Calculation of Blast Loads for Application to Structural Components. Administrative Arrangement No JRC 32253-2011 with DG-HOME Activity A5 - Blast Simulation Technology Development

This technical report describes a procedure that can be followed for the calculation of the loads to be applied to a structure as a consequence of a blast. The report considers explosions taking place outside a building, which are not addressed directly at the relevant European Standards (Eurocode EN1991-1-7) dealing with accidental loading scenarios. The aim is the production of a simple, self-contained guide enabling the structural engineer to conduct a preliminary design of buildings for possible terrorist attacks. Aspects of the theory of blast waves have been included at an introductory level. The approach of the empirical methods for the prediction of blast loads has been chosen, which is more straightforward and has resulted from extensive experimental testing. For the determination of the main blast parameters, several graphs and diagrams have been included, which have been collected and properly adapted from several authoritative sources. This should make the load calculation procedure easier to grasp and less demanding in terms of mathematical complexity and computational capacity. Selected case studies are also presented in order to demonstrate through simplified examples the steps that must be followed for the calculation of blast pressures on the surfaces of a structure.JRC.G.4-European laboratory for structural assessmen

Progressive collapse risk analysis: literature survey, relevant construction standards and guidelines

A technical literature survey has been conducted concerning the problems of building robustness and progressive collapse. These issues gained special interest in construction after the partial collapse of the Ronan Point apartment building in London in 1968. Enhanced interest appeared again after the disproportionate collapse of the A.P. Murrah Federal Building in Oklahoma City in 1995, and the total collapse of the World Trade Center towers in 2001, both caused by terrorist attacks. This report, which is an updated version of the 2009 one, aims at summarising the state-of-the-art in the subject of progressive collapse risk of civil engineering structures. First, a list of main terms and definitions related to progressive collapse are presented. Then, a review of procedures and strategies for progressive collapse avoidance is provided, based on selected EU and US design codes, standards and guidelines. A review of research efforts and results in the field follows, as reported in international journals and conference papers. Different proposals of robustness measures of structures are also examined, and some characteristic cases of progressive collapses of real buildings are presented.JRC.G.5-European laboratory for structural assessmen

Development of a Hopkinson bar apparatus for testing soft materials: application to a closed-cell aluminum foam

An increasing interest in lightweight metallic foams for automotive, aerospace and other applications has been observed in recent years. This is mainly due to the weight reduction that can be achieved using foams and for their mechanical energy absorption and acoustic damping capabilities. An accurate knowledge of the mechanical behavior of these materials, especially under dynamic loadings, is thus necessary. Unfortunately, metal foams and in general “soft” materials exhibit a series of peculiarities that make difficult the adoption of standard testing techniques for their high strain-rate characterization. This paper presents an innovative apparatus, where high strain-rate tests of metal foams or other soft materials can be performed by exploiting the operating principle of the Hopkinson bar methods. Using the pre-stress method to generate directly a long compression pulse (compared with traditional SHPB), a displacement of about 20 mm can be applied to the specimen with a single propagating wave, suitable for evaluating the whole stress-strain curve of medium-sized cell foams (pores of about 1-2 mm). The potential of this testing rig is shown in the characterization of a closed-cell aluminum foam, where all the above features are amply demonstrated.JRC.G.4-European laboratory for structural assessmen

Review on vehicle barrier protection guidance

A search and review of publicly available documents with guidance on the security of designated spaces against vehicle-ramming attacks has been conducted. The current report provides a list of these sources, which focus on the protection of public spaces, such as pedestrian areas, tourist sites, city squares or other perimeter protected areas. The list aims at bringing to the interested security stakeholders information on measures to prevent potential attacks and/or mitigate their consequences by properly designed and tested barrier systems.JRC.E.4-Safety and Security of Building

Review on Soft target/Public space protection guidance

The current document provides a list of the available information sources focusing on the protection of soft targets against terrorist and other types of malicious extremist attacks. The list aims at bringing to the interested security stakeholder existing documents with information and practical guidance on measures to prevent a potential attack and to mitigate the consequences, should such an attack materializes. The collected documents do not address critical infrastructure, but they mainly focus on the so-called soft targets, the term being used to represent vulnerable material or human assets, which in principle should not be specifically protected. However, such targets are often selected by terrorists in their effort to maximize casualties, inflict fear to the population and attain media coverage. The documents are grouped according to the following broad domains relating to soft targets: public places, education/religious/health installations, transport, building facades, urban resilience, security planning & risk management, policy/regulation/finance, people involvement, and drones. The referenced information sources originate from various countries and bodies, such as UK, France, Sweden, Czech Republic, USA, Australia etc. The list is quite comprehensive but it is limited to the publicly available documents and practically to those found in English and French.JRC.E.4-Safety and Security of Building

