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Structural FireEngineering in TallBuildings

Dr Susan DeenyArup

25th Nov 2011

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Arup | Fire Engineering Design

- Strategic Advice to Architects & Engineers-

Strategic Advice to building owners/operators- Backed up by

- Detailed analysis methods- Fire Science- Fire Research- Risk & Hazard Assessment

Business consulting- Strategic advice to building/Infrastructure

owners- Address Property Protection- Address Business Continuity

- Impacts:- Insurance premiums- Operations- Staffing- Costs

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Where in the world

Australia

MelbourneSydneyPerthBrisbane

Europe

DublinMadridBerlinAmsterdam

Asia

Hong KongBeijingSingapore

USA

San FranciscoLABostonNew York

UK

LondonManchesterBirminghamSheffieldBristolGlasgowEdinburghLeeds

Middle East

DubaiDoha

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Overview

Structural Fire Engineering Approaches- Prescriptive/Performance based design

Structural Fire Design Case Study-

Performance based design of a tall steel-concrete compositestructure

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Structural Fire Design - Approaches

Empirical - Fire resistance testing ofisolated structural elements

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Structural Fire Engineering - Approaches

Analytical & Numerical

Aims to:- address fire safety concerns- calculate actual structural response

Various methods of fire protection optimisation Largely restricted to steel structures

- Concrete assumed to have high inherent protection- Steel structural behaviour is more straight forward

Varying scales of analysis possible

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Typical Process

1. Design Fire Available fuel load and ventilation Compartment geometry2. Heat Transfer Relative locations of fire and structural member(s) Member geometry Applied protection3. Structural Assessment

Material properties change (strength/stiffness) Thermal expansion Level of restraint

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High temperature structural interactions

Materials expand when heated

Thermal ExpansionDifferential heating leads to differential expansion

Thermal Bowing Vertical deflectionsRestraint to expansion develops high forces (MN)

High compression in heating High tension in cooling

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Cardington Large Building Test Frame Program

Tests were done following Broadgatefire, London 1990

8 storeys, 5 x 3 bays, composite metal

deck floors

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After the test

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Load Carrying Mechanisms

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Load Carrying Mechanisms

New mechanisms allows for reduction in Fire Protection

Fire Protection RequiredUnprotected Steel

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High temperature structural interactions

Materials expand when heated

Thermal ExpansionDifferential heating leads to differential expansion

Thermal Bowing Vertical deflectionsRestraint to expansion develops high forces (MN)

High compression in heating High tension in cooling

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Choosing the appropriate scale

Single element checks ignore :

Thermal expansion effect ofbeam expansion for columns Potential load redistributionJustified for local exposure where

overall stability can be shown.

Global assessment:

Ensure structural robustness Load re-distribution and potentialoptimisation of protection

Appropriate for tall building design

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Case Study:Heron Tower, London

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Heron Tower

46 Storey Office Building in City ofLondon

3-storey atriums forming villages First ever project to consider the

robustness of a structure in a multi-storey fire.

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Heron Tower

Typical Village

Compartment floor

Atrium

floors

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Key issues

Optimisation of structural fire protection scheme Potential for fire occurring over three floors due to open atrium Structural fire analysis undertaken for 3 full floors heated simultaneously

Specific changes and detailing to enhance structural fire response Enhanced structural response to fire, relative to a code compliant building.

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Design fire protection layout

Cost savings to project

- Reduction in the overall building fire resistance rating- Removal of passive fire protection material from infill

secondary beams.

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Heron Tower Design Fires

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Model Extent : Single Floor Model

(Slab omitted for clarity)

Storey height of 4128mm

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Model Extent : Village Model

Storey height of 4128mm

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Heron Tower Multi-storey fire

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Heron Tower Findings of Analyses

Stability and Compartmentation maintained

Robust Response

- Use of solid section members- Increased protection to internal columns- Additional reinforcement in key areas of the floor slab and

enhanced ductility for the beam to column connections.

Similar level of response between Engineered and Code

Compliant protections Layouts

Level of Safety Demonstrated, Not Assumed

Approach was approved by the City of London DS

- First building approved in UK using multi-storey fire

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Heron Tower Site visit

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Conclusion Structural Fire Engineering

- Significant research in this field over the last 10-15 years- Many simple methods available that can be applied to many

projects

- Advanced methods:- Test the structure- Allow unprotected secondary steel- Prescriptive fire resistance ratings are not always conservative

- Understanding of structural fire response informs robust design- In innovative design is it reasonable to ignore fire induced

forces?