bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismic Analysis of Concrete Gravity Dams: Nonlinear Fracture Mechanics Models and Size-Scale Effects
Authors: Paggi Marco , Ferro Giuseppe , Braga Franco
Published: August 2011

The phenomenon of interface crack propagation in concrete gravity dams underseismic loading is herein addressed. This problem is particularly important from the engineeringpoint of view. In fact, besides Mixed-Mode crack growth in concrete, dam failure is oftenthe result of crack propagation along the rock-concrete interface at the dam foundation. Toanalyze such a problem, the generalized interface constitutive law recently proposed by the¯rst author is used to proper modelling the phenomenon of crack closing and reopening at theinterface. A damage variable is also introduced in the cohesive zone formulation in order topredict crack propagation under repeated loadings. Special attention is given to the complexityresulting from the solution of the nonlinear dynamic problem and to the choice of the interfaceconstitutive parameters, taking into account the important size-scale e®ects observed in thesecyclopic structures. Numerical examples will show the capabilities of the proposed approachwhen applied to concrete gravity dams.
Experimental Study on Performance Evaluation of an Indonesian R/C Building Damaged by the 2009 Sumatra Earthquake
Authors: Sanada Yasushi , Nitta Yoshiaki , Tomonaga Takuya , Sashima Yuta
Published: August 2011

The 2009 Sumatra, Indonesia earthquake attacked Padang, which is the capital of West Sumatra province, and damaged a large number of reinforced concrete (R/C) buildings. The first author of this paper had conducted a post-earthquake field investigation in Padang. As a result, it was found that one of typical damage to buildings was beam-column joint failure. This damage was caused by poor structural details at joints, nevertheless appropriate details were provided in the Indonesian design regulation. In this study, the structural performance of a typical beam-column joint was experimentally evaluated to investigate the seismic performance of earthquake-damaged buildings. The test results revealed that joint failure occurred prior to beam/column yielding. This means that the actual seismic performance of damaged buildings was less than the design calculations in which joint failure had not been assumed.
Dynamic Fracture of Concrete–3D Numerical Study of Compact Tension Specimen
Authors: Ožbolt Joško , Sharma Akanshu , Reinhardt Hans Wolf
Published: August 2011

The behavior of concrete structures is strongly influenced by the loading rate. Compared to quasi-static loading concrete loaded by impact loading acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia forces activated. Both influences are clearly demonstrated in experiments. For concrete structures, which exhibit damage and fracture phenomena, the failure mode and cracking pattern depend on loading rate. Moreover, theoretical and experimental investigations indicate that after the crack reaches critical speed of propagation there is crack branching. The present paper focuses on 3D finite-element study of the crack propagation of the concrete compact tension specimen. The rate sensitive microplane model is used as a constitutive law for concrete. The strain-rate influence is captured by the activation energy theory. Inertia forces are implicitly accounted for through dynamic finite element analysis. The results of the study show that the fracture of the specimen strongly depends on the loading rate. For relatively low loading rates there is a single crack due to the mode-I fracture. However, with the increase of loading rate crack branching is observed. Up to certain threshold (critical) loading rate the maximal crack velocity increases with increase of loading rate, however, for higher loading rates maximal velocity of the crack propagation becomes independent of the loading rate. The critical crack velocity at the onset of crack branching is found to be approximately 500 to 600 m/s.
Pressure of Snow Avalanches against Buildings
Authors: Bovet Eloise , Chiaia Bernardino , De Biagi Valerio , Frigo Barbara
Published: August 2011

The paper aims to analyse the e ects of topography and building position on themagnitude of pressure exerted by snow avalanches against buildings, through a structural backanalysis and numerical uid-dynamics. Studying a real snow avalanche impact occurred in2008 which destroyed a village in Valsavarenche (Aosta Valley - IT), the attention is focused onthe avalanche ow deviation caused by the destructive interaction with a rst building, whichprotected part of a second building beyond it. By means of photographical and in situ survey,a detailed description of avalanche geometrical, dynamical and physical properties is outlined.A structural investigation, based both on debris arrangement and on measurements on theundamaged parts of buildings is also carried out.Thus, a back analysis is carried out in order to de ne collapse dynamics and to estimate theupper and the lower bound of impact pressure. Afterwards, numerical uid-dynamical analysesare performed to simulate di erent impact scenarios and to understand the e ects of obstacleson avalanche behavior: a qualitative measure of the interactions among buildings, which maymutually protect one another, is obtained.
Investigation of Concrete Slabs under Impact Load
Authors: Hummeltenberg Anja , Beckmann Birgit , Weber Tony , Curbach Manfred
Published: August 2011

