Design Codes and General Design Guidance

The philosophies behind design codes with particular reference to the use of modern limit state design are presented in this chapter. Comments are made on the design life of temporary structures which vary considerably between different countries. Design codes of the USA, Europe and Australia/New Zealand for temporary structures are compared with particular reference to the loads combinations and the partial factors applied. It is noted that whilst the European design codes do not specify how construction, use and disassembly of the temporary structures are to be executed the USA code for scaffolding includes such specification. The Hong Kong code for bamboo scaffolds is described showing the similarities and differences between bamboo and metal scaffolds. The chapter concludes with design examples for selected temporary structures based on design codes.

Historical Survey

Chapter 2 overviews the historical development and past research into temporary structures from 1970 up to 2016 and describe the various problems that have occurred necessitating changes to traditional design and construction techniques. The survey covers tubular, proprietary and modular scaffolds, bridge falsework as well as bridge construction equipment. Particular areas emphasised are the changes introduced by the use of advanced structural analysis techniques and the need for changes in procedures following the analyses of collapses of temporary structures. An overview of various solutions is presented, including the use of different materials (steel, aluminium, timber and bamboo). The chapter shows that same analysis procedures are used for these different materials. The chapter then overviews the actions acting on temporary structures such as permanent loads and variable construction loads and finishes with an introduction to failures of falsework and scaffolding structures.

Introduction

Chapter 1 is an introduction to the book and provides an overview of the areas in which temporary structures are used, namely the construction and repair of buildings and bridges. A description of the different types of temporary structures is given together with an overview of the problems which may arise in temporary structures projects. The differences between temporary structures projects and projects for permanent structures are highlighted. An introduction to the particularities of the design, assembly, maintenance and operation of temporary structures is presented in this chapter. It is also emphasised that the book compares the design codes used in the USA, Europe, Australia and Hong Kong. Finally, the chapter concludes with an overview of the remaining chapters of the book.

Analysis of Collapses

This chapter presents the procedural, enabling and triggering causes of temporary structures collapses, with an emphasis on falsework and scaffolding. The review into collapses described in Chapter 2 is extended by investigating in detail the causes of collapse in temporary structures and providing comprehensive lists of faults which can occur during design, erection, use and disassembly of these structures. As bridge falsework collapses are more commonly reported, with usually greater financial implications and greater risks to life, a survey, conducted by André, is summarised showing that these collapses occur regularly throughout the world. The chapter concludes with the presentation of two examples of forensic analyses, namely of a scaffold collapse and of a bridge falsework collapse.

Quality Management

Ensuring that temporary structures projects are managed well so that budgets are maintained and safety is ensured throughout the project is the objective of this chapter. The chapter presents recommendations for the quality control, quality assurance and quality improvement processes to be undertaken in the design, assembly, use and maintenance of the temporary structures to reduce the associated risks. The chapter starts by discussing the importance of having clear management structures for projects involving collaboration between the client, designer and the construction engineer. This leads to the importance of an overall project supervisor, sometimes called a Temporary Works Controller, who has ultimate authority for the safe execution of the project. The use of Structural Health Monitoring is described with particular reference to its ability to make the erection of temporary structures projects safer.

Structural Safety

This chapter presents and discusses the principles, methods and the associated limitations that currently are seen as the state-of-the-art in structural safety. The basis for understanding the design philosophy of modern design codes is provided. Innovative concepts in safety, starting with definitions of risk, reliability, fragility and a new definition of structural robustness are presented. Uncertainties are discussed and a risk management framework for structural design is proposed. A probabilistic structural design philosophy is presented detailing a new methodology for analysing structural fragility and the robustness of structures against failure. An example is presented determining the robustness of a falsework structure against collapse. Strategies to enhance structural robustness and structural safety are given. An improved design methodology for temporary structures is presented and detailed, and an example is provided. Finally, the chapter discusses the use of reduction factors when determining design action values for the design of temporary structures.

Structural Analysis

This chapter develops the components required for successful modelling of temporary structures. It presents the principles, methods and the associated limitations that currently are seen as the state-of-the-art in structural analysis using the Finite Element Method. Material models of steel, aluminium and bamboo are presented with an emphasis on linear and multilinear models for steel and the Ramberg-Osgood model for aluminium. Models are presented for braces, props, beam-to-column connections, top connections, base connections and column-to-column connections based on the latest theoretical and experimental procedures developed by the authors and co-workers. Examples of two and three dimensional models are then developed for access scaffolds, bridge falsework and bamboo scaffolds. Finally, the chapter presents information on the effects of ground modelling and on advanced wind engineering using complex numerical methods.

Actions

This chapter presents a general description and discussion of the actions applied to temporary structures such as construction loads, wind loads, impact loads and unidentified hazard events. A classification of actions is presented. Actions are classified into permanent actions such as self-weight, lateral loads by soil or water; and variable actions such as live loads, earthquakes and wind loads. Comparisons are made between design provisions for loads as specified by European, USA and Australian design codes and standards. Methods to estimate the main effects of the actions on temporary structures are presented. The latest research into wind on temporary structures is a significant part of this chapter with its implications to the correct wind forces acting on temporary structures when turbulence and orography are taken into account.