Structural Design for Fire Safety

Andrew H. Buchanan, Anthony Kwabena Abu

• Publisher: Wiley
• Year: 2016
• ISBN:
  9781118700396
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Structural Design for Fire Safety, 2 nd edition

Andrew H. Buchanan, University of Canterbury, New Zealand

Anthony K. Abu, University of Canterbury, New Zealand

A practical and informative guide to structural fire engineering

This book presents a comprehensive overview of structural fire engineering. An update on the first edition, the book describes new developments in the past ten years, including advanced calculation methods and computer programs. Further additions include: calculation methods for membrane action in floor slabs exposed to fires; a chapter on composite steel-concrete construction; and case studies of structural collapses.

The book begins with an introduction to fire safety in buildings, from fire growth and development to the devastating effects of severe fires on large building structures. Methods of calculating fire severity and fire resistance are then described in detail, together with both simple and advanced methods for assessing and designing for structural fire safety in buildings constructed from structural steel, reinforced concrete, or structural timber.

Structural Design for Fire Safety, 2nd edition bridges the information gap between fire safety engineers, structural engineers and building officials, and it will be useful for many others including architects, code writers, building designers, and firefighters.

Key features:

• Updated references to current research, as well as new end-of-chapter questions and worked examples.

•Authors experienced in teaching, researching, and applying structural fire engineering in real buildings.

• A focus on basic principles rather than specific building code requirements, for an international audience.

An essential guide for structural engineers who wish to improve their understanding of buildings exposed to severe fires and an ideal textbook for introductory or advanced courses in structural fire engineering.

1
Introduction

This book is an introduction to the structural design of buildings and building elements exposed to fire. Structural fire resistance is discussed in relation to overall concepts of building fire safety. The book brings together, from many sources, a large volume of material relating to the fire resistance of building structures. It starts with fundamentals, giving an introduction to fires and fire safety, outlining the important contribution of structural fire resistance to overall fire safety.

Methods of calculating fire severity and achieving fire resistance are described, including fire performance of the main structural materials. The most important parts of the book are the design sections, where the earlier material is synthesised and recommendations are made for rational design of building elements and structures exposed to fires.

This book refers to codes and standards as little as possible. The emphasis is on understanding structural behaviour in fire from first principles, allowing structural fire safety to be provided using rational engineering methods based on national structural design codes.

1.1 Objective and Target Audience

This book is primarily written for practising structural engineers and students in structural engineering who need to assess the structural performance of steel, concrete or timber structures exposed to unwanted fires. A basic knowledge of structural mechanics and structural design is assumed. The coverage of fire science in this book is superficial, but sufficient as a starting point for structural engineers and building designers. For more detail, readers should consult recognised texts such as Quintiere (1998), Karlsson and Quintiere (2000) and Drysdale (2011), and the Handbook of the Society of Fire Protection Engineers (SFPE, 2008). This book will help fire engineers in their discussions with structural engineers, and will also be useful to architects, building inspectors, code officials, firefighters, students, researchers and others interested in building fire safety.

A structural engineer who has followed this book should be able to:

• interpret the intentions of code requirements for structural fire safety;
• understand the concepts of fire severity and fire resistance;
• estimate time–temperature curves for fully developed compartment fires;
• design steel, concrete, steel‐concrete composite, or timber structures to resist fire exposure;
• assess the fire performance of existing structures.

1.2 Fire Safety

Unwanted fire is a destructive force that causes many thousands of deaths and billions of dollars of property loss each year. People around the world expect that their homes and workplaces will be safe from the ravages of an unwanted fire. Unfortunately, fires can occur in almost any kind of building, often when least expected. The safety of the occupants depends on many factors in the design and construction of buildings, often focusing on the escape of people from burning buildings. Occupant escape and firefighter access is only possible if buildings and parts of buildings will not collapse in a fire or allow the fire to spread. Fire safety science is a rapidly expanding multi‐disciplinary field of study. It requires integration of many different fields of science and engineering, some of which are summarized in this book.

Fire deaths and property losses could be eliminated if all fires were prevented, or if all fires were extinguished at the size of a match flame. Much can be done to reduce the probability of occurrence, but it is impossible to prevent all major fires. Given that some fires will always occur, there are many strategies for reducing their impact, and some combination of these will generally be used by designers. The best proven fire safety technology is the provision of automatic fire sprinklers because they have been shown to have a very high probability of controlling or extinguishing any fire. It is also necessary to provide facilities for the detection and notification of fires, safe travel paths for the movement of occupants and firefighters, barriers to control the spread of fire and smoke, and structures which will not collapse prematurely when exposed to fire. The proper selection, design and use of building materials is very important, hence this book.

