Building Blast Analysis - BMT Fluid Mechanics

1 Building Blast Analysiswind engineering & architectural aerodynamicsLondon | Hong Kong | Kuala Lumpur | Abu Dhabi | Dubai | Shanghai | Houstondynamic loading produced by the detonation of high-explosive materials is, unfortunately, an increasingly important load case that designers of important structures need to consider for the safety of the people interacting with the structure and integrity of the structure itself. Tel: +44 20 8614 4400 Fax: +44 20 8943 3224 Email: Website: recent years, considerable attention has been given to explosive loads on landmark structures as a result of both accidental and intentional events.

2 At the same time, Building designers the world over have been increasingly pushing the boundaries on design with ever more demanding architectural and structural forms and utilizing advanced structural materials and methods. understanding how these designs and materials are able to withstand Blast loads and maintain structural integrity is now no longer possible with semi-empirical methods without making highly conservative assumptions that drive up asset cost and compromise design. the balance of compromising design for the safety of the structure is heavily influenced by the acceptable level of risk.

3 A risk-based approach to design for Blast loading should be taken where accurate methods are employed to assess the consequence of an event, and combined with the likelihood of an event occurring. Bmt have taken their extensive experience in risk-based explosion load Analysis from the oil and gas industry and coupled it with class-leading software for non-linear dynamic structural finite element Analysis (Fea), and unparalleled knowledge of structural environmental loadings to provide the construction industry a complete package for Blast load design. the approach that Bmt provide through all stages of design ensures that the risk posed to Building occupants and structural integrity from terrorist and other explosions is significantly identification of key threats is the first stage of any Blast study for a new development.

4 Explosion threat scenarios are typically specified in terms of an explosive charge weight at a standoff distance from the target structure. Bmt works closely with security consultants and governmental bodies to determine the likelihood of a given scenario occurring. Key services identification and assessment of likely threat scenarios Blast load Prediction non-linear dynamic structural Analysis to assess resistance to Blast loading Analysis of Blast resistant fa ade and glazing systems advice on Blast resistant design and development of mitigation measures risk-based assessments determination of protection levels Building evacuation Analysis Key BeneFits risk-based assessment of security related threats cost effective structural and fa ade designs that balance an acceptable level of risk interactive solution development iterative

5 Design optimisation visualisations of the Blast waves, cladding and structural response to aid design development Blast loadsthreat assessmentOverpressure resulting from a small device (~20kg TNT equivalent) detonated in a built-up urban area. Reflection of the Blast wave-front is shown, resulting in successive cycles of quantification of Blast loads on structures from explosion events requires the accurate modelling of peak overpressures and the associated impulse from the expanding gases of detonation as well as taking into account the geometric effects of Blast wave reflection and diffraction.

6 The recent developments in the fields of computational Fluid dynamics (cFd) and non-linear Finite element Analysis (Fea) have meant there have been significant advances in the prediction of Blast loads that were not possible up until recently. accurate explosionloads and structural responses can now be modelled using software that couples these technologies for complex designs and for a range of threat use advanced three-dimensional cFd software to calculate the evolution and movement of the Blast pressure wave through the air and its interaction with surrounding structures. the end result is an accurate Blast pressure distribution across the structure that is then coupled to the dynamic structural response of a structure s occupants by the fa ade system is the first line of defence against Blast .

7 However, for extreme events or events where terrorists target weak points in a structure s design, the integrity of the structure is vitally important. Bmt can carry out detailed Blast Analysis to ensure that the structure is robust enough to maintain integrity for an acceptable Blast risk event through the development of alternate load paths. the Analysis of structural elements to resist Blast loading requires a dynamic Analysis with non-linear ductile response where ultimate limit state assessments are carried out. where complete structural failure is predicted, Bmt can work with the Building designer to develop alternative load paths and mitigation of structural elementsdesign of Protected sPacesdesign advice & mitigation measuresin some buildings, it is necessary to design protected spaces that are hardened to resist the effects of external explosions and protect the occupants inside or a critical piece of equipment.

8 In the event of a bomb threat, sometimes it is safer for the Building occupants to seek internal shelter or to evacuate through subterranean exits due to the high risk of injury from falling glass and other debris that occurs over a wide area. Bomb shelter areas (Bsas) are ideally located in basements using reinforced concrete and away from areas exposed to high Blast and direct fragment hazards. to ensure that the Bsa does not become a hazard itself to evacuees, it is vitally important to determine the protection offered for a range of threats. in other words, its limiting Blast capacity must be are able to determine the limiting capacity of a Bsa from a Blast by modelling the structural integrity of the Building and shelter for a range of Blast threats.

9 The Analysis of the modelling results can be used to determine the optimum location of the Bsa and identify ways for strengthening the the early stages of a structure s design, Bmt can provide advice on good design practice for Blast resistance and mitigation measures to reduce the risk of damage from bomb blasts. often this requires an assessment of the buildings external form to identify areas of re-entrant corners, cantilevered upper floors/set-backs of the lower floors, recesses, internal courtyards and arcades which will exacerbate the effects of an external bomb Blast . Bmt then work with the Building designers to reduce these problem areas and introduce mitigation schemes such as convexly curved or faceted facades and barrier schemes around the Building s proliferation of fully glazed facades in new Building designs means that the importance of glazing system design to resist Blast loading is more important than fragmentation and subsequent projection of glass fragments from bomb blasts is frequently the highest threat to human life.

10 Ordinary annealed or toughened glass forms elongated shards and small fragments when subjected to Blast loads of sufficient strength that will travel at high speed and cause severe or lethal injuries to personnel and extensive damage to fixtures, fittings and equipment. appropriately supported laminated glass panels have far superior Blast resistance properties that allow them to absorb energy with little or no key to optimum protection from laminated glazing systems is the laminate composition and the support system. Bmt s advanced non-linear Fea tools are capable of modelling the failure mechanism of glazing laminates and the supporting system to identify areas of design that can be optimised for maximum protection.