impacting particle/impacted substrate): copper/aluminium, aluminium/copper, copper/copper, and aluminium/aluminium. A systematic analysis of a single impact was carried out considering different parameters, such as the initial impact velocity, initial temperature and contact angle, which affect the deposition process and subsequently the mechanical properties of coating. Three numerical methods have been evaluated and their performances are discussed for various simulation settings: (i) modelling in a Lagrangian reference frame; (ii) modelling using adaptive remeshing in an Arbitrary Lagrangian Eulerian (ALE) reference frame; and (iii), modelling in a CEL reference frame. It is found that the Coupled Eulerian Lagrangian (CEL) method has more advantages to simulate the large deformation of materials, and is also more efficient to prevent the excessive distortion of the mesh. A comparison between simulation results and experimental data from the literature was performed. Nevertheless, the CEL method is implicitly isothermal for ABAQUS v6.10, whereas the modelling in the classical Lagrangian reference frame does include coupled thermo-mechanical effects with a local increase of the temperature near the interface — due to friction — and for the highly plastically deformed elements — due to the heat dissipation linked to plasticity. A local rise of temperature at the impact surface may also be observed for oblique impacts. Finally a first attempt to simulate the deposition of several particles is made with a 3D CEL model, resulting in the creation of porosity at the interface between particles.

A gas explosion in an offshore platform may result in loss of life, pollution, and critical damage to facilities. Safety critical structural elements of these facilities have to be designed to withstand high explosion loads. The present study discusses methodologies for explosion risk assessment (ERA) of safety critical structural elements and introduces a coupled Eulerian–Lagrangian (CEL) method to improve the accuracy of the dynamic structural response under explosion loading. The design accidental load is defined by explosion risk analyses in terms of drag pressure, differential pressure, and overpressure. In current practice, an explosion pressure-time history is simplified into a triangular shape and uniformly applied to the surface of the impacted structures. This approach cannot account for the interaction between elastic waves (normally solved by the Lagrangian method) in the structure and compression waves (normally solved by the Eulerian method) in air. The CEL method which accounts for fluid–structure interaction has been experimentally validated and leads to more realistic predictions of the dynamic response of structures when compared to other analysis methods. The plastic strains derived from the CEL analysis can be approximately 50% lower than those predicted by Lagrangian analysis. Therefore, significant potential weight reduction can be achieved using the CEL method for gas explosion analysis.

Some structures, both military and civilian, might experience explosive loads during their service life. Owing to high uncertainties in blast load predictions and structural parameters, accurate assessment of the performances of structures under explosion loads is a challenging task. For example, a number of experimental studies using fiber-reinforced plastic (FRP) strengthening of RC structures have been reported in the literature. Most of these studies demonstrate that FRP strengthening is effective in increasing the blast load–carrying capacities of RC structures. However, significant variations in the effectiveness of FRP strengthening have also been observed owing to the large uncertainties in blast loading, RC and FRP material properties, and workmanship in preparing the test specimens and conducting experimental tests. Very few studies that take into consideration these uncertainties in analyzing the effectiveness of FRP strengthening of RC structures on blast loading resistance can be found in the literature. This study performs a reliability analysis to assess the performance of RC columns with or without FRP strengthening in resisting blast loads. Statistical variations of blast loading predictions derived in a previous study are adopted in this study. To define structural performance, pressure-impulse (P-I) curves with a damage criterion on the basis of axial load-carrying capacity that were developed in previous studies for RC columns without strengthening or with FRP strip, FRP wrap, or both FRP strip and wrap strengthening are used. Considering the uncertainties in blast loading predictions and RC column and FRP material properties and dimensions, limit-state functions corresponding to different damage levels of RC columns with or without FRP strengthening are formulated. The statistical variations of blast loading, RC column dimension, longitudinal and transverse reinforcement ratio, and concrete, steel, and FRP material strength and FRP thickness are considered. The failure probabilities of RC columns corresponding to different damage levels with or without FRP strengthening are calculated. The effectiveness of FRP strengthening on the RC column’s blast loading resistance capacities is discussed. The importance of considering the random fluctuations on blast loading and RC column parameters in assessing the blast loading effect on RC columns is demonstrated. A structural system reliability analysis is also carried out to examine the probability of structural collapse as a result of blast loading applied to the front of an example two-span multistory RC frame. The results obtained in this study demonstrate the effectiveness of FRP strengthening on structure protection and can also be used to assess RC structure performance under blast loadings.