The behaviour of concrete slabs under dynamic load such as rock fall or vehicle impact isinvestigated in this work. The aim of this study is to enlarge the knowledge concerning thesubsequent reinforcing of concrete slabs and its inuence on their behaviour under impact load.Therefore, the results of the drop tower experiments with standard concrete, high performanceconcrete (HPC) and ultra-high performance concrete (UHPC) are compared and interpreted.The analysis of the test results focuses on the qualitative evaluation of the protective e ectand on the quantitative evaluation of measurement results. Regarding the protective e ect, theinuence of the additional steel stirrup reinforcement is rather small. In contrast, the subsequentfabric reinforcement prevents the perforation of the concrete slabs. The behaviour of steel fabricand carbon fabric is compared. Although particular di erences in fracture behaviour are seen,both types of fabric reinforcement obviate total punch-through and, hence, vastly enhance theprotective performance. Comparing the stamping cones and analysing the extent of damage, theprotective capacity of di erent concrete slabs is evaluated. Within the quantitative evaluationof the measurement results, the evolution of strains and strain rates is being considered. Onthe top side of the concrete slabs, the strain is measured as tensile strain in the rst spellafter load application, turning into compressive strain later on. The evolution of strains andstrain rates indicates wave propagation. Beside the strain results, special attention is paid tothe correlation of di erent measurement techniques. The results of strain gauges, accelerometer,load cells and photogrammetry are contextualised and therefore show the change from the localmaterial behaviour to the global structure response in temporal sequence.
Evaluation of Dynamic Collapse Behavior of Steel Moment Frames Damaged by Blast
Authors: Lee Kyung Koo , Chung Lan , Lee Sang Hyun , Park Tae Won , Rho Jieun
Published: August 2011

Blast effects on structures and blast mitigation strategies have been vigorously studied in the world. The alternate path method, or common progressive collapse analysis method, of structures assumes the threat-independent removal of vertical load-carrying elements. However, in reality, a blast-induced column-missing event will produce the damage on adjacent structural elements and the rapid dynamic response of the structures. In this study, the strain rate effects on the dynamic collapse behavior of steel moment frames are investigated by performing the blast-induced sequential progressive collapse analysis. Then, the improvement of the progressive collapse analysis method is discussed based on the numerical results.
Recent Efforts on Blast Damage Mitigation for Dams
Authors: Sharp Michael K. , Seda-Sanabria Yazmin , Matheu Enrique E.
Published: August 2011

This paper describes collaborative research efforts conducted between the U.S. Army Corps of Engineers (USACE) and the U.S. Department of Homeland Security (DHS). The USACE, through its U.S. Army Engineer Research and Development Center (ERDC), has focused efforts on the development of a collaborative research program to address technical gaps related to risk and blast mitigation for dams. These research efforts involve experimental and analytical tasks designed to improve blast damage prediction capabilities for dams, navigation locks, and levee systems resulting from vehicle and waterborne delivery scenarios. The outcomes from these efforts can inform USACE’s priorities, which include refining the current understanding of the effects of potential attacks, the vulnerabilities and weaknesses of its critical assets to various threat conditions, and the local and regional consequences of those attacks in order to develop appropriate protective measures and recovery technologies.
BlastWall: An Integrated Wall and Window Retrofit System
Authors: Hadden David , Cleave Roger , Fischer Kai
Published: August 2011

Exterior wall infill panels of non-loadbearing masonry, often with window openings, are commonly used in buildings around the world. While the structural frame may possess a good level of resistance to explosion loading the masonry wall panels are often relatively weak and liable to sudden, brittle failure when subjected to blast loads with the result that hazardous debris is thrown into the interior of the building. Blast resistant windows can be set into openings in the masonry wall panels; however failure of the wall may occur at a lower load than that against which the window would survive if it was adequately supported. The BlastWall research project was carried out by a consortium of industry partners and research institutions with the aim of developing a practical integrated wall and window retrofit system to mitigate the hazards to building occupants and critical equipment from the failure of masonry wall infill panels under external blast loading. Utilising elements of Tecdur® technology, the BlastWall system proved successful under loading at EXV15, with since-proven potential for even higher performance. The system is supported by a software tool that allows its components to be tailored to suit a wide range of existing materials, dimensions and loading conditions. This paper describes the project objectives, the BlastWall system and its components, including the software tool, and the trials carried during system development resulting in overall proof of concept.
Performance of Different Seismic Retrofitting Techniques in Case of Blast-Induced Progressive Collapse
Authors: Asprone Domenico , Jalayer Fatemeh , Prota Andrea , Manfredi Gaetano
Published: August 2011

Extreme loading conditions such as man-made malicious actions, fires or natural events could induce local failure mechanisms (e.g., a loss of a member) which may trigger progressive collapse. The design or the assessment of a critical infrastructure needs to address the possibility of such an extreme circumstance taking place during its effective life-time. It is observed that blast-induced progressive collapse mechanisms involve non-linear structural behavior similar to that due to earthquakes. This work focuses on probabilistic analysis of progressive collapse of a typical RC structure, induced by a blast event. The objective is to verify the effectiveness of seismic retrofitting schemes against explosions and the eventual 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 simulation method is employed to generate various realizations of the uncertain parameters within the problem. For a given realization, various component-level dynamic analyses are preformed within a certain range of distance, in order to quantify and locate the damage induced by shock wave on structural elements. As a case study, a 5-storey reinforced concrete frame structure designed for gravity loading only is considered. As possible retrofitting schemes, steel bracing, FRP wrapping and RC jacketing are compared. The probability of collapse considering both blast and earthquake for the structure before and after retrofit are compared.
Aerodynamic Damping and Fluid-Structure Interaction of Blast Loaded Flexible Structures
Authors: Teich Martien , Gebbeken Norbert , Larcher Martin
Published: August 2011

