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Technical advances in lightweight structure design.

Rudi_Enos_Design

The tragic happenings in the summer of 2011 have focused the music

industry on the issues of temporary structure design. All safety engineeringcomes down to a few basic truths; Is that hand rail strong enough to hold acrowd?, Is that length of truss strong enough to suspend the rig?, Are thosefire exits and exit distances enough to evacuate the venue safely?.

All of these issues require calculation. To undertake the calculations for crowdemergency exit requirements, it is possible to do so by hand or mentally, oruse a simple spreadsheet. When analysing complex trussing systems orcomplete structures those tools are often inadequate. The modern engineeruses software tools such as FEA Packages (Finite Element Analysis) which

break down the load requirements and graphically show the range of forceswhen compared to the member properties. This is often called NumericAnalysis.

Basic Finite Element Theory (You may wish to skip this paragraph, it is a bittechnical).

Perhaps FEA ought to be called Finite Element Analysis and Simulationsoftware. The software breaks down the components of the assembly intosmall (finite) parts and calculates the result of applying a simulated load. Thisfinite part of the calculation then acts upon all other parts of the object being

modelled. Within each of these modelling schemes, the software usesnumerous algorithms (functions) which may make the system behave linearlyor non-linearly. Linear systems are far less complex and generally do not takeinto account plastic deformation. Non-linear systems do account for plasticdeformation, and many also are capable of testing a material all the way tofracture. To conclude, modern software takes real world problems,investigates the potential forces, tests and analyses the suitability of thematerials and member sizes for the intended project.

Traditionally the engineer defines the operating parameters for the intendedstructure, determines member sizes (usually steel or aluminium tube for say,

trussing or a stage deck), check connection parts such as pins or bolts(connections simply must be stronger than the component), and determinethe overall the stability of the project, usually by bracing.

For an outdoor stage roof, this will involve applying the wind load from therelevant building code, in the case of a temporary structure, BS EN13782:2005, Temporary structures. Tents. Safety. For the first time, engineershave a set of rules, enforceable by law that give direct instruction on windloadings. Before 13782 engineers had to determine wind speeds and loadsfrom (in the UK) National Building Codes), or by wind tunnel tests onrepresentative models.

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Change the wind load, it changes everything. All of these are separateoperations often using several different software suites. If some parameterschange, the whole process using different packages must be repeated.

Once the wind loads are arrived at, the software applies the forces (in a virtual

wind tunnel) by calculating the pressure co-efficient for each finite polygon ofthe software mesh representing the roof surface and indeed the wind forceson the trussing and or supports. The components of the structure are thenshown in their displaced state (showing the distortion under load), and theoutput forces of every part of the structure shown.

In 2011, new software has been introduced which is purpose built to providethe ultimate design aide for temporary structures. Some of the numeric matrixsolvers were licensed from NASA. The software provides a unified approachto analysis which integrates all of the previously separate processes, oftenusing predetermined element libraries.

The program provides engineers with everything they need for the design andoptimisation of roof, cable and steel structural systems. It provides a series oftools which simulate wind loads (although it is not a virtual wind tunnel, calledCFD, Computational Fluid Dynamics), and automatically loads the structure,undertakes the static analysis at the touch of a button, and automaticallyprovides the member sizing to determine the support design. After this, thesoftware breaks down the three dimensional surface (if required) into twodimensional flat cutting patterns for manufacture based upon a given fabricwidth.

The conclusion to all this preamble is that event industry professional has avastly better set of tools to assess the potential performance of temporarystructures. That means that a more informed approach can be made whichcan only improve the performance of the structure. Technology alone can notprovide the impetus to change for the better but can provide the same sort ofimprovements that many advances from the space age have produced.

The temporary structures market has seen similar if less obvious changes.The structures are inherently safer than their 1990 equivalent. Modernstructures use many new materials and technologies to deliver a product and

service that is at the cutting edge of what the events industry can supply. Theuse of computer design and analysis software to predict the performance oftemporary structures matches the practice of many engineering offices in theaerospace and motor racing industries.

We have the tools to deliver safer, better structures. What is required is thewillpower to implement new work practices and inspection techniques tomatch those advances. It is for the events industry to provide the willpower.