BUILDINGS, STRUCTURES Design of steel buildings to resist ... · buildings across the town of West...

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Design of steel buildings to resist explosions Convenonal building structures are not normally designed to resist the effects of external explosions caused by industrial accidents. Because the magnitude of such explosions is significantly greater than typical design loads, structures located within a large area both on and off an industrial site are suscepble to severe damage. BUILDINGS, STRUCTURES P ast incidents have demonstrated this. For example, in Buncefield (2005) the overfilling of a petrol tank led to the rapid formation of a large vapour cloud and a violent explosion damaging buildings within a 2 km radius and in Azote de France (2001) an explosion at an ammonium nitrate store killed 30 people, injuring many more and damaging buildings within a 4 km radius. More recently (April 2013), an explosion at a fertiliser factory killed 14 people and destroyed or damaged more than 150 buildings across the town of West in Texas, USA. The nature of the loading imparted to buildings exposed to such explosions is very unusual and differs in many respects, not just in magnitude but also in nature, from the loads which buildings are normally designed for. First, the structure is loaded by means of a compression (shock) wave over large areas of its elevations causing widespread damage (for example, see image showing the damage to the Northgate Building adjacent to the Buncefield site). Second, the duration of the shock wave is of the order of milliseconds. Third, the explosion applies the most severe loads to the nearest elements, both vertical and horizontal, with little regard to their stiffness (unlike, for example, earthquakes which shake an entire building, but produce mostly horizontal loads at floor-slab levels, concentrated in the laterally stiffer structural systems). Fourth is the uplift pressure load that acts on floors and is unique to blast. The blast shock wave acts up against the underside of the floor slabs at upper stories – a load condition for which neither the slab nor the beam-column connection of the beam supporting the slab are designed. This is very important since many buildings rely on the floor slabs to act as diaphragms which transfer lateral loads to the building’s stability system (e.g. bracing or core/shear walls). To address these issues, SCI is leading a major European project to develop design rules for low to medium rise office buildings, typical of those commonly found on and adjacent to industrial sites. A combination of experimental and advanced numerical studies are being used to develop simplified analysis tools and Eurocode style design rules to achieve robust designs that avoid disproportionate damage. As part of this project, a reference office building typical of business park commercial offices will be selected and designed for normal office use. This will provide a basis for testing the project’s recommendations for design of new buildings and for retrofitting existing buildings. Explosion scenarios will be defined which are representative of accidents involving hazardous substances (e.g. ammonium nitrate, sodium chlorate, ethylene oxide/propylene oxide and flammable vapour clouds). These scenarios will be developed using computational fluid dynamics, testing on a scale model of Northgate Building the building and experience from recent industrial accidents. In order to develop an understanding of the response of the key building components, a series of full scale tests are planned. These include cladding tests, connection tests and tests on composite floor slabs. In the latter case, the in-plane shear stiffness of the composite floor will be measured both before and after exposure to out-of-plane explosion loads. The tests results will be used to validate nonlinear finite element (FE) models of the connections between the cladding and the frame, for the response of the composite floor slab, the interaction between the floor slab and its supporting beams and for the connections between steel members. Using the validated numerical models, the reference building will be studied using nonlinear FE analysis for its sensitivity to global failure when subjected to realistic blast loads. The study will go on to consider methods of preventing global failure and to explore structural retrofitting techniques. The project outputs will be used to develop simplified analysis software and a design guide for low to medium rise steel framed buildings to resist actions due to explosions. The reference building will be re-designed in accordance with the guide to illustrate the use of the design methodologies and a specific section will be devoted to guidance for retrofitting existing buildings. For further information please contact Bassam Burgan, Director of SCI (01344 636525; E-mail: [email protected]). 7 www.innovationandresearchfocus.org.uk Innovation & Research Focus Issue 95 NOVEMBER 2013

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Page 1: BUILDINGS, STRUCTURES Design of steel buildings to resist ... · buildings across the town of West in Texas, USA. The nature of the loading imparted to buildings exposed to such explosions

7www.innovationandresearchfocus.org.uk Innovation & Research Focus Issue 95 NOVEMBER 2013

Design of steel buildings to resist explosions Conventi onal building structures are not normally designed to resist the eff ects of external explosions caused by industrial accidents. Because the magnitude of such explosions is signifi cantly greater than typical design loads, structures located within a large area both on and off an industrial site are suscepti ble to severe damage.

