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The Structural Engineer

All the articles from the January 2018 issue.

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The Structural Engineer

The Grenfell Tower tragedy in London last June was a stark reminder of how rapidly a fire can spread and the horror which it can cause. In the wake of this disaster, the UK construction industry is actively examining what can be done to minimise the risk of similar tragedies in the future. It is likely that one of the recommendations will be a clearer identification of responsibilities, but whatever the outcome it will clearly be helpful for all members of the design team to have a good understanding of all aspects of fire safety, as well as detailed knowledge about those aspects under their direct control.

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The Structural Engineer

Fire is a basic hazard which can devastate buildings, cities and regions. It is therefore an essential part of an engineer’s skill set to understand and control the risk. Control is a key word, for the risk can never be eliminated, as the recent Grenfell Tower fire in London reminds us. That event was truly a nightmare: an out-of-control fire destroying a whole residential tower, killing 71 occupants. In the same contemporary timeframe, wild fires in California destroyed approx. 9000 structures and left over 40 dead, reminding us of the consequences of regional fires.

How these catastrophes happened is yet to be established. It is said that lessons should be learned, and so they should, since the history of fire engineering is largely one of reaction to disasters. As a start, it’s worth observing, as some of the papers in this special issue do, that the basic skills of ‘fire engineering’ are probably absent among many of us. That situation stems partly from an omission of basic training; perhaps from a feeling that this is a speciality for others, and perhaps because advances have been rapid. This is unsatisfactory and unsafe. Fire protection needs to be ensured overall between the architects, plant engineers and structural engineers who make up any project team: we have collective obligations to make buildings ‘safe’.

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The Structural Engineer

A paper written as a collaboration between AECOM fire engineers and structural engineers in an effort to elevate the subject and improve our mutual understanding of structural performance in fire. Intended as a high-level introduction for practising structural engineers.

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The Structural Engineer

Most structures in Europe are constructed using limit state design methods. Most of these structures are protected against some form of specified fire scenario. However, only a small minority of projects link these two major considerations together to form part of a unified structural fire design process.

The Eurocodes provide designers with the necessary procedures to undertake an accurate and economical structural fire design, yet few engineers ever consider undertaking such an assessment.

This article will focus on the load actions and combinations to be considered that enable the engineer to perform an adequate structural assessment for the accidental limit state in fire. It will also cover important considerations to ensure that any structural fire engineering strategy is appropriately aligned, and the key information is available within the contract chain to facilitate this performance-based approach.

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The Structural Engineer

The next edition of the ASCE/SEI 7 standard commences a new and groundbreaking industry-consensus standard of care for structural fire protection in the USA, and other adopting jurisdictions. The default option is termed standard fire resistance design, and is based on a long-standing empirical indexing system that excludes consideration of realistic thermal demands and structural system response.

The only permitted alternative to standard fire resistance design is structural fire engineering (SFE), as constituted in the new Appendix E. SFE explicitly evaluates the demand and capacity of structural systems under fire loading in a similar manner as other design loads are treated in structural engineering practice.

Due to common misconceptions and lack of industry guidance, designers often erroneously intermingle these two approaches in order to justify structural fire protection variances. To combat this poor practice, recent industry efforts in the USA have focused on formally bifurcating these two design options, and providing specific requirements for the SFE approach.

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The Structural Engineer

Fire protection of composite beams with large web openings is an important design issue, especially when using intumescent coatings. This is due to higher web slenderness and differential thermal heating through the web openings in fire. Previous tests on composite beams, however, have involved simple support conditions and were performed under a standard fire temperature–time regime.

As performance-based design of fire-protected steel structures becomes more prevalent, it is important to investigate the behaviour of protected beams with web openings in complete frames under natural fires. This paper outlines the technical background before considering the development of more realistic performance within the design of optimised fire-protection systems of composite floor plates

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The Structural Engineer

This article will present a state-of-the-art method which is an amalgamation of several recent research studies from various authors to determine the required structural fire resistance period of buildings. The bespoke approach is based on the Monte-Carlo probability method, which considers not only a range of fully developed compartment fires, but also the phenomenon of travelling fires in increasingly open-plan spaces. An improvement is made on the random selection of compartments depending on the use and area of the individual compartments. A case study is presented in which the probability method is applied to a steel-framed office building in Scotland. The fire resistance period for the building is reduced from the code-required 120 minutes to 60 minutes.