The subject matter of this study is to use numerical simulation methods to study the influence of the temperature of particles and substrates on the post-deposition coating during the multi-particle deposition process of cold spray. The goal is to study the temperature of Al6061 particles and the temperature of the substrate, which are factors that have a greater impact on the deposited coating, and to observe the shape of the coating and the temperature distribution of the cross-section of the substrate after deposition. The tasks to be solved are as follows: use Python scripts to model multi-particles, generate and randomly assign positions according to particle size distribution in the Euler domain, and establish a cold spray multi-particle collision model to simulate the process of cold spray deposition. The following methods were used: The influence of temperature and substrate temperature on the deposited coating was studied through a single variable method; the Coupled Eulerian Lagrangian (CEL) method was used to simulate the collision process of cold-sprayed Al6061 multi-particles. The following results were obtained: changing the temperature of Al6061 particles has a more obvious control effect on the porosity of the deposited coating; after particles of different temperatures impact the constant-temperature substrate, the high-temperature area on the surface of the substrate is mainly located at the junction of pits; after the particle temperature reaches 650K, the coating changes after deposition are no longer significant, indicating an optimal temperature range for Al6061 particle deposition; increasing the temperature of the substrate can increase the depth of particle deposition on the substrate; at the same time, it serves as a reference basis for further using the CEL method to predict the porosity of the Al6061 coating. Conclusions. The scientific novelty of the results obtained is as follows: 1) powder preheating can effectively reduce the porosity of Al6061 coating; 2) the CEL method has good robustness and is used to simulate cold spray multi-particle deposition to monitor the porosity of the coating, which cannot be achieved by the SPH and ALE methods.

Subsea pipelines located in harbour areas and shipping lanes are subjected to potential damage due to impact of anchor dragging. Such pipelines are usually covered with rock berms for protection. Due to the high costs associated with the installation of offshore rock berms, there is a need to optimise the rock berm size such that the rock quantities are reduced while still providing adequate protection for the pipeline. Analysis of anchor dragging near a rock-covered pipeline involves quantifying the complex interaction between the anchor, the anchor chain, the soil and the pipeline-rock system. In the present study, Coupled Eulerian-Lagrangian (CEL) finite element method is used to simulate the complex soil deformation and flow during the anchor dragging, thereby providing better understanding of the underlying mechanisms of the problem. This paper presents results of CEL analyses of anchor dragging near a pipeline covered by rock berms of different sizes. The simulated trajectories of the anchor during the dragging are shown to be in good agreement with the experimental results of Gaudin et al. (2009). This shows the ability of the present method in giving more rigorous solutions and better predictions of rock berm protective capacities. This paper also illustrates the use of the present analysis for optimizing the rock berm design and hence enabling significant cost savings.

The simulation of large deformation problems in geotechnical engineering has gained increasing interest in recent years. This is partly due to new technologies and industry requirements (e.g. the installation of new foundations in the offshore industry), the improved availability of numerical methods that can handle large deformations and the overall improvement in computational hardware.

Impulsive blast sound from activity at DoD facilities, generated by artillery firing or ordnance, or demolition explosions, can cause structural blast damage or adverse community impact. This paper provides a detailed model, not widely available, for the probability of such damage starting with models for blast pressure loading and blast duration as a function of distance and TNTequivalent weight of the blast charge. This is followed by summaries of statistical models for blast propagation and diffraction and reflection effects on blast loading on buildings. Then, analytical models for the velocity response of building structures to the blast loads and key evaluation of the stress response to this structural velocity are provided. All of this is supported by data on critical configuration and physical parameters of the various types of responding structure to the blast loads and a summary of the failure data for these structures to the blast loads. Emphasis is placed on blast damage to windows. The paper ends with a useful and extensive development of the Probability of Damage (POD) for structure to blast loading. A comparison is also made between predicted and actual window damage observed from an accidental explosion near an apartment complex. Two Appendices are provided for: (A), the TNT-equivalent weight for a wide range of explosives and ordnance and (B), a definition of the Step-by-Step procedures used to carry out computation of the POD from blast from military training operations for a wide range of structures but mostly windows.

