Time filter

Source Type

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.


Karinski Y.S.,National Building Research Institute | Feldgun V.R.,National Building Research Institute | Yankelevsky D.Z.,National Building Research Institute
International Journal of Impact Engineering | Year: 2012

The paper presents a study aimed at understanding the blast pressure action on an inclusion embedded in soil due to a nearby underground explosion. The soil is modeled as an elastic plastic material with irreversible bulk and deviatoric strains for which the modified Godunov method has been applied. Two common geometrical inclusions are investigated (circular and rectangular) and the pressure distribution along their circumferences has been studied for various standoff distances from the initial explosive's cavity center. When the standoff distance is relatively small, the envelope of the pressure distribution shows that the maximum dynamic pressure is developed at some distance away from the axis of symmetry, otherwise asymmetrical pressure distribution is observed. © 2012 Elsevier Ltd. All rights reserved.


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.,National Building Research Institute | Yankelevsky D.Z.,National Building Research Institute | Karinski Y.S.,National Building Research Institute
International Journal of Impact Engineering | Year: 2016

The present paper aims at studying the blast response of rectangular elastic thin plates that undergo large deflections. The geometrically nonlinear behavior of the rectangular plate is presented in a nonlinear SDOF model and its detailed analysis is followed. Deflections, as well as bending stresses and membrane stresses for plates with immovable edges and with fully clamped or simply supported flexural edge conditions, are calculated to a uniformly distributed blast pressure loading. Validation of the SDOF technique is carried out through numerous comparisons of large amplitude response of square and rectangular plates under real blast loading, for both clamped and simply supported boundary conditions, with several experimental data as well as with numerical solutions obtained by various authors using the nonlinear Von Karman theory of plates. The coefficients of the nonlinear SDOF model are presented for various support (simple support and clamped) and edge stress conditions (immovable constrained, movable, and stress free). The useful expressions of the Airy function as well as of the dynamic membrane stresses are obtained for the above boundary conditions. A comparison of static and dynamic nonlinear solutions is performed. The relationship between the dimensionless deflection and the maximum membrane stresses is studied as well as their relationship with the corresponding maximum bending stresses. The nonlinear SDOF model has been compared with experimental data and with numerical (FEM, FDM) predictions and good agreement is obtained. © 2015 Elsevier Ltd. All rights reserved.


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.


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.


Feldgun V.R.,National Building Research Institute | Karinski Y.S.,National Building Research Institute | Yankelevsky D.Z.,National Building Research Institute
International Journal of Impact Engineering | Year: 2011

The paper presents a study aiming at simulation of some characteristics of an interior explosion within a room with an opening, that is initially closed by a heavy cover, and is gradually opened due to the pressures exerted by the explosion products. An effective simplified model of explosion venting due to separation of the protective cover has been developed. The developed model with lumped parameters is based on the Bernoulli equation and describes the quasi-stationary venting phase of the interior explosion. The initial internal gas pressure induced by the very short non-stationary phase is predicted by the developed approximate analytical formula, based on the full energy conservation law. The formula yields very good agreement with experimental data and with numerical analysis results. The simulation of the unsteady outflow from a cylindrical high-pressure vessel upon a sudden separation of the cover has shown that the developed simplified model yields the integral characteristics of the outflow process (such as a maximum cover's velocity and displacement etc.) with reasonable accuracy. The proposed approach is demonstrated by the simulation of gas outflow from a chamber upon a sudden separation of the cover or upon a rectangular shutter rotation about a fixed line hinge. The analysis has been performed using the developed simplified approach and through simulations with AUTODYN. A good correspondence between both methods has been obtained. The effect of gravity on the protective cover velocity and displacement has been also examined. © 2011 Elsevier Ltd. All rights reserved.


Feldgun V.R.,National Building Research Institute | Karinski Y.S.,National Building Research Institute | Yankelevsky D.Z.,National Building Research Institute
Structural Engineering and Mechanics | Year: 2011

The paper presents a study aimed at understanding some characteristics of an interior explosion within a room with limited or no venting. The explosion may occur in ammunition storage or result from a terrorist action or from a warhead that had penetrated into this room. The study includes numerical simulations of the problem and analytical derivations. Different types of analysis (1-D, 2-D and 3-D analysis) were performed for a room with rigid walls and the results were analyzed. For the 3D problem the effect of the charge size and its location within the room was investigated and a new insight regarding the pressure distribution on the interior wall as function of these parameters has been gained. The numerical analyses were carried out using the Eulerian multi-material approach. Further, an approximate analytical formula to predict the residual internal pressure was developed. The formula is based on the conservation law of total energy and its implementation yields very good agreement with the results obtained numerically using the complete statement of the problem for a wide range of explosive weights and room sizes that is expressed through a non-dimensional parameter. This new formula is superior to existing literature recommendations and compares considerably better with the above numerical results.


Dancygier A.N.,National Building Research Institute | Katz A.,National Building Research Institute | Wexler U.,National Building Research Institute
Materials and Structures/Materiaux et Constructions | Year: 2010

This paper describes an experimental study that consisted of pullout tests of deformed reinforcing bars in NSC and HSC specimens, with and without hooked-end steel fibers. Two types of test setups were applied, direct and flexural tests, and three bar diameters were tested (8, 12 and 20 mm). The experimental setups were based on standard RILEM pullout (direct) and beam tests, with several modifications. The experimental program included study of the effects of concrete strength and inclusion of steel fibers on the bond strength, as well as the influence of bar geometry and concrete cover. Discussion of the results shows coupling of these effects and proposes an empirical expression that represents this coupling. The results from the current study are also compared with the design bond strengths specified in American and European standards as well as a known model. © RILEM 2009.


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.

Loading National Building Research Institute collaborators
Loading National Building Research Institute collaborators