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The Structural Engineer

Heat-induced explosive spalling in fire poses a credible risk to concrete structures, and has received considerable research attention in recent decades. However, no validated guidance to enable the design of concrete mixes to prevent spalling, nor any established, widely verified, repeatable test methods are yet available to confidently quantify or demonstrate spalling resistance for a particular mix in a given application. As a result, no models yet exist that can predict spalling with sufficient confidence to be used in design.

This paper summarises contemporary research on heat-induced concrete spalling, with particular emphasis on design for fire of concrete-lined tunnels. The topic is also relevant for modern concrete buildings. A novel, repeatable and economical testing method to reduce project risk by quantifying the propensity of concrete mixes for spalling under a range of different thermal and mechanical conditions is described. The intent of this paper is to present the limitations of knowledge to enable design for heat-induced spalling, and to highlight research currently under way to overcome some of the issues faced in practice.

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The Structural Engineer

Designers of the built environment are currently focused on creating new materials for construction, or innovating new construction methods with traditional construction materials. This is part of the very complex challenge of balancing environmental issues, such as energy use, with the ongoing market demand for reducing construction costs and time.

This has led to a rapid rise in the uptake of timber, such as glued laminated timber (glulam) and cross-laminated timber (CLT), particularly in the design of multistorey residential buildings.

This paper focuses on the design of tall timber construction for which many hybrid and composite forms of timber are being developed, resulting in a wide range of structural typologies.

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The Structural Engineer

Construction site fires can be significant events creating risks to life safety as well as causing extensive property damage. During the build process, timber-frame structures can be vulnerable to ignition, whether from a construction process, accident or arson attack.

This paper describes the thinking and background behind the fire model underpinning risk-mitigation techniques used for structural timber buildings. The work has evolved from over six years of industry-based research and fire testing, which has led to the Health and Safety Executive endorsing the principles presented. Martin Milner has been the project manager and engineer representing the Structural Timber Association on this work.

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The Structural Engineer

Performance-based structural fire design can play an important part in delivering iconic buildings. Early design team engagement with critical issues, including fire safety considerations, allows a holistic solution to be developed, in contrast to post-applied fire engineering which could severely compromise the original design intent.

Four Pancras Square (London) is a successful example of where early fire engineering engagement has helped deliver an iconic design. The building features an external, fully load-bearing, weathering steel frame, with a storey-deep Vierendeel transfer truss. To allow the weathering steel to develop its protective patina and achieve the desired aesthetic, it must be left untreated and exposed; this is in conflict with traditional fire resistance solutions.

This paper documents the key steps undertaken in realising the building and describes how they were tackled at the interface of the fire and structural engineering disciplines. These include quantification of the design goals, selection of the fire constraints, understanding the behaviour of unconventional steel, quantifying thermal exposure for external elements and, finally, quantification of structural response in fire.

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The Structural Engineer

Structural fire engineering is often adopted in large open-plan structuressuch as airport terminals, railway stations, etc., where the low fire risk can be directly conceived and a structural fire analysis may bring significant savings on structural fire protective coatings. In some recent cases, structural fire engineering approaches have also been applied to landmark high-rise buildings in China. This paper introduces four different examples of such methods with varying motivations, approaches and ultimate design schemes, to provide readers with an insight into the commercial application of structural fire engineering in China.

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The Structural Engineer

The first edition of this book, authored only by Prof. Buchanan, was published in 2002. It was the first comprehensive publication in the field of structural fire engineering and a key reference for international undergraduate/postgraduate courses in this area.

The field of structural fire engineering is rapidly evolving and there have been a number of developments since 2001 – notably the collapse of the World Trade Center towers in New York and subsequent research on the structural fire response of complex structures, and the rally in innovation of structural forms, construction methods and materials (modular construction, high-strength materials, etc).

In this second edition, Prof. Buchanan was joined by Dr Abu and the authors tried to fill some of these gaps.

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The Structural Engineer

This month's letters are on the former Institution Yearbook, the magazine's 'And finally...' brainteasers, chases in party walls, building control procedures and the merits of life drawing classes.

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The Structural Engineer

Upcoming events at HQ and around the Regional Groups.

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The Structural Engineer

In this section we shine a spotlight on papers recently published in Structures – the Research Journal of The Institution of Structural Engineers.

This month, we preview the latest issue (Volume 12), with Editor-in-Chief, Professor Leroy Gardner, selecting three highlights from the issue.

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The Structural Engineer

Enquiries received in the Library on fire engineering can be categorised broadly into six headings.
* Fire properties and performance of materials
* Fire-resistant design
*Fire management
* Fire damage assessment and repair
* Standards
* Case studies

This article lists a selection of what the Library has on these subjects and the most frequently requested items.

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