The loading and response of structures to explosive blast loading is subject to uncertainty and variability. This uncertainty can be caused by variability of dimensions and material properties, model errors, environment, etc. Limit state and LRFD design codes for reinforced concrete and steel have been derived from probabilistic and structural reliability methods to ensure that new and existing structures satisfy an acceptable level of risk. These techniques can be applied to the area of structural response of structures subject to explosive blast loading. Government spending on homeland security is projected to reach $300 billion by 2016. The use of decision theory to determine acceptability of risk is crucial to prioritise protective measures for built infrastructure. Probabilistic methods will be used to quantify the probability of damage or collapse of Reinforced Concrete (RC) columns. In this paper, Monte-Carlo simulation and probabilistic methods are used as the computational tool that incorporates uncertainties associated with blast loads and material and dimensional properties. The prediction of damage is based on load-bearing capacity of the structure. The structural reliability analysis calculates: (i) variability of structural response and (ii) damage and collapse risks RC columns subject to various explosive threat scenarios. If the protective measure is increased stand-off, then structural reliability methods are used to assess risk reduction due to such a protective measure. Decision-support criteria based on net present value (net benefit) and expected utility to consider risk aversion are described herein. The key innovation is incorporating uncertainty modelling in the decision analysis. This analysis will then consider threat likelihood, cost of security measures, risk reduction and expected losses to compare the costs and benefits of security measures to decide the optimal protective measures to buildings.

The impact load of boulders transported by debris flow is crucial in designing protective structures constructed along the potential flow paths. In this study, the Coupled Eulerian-Lagrangian (CEL) method is applied to establish a three-dimensional model for analysing debris flow, boulders, and barrier interactions in various scenarios, with an Australian rivulet serving as a case study. The proposed CEL method was verified by simulating the runout and impact behaviour based on experimental granular and debris flow tests. Subsequently, a comprehensive series of numerical simulations explores the impacts of transported boulders on a rigid tooth barrier, encompassing various boulder shapes and sizes. The results indicate a direct correlation between boulder size and impact force, while the influence of boulder shape on peak impact force is minimal. Nevertheless, boulder shape affects the arrival time, as noted with increased boulder size. Although boulder dimensions remain the primary factor affecting impact force, variations in the geometry are observed to influence the overall dynamics of debris flow-boulder interactions. This study proposes a procedure for assessing barrier impact forces through simulations combining debris flow and boulder transport with the CEL method. The research presents the effectiveness of the CEL method in estimating the impact force of media transported by debris flows in intricate 3D terrains. The findings contribute significantly to the existing measures for assessing the risk of debris flows.

<p>  In slope stability analysis, two-dimensional (2D) analysis techniques are usually applied due to its simplicity and extensive applicability. Given that slope failures are three-dimensional (3D) in nature, especially in the slope with complex geometry, a 3D slope stability analysis could lead to more reasonable results [1]. In slope stability analyses, limit equilibrium method (LEM) and finite element method (FEM) are widely used. Note that LEM only satisfies equations of statics and does not consider strain and displacement compatibility; FEM may encounter significant mesh distortion during large deformations where convergence difficulty and the analysis may be terminated before the slope reaches failure [2]. In the study, a Coupled Eulerian-Lagrangian (CEL) method, which allows materials to flow through fixed meshes regardless of distortions, was utilized to investigate 3D slope stability [3]. Validation of the numerical modeling was first presented using a typically assumed 3D slope. After the validation, various types of slopes (i.e. turning corners, convex- and concave-shaped surfaces) with various boundary conditions (unrestrained, semi-restrained, and fully restrained) are carefully conducted to examine the 3D slope stability. It is anticipated the 3D analyses can shed some light on the slope stability analysis with extreme or complex geometry cases and provide more reasonable results.</p><p> </p><p>REFERENCE</p><ol><li>T.-K. Nian, R.-Q. Huang, S.-S. Wan, and G.-Q. Chen (2012): Three-dimensional strength-reduction finite element analysis of slopes: geometric effects. Canadian Geotechnical Journal, 49: 574–588.</li> <li>C. Hung, C.-H. Liu, G.-W. Lin and Ben Leshchinsky (2019): The Aso-Bridge coseismic landslide: a numerical investigation of failure and runout behavior using finite and discrete element methods. Bulletin of Engineering Geology and the Environment. doi: 10.1007/s10064-018-1309-3.</li> <li>C. Han. Lin, C. Hung and T.-Y. Hsu (2020): Investigations of granular material behaviors using coupled Eulerian-Lagrangian technique: From granular collapse to fluid-structure interaction. Computers and Geotechnics (under review).</li> </ol><p> </p><p> </p>