This paper analyses the e ects of air-structure interaction of systems subjectedto weak blast loads. While these coupling e ects are negligible for typical steel or concretestructures, they may dominate the dynamic response of lighter and more exible (compliant)systems like membranes, blast curtains or cable facades. For these light and exible systems,a classical decoupled analysis, i.e., neglecting the inuence of the surrounding air, might sig-ni cantly overestimate the deections and strains. However, we show that the coupling e ectscan be accounted for by basically adding a viscous aerodynamic damping force. We discussand compare two approaches how to obtain the aerodynamic damping term. With decreasingstructural sti ness and mass, the damping contribution of air increases signi cantly. The resultsof Hydrocode simulations are presented, and an outlook into further areas of research is given.
The Effect of Anchorages on FRP Strengthening of RC Walls to Resist Blast Loads
Authors: Mutalib Azrul A. , Hao Hong
Published: August 2011

In this paper, the effectiveness of strengthening reinforced concrete (RC) walls with fiber reinforced polymer (FRP) bonded to RC wall with epoxy, or with epoxy plus additional boundary anchors, or distributed anchors to resist blast loads is studied. Both the bonding and anchorage strengths are modeled in numerical simulations. FRP and anchor debonding failures are modeled in the simulation. Based on numerical results, pressure-impulse (P-I) diagrams of FRP composite strengthened RC walls are generated using numerical analyses. The results show that the RC wall strengthened with FRP and anchors displays an increase in the impulse and pressure asymptote of the P-I curve as compared to those strengthened with FRP only, indicating that placing anchors to prevent FRP debonding or peeling-off increase the RC slab load carrying capacities in both the impulsive and quasi-static region.
How to Determine the Dynamic Fracture Energy of Concrete. Theoretical Considerations and Experimental Evidence
Authors: Weerheijm Jaap , Vegt Ilse
Published: August 2011

Data on the dynamic fracture energy of concrete are scarce and also not consistent due to different test methods, data analyses and definitions. In [1] the authors summarized and evaluated the test methods. Suggestions for the standardization of dynamic tensile testing were given. In the current paper the discussion is continued. First, definitions for the fracture energy and the relevant parameters are given. Next, theoretical considerations are given for the different rate dependency regimes of the dynamic tensile strength. Fracture and damage mechanics form the basis for the theoretical modeling. Based on the same principles, it is shown that the enhancement of the fracture energy occurs at higher loading rates than for the tensile strength. Phenomenological models to quantify the dynamic fracture energy are still lacking. To quantify the dynamic fracture energy, uniaxial test conditions are required. The Hopkinson bar technique meets this requirement. The paper presents and evaluates available data and relates these to the theoretical considerations.
Strength of Masonry Walls Retrofitted with Epoxy Resin Injection
Authors: Araki Hideo , Yasojima Akira , Kagawa Junichi
Published: August 2011

This paper presents the results of the fundamental loading tests with brick elements strengthened by the epoxy resin injection method. Three types of loading tests were performed to evaluate the effects of epoxy resin injection on compressive, shear, and flexural characteristics. The variables considered in this experiment were the strength of the mortar and the applied axial force. To verify the effects of this strengthening method, seismic loading tests were performed on three brick walls. From the test results, an increase in the strength of the element was observed in each test. However, the strength of the mortar did not affect the shear and flexural strength of the brick elements. We proposed equations to estimate the strength of the elements strengthened by the epoxy resin injection method. Improvements to the seismic performance of the brick wall strengthened with epoxy resin were explicitly confirmed.
Compressive Behavior of Plain and Fiber-Reinforced High-Strength Concrete Subjected to High Strain Rate Loading
Authors: Wang Sha Sha , Zhang Min Hong , Quek Ser Tong
Published: August 2011

This paper presents a laboratory experimental study on the effect of high strain rate on compressive behavior of plain and fiber-reinforce high-strength concrete (FRHSC) with similar strength of 80-90 MPa. Steel fibers, polyethylene fibers, and a combination of these were used in the FRHSC. A split Hopkinson pressure bar equipment was used to determine the concrete behavior at strain rates from about 30 to 300 s-1. The ratio of the strength at high strain rates to that at static loading condition, namely dynamic increase factor (DIF), of the concretes was determined and compared with that recommended by CEB-FIP code. Fracture patterns of the specimens at high strain rates are described and discussed as well. Results indicate that the CEB-FIP equation is applicable to the plain high strength concrete, but overestimates the DIF of the FRHSC at strain rates beyond a transition strain rate of 30 s-1. Based on the experimental results, a modified equation on DIF is proposed for the FRHSC.
Beam-Column Joint Retrofitting with High Performance Fiber Reinforced Concrete Jacketing
Authors: Beschi Consuelo , Meda Alberto , Riva Paolo
Published: August 2011

