Taking the Knocks

Impact performance is an important issue when it comes to selecting the appropriate wall or partition system for a particular application. Gyproc’s Technical Development Manager, Jason Hird, examines some of the issues to consider when selecting lightweight walling systems.

Depending on the type of building and location within the building, partition walls are subjected to a wide range of impact levels and types on a daily basis – and choosing the most appropriate construction for each different application can therefore be a challenge for the building designer.

It is easy to over-engineer the wall systems, but that can add unnecessarily to the cost and installation time and impact on both project viability and scheduling. On the other hand, selecting systems that do not have the strength or durability needed for the applications will involve expensive ongoing maintenance and may require upgrading or replacement, when the building is occupied.

Assessing the risk

Before it is possible to choose a solution, it is important to categorise, at the design stage, the type and extent of the impact risk to which a particular partition may be exposed. A popular choice amongst many designers would be to follow the British Standard - BS 5234.  This is a useful reference document, as it includes a series of duty ratings which relate the strength and robustness of a partition system against specific end-use applications.

The four partition ‘Duty’ categories, which cover most day-to-day building applications are:
Light Duty - for areas where there is little chance of misuse. Examples would include family rooms and bedrooms in most single-family homes.

• Medium Duty – for areas where persons generally take care, but there is some chance of accidental damage occurring.. Examples here include offices, and stairways and common areas in multi-family homes.
• Heavy Duty – for areas used by the public without incentive to exercise care, and therefore there is a higher chance of misuse. Typical areas include school classrooms, gyms and corridors and entryways in high risk multi-family buildings. 
• Severe Duty – for high traffic areas subject to abnormally rough use or vandalism. Examples include corridors and stairwells in schools and hospitals, detention buildings or heavy industrial areas.

There are, of course, applications which fall outside of the normal Duty categories, such as data storage and payroll rooms, where security may be an issue and additional protection is required to prevent deliberate penetration of the partition, or structures that require even higher performance to withstand possible bomb blasts such as car bombs. Lightweight Gyproc partition systems are commonly used in both of these application areas, but are subject to special design detailing, depending on the type of risk involved.  Contact our Technical Team for further information.

Other considerations

As well as providing protection against impacts, there are a number of other considerations when selecting partition systems:

• Rigidity – even if the partition is considered satisfactory for the level of impact risk envisaged, when pressure is applied to one side, the lateral deflection or flex of the partition needs to be within acceptable design limits.  Typically most partitions are designed to a minimum rigidity or ‘character stiffness’ of L/240 where ‘L’ is the unsupported height of the partition.  This design criteria is normally tested under an applied Uniformly Distributed Load (UDL) of 200 Pascal’s (Pa), which is the equivalent of around 20kg/m² of force over the whole partition area.  Gyproc partitions are designed in accordance with this, however should an alternative design criteria be required then we are able to provide you with a specification to suit.  This may be where high reaching partitions are specified where often a lower limiting deflection rate of L/125 may be acceptable, or where a dividing wall in an area that maybe subjected to wind loading and may require a higher specification, such as L/240 at 500Pa.
• Fire and acoustic performance requirements – it may well be that the requirements for fire and acoustic protection can only be satisfied using a partition design with a higher BS 5234 Duty Rating than required to satisfy the impact risk. In this case, the fire and acoustic requirements will take precedence.
• Door detailing – in Heavy and Severe Duty partitions, it will generally be necessary to reinforce the door detail in order to limit deflection and damage during partition testing.   Example details are available from Gyproc for a range of partition types.
• Heavy fixtures and fittings – it may be necessary to increase the partition strength or include additional reinforcements to accommodate specific fixings, such as sanitaryware items in bathrooms.   Example details are again available from Gyproc for a range of fixtures and weights.

Testing for impact resistance

In order to achieve the BS 5234 Duty ratings, Part 2 of the standard lays down a strict series of tests that a partition system must pass. These tests are designed to assess in a number of key areas:

• Partition stiffness – designed to measure deflection caused by application of a point load.
• Hard body impact – designed to measure resistance to damage and resistance to perforation caused by impact from a hard object.
• Soft body impact – designed to assess resistance to aesthetic damage and structural damage caused by a body striking the partition face.
• Door slamming – to assess deformation and damage to the partition as a result of continuous door slamming.

The standard also includes optional tests to measure the effect of crowd pressure and pull-out strength for both heavyweight and lightweight anchorages.

Lightweight systems versus masonry

Whilst historically designers have turned to heavy masonry construction to provide higher levels of impact resistance in at-risk areas, modern lightweight metal frame systems are today capable of providing equivalent levels of impact resistance at a fraction of the weight and without the construction and drying out delays associated with masonry.

Unlike masonry walls, that can crack and lose integrity as a result of impacts, lightweight Gyproc metal systems, due to their inherent flexibility, will absorb and disperse impact energy, without lasting deflection. This property of lightweight construction has led to the development of sophisticated blast-proof and bomb-proof walls for high risk areas, with tests showing that lightweight walls provide extra protection from shrapnel and flying debris as they are able to maintain integrity, even when close proximity blasts are involved.

The additional performance and time benefits of lightweight Gyproc systems mean that they are increasingly being adopted for more demanding applications, adding to savings in structural weight and foundation costs, providing space benefits and helping project timings through more fast-track installation techniques.

Gyproc systems for impact resistance

Gyproc systems have been tested against BS 5234 and are capable of achieving all four levels of Duty rating, subject to the type and thickness of lining board used.

Gyproc GypWall ROBUST has been specifically designed to provide a high impact resistant partition for commercial, healthcare and educational buildings, where a more durable structure is required. It has the benefit of providing BS 5234 Severe Duty performance, coupled with 60 minutes fire resistance and high acoustics, in just a single layer of 15mm Gyproc DuraLine board lining. This significantly reduces material costs and installation cost and time compared with traditional double-boarded or masonry alternatives.

The additional impact resistance provided by the Gyproc DuraLine board is due to a combination of board weight, heavy duty paper facing and glass fibre and other additives which have been added for additional strength in the aerated gypsum core.

Generally speaking the impact performance of a partition is limited by the type of board facing, with single layer Gyproc boards achieving the following maximum BS 5234 ratings in Gyproc systems:

• Medium Duty - Gyproc Regular (12.5mm and 15mm); Gyproc FireStop (12.5mm)
• Heavy Duty -  Gyproc FireStop (15mm)
• Severe Duty – Gyproc DuraLine (15mm)

For further information on impact resistant boards and systems please contact the Gyproc Technical Team or see the new Gyproc White Book on line at www.gyproc.ae/literature.