Actions

Actions

Copyright: © 2017 |Pages: 73
DOI: 10.4018/978-1-5225-2199-0.ch003
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Abstract

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.
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3.1 Introduction

Every temporary structures project is a unique endeavour, given a particular set of challenges and a specific context. The planning, design, execution and operation processes vary with the application, the site where it will be used and the role of temporary structures in the construction process. Therefore, temporary structures are exposed to a multiplicity of natural and/or man-originated hazardous events.

From a temporary structures’ design and operation perspective, there are a large variety of design challenges related to actions, originating from the diversity of the panoply of applications, geography of the site and climate exposure where temporary structures are used. For example, temporary structures can be used in prefabricated (precast) or cast-in-place (in situ) concrete construction, in residential buildings or multi-span bridges, in areas with significant seismic hazards or with challenging geotechnical conditions, in urban or rural areas under possible hurricane wind forces.

Many of the hazards have been appropriately researched and rules have been incorporated in existing codes of practice or guidance documents. However, there are still gaps of knowledge that need to be filled, with emphasis on the risks originating from human interaction, namely human errors during all phases of temporary structures life cycle.

The aim of this Chapter is to introduce the main types of actions due to external hazard events that are relevant to temporary structures, discuss the challenges associated with their characterisation and quantification, and provide an understanding on how specific actions can affect the performance of different types of temporary structures. The Chapter also identifies aspects that are not covered by existing structural design codes and presents state-of-the-art methods that help to overcome these limitations. Additionally, means to simulate internal hazards due to uncertainties and errors during design, assembly and operation of temporary structures are also analysed.

On the basis of this Chapter it is expected that the reader will acquire knowledge on the following topics:

  • 1.

    Classification of actions.

  • 2.

    Typologies of different construction actions and their effects on temporary structures.

  • 3.

    Assessment of wind actions and their effects on temporary structures.

  • 4.

    Potential influence of ground characteristics on temporary structures performance.

  • 5.

    Assessment of human motion actions and their effects on temporary structures, typically temporary stands and stages.

  • 6.

    Assessment of accidental actions relevant to temporary structures, such as vehicle impacts and earthquakes.

  • 7.

    Assessment of notional actions that simulate the effects of unidentified hazard events during design, assembly and use of temporary structures.

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3.2 Design Codes

Actions relevant to temporary structures can be determined from the suite of European structural design standards (named the Eurocodes), ASCE 7 (ASCE, 2010) in the USA or Parts 0 to 4 of AS 1170 in Australia and New Zealand, for example. For temporary structures, further guidance is given in BS EN 12811 (BSI, 2004b) for scaffolds, in BS EN 12812 (BSI, 2011b) and BS 5975 (BSI, 2011a) for falsework, and in ASCE/SEI 37 (ASCE, 2014) and BS EN 1991-1-6 (BSI, 2005b) for temporary structures in general. In the USA, the AASHTO bridge code (AASHTO, 2016) and the AASHTO design guide for bridge falsework (AASHTO, 2008), can also be also used to determine design actions. See also Chapter 6.

The ASCE/SEI 37 provides the design loads and load combinations for temporary structures used during construction, as well as for partially completed structures during their construction phases. This standard addresses not only permanent and variable loads due to the construction but also environmental loads, the minimum values of the partial factors and the relevant load combinations to be considered, in accordance with the Limit States design philosophy.

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