Arja Saarenheimo

Design of blast-loaded glazing windows and facades: A review of essential requirements towards standardization

The determination of the blast protection level of laminated glass windows and facades is of crucial importance, and it is normally done by using experimental investigations. In recent years numerical methods have become much more powerful also with respect to this kind of application. This paper attempts to give a first idea of a possible standardization concerning such numerical simulations. Attention is drawn to the representation of the blast loading and to the proper description of the behaviour of the material of the mentioned products, to the geometrical meshing, and to the modelling of the connections of the glass components to the main structure. The need to validate the numerical models against reliable experimental data, some of which are indicated, is underlined.

Comparison of approaches for estimating pipe rupture frequencies for risk-informed in-service inspections

Abstract This paper describes the comparative study of two approaches to estimate pipe leak and rupture frequencies for piping. One method is based on a probabilistic fracture mechanistic model while the other one is based on statistical estimation of rupture frequencies from a large database. In order to be able to compare the approaches and their results, the rupture frequencies of some selected welds have been estimated using both of these methods. This paper highlights the differences both in methods, input data, need and use of plant specific information and need of expert judgement. The study focuses on one specific degradation mechanism, namely the intergranular stress corrosion cracking. This is the major degradation mechanism in old stainless steel piping in BWR environment, and its growth is influenced by material properties, stresses and water chemistry.

Fracture behaviour of large scale pressure vessels in the hydrotest

Abstract Within the Nordic Countries a four-year research programme in the area of elastic-plastic fracture mechanics was initiated in 1985. This programme aims to assess the leak-before-break (LBB) criteria for pressure vessels and piping. The main experimental effort of the programme is to rupture large size pressure vessels, one having dimensions resembling those of a nuclear reactor pressure vessel, under internal pressure. Artificial flaws were made on the inner wall of the vessels. The dimensions of the flaws were defined by calculations so that the LBB condition was just anticipated during the test. For the time being two tests have been performed. The first test with a large pressure vessel was pressurized by water at 60°C, which was the lowest acceptable temperature for the hydrotest. In this paper experimental details including flaw preparation, instrumentation and material characterization are described. The fracture behaviour as well as experimental results of the tests are reported and compared to the analytical solutions of the analyses.

Validation of experimental and computational fracture assessment methods for flawed pressure components

Abstract Safety and integrity assessments of pressure boundary components require reliable knowledge of the material property values and the validated experimental and computational analysis methods. To improve the accuracy and validity of the experimental and computational fracture assessment methods, a four year Nordic research programme under the auspices of the Nordic Liaison Committee of Atomic Energy was initiated in 1985 and is now under completion. The main technical objective of the programme was to clarify how catastrophic failure can be prevented in pressure vessels and pipings. Experiments with small fracture mechanics specimens and pressure vessels were performed to validate the computational fracture assessment analysis. Two tests were conducted on a decommissioned full-scale chemical reactor pressure vessel from an oil refinery plant, and were extensively instrumented, e.g. by utilizing a 64-channel acoustic emission monitoring system. The scattering of their material property values were determined by numerous fracture mechanics samples. In addition, as a part of the experimental work, the reactor pressure vessel was repaired by welding after the first test. The repair was carried out without postweld heat treatment and welding was done by applying the temper-bead technique. Residual stresses were measured during and after welding. Different fracture assessment methods were developed and subsequently applied to the tested components. Inter-laboratory round robin programmes with the participation of several laboratories were arranged to examine elastic-plastic finite element calculations and fracture mechanics testing.

Fracture behaviour simulation of flawed full scale pressure vessel

Abstract In 1985 a four year research programme in elastic-plastic fracture mechanics was initiated within the Nordic countries. The aim of the programme was to verify the methods used for fracture analysis of real structures. A large cylindrical pressure vessel, having dimensions resembling those of a nuclear reactor pressure vessel, was tested in 1986. An artificial sharp axial surface flaw was made on the inner wall of the vessel. One of the circumferential welds intersected the crack at its midpoint. Failure of the vessel occurred as local rupture in the weld area. A maintenance deck, which was located around the midsection of the pressure vessel, was partially removed so as to prevent interference with the expected vessel deformations upon pressurization. After the test, two three-dimensional nonlinear finite element analyses were performed taking into account the existence of the circumferential weld in the ligament. In the first case, the original flawed structure was modelled allowing for different stress-strain curves of the base and weld material. In the second analysis, the model included a short through-the-wall crack in the weldment. Additionally, a simple two-dimensional analysis was made assuming the crack to be infinitely long in the axial direction. A three-dimensional analysis was repeated without considering the effect of the maintenance deck. For fracture mechanics evaluation, J- integrals along the crack front were calculated. In this paper, results of the three-dimensional analyses are reported and compared to experimental findings.