This research studies the numerical simulation of the finite element method for bird strike using a hemispherical-ended cylinder bird model with varying length-to-diameter (L/D) ratio, namely 1.4; 1.5; 1.6; 1.7; 1.8; 1.9; and 2.0. Birds are modelled with elastic, plastic, and hydrodynamic behaviour. The bird model uses the Coupled Eulerian-Lagrangian (CEL) method with impact speeds of 100 ms-1, 200 ms-1, and 300 ms-1. The simulation results show that the Hugoniot pressure value is around 15-36 times higher than stagnation pressure in L/D 1.4; 14-36 times in L/D 1.5; 13-30 times in L/D 1.6; 12-32 times in L/D 1.7; 12-26 times in L/D 1.8; 13-30 times in L/D 1.9; and 13-29 times in L/D 2.0. It was found that the highest Hugoniot and stagnation pressure were in L/D 1.5 and 1.8, while the lowest Hugoniot and stagnation pressure were in L/D 2.0 and 1.5, respectively. In addition, the error of the numerical results of the average Hugoniot and stagnation pressure value compared to the analytic was 2.9% and 7%, respectively.Â

Computer simulations are widely used in modern automotive industry to design effective restraint systems, such as airbags. Until recently, the uniform pressure method (UPM), which assumes uniform pressure distributions inside the airbag, is mostly used in the design of airbags. The uniform pressure method is appropriate with fully inflated airbags interacting with in-position or belted occupants. However, with recent safety regulations for protecting occupants of various sizes and seating positions as well as the implementation of side airbags, Out-of-Positions (OOP) simulations are becoming more and more important for airbag suppliers and the OEMs. To simulate OOP cases, gas flow approaches are implemented in various commercial finite element codes in different forms. This paper discusses the recent developments in the Coupled Eulerian-Lagrangian (CEL) method for airbag deployment simulations available in Abaqus/Explicit. A passenger airbag model was selected for the evaluation of accuracy of the CEL method. This paper also discusses some advanced Coupled Eulerian-Lagrangian method features available in Abaqus/Explicit in order to facilitate efficient occupant safety simulations.

Cold spray is a solid-state deposition technology widely used in additive manufacturing. The particles temperature is mostly used to adjust the porosity of the coating. This article uses Pyhon script to model the multi-particle model; then the multi-particle model is nested in the CEL deposition model to simulate the actual cold spray multi-particle deposition process; The CEL method has the characteristics of high accuracy and robustness and was selected as the simulation method for the multi-particle deposition model. The porosity of the coating is expressed by studying the value of the EVF void area in the Euler domain. Multiple groups of samples were taken on the coating surface to calculate the porosity of each group, and the average value was finally taken as the porosity of the entire coating. Numerical results show that increasing the particle temperature can effectively reduce the porosity of the coating. The average porosity of the coating under the particles temperature conditions are 600 K: 5.08 %; 650 K: 4.02 %; 700 K: 3.58 %; deposition completed the inside of the coating appears to be compacted. The substrate temperature will affect the combination of the coating and the substrate. It is recommended that the temperature difference between the particles and the substrate should not be too large. The CEL method simulates the process of cold spray multi-particle deposition, which is an effective method to observe and predict the porosity of the coating, which is also unachievable by the SPH and ALE methods.