Temporary demountable structures
The Institution of Structural Engineers has published a guidance note on the procurement and use of demountable structures. This aims to remind people of their legal responsibilities when procuring and using temporary demountable structures for events.
Temporary demountable structures include marquees, grandstands, stages, and related structures that are used at a wide range of public and private events
These types of structures are usually designed to be easily and quickly erected and dismantled and are capable of adaptation to different situations. This often means that, from a structural engineering perspective, they are relatively lightweight, made from slender components and need to be designed, erected, and inspected by competent persons before they are used.
The Institution of Structural Engineers, supported by the Health and Safety Executive, has published guidance on Temporary Demountable Structures. This fourth edition contains essential information on the procurement, design, erection and use of temporary demountable structures, including: grandstands; stages; fabric structures; hospitality units; and fencing and barriers. Towers and masts that support media facilities are also included.
Demountable structures are widely used for a variety of functions at public and private events and can be found at exhibitions, sporting events, musical concerts and social occasions. Some may carry substantial numbers of people during major events and structural safety is extremely important.
What’s in the guidance?
Detailed recommendations are given for grandstands, stages and special structures. There is a section on fabric structures and further advice on ancillary and special structures to support lighting equipment, video screens, loudspeakers, and the like.
The Guide is based on practice in the UK and Europe but the principles described are appropriate for application elsewhere. It is also intended for clients, event organisers and venue owners, designers, regulatory and local authorities, as well as contractors and suppliers of demountable structures. It is concerned with the structural safety and adequacy of demountable structures used for temporary purposes and also with the overall planning and management of events.
The temporary structures industry differs from that of permanent structures in that it is much more fluid. At many events there are short timescales for the whole design and construction process. Responsibilities may be divided with no clear chain of command and regulations are complex. A temporary stage may be erected for a small event, the performance held, and the structure dismantled within a few days. Large events usually have a formal management process in place but there are still anomalies with control and with quality assurance.
Another difference with more traditional buildings is that imposed loads from people and wind are relatively high in proportion to dead load. There is more dynamic behaviour involved and different hazards to be considered. Very large numbers of spectators are accommodated in such structures so the life-safety risks have to be taken extremely seriously.
The SGSA contributed to the development of the guidance via the Advisory Group on Temporary Structures.
Rotting plywood decking on grandstand
A firm that undertakes visual structural inspections of temporary demountable grandstands for a number of sporting venues in the UK has published a report on plywood decking timber following an inspection of a grandstand, when a decking board failed whilst being walked on due to rotting.
Although temporary in nature, demountable structures can remain standing for several months exposed to the elements. In some cases, it is known that venues utilise them as permanent structures.
The report highlights the importance of the various stand suppliers/installers working together to develop a coordinated approach to the management of these types of structures. Robust pre-inspection regimes or indeed insitu tests need to be developed which are backed up with comprehensive audit trails that clients and event organisers can rely on.
Other key learning outcomes from the report are:
- Inspection regimes should take into account how long a structure has been standing, or has been in storage, since it was last dismantled and checked.
- Consider the potential for degradation of all elements and check for hidden defects, particularly in timber decking.
- Temporary demountable structures: Guidance on procurement, design and use provides significant guidance.
- Stand suppliers should be aware of the potential for hidden degradation at the edges of plywood decking.