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Explosionsschutz von Fenstern und Fassaden: Angewandte Grundlagen und Methoden
Abstract
Blast resistance of windows and facades: Applied fundamentals and methods. Explosion events represent an extraordinary action for buildings and the envelope. Causes include terrorist attacks and accidents as well as armed conflicts. Debris and fragments resulting from the failure of windows and facades endanger people inside and outside the building. For buildings at risk, blast resistance should be considered in the design (Security by Design). However, the design and construction of a blast-resistant building envelope is not a trivial task. The goal of this article is to give an introduction to blast resistance. Beside fundamentals of blast and structural behavior, failure modes of windows and methods for the verification of blast resistance are described.
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Blast loading scenarios and the corresponding hazards have to be evaluated for infrastructure elements and buildings especially at industrial sites for safety and security issues. Point fixed corrugated metal sheets are often applied as façade elements and can become a hazard for humans if they are pulled off.
This paper investigates the dynamic bearing capacity of such structural members in terms of their general bending behavior in the middle of the span and pull-out behaviors at the fixing points. The elements are fixed at two sides and the load transfer is uniaxial. An experimental series with static and dynamic tests forms the basis to identify the predominant failure modes and to quantify the maximum stress values that can be absorbed until the investigated structural members fail.
The experimental findings are applied to create and to optimize an engineering model for the fast and effective assessment of the structural response. The aim is the derivation of a validated model which is capable to predict the blast loading behavior of metal sheets including arbitrary dimensions, material properties, and screw connections. Results of this study can be integrated into a systematic risk and resilience management process to assess expected damage effects and the evaluation of robustness.
Protective glazing is an important field of research and development as most common injuries resulting from an explosion event in urban territory are caused by the occurring shock wave and accelerated fragments of failed glass structures. In this context a selection of laminated glass specimens differing in lamination technique, extent of tempering and interlayer material is tested in shock tube experiments at the facilities of the Bundeswehr Technical Center 52 (WTD 52) in Oberjettenberg. Unlike conservative testing the specimen is subjected to a combination of blast and temperature loading. The influence of the interlayer temperature on the laminate behavior is examined according to the elastic response of the composite. Furthermore the paper focusses on the residual load carrying capacity after fracture of the glass component. An assessment of the specimen performance is undertaken by a work balance approach, which leads to the determination of energy dissipation capacities in elastic and damage configurations. This method is suitable for a further breakdown of internal work and dissipation processes. Fracture patterns are evaluated to identify crack densities along paths of principal normal stress. The average strain and strain rates close to originated crack centers are determined. Finally the testing results are superimposed to estimate the impact of material and loading parameters on the overall performance.
Bemessungslasten auf Tragwerke aus Explosionsszenarien müssen immer individuell untersucht werden Für die Bemessung von Tragwerken, die einer Ex- plosion ausgesetzt sind, wird die bemessungsrele- vante Einwirkung benötigt. Im folgenden Aufsatz wird die Berechnung der Bemessungslasten aus Explosionsszenarien gezeigt und die Bestimmung des reflektierten Spitzenüberdruckes bzw. des Re- flexionsfaktors bei der senkrechten Reflexion von Luftstoßwellen beschrieben. Fazit: Jeder Einzelfall muss individuell untersucht werden. Im Falle der Ferndetonation können die Einwirkungsparame- ter reflektierter Spitzenüberdruck und Dauer der positiven Druckphase bestimmt werden. Der re- flektierte Druck und der Reflexionsfaktor bei der senkrechten Reflexion einer Luftstoßwelle an einer starren Oberfläche werden explizit berechnet. Ab- schließend wird untersucht, wie sich der Reflexi- onsfaktor bei nachgiebigen im Vergleich zu starren Materialien ändert. Damit wird überprüft, wann die Annahme einer starren Reflexion gültig ist*.
Dieses Kapitel beschreibt die Gef?hrdung der Stahlkonstruktion aus direkter Explosionseinwirkung bei Nah- und Ferndetonation. Liegenschaftsbezogene Planungsans?tze liegen hierbei au?erhalb der Tragwerkskonzepte, sofern deren Realisierung nicht eigenst?ndige Strukturelemente ben?tigt. Der bauliche Brandschutz auf Tragwerksebene beruht auf der Zielsetzung, dass Tragf?higkeitsverminderungen infolge Brandeinwirkung durch Kr?fteumlagerungen in angrenzende Bauwerksbereiche kompensiert werden k?nnen, um ein lokales Versagen auszuschlie?en. Die Vermeidung des lokalen Versagens ist ein rein bauteilbezogener Planungsansatz, der jedoch Robustheit ohne weitere tragwerksbezogene Ma?nahmen gew?hrleisten kann. Ma?nahmen des anlagentechnischen Brandschutzes fokussieren prim?r auf die Alarmierung und die Erhaltung einer rauch- und gasarmen Atmosph?re, um Geb?udenutzern das ?berleben und die Flucht zu erm?glichen. Das Kapitel beschreibt die auf Fenster und Fassaden einwirkenden Belastungen infolge einer Explosion sowie M?glichkeiten zur Entwicklung und Verbesserung von Schutzkonstruktionen durch Versuche und numerische Simulationen. Die weiteren Entwicklungen zielen neben einer Verfeinerung des rechnerischen Modells durch Ber?cksichtigung eines verbesserten und realistischeren Materialverhaltens auf die genauere rechnerische Simulation des Versagensvorganges ab.
The standard approach in protective design is to model blast loads with a triangular pulse shape which is characterized by the peak reflected overpressure and the reflected impulse. The US and European threat levels, GSA and ISO EXV, define pressure-impulse combinations for blast load characterization. However, this approach neglects the underpressure phase. The actual decay of a blast load is nonlinear and can be modeled more accurately with an exponential approach which takes into account the underpressure phase. When considering underpressure effects, however, special attention should be paid to the modeling of the different reflection effects for the over- and underpressure phase. The authors derive a new reflection coefficient for the maximum underpressure. Based on a single degree of freedom system, the authors then determine the influence of the reflected underpressure phase for different systems. Especially for flexible systems subjected to weak blast loads, the underpressure significantly dominates the structural response. In these cases, the standard triangular approach is not on the safe side. This paper presents new demarcation criteria to rapidly assess the influence of the underpressure phase.
After an initial qualitative characterization of the properties of
explosions in the atmosphere and their blast and shock propagation
effects, attention is given to the underlying quantitative principles of
explosive energy release, including the scaling laws for explosions and
internal blast effects from confined explosions. The dynamic loads that
blast waves impose on representative structures are then characterized,
with attention to resulting structural damage. A major feature of the
present treatment is the use of the dimensionless Mach number in all
shock equations; a further simplification is furnished by first
developing mathematical equations for shock in steady flow, and then
applying these equations to explosive shock by simple transformation of
coordinates.
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