The possibility of strengthening existing R/C structures with a new technique based on the application of a High Performance Fiber Reinforced Concrete jacket is investigated herein, with the aim of studying the effectiveness of this technique for seismic retrofitting. The results of a beam-column joint full scale test simulating the behavior of existing beam-column joints are presented. The specimen have been subjected first to static loads and after to cyclic actions with increasing amplitude, up to failure. The tests demonstrated that, with the application of a HPFRC jacket, it was possible to remarkably increase the bearing capacity of the columns reaching also an adequate level of ductility, and the resistance of the beam column joints, with very little visible damage, thanks to the tensile strength contribution of HPFRC.
Numerical Simulations on Impact Resistant Behavior of Rahmen-Slab Type RC Structures
Authors: Kon-No Hisashi , Nishi Hiroaki , Yamaguchi Satoru , Sawamatsu Toshikazu , Kishi Norimitsu
Published: August 2011

In this paper, in order to gain basic knowledge of the dynamic response charac-teristics of rockfall protection galleries, falling-weight impact tests of the small size frame-slabtype reinforced concrete (RC) structures were conducted and the impact-resistant behaviorwas investigated. Also, to establish the prediction method for accumulated damage and resid-ual load-carrying capacity of the structures under repeated impact loading, a three-dimensionalelasto-plastic FE analysis method was proposed. Its applicability is discussed by comparing withthe experimental results. The following results are obtained from this study: (1) under impactloading, the structures reach the ultimate state in the punching shear-failure mode; and (2)accumulated damage of the galleries can be rationally evaluated by using the time history ofdeﬂection and crack patterns obtained by applying the proposed numerical analysis method.
Experimental Investigation on Soft-Story RC Frames Retrofitted by Hybrid Wall Technique
Authors: Sunagawa Tomomi , Javadi Pasha , Maeda Koki , Yamakawa Tetsuo
Published: August 2011

In this paper, a new retrofit method, which is called “Hybrid Wall Technique”, is proposed for retrofitting soft-story RC frames. In the proposed technique, steel plates encase the boundary RC columns, and connect to additional steel plates at the bay of the frame with the help of high-strength bolts. After installation of steel plates and high-strength bolts, which are also used as formworks, the additional concrete is cast. Structural performance of the proposed metho­­­d is verified by experimental investigations conducted on one-bay one-story RC frames. One non-retrofitted frame and three frames retrofitted by thick or thin hybrid walls were evaluated experimentally.
Axial Performance of Various Strengthening Methods Applied on Full-Scale Rectangular RC Columns
Authors: Chen Pei Ching , Lin Min Lang , Wu Yin Han
Published: August 2011

The performance of RC columns subjected to axial force is relative to the confinement. CFRP wrapping, a generally adopted retrofit method, was proved not to effectively provide confining force due to the bulging effect on the column face. Therefore, this paper is focused on the performance of the retrofitted full-scale rectangular RC columns using different retrofit schemes including the proposed CFRP wrapping conjugated with CFRP anchors method. A total of eleven rectangular RC columns with low transverse reinforcement ratio were constructed. Among them, one was tested as benchmark; one was purposely constructed with larger transverse reinforcement ratio; five were retrofitted by using CFRP wrapping and CFRP anchors; and the other four were retrofitted by using different shapes of steel jacketing alone or with adhesive anchors. All the specimens were subjected to monotonic incremental axial force until failure occurred. Experimental results demonstrated that the ductility of the specimens retrofitted by using CFRP wrapping with CFRP anchors was significantly improved compared with those retrofitted by using only CFRP wrapping. On the other hand, the specimen with octagonal steel jacketing performed better than all other specimens not only on ductility but also on strength. Finally, a novel numerical model considering the contribution of the retrofit material will be proposed and validated in the future.
A Study of FRP–Concrete Bond under Impact
Authors: Khalighi Yashar , Banthia Nemy
Published: August 2011

Our understanding of how the bond between FRP and concrete performs under impact loading is severely limited. In this paper, bond performance of Sprayed FRP with concrete was studied under impact loading. A novel 550 mm × 150 mm × 150 mm notched specimen was developed and a 75 mm wide strip of Sprayed FRP was applied to strengthen the specimen. A novel test set-up designed to minimize the influence of specimen rebound after impact as well as eliminate the need to correct the load data for inertial effects was developed. FRP strains were measured using strain gauges carefully installed on the FRP, and the bond stress was calculated using the differential strain values. A kinematics analysis was also performed to translate the vertical deflections into strain values. Three types of surface preparation methods (water jetting, sand blasting, and jack hammering) were studied. Specimens are tested under four different strain rates (four different hammer heights of 250, 500, 750, and 1000 m) and the results were compared with quasi static values using loading rates of 0.005, 0.05, and 0.5 mm/min. Results showed that sand blasting is the most effective surface preparation method resulting in the highest bond strength values. Impact results were characterized using a Dynamic Improvement Factor (DIF). Results indicate that the FRP–concrete bond is highly strain sensitive, and in general the bond strength increases and the fracture energy decreases under higher rates of strain. Untreated specimens are shown to be more strain-rate sensitive than the surface treated ones.
A New Passive Seismic Control Device for Protection of Structures under Anomalous Seismic Events
Authors: Cancellara Donato , Pasquino Mario
Published: August 2011

