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Edri I.,Combat Engineering Corps | Feldgun V.R.,Technion - Israel Institute of Technology | Karinski Y.S.,Technion - Israel Institute of Technology | Yankelevsky D.Z.,National Building Research Institute
International Journal of Protective Structures | Year: 2012

This paper aims at extending our understanding with regard to some characteristics of an interior explosion within a room with limited venting. An interior explosion may be the result of an ammunition storage explosion, or an explosive charge as part of a terrorist action or a warhead explosion that follows its penetration into a closed space in a military action. Full scale experiments have been performed with a TNT charge detonated at the center of a single room sized space with rigid boundaries. The room has a limited size opening for venting at the ceiling. Numerical simulations of the problem have been performed using AUTODYN Ver. 12.1 and compared with the experimental measurements. Some deviations between the measured pressure and the predicted pressure motivated the present study in an attempt to study the effect of the additional energy released due to the burning of the detonation products reacting with the surrounding oxygen. The study that is described in this paper enhanced our understanding. Incorporation of this effect considerably improved the predictions. The present study clarified when, how and to what extent the afterburning should be introduced in the analysis.

Feldgun V.R.,Technion - Israel Institute of Technology | Karinski Y.S.,Technion - Israel Institute of Technology | Yankelevsky D.Z.,National Building Research Institute
International Journal of Protective Structures | Year: 2013

The paper presents the analysis of a buried explosion in the proximity of a tunnel in a soil medium. The soil is modeled as an elastic plastic material with irreversible bulk and deviatoric strains. The tunnel lining is modeled as an elastic plastic Timoshenko shell. An inclusion is placed in soil between the explosion source and the tunnel and its effect on the tunnel response is investigated. A coupled approach is proposed to allow to perform stable calculations of that complex problem and to follow the development of the large deformations and distortions of the tunnel lining's shape, as well as the large deformations of the explosive cavity. The effect of the rigid single inclusion or of the set of rigid inclusions located between the charge and the lined tunnel on the tunnel lining's response has been studied. When the inclusion is relatively distant from the lining, even a small inclusion improves the state of displacement and pressure of the lining, while when the inclusion is placed close to the lining, the lining's displacements increase. When the inclusion is small, its size slightly affects the lining shape while for middle sized inclusion the permanent displacement sharply decreases. Compared to the case of a single inclusion, a set of intermediate inclusions of the same size slightly decrease the peak stress at the front point and more significantly protects the periphery zone. The usage of larger inclusions yields better protection of the lining front part.

Hanaor A.,National Building Research Institute
International Journal of Space Structures | Year: 2011

The paper presents a concise overview of the main features of design and behaviour of reticulated spatial structures, and specifically double layer grids (DLGs) and single layer braced domes. Emphasis is laid on behavioural aspects which are peculiar to these structural systems and which require special attention in design. Some of these features: A susceptibility to progressive collapse; An important role played by joint rigidity, even in stiff systems like DLGs; Sensitivity to imperfections such as member lack of fit in DLGs, and geometrical distortions in shallow domes. Design strategies to deal with these problems and enhance structural efficiency are proposed.

Feldgun V.R.,Technion - Israel Institute of Technology | Karinski Y.S.,Technion - Israel Institute of Technology | Yankelevsky D.Z.,National Building Research Institute
International Journal of Protective Structures | Year: 2013

The paper presents an investigation on the response of a buried structure in a soft soil layer above a rock bed that is subjected to blast loading. A comprehensive approach to simulate the behavior of soft soil with a buried structure laying over a rock mass due to the dynamic (explosive) action in the rock mass is presented. The numerical algorithm was developed to simulate the shock wave propagation within the medium, considering both the bulk and deviatoric damage and taking into account the possible shear damage accumulation. It takes into account the contact conditions between the layers to simulate the shock wave transmission and the soil-structure interaction including their possible separation. The soil-lining interaction problem is solved by a combination of the variational-difference method (for the lining) and of the Godunov's method (for the soil). The coupling of these two approaches is performed by calculation of the contact stresses and velocities on the soil-lining boundary. Two types of the soil models were investigated - an ideal elastic plastic medium and an irreversible compressible medium with failure in bulk tension - and the results were compared with each other. The analysis of the free surface and interface velocities and displacements as well as the contact stresses and the damage at the media interface were carried out. The effects of the relative cover thickness on the interface and free surface behavior is studied. Analysis of the contact stresses at the soil-tunnel interface, was carried out. The effect of the charge location as well as the effect of the soil-rock interface on the tunnel's response was investigated.

Kenny A.,National Building Research Institute | Katz A.,National Building Research Institute
Cement and Concrete Composites | Year: 2015

The relationship between concrete mix properties and the properties of the interfacial transition zone (ITZ) formed around embedded rebar was investigated. Multiple samples of various mix compositions and bar orientations were prepared so as to represent common concrete technology. Water-to-cement ratios varied from 0.40 to 0.65 and powder (cement + limestone filler) contents ranged from 362 kg/m3 to 564 kg/m3. Over 1300 BSE images of the steel-concrete interface were taken and analyzed automatically. Statistical methods were used to identify correlations between ITZ properties and mix composition or fresh mix properties. A single large void was identified beneath all horizontal bars regardless of concrete composition. The ITZ around vertical bars was more uniform and extended around the entire rebar. No clear relationship was found between ITZ thickness and mix composition or fresh mix properties for either vertical or horizontal bar orientations. The degree of ITZ variability beneath horizontal bars clearly depends, however, on the bleeding properties of the mix. The distance from steel surface to the closest concrete solid, which influences the chemistry over the surface of the steel, is affected by precipitation of hydration products in horizontal bars, but not by mix composition. © 2015 Elsevier Ltd. All rights reserved.

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