BUILDINGS, STRUCTURES

Past incidents have demonstrated this. For example, in Buncefi eld (2005) the overfi lling of a petrol tank led

to the rapid formation of a large vapour cloud and a violent explosion damaging buildings within a 2 km radius and in Azote de France (2001) an explosion at an ammonium nitrate store killed 30 people, injuring many more and damaging buildings within a 4 km radius. More recently (April 2013), an explosion at a fertiliser factory killed 14 people and destroyed or damaged more than 150 buildings across the town of West in Texas, USA.

The nature of the loading imparted to buildings exposed to such explosions is very unusual and differs in many respects, not just in magnitude but also in nature, from the loads which buildings are normally designed for.

First, the structure is loaded by means of a compression (shock) wave over large areas of its elevations causing widespread damage (for example, see image showing the damage to the Northgate Building adjacent to the Buncefi eld site). Second, the duration of the shock wave is of the order of milliseconds. Third, the explosion applies the most severe loads to the nearest elements, both vertical and horizontal, with little regard to their stiffness (unlike, for example, earthquakes which shake an entire building, but produce mostly horizontal loads at fl oor-slab levels, concentrated in the laterally stiffer structural systems). Fourth is the uplift pressure load that acts on fl oors and is unique to blast. The blast shock wave acts up against the underside of the fl oor slabs at upper stories – a load condition for which neither the slab nor the beam-column connection of the beam supporting the slab

are designed. This is very important since many buildings rely on the fl oor slabs to act as diaphragms which transfer lateral loads to the building’s stability system (e.g. bracing or core/shear walls).

To address these issues, SCI is leading a major European project to develop design rules for low to medium rise offi ce buildings, typical of those commonly found on and adjacent to industrial sites. A combination of experimental and advanced numerical studies are being used to develop simplifi ed analysis tools and Eurocode style design rules to achieve robust designs that avoid disproportionate damage.

As part of this project, a reference offi ce building typical of business park commercial offi ces will be selected and designed for normal offi ce use. This will provide a basis for testing the project’s recommendations for design of new buildings and for retrofi tting existing buildings. Explosion scenarios will be defi ned which are representative of accidents involving hazardous substances (e.g. ammonium nitrate, sodium chlorate, ethylene oxide/propylene oxide and fl ammable vapour clouds). These scenarios will be developed using computational fl uid dynamics, testing on a scale model of

Northgate Building the building and experience from recent industrial accidents.

In order to develop an understanding of the response of the key building components, a series of full scale tests are planned. These include cladding tests, connection tests and tests on composite fl oor slabs. In the latter case, the in-plane shear stiffness of the composite fl oor will be measured both before and after exposure to out-of-plane explosion loads. The tests results will be used to validate nonlinear fi nite element (FE) models of the connections between the cladding and the frame, for the response of the composite fl oor slab, the interaction between the fl oor slab and its supporting beams and for the connections between steel members. Using the validated numerical models, the reference building will be studied using nonlinear FE analysis for its sensitivity to global failure when subjected to realistic blast loads. The study will go on to consider methods of preventing global failure and to explore structural retrofi tting techniques.

The project outputs will be used to develop simplifi ed analysis software and a design guide for low to medium rise steel framed buildings to resist actions due to explosions. The reference building will be re-designed in accordance with the guide to illustrate the use of the design methodologies and a specifi c section will be devoted to guidance for retrofi tting existing buildings.

For further information please contact Bassam Burgan, Director of SCI (01344 636525; E-mail: [email protected]).

7www.innovationandresearchfocus.org.uk Innovation & Research Focus Issue 95 NOVEMBER 2013