In this paper, the possibility offered by the Base Isolation System, designed according to the strategy of limitation seismic force, in order to ensure a significant level of robustness to the isolated superstructure, has been analyzed. In according to the strategy of limitation seismic force, a new seismic isolator called HDHSI (High Damping Hybrid Seismic Isolator) is proposed, obtained by the assembly in series of a LRB (Lead Rubber Bearing) and a FS (Friction Slider) with high friction coefficient. The HDHSI device is in contrast to the R-FBI (Resilient-Friction Base Isolation) isolator and is the optimization of the EDF (Electricité De France) system. A modeling with HDHSI devise has been presented by using nonlinear finite elements NLlink (Nonlinear link) and nonlinear dynamic analysis for a SDOF system with harmonic force, in order to characterize the cycle-hysteretic behavior of the device for different levels of shear deformation, are performed. Nonlinear dynamic analysis for a RC structure, base isolated by the proposed devices, are performed. As seismic actions, have been adopted the following registrations: an anomalous earthquakes for intensity and in particular El Centro earthquake (N00W component, 1940) with different amplification factors; an anomalous earthquake for frequency content and in particular Erzincan earthquake (N90W component, 1992).
Computer-Aided Design of Protective Structures: Numerical Simulations and Experimental Validation
Authors: Dey Sumita , Børvik Tore , Hopperstad Odd Sture
Published: August 2011

This paper aims through several numerical studies to highlight some effects of layering plates in ballistic protection. The possible increase in perforation resistance by varying the material properties of the plates, the individual plate thickness (the total plate thickness is constant) and the stacking of individual plates in a double-layered target when struck by blunt and ogival nose projectiles has been investigated. This was done by conducting non-linear finite element simulations of the perforation process using an experimentally validated numerical model and an explicit finite element code. These studies are difficult to carry out experimentally due to the many materials and thicknesses involved and computer-aided design is thus an attractive approach. The numerical design indicates that it is possible to considerably increase the overall ballistic protection level by using double-layered plates and a proper design. Some of the most promising designs were then selected for experimental validation. The experimental tests gave completely opposite results than the computer-aided design, and the reasons for this will be discussed in some detail.
Simulation of Laminated Glass Loaded by Air Blast Waves
Authors: Larcher Martin , Teich Martien , Gebbeken Norbert , Solomos George , Casadei Folco , Falcon Grecia A. , Sarmiento Sonja L.
Published: August 2011

In this paper, several material models are analyzed in order to represent and compare the behaviour of laminated glass subjected to blast loads. LS-DYNA and EUROPLEXUS are used for numerical simulation. These codes have different capabilities to describe the mechanical problem, especially the failure behaviour. The results of the simulations are compared to laboratory experimental results in order to validate the accuracy of the material models.
Designing a High Energy Rockfall Kit
Authors: Boutillier Benoit , Clarke Alice , Huber Denis
Published: August 2011

The present study deals with flexible structures which protect human lives and buildings against falling rocks with a high energy, up to 5 000 kJ. These rockfall kits have to match the new European standard ETAG 027 which requires different specific full scale tests. To reach high level of performance, these flexible barriers have to be studied in details. First, each main component such as net sets and dissipating devices, have been studied separately. The Anti Sub Marine net was then chosen for its elasticity and isotropic behavior. The best parameters for braking systems have been defined by different tests. Then, the complete design of the structure was performed according to several criteria such as the position of brakes, the post height, the easy repair, the independence of modules and the final cost (kit with its global installation). Finally, the design which fit the best of our criteria was used to perform full scale tests. After some trials, the so-called HC RP® 3 000 kJ and 5 000 kJ kits matched the ETAG 027 requirements. All kits need lateral anchors to stabilize lateral posts during the impact. All the posts are H-shaped and a central net brake is used.
Analytical Model for Rockfall Protection Galleries - a Blind Prediction of Test Results and Conclusion
Authors: Schellenberg Kristian , Kishi Norimitsu , Kon-No Hisashi
Published: August 2011

A system of multiple degrees of freedom composed out of three masses and three springs has been presented in 2008 for analyzing rockfall impacts on protective structures covered by a cushion layer. The model has then been used for a blind prediction of a large-scale test carried out in Sapporo, Japan, in November 2009. The test results showed substantial deviations from the blind predictions, which led to a deeper evaluation of the model input parameters showing a significant influence of the modeling properties for the cushion layer on the overall results. The cushion properties include also assumptions for the loading geometry and the definition of the parameters can be challenging. This paper introduces the test setup and the selected parameters in the proposed model for the blind prediction. After comparison with the test results, adjustments in the input parameters in order to match the test results have been evaluated. Conclusions for the application of the model as well as for further model improvements are drawn.
Numerical Analysis of Vehicle Suspension System Response Subjected to Blast Wave
Authors: Baranowski Pawel , Malachowski Jerzy , Niezgoda Tadeusz
Published: August 2011