1.3 Performance‐based Design

1.3.1 Fundamentals of Performance‐based Design

Until recently, most design for fire safety has been based on prescriptive building codes, with little or no opportunity for designers to take a rational engineering approach. Many countries have recently adopted performance‐based building codes which allow designers to use any fire safety strategy they wish, provided that adequate safety can be demonstrated (Hurley and Bukowski, 2008). In general terms, a prescriptive code states how a building is to be constructed whereas a performance‐based code states how a building is to perform under a wide range of conditions (Custer and Meacham, 1997).

Some prescriptive building codes give the opportunity for performance‐based selection of structural assemblies. For example, if a code specifies a floor with a fire resistance rating of two hours, the designer has the freedom to select from a wide range of approved floor systems which have sufficient fire resistance. This book provides tools for assessing the fire performance of structural elements which have been tested, as well as those with different geometry, loads or fire exposure from those tested.

In the development of new codes, many countries have adopted a multi‐level hierarchical performance‐based code format as shown in Figure 1.1. At the highest levels, there is legislation specifying the overall goals, functional objectives and required performance which must be achieved in all buildings. At a lower implementation level, there is a selection of alternative means of achieving those goals. The three most common options are:

1. A prescriptive ‘Acceptable Solution’ (sometimes call a ‘deemed‐to‐satisfy’ solution).
2. An approved standard calculation method.
3. A performance‐based ‘Alternative Design’ which is a more comprehensive fire engineering design from first principles.

Figure 1.1 Typical hierarchical relationship for performance‐based design

Standard calculation methods are still being developed for widespread use, so compliance with performance‐based codes in most countries is usually achieved by simply meeting the requirements of the Acceptable Solution, with options 2 and 3 being used for special cases or very important buildings. Alternative Designs can sometimes be used to justify variations from the Acceptable Solution in order to provide improved safety, cost savings, or other benefits.

The code environment in New Zealand (described by Spearpoint, 2008), is similar to that in England, Australia and some Scandinavian countries. Moves towards performance‐based codes are being taken in the United States (SFPE, 2000). Codes are different around the world, but the objectives are similar; that is to protect life and property from the effects of fire (ABCB, 2005). It is not easy to produce or use performance‐based fire codes for many reasons; fire safety is part of a complex system of many interacting variables, there are so many possible strategies that it is not simple to assess performance in quantitative terms, and there is lack of information on behaviour of fires and the performance of people and buildings exposed to fires. A number of useful documents have been produced to assist users of performance‐based codes, including Custer and Meacham (1997), BS7974 (BSI, 2001), ABCB (2005), Spearpoint (2008) and ISO 23932 (2009). This book provides useful additional information, addressing the design of structures for fire safety, which is a small but important segment of the overall provision of fire safety.

1.3.2 Documentation and Quality Control

As the provision of fire safety in buildings moves away from blind adherence to prescriptive codes towards rational engineering which meets specified performance goals, the need for comprehensive documentation and quality control becomes increasingly important. It is recommended (ABCB, 2005; ISO, 2009) that quantitative calculations be put in context with a ‘qualitative design review’ which defines the objectives and acceptance criteria for the design, identifies potential hazards and fire scenarios, and reviews the overall design and fire safety features. The review and accompanying calculations should be included in a comprehensive report which describes the building and the complete fire design process (Caldwell et al., 1999). The report should address installation and maintenance of the fire protection features, and management of the building to ensure fire safety, with reference to drawings and documentation from other consultants.

It is important to consider quality control of fire safety throughout the design, construction and eventual use of the building, starting as early as possible in the planning process. Changes to the design often occur during construction, and these may affect fire safety if the significance of the original details is not well documented and well understood on the job site. The approving or checking authorities should also prepare a comprehensive report describing the design and the basis on which it is accepted or rejected. Those taking responsibility for design, approval and site inspection must be suitably qualified. The reliability of active and passive fire protection will depend on the quality of the construction, including workmanship and supervision.

1.3.3 Risk Assessment

Fire safety is all about risk. The probability of a serious fire in any building is low, but the possible consequences of such a fire a...