Josef Eibl

Numerical analysis of high speed concrete fragmentation using a meshfree Lagrangian method

The topic of this paper is the fragmentation of concrete due to explosive loading. A meshfree Lagrangian method called smooth particle hydrodynamics (SPH) is used in the numerical simulation. A macroscopic constitutive law for concrete is implemented in the SPH-Code. It is shown that the SPH-method is able to simulate the damage of concrete slabs under contact detonation. The numerical results are compared with the data from two tests. The good agreement between them suggests that the SPH-program can predict the correct maximum pressures as well as the damage of the concrete slabs. Finally the fragment distributions of the tests and the numerical calculations are compared.

Crack velocity in concrete

Abstract An experimental investigation to determine the crack velocity in concrete is discussed. Apart from the description of the equipment and the measurement technique, main attention is paid to the results and their dependence on strain rate. Finite element calculations which were carried out using a special constitutive model for the descending branch of concrete under tensile loading show that the maximum value of crack velocity is strongly affected by the shape of the stress-strain diagram.

Severe accident containment loads and possible design concepts of future large pressurized water reactors

The risk of present-day light water reactors is dominated by the consequences of core melt accidents followed by a failure of the outer containment. Although such events would have very low frequencies of occurrence, their risk cannot be neglected in the future. Therefore, specifications for mechanical loads and heat loads to the containment are analyzed, and design modifications are proposed, explaining how the containment can withstand the consequences of core melts. As a result, the radiological impact outside of the containment will be drastically decreased. Evacuation of the population outside of the reactor plant will no longer be necessary in the case of a core melt.

An attempt to explain strength increase due to high loading rates

Abstract Most materials such as steel, concrete, ceramics, polymers, etc. show an increase of strength due to high loading rates. A number of mathematical equations are available to describe this behaviour. Nevertheless the physical reasons for these observations are still unknown. The common behaviour of a number of materials leads to the assumption that at least some explanations are material independent. Due to this reason the results of the research done at the Institute for Concrete Structures in Karlsruhe are presented in this paper to furnish new ideas for the material research due to dynamic loading.

Impact research for containment design

Abstract Engaged for many years in research work concerning the safety and integrity of nuclear containments, the first author has performed numerous theoretical and experimental investigations at this institute. Airplane crashes on nuclear power plants, as well as containment attacks by detonation and missiles generated by bursting vessels have been studied with respect to practical design. Also, a series of fundamental researches has been done to evaluate constitutive laws for shockwaves in concrete and constitutive relations for concrete with regard to strain rate effects. Further investigations have focused on friction phenomena for projectiles impinging on concrete.

Inherently safe containments for nuclear power plants

Abstract Nuclear energy cannot be avoided in the near future. To regain public acceptance the safety of nuclear power plants has to be increased. Consequently, feasibility studies have been carried out for a containment proposal for future pressurized water reactors which will keep people unharmed even in the case of severe nuclear accidents under the assumption “all that can go wrong, will go wrong”. The main features of the design concept are a core melt cooling and retention device, a passively acting cooling system to remove the decay heat and a double-wall containment which is able to withstand high static and dynamic internal pressures due to hydrogen detonation. Internal structures are designed to resist extreme loadings resulting from various accident scenarios including in-vessel steam explosion and vessel failure under high system pressure.

Advances in the analysis and design of concrete structures, metal containments and liner plate for extreme loads

The material presented in this paper summarizes the progress that has been made in the analysis, design, and testing of concrete structures. The material is summarized in the following documents: 1. Part I - Containment Design Criteria and Loading Combinations - J.D. Stevenson (Stevenson and Associates, Cleveland, Ohio, USA) 2. Part II - Reinforced and Prestressed Concrete Behavior - J. Eibl and M. Curbach (Karlsruhe University, Karlsruhe, Germany) 3. Part III - Concrete Containment Analysis, Design and Related Testing - T.E. Johnson and M.A. Daye (Bechtel Power Corporation, Gaithersburg, Maryland USA) 4. Part IV - Impact and Impulse Loading and Response Prediction - J.D. Riera (School of Engineering - UFRGS, Porto Alegre, RS, Brazil) 5. Part V - Metal Containments and Liner Plate Systems - N.J. Krutzik (Siemens AG, Offenbach Am Main, Germany) 6. Part VI - Prestressed Reactor Vessel Design, Testing and Analysis - J. Nemet (Austrian Research Center, Seibersdorf, Austria) and K.T.S. Iyengar (Indian Institute of Science, Bangalore, India).

Feasibility study for a containment to resist core-melt accidents

A feasibility study has been performed for a light water reactor containment able to resist even severe accidents by passive means. Upper-bound design loads have been considered for all physically possible scenarios after a core-melt accident as determined by Kernforschungszentrum Karlsruhe. The essential layout of this containment is presented. Based on the main system features of a German 1,300-MW Convoy reactor type, internal static pressure, hydrogen detonation, failure of the pressure vessel under high pressure, and steam explosion, respectively, have been regarded as well as such external loads as an airplane crash, earthquake, gas explosion, and so forth. The containment can remove the decay heat by purely passive means, and it is believed that the design can be realized at reasonable costs.

Experiments on concrete under shock loading

On detonations or hypervelocity impacts concrete structures are loaded with shockwaves. These shockwaves cause a steep increase in pressure within the wavefiont which propagates at high velocity. For a numerical simulation of such process a constitutive material law F = f (E, E, T) is needed which adequately describes concrete under these conditions. As basis for such a constitutive law tests on concrete under explosive loads were performed and different material parameters were investigated. We report our approach to measure material parameters during tests with different explosive charges on concrete and our model tests for demolition work. We got first experience in using a new temperature sensor, called the atomic layer thermopile, to measure the temperature raise caused by the adiabatic compression. This sensor was developed for performance measurement of high energetic laser pukes, The mode of operation of this sensor is based on the temperature g-adient between the sensor surface and the base of the device. Very fast response time is possible, because there is no need of getting a complete heat transfer from the ambient concrete temperature to the whole sensor. Responsible for the output voltage proportional to the temperature rise is the thermal Seebeck-effect which can be splitted in a longitudinal and a transversal component due to the orientation of the layers. For stress measurement manganin gauges and for strain measurement ordinary strain gauges were used. For the application of these methods at high velocity loads in concrete special encapsulations are needed in order to save the functionality and to provide fast rise times of the output signals. Results of the measurements will be shown and remaining problems will be discussed.

The SPH/MLSPH Method for the Simulation of High Velocity Concrete Fragmentation

The topic of this paper is the application of the SPH/MLSPH-method to high velocity concrete fragmentation. After a short review of the SPH/MLSPH method, a beam under static concentric loading and linear elastic material behavior is considered to show the advantage of MLSPH in opposite to SPH. A constitutive law for concrete taking into account the dynamic strength increase under high velocity loading is briefly proposed. Finally, the application of the SPH/MLSPH-Code in conjunction with this constitutive law for concrete onto two concrete slabs under contact detonation is discussed. The SPH and MLSPH-results obtained with different particle number and smoothing lengths are compared with the experimental results.