This paper presents the development process of a numerical model for a terrain vehicle suspension system. Geometry of the tire and other suspension elements were achieved using reverse engineering technology. In the next step, numerical analyses of the suspension system subjected to blast wave were carried out with two different techniques, e.g. SPH (Smoothed Particle Hydrodynamics) method and the blast wave Conwep model.
Meso-Scale Simulation of Concrete: Blast and Penetration Effects and AAR Degradation
Authors: Cusatis Gianluca , Di Luzio Giovanni , Cedolin Luigi
Published: August 2011

The study of concrete dam subjected to extreme loading conditions require theadoption of accurate constitutive equations. In this paper some recent results on the meso-scalesimulation of blast and penetration e ects on concrete will be discussed. The adopted meso-scale constitutive equation is the so-called Lattice Discrete Particle Model (LDPM) recentlyformulated at Rensselaer Polytechnic Institute. LDPM can accurately describe the macroscopicbehavior of quasi-brittle materials, and especially concrete, during elastic, fracturing, softening,and hardening regimes. Tensile dominated experimental tests under both dynamic conditionswere numerically simulated. After presenting examples of simulations relevant to quasi-staticand dynamic concrete behavior, LDPM simulation of the e ect of air blast pressure, on concretewill be discussed. Finally, the problem of the extrapolations of laboratory tests to actual in-situconditions is also presented.
On the Fire Scenario in Road Tunnels: A Comparison between Zone and Field Models
Authors: Bamonte Patrick , Felicetti Roberto , Gambarova Pietro G. , Nafarieh Alireza
Published: August 2011

Some catastrophic ﬁres occurred in the last 15 years in both road and railway tunnels usedby millions of people are turning the attention of the engineering community towards the assessmentof the structural safety of tunnels, both during and after a ﬁre. To this end, a realistic description ofﬁre propagation and a reliable picture of the thermal ﬁeld are mandatory, in order to evaluate thethermal load acting on the lining and the partitions. With reference to a rather common road-tunnelgeometry, three possible thermal inputs representing as many levels of ﬁre severity are consideredhere, namely the burning of a car, of a bus and of a heavy-goods vehicle (HGV). The ﬁre scenariois ﬁrstly modeled by means of a rather simple but handy code based on a two-zone model for thedescription of the ﬁre in each compartment. Later, a more complex code based on computational ﬂuiddynamics applied to the simulation of ﬁre development (Fire Dynamics Simulator - FDS) is used toallow a comparison between the numerical results obtained in either way, and to check to what extentsome available experimental results concerning similar tunnels can be ﬁtted. The ﬁtting shows that- by properly subdividing the tunnel (that has no compartments) into a suitable number of “virtual”compartments - the agreement between the two codes is very good, as well as that between numericaland experimental results.
Multi-Hazard Assessment of Steel Hangar Structures Subjected to Seismic and Wind Loads
Authors: Chiodi Remo , Asprone Domenico , Maimone Filippo , Prota Andrea , Ricciardelli Francesco
Published: August 2011

The Italian wind climate is characterized by rather low annual average wind velocity, and moderately high extremes; on the other hand, Italy is one of the most seismic countries in the Mediterranean area, both in terms of frequency and intensity of earthquake occurrences . These events have to be examined to define a reliable prediction of extreme loads, and a probabilistic multi-hazard approach can be employed to investigate the performance of a structure under critical events and to ensure its acceptable performance during its entire lifetime. This paper examines the case of steel airport hangars located in areas with low seismicity, where the contribution of the wind risk can represent the most important hazard. In this framework the wind vulnerability has to be characterized with a probabilistic approach and all possible failure mechanism induced by wind loads have to be analyzed. The main objective of this paper is to provide a tool for assessment and retrofit of existing structures, as well as for the design of new structures.
Assessment Spectra for Structures Subject to Passing Underground Trains
Authors: Behnamfar Farhad , Nikbakht Razieh
Published: August 2011

Underground trains passing below structures may produce vibrations harming occupants and nonstructural elements, though they do not usually result in structural damage. This is a problem of more importance when assessing buildings such as libraries, hospitals, laboratories, museums, etc. To prepare simple tools to fulfill design needs, in this paper assessment spectra for various underground trains moving with different velocities are calculated. Using these spectra, without resorting to the time consuming and costly analysis of a tunnel-soil system under moving loads, the maximum structural responses can be calculated rapidly. To make this end, the soil-tunnel interaction is modeled using a 3D finite difference scheme under the standard moving train loads. The dynamic analysis of such a system results in the ground surface vibration time histories at different distances from the tunnel axis. Then the maximum values of velocity responses are calculated for an SDF dynamical system. The above calculations are accomplished for different train velocities, tunnel depths, distances from tunnel, and soil types, and are presented as assessment velocity spectra.
Numerical Modelling of Honeycomb Energy Dissipating Materials
Authors: Reay Jonathan , Bennett Terry , Tyas Andy
Published: August 2011