Simulation of blast waves by using mapping technology in EUROPLEXUS

Finite element or finite volume simulations for the development of blast waves by using a model for the explosion of the solid itself need very fine meshes in the explosive and in the zone around the explosive. Structures may have a long distance to the source of the explosive. This leads often to very big meshes with many elements. The explosive is meshed often only coarse and therefore the results are not very accurate. There are several possibilities to deal with this problem. Large 3D calculations with a solid TNT model using a JWL-equation can be used but they are more effective when the results of one finer mesh could be mapped in a coarser mesh after some calculation steps. When the blast wave reaches a certain distance to the charge, the small elements inside the charge are not needed any more since the pressure ratio is decreased strongly. These small elements results in very small time steps for the full model. The report shows the implementation of the mapping algorithm in EUROPLEXUS and several validation tests of the method.JRC.G.4-European laboratory for structural assessmen

BLAST Simulator Project: Performance assessment and preliminary tests. Administrative Arrangement No JRC 32253-2011 with DG HOME Activity A5 – Blast Simulation Technology Development

The Blast Simulator project involves the development of an apparatus able to reproduce the effects of a blast pressure wave on large scale structural components (such as columns, walls, etc.) with the objective to improve their strength in these severe loading situations. This technical report presents the setting up and the performance assessment of the prototype blast actuator developed at the JRC. The first preliminary tests performed have been described and evaluated. Satisfactory results have been obtained with respect to impacting masses and velocities and with the finally obtained pressure values.JRC.G.5-European laboratory for structural assessmen

Advances in the Hopkinson bar testing of irradiated/non-irradiated nuclear materials and large specimens

A brief review of the technological advances of the Hopkinson bar technique in tension for the study of irradiated/non-irradiated nuclear materials and the development of this technology for large specimens is presented. Comparisons are made of the dynamic behaviour of non-irradiated and irradiated materials previously subjected to creep, low cycle fatigue and irradiation (2, 10 and 30 displacements per atom). In particular, complete results of the effect of irradiation on the dynamic mechanical properties of AISI304L steel, tested at 20, 400 and 550◦C are presented. These high strain rate tests have been performed with a modified Hopkinson bar (MHB), installed inside a hot cell. Examples of testing large nuclear steel specimens with a very large Hopkinson bar are also shown. The results overall demonstrate the capability of the MHB to efficiently reproduce the material stress conditions in case of accidental internal and external dynamic loadings in nuclear reactors, thus contributing to the important process of their structural assessment.JRC.G.4-European laboratory for structural assessmen

Compressive behaviour of dam concrete at higher strain rates

The mechanical behaviour of concrete when subjected to impact or blast has still many aspects requiring further study. Dam concrete is characterized by large coarse aggregates, hence large specimen sizes are needed in order to study a representative volume of the material. Exploiting an innovative equipment, based on Hopkinson bar techniques, the dynamic behaviour of concrete of 64~mm maximum aggregate size has been investigated. Direct dynamic compression tests have been performed on medium and large size cylindrical samples. Full stress-strain curves have been obtained, which have allowed the estimation of fracturing energies and of the relevant dynamic increase factor. The experimental campaign has also included a reference standard concrete in order to highlight the peculiarity of the dam concrete at high strain rates and to validate the transition of this type of testing to very large specimens.JRC.G.4-European laboratory for structural assessmen

Numerical simulations in support of the blast actuator development

Nowadays there is a need to develop special techniques to protect the critical infrastructures from exposing events. The use of real explosive material on the experiments is very expensive and a lot of security measures should be taken. Especially in the case that the test should be repeated many times in order to obtain accurate results is almost impossible to perform the real explosive experiments. That for came up the idea of a blast simulator that can reproduce an explosive charge in a most economic and controllable way. The setup of such an apparatus is a very difficult task where many details should be studied. The most appropriate way to study the several parameters that influence the performance of the blast actuator is to use numerical simulation techniques. This report performs numerous numerical investigations and gives answers to many questions concerning the performance of the impacting mass of the blast actuator on the specimen. The numerical results have been generated with the fast explicit transient dynamic finite element code EUROPLEXUS.JRC.G.5-European laboratory for structural assessmen