Recommendations for the improvement of existing European norms for testing the resistance of windows and glazed facades to explosive effects

It is important to protect critical buildings (shopping centres, government buildings and embassies), infrastructure and utilities, train and underground stations from being damaged, destroyed or disrupted by deliberate acts of terrorism, criminal activity and malicious behaviour. Normal regulations and building guidelines do not generally take into account these threats. The introduction of appropriate regulations or guidelines, where deemed necessary, should enhance the resilience of buildings and infrastructures against explosion incidents. In order to protect the built infrastructure, testing methods are required which can answer the question whether certain building elements can withstand certain loading conditions created by an explosive event. The applicable state-of-the-art techniques may include either experimental or numerical methods, or a combination of both. Therefore, the thematic group (TG) on the resistance of structures to explosion effects was formed in order to bring the required expertise together, to make it commonly available and to find and define harmonised methods and solutions which can be provided to the decision-makers responsible for critical infrastructure protection. The TG described in a fist report [JPC87202] the physical phenomena which have to be understood in order to ensure a proper testing of the elements and a correct interpretation of the results. In a second step, the differences between the existing standards for testing blast-resistant glazing and windows have been derived, and a basis for fundamental recommendations for the future development of the suite of European standards has been addressed [JRC94930]. Based on the prior findings, this report now formulates the proper enhancements of the existing standards in terms of actual recommendations for the improvement of the test standards.

Resistance of structures to explosion effects. Review report of testing methods

It is important to protect critical buildings (shopping centres, government buildings and embassies), infrastructure and utilities, train and underground stations against being damaged, destroyed or disrupted by deliberate acts of terrorism, criminal activity and malicious behaviour. Normal regulations and building guidelines do not generally take into account these threats. The introduction of regulations or guidelines should support the resilience of the buildings and infrastructure against explosive incidents. In order to protect the infrastructure, methods are required to quantify the resistance of structural elements against explosive loading and to assess the hazards resulting from failure of an element. The applicable state-of-the-art techniques may be either experimental or numerical methods, or a combination of both. Therefore, the thematic group (TG) on the resistance of structures to explosion effects was formed in order to bring the required expertise together, make it commonly available and to find and define harmonised methods and solutions which can be provided to the decision-makers responsible for critical infrastructure protection. This first report of the TG gives a comprehensive summary of the existing methods which can be used to analyse and test the resistance of glazing and windows under blast-loading conditions. Within this context, the experimental methods of testing using high explosives and testing using blast simulators called shock tubes is presented and explained. In addition, the potential of numerical simulations is highlighted in terms of their applicability to the different glass materials. A short, comprehensive theoretical background is given for each method. Based on this, each method is described with its requirements, realisation and the related measurement techniques. Furthermore, an interpretation of the measurements is highlighted. For the numerical simulations, the basic discretisation and calculations schemes are presented in combination with the available constitutive material descriptions for the different significant materials. Finally the chances for verification and validation of the numerical results are presented. Hence the report builds the basis for an actual evaluation of the different test methods and their applicability to certain problems, and provides helpful information for critical infrastructure stakeholders, owners and operators considering the structural resistance of the infrastructure to the effects of explosion in a comprehensive document.

Numerical and Experimental Studies on Impact Loaded Concrete Structures

An experimental set-up has been constructed for medium scale impact tests. The main objective of this effort is to provide data for the calibration and verification of numerical models of a loading scenario where an aircraft impacts against a nuclear power plant. One goal is to develop and take in use numerical methods for predicting response of reinforced concrete structures to impacts of deformable projectiles that may contain combustible liquid (“fuel”). Loading, structural behaviour, like collapsing mechanism and the damage grade, will be predicted by simple analytical methods and using non-linear FE-method. In the so-called Riera method the behavior of the missile material is assumed to be rigid plastic or rigid visco-plastic. Using elastic plastic and elastic visco-plastic material models calculations are carried out by ABAQUS/Explicit finite element code, assuming axisymmetric deformation mode for the missile. With both methods, typically, the impact force time history, the velocity of the missile rear end and the missile shortening during the impact were recorded for comparisons.Copyright

Recommendations for a new generation of standards for testing numerical assessment of blast-loaded glass windows

The determination of the blast protection level of civil engineering buildings components against explosive effects represents a design topic of crucial importance, in current practice. However, some key aspects of blast resistant structures design have been only marginally considered in the last decade, and currently still require appropriate regulations. This is especially true in the case of glass windows and facades, where the intrinsic material brittleness is the major influencing parameter for blast-resistant assemblies. While blast assessment of buildings and systems is usually achieved by means of experimental investigations, as well as Finite-Element numerical simulations, general regulations and guidelines are currently missing. In this regard, the European Reference Network for Critical Infrastructure Protection - Task Group (ERNCIP-TG) “Resistance of Structures to Explosion Effects” attempts to develop guidelines and recommendations aimed to harmonise test procedures in experimental testing of glass windows under blast, as well as standardized approaches for their vulnerability assessment via Finite Element numerical modelling. In this paper, major ERNCIP-TG outcomes and next challenges are briefly summarized.

A set of essential requirements towards standardising the numerical simulation of blast-loaded windows and facades

The determination of the blast protection level of laminated glass windows and facades is of crucial importance, and it is normally done by using experimental investigations. In recent years numerical methods have become much more powerful also with respect to this kind of application. This report attempts to give a first idea of a possible standardisation concerning such numerical simulations. Attention is drawn to the representation of the blast loading and of the behaviour of the material of the mentioned products, to the geometrical meshing, as well as to the modelling of the connections of the glass components to the main structure. The need to validate the numerical models against reliable experimental data, some of which are indicated, is underlined.