Cardboard honeycomb energy dissipating material (EDM) is used extensively forprotection of cargo that is air dropped. Whilst air dropped containers are deployed withparachutes, a signiﬁcant amount of energy still requires dissipating on impact with the ground.The speciﬁcation of cardboard EDM in dynamic applications has tended to be ad-hoc withno thorough understanding of the energy absorbing characteristics of the material. This paperseeks to address this gap in knowledge.
A Parametric Analysis of the Strength-Porosity Relationship of Green Compacts Formed through Powder Compaction Route
Authors: Nor S.S.M. , Rahman Mujibur M. , Rahman A. T. A. , Tarlochan F. , Rahman H. Y.
Published: August 2011

The strength of a green compacts formed through warm powder compaction route is strongly dependent on the forming load and temperature. As the forming load increases, the powder particles move from its initial position by sliding among them and die wall. This movement results in new arrangement and packing order of the particles. However, due to this movement, pores among the particles are generated that affects the mechanical properties of the green compacts. Having pores in green compacts lead to strain intensification at ligaments between pores during sintering at later stage, hence serve as areas for crack initiation. Therefore, as the powder forming relates directly to the load and temperature, strength to porosity relationship has to be analyzed based on those parameters. This paper presents the effect of porosity to the strength of green compacts formed at different load and temperature (70 kN to 130 kN; 30°C to 200°C). The bending strengths of green compacts are measured while Scanning Electron Microscopy is used for porosity evaluation. It has been found from the results that porosity and strength are related to each other at all forming parameters. In addition, high forming load and temperature give better strength due to porosity reduction.
Fabrication and Performance Evaluation of OPCM Array Transducer
Authors: Luo Ying , Wang Zi Ping
Published: August 2011

Orthotropic piezoelectric compose material (OPCM) is used as functional material for a new OPCM array transducer which can be applied in a wide range of fields such as natural gas, power industry, aero-space, and other non-destructive evaluation fields. The development of ultrasonic array transducer is still in the initial stages and it can be strongly enhanced by using design tools. The transducer is designed by flat construction and composed of backing layer, OPCM array element and protective layer. A procedure and a specific constitutive model are presented in this work together with simulation of OPCM element transducer of general array parameters and matching layer thickness. Models are required for the design and fabrication of OPCM array transducer. Also the properties of frequency, impedance, directivity and relative sensitivity distribution are measured from calibration experiment. The OPCM array transducer is excited by voltage and the corresponding sensitivity analysis is presented. To frequency and impedance, the experimental results show that the bandwidth is increased and the effects of side and grating lobe are reduced by using the matching layer. The OPCM array transducer has orthotropic performance. This special performance can be used to actuate and sense the stress wave in special direction.
Investigation of Shrinkage in Softwood Using Digital Image Correlation Method
Authors: Peng Ming Kai , Chui Ying Hei , Ho Yi Chiech , Wang Wei Chung , Zhou Yao Tang
Published: August 2011

Distortion in lumber, such as twist, cup, spring and bow, can cause serious problems for its use in service. Lumber distortion is largely a result of differential shrinkage in wood in different directions and the presence of different types of wood (i.e. juvenile and mature wood) in a single piece. Shrinkage varies within tree because of different types of wood. In this paper, the digital image correlation (DIC) method was used to investigate shrinkage variation within tree. The DIC method is an image-based, non-contact and full-field displacement and strain measurement method. Two softwood species grown in Eastern Canada, jack pine and white spruce, were used in this study. In this paper, average full-field shrinkage over each growth ring was measured, and the growth ring position in relation to pith of the tree was recorded. The shrinkage variations in the radial, tangential and longitudinal directions in a tree stem are presented. The work described in this paper is part of a larger study to develop a modeling technique to predict distortion of lumber based on its position in a tree stem.
Initiation and Growth of Pits and Cracks in Corrosion Fatigue for High Strength Aluminium Alloy Observed by Micro Computed-Tomography Using Ultra-Bright Synchrotron Radiation
Authors: Nakai Yoshikazu , Shiozawa Daiki
Published: August 2011

Measurement of shape and dimension of pits and cracks formed in corrosion fatigue tests of a high-strength aluminium alloy, 7075-T651 were conducted by computed-tomography using ultra bright synchrotron radiation X-ray. Complex corrosion process could be observed and detail shapes of corrosion pits could be identified. Sometimes, corrosion pit and corroded area were formed under passive film, and those were not observed from the surface.
Rolling Contact Fatigue of Titanium Alloys Coated by Gas Nitriding Using a Q-Sw Laser
Authors: Rozwadowska Justyna , Kida Katsuyuki , Santos Edson Costa , Honda Takashi , Koike Hitonobu , Kashima Yuji , Kanemasu K. , Matsumoto R.
Published: August 2011

The influence of gas nitriding of commercial pure titanium and Ti-6Al-4V (Ti64) alloy by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. Despite very good biocompatibility, high strength to weight ratio and corrosion resistance, the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. Fretting and wear related aspects become important issues when titanium alloys are used in rolling contact applications. Titanium bearings are employed in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defense industries). In this work, a Q-sw laser was used to coat pure commercial titanium and Ti-6Al-4V bearings with TiN in a closed chamber in nitrogen atmosphere. The samples were tested under water by using a thrust-type rolling contact fatigue machine. The microstructure, morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and electron backscatter diffraction (EBSD). By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter, thin TiN coats of 1 to 3 mm were produced. The wear loss of the coated samples was at least ten times lower than that of the uncoated bearings.
The Influence of Stress Ratio on Changes in Magnetic Flux Density around Fatigue Crack Tips of Carbon Tool Steel
Authors: Honda Takashi , Kida Katsuyuki , Santos Edson Costa , Koike Hitonobu , Rozwadowska Justyna , Uryu Megumi , Houri K. , Tanabe Hirotaka
Published: August 2011

Fatigue failure of steel occurs when cracks form in a component and continue to grow to a size large enough to cause fracture. In order to understand the strength of a steel component, it is important to locate these cracks. We developed a scanning Hall probe microscope (SHPM), equipped with GaAs film sensors to observe fatigue cracks at room temperature in air while they were growing. In our previous works [1,2], the correlation between crack growth and magnetic field in high carbon tool steels (JIS SKS93 and JIS SUJ2) were determined. We also reported the sensitivity of the SHPM equipped with a three-dimensional line-probe that was developed to decrease the sensor gaps. By using the line-probe sensor we succeeded to measure the magnetic flux density distributions in very close proximity to the specimen’s surface. However, in order to further understand the relation between magnetic flux density and crack growth, other materials, microstructures and fatigue test conditions should be evaluated. In the present work, we focus on the effect of stress ratios on the changes of the magnetic flux density in annealed carbon tool steel.
The Study of Stress Corrosion Cracking in Aluminum Alloy 7075(W) under Tensile Loading by Eddy Current Measurement
Authors: Dollah Mahmood
Published: August 2011

The double cantilever beam has been widely used in the past and has proved one of the most popular designs for measuring the growth rate of stress corrosion cracks in materials. In this study, the double cantilever beam specimens were used to study the effect of tensile loading on stress corrosion cracking behaviour in aluminium alloy 7075(W). Cracks initiated readily in 3.5%NaCl solution with tensile loading conditions. Stress Corrosion Cracking (SCC) development was found to follow an intergranular path, which strongly depended on microstructure of material. Tests also were carried out to measure the threshold stress intensity, KISCC, which SCC would not occur. The SCC test was explained by an active path mechanism due to the galvanic interaction between grain boundary precipitates and adjacent precipitate-free zones. Crack lengths were measured with an eddy current bore probe and confirmed by optical metallography. The data from the eddy current tests on real stress corrosion cracks were used to construct an eddy current calibration curve for predicting stress corrosion crack lengths of aluminium alloy 7075(W).
High Velocity Nano Alumina Wet Milling in Zirconia and Corundum Mills
Authors: Meor Yusoff M.S. , Wilfred Paulus , Masliana Muslimin
Published: August 2011

The paper presents a study on the effect of high energy milling to the crystallite size and lattice strain of α-alumina in zirconia and corundum mills. A Fritsch Pervesette 7 which has a maximum milling speed of 1100 rpm was used for this comparison. Milled samples were analyzed using the X-Ray Diffraction (XRD) technique to calculate for the crystallite size using the Scherrer method while lattice strain was determined by the Tangent method. Scanning electron microscope (SEM) was also used to determine changes in the morphology of the alumina powder sample after the milling process. Zirconia was found to be the better abrasive material and the optimum conditions used to obtain the smallest crystallite size of 51.2 nm are milling speed and time of 1100 rpm and 180 minutes respectively.
Crack-Tip Shielding Effect on Fatigue Crack Propagation in Porous Silicon Carbide
Authors: Tanaka Keisuke , Kita Yasuki
Published: August 2011

A sharply notched specimen of porous silicon carbide with porosity of 37% was fatigued under four-point bending. The opening displacement of a fatigue crack was measured at several positions along cracks by using scanning electron microscopy. The crack propagation curve was divided into stages I, II, and III. The crack propagation rate first decreased with crack extension in stage I and became constant in stage II. In stage III, the crack propagation rate increased again. The range of crack opening displacement measured in SEM was lower than that calculated from the applied load range by FEM, suggesting that the anomalous variation of the crack propagation rate with crack extension was caused by crack-tip shielding due to crack face contact. The crack-tip stress intensity factor was estimated as a true crack driving force from the relation between the crack opening displacement and the applied load. The amount of crack-tip shielding increased very quickly with crack extension, reducing the crack-tip stress intensity factor in stage I. In stage II, the increasing applied stress intensity factor is balanced by the increase in the crack-tip shielding. The crack-tip stress intensity factor increases with crack extension in stage III.