Fastener Testing

The deadline to have structural timber fasteners and fixings placed on the UK market with UKCA Marking is fast approaching. Here Hugh Mansfield-Williams, technical manager at BM TRADA, discusses the standards and tests that these products need to be tested against to support UKCA Marking to ensure they are compliant for placing on the UK market.

Save for being New Year’s Day, the 1^st of January 2023 may seem like an innocuous date that is far off in the future. However, that could not be further from the truth for manufacturers of structural timber fasteners and fixings.

The date actually marks the cut-off point to have fasteners and fixings marked as UKCA (UK Conformity Assessed) products. This is a new UK product marking requirement used for goods being placed on the market in Great Britain (England, Wales and Scotland). The marking covers most goods that previously required CE Marking in the EU.

For structural timber connections, whether the fasteners and fixings are forming timber-to-timber or metal-to-timber joints, virtually every variation of the product must be tested so that its performance can be declared in accordance with the applicable standard. With hundreds of different types of fasteners and fixings, the challenge is, how should they be tested to achieve the UKCA Marking before the deadline?

The UK Construction Products Regulations

By applying the UKCA Marking to structural timber fasteners and fixings, manufacturers are adhering to the Construction Products Regulations in the UK (UK CPR). The UK CPR is very similar to the EU-wide Construction Products Regulation (EU CPR), which has been in force since 2013. This regulation lays down ’harmonised’ rules for assessing the conformity of construction products as a pre-requisite to placing the product on the EU market. The EU CPR has been incorporated in the UK CPR, although naturally all references to the EU have been removed, with some changes in terminology such as ‘harmonised’ standards becoming ‘designated’ standards and ‘Notified Bodies’ becoming ’Approved Bodies’.

Within the UK CPR, there are five attestation systems, each with different combinations of tasks for manufacturers and Conformity Assessment Bodies (CAB). Products are categorised on risk to determine which system they belong to.

System 4 is the most basic level with no tasks for the CAB, i.e no auditing, certification or surveillance is required. Manufacturers carry out any assessment required and declare the performance of the product. The other extreme is System 1+, which requires a CAB to undertake a range of tasks given the associated high risk and subsequent danger if the product fails. These products are typically difficult to assess once they are manufactured, so the CAB is not only involved in the initial assessment and ongoing surveillance visits, but also tests samples of regular production.

Structural fasteners and fixings for timber sit in System 3. This means any dowel-type fasteners, i.e nails, screws, staples, steel dowels, and bolts with nuts, that are designated for use in structural timber connections, must all be tested in accordance with the designated standard, BS EN 14592. Such testing must take place in a UK-based Approved Laboratory that is accredited by UKAS (United Kingdom Accreditation Service) and listed on the appropriate DLUHC (Department for Levelling Up, Housing and Communities) website. It should be noted that even if these fasteners and fixings have been tested since 2013 in an EU Notified Laboratory outside the UK, they will still need to be tested again in a UK Approved Laboratory to support UKCA Marking.

Putting fasteners and fixings to the test

Looking at the actual testing processes, not all fasteners and fixings will be subject to the same tests, and test processes will all depend on the type of fastener or fixing.

As an example, some testing will merely involve measuring the product’s geometry and dimensions to ensure that it fits with the advertised product description and specification. Alongside the geometry, the Approved Laboratory may also ‘test’ the yield moment of the fastener by static calculations – based on the yield strength of the steel the fastener is fabricated from. Bolts and dowels are examples of dowel-type fasteners that will require no mechanical testing.

Nails and staples on the other hand, whether loose or collated for use with nail guns, will undergo both geometry measurements and mechanical testing. BS EN 14592 refers to various supporting standards for the test methods including:

• BS EN 1382 for withdrawal resistance (also known as a pull-out test), which indicates how much force it takes to pull the nail or staple from the timber for a certain length of point-side penetration.
• BS EN 1383 for resistance to head pull-through. This test is similar to the withdrawal testing, but it shows how much force is required to pull the head of a nail or staple through the head-side timber.
• BS EN 1383 for resistance to head pull-off. This test is essentially the same as the head pull-through test, but a steel plate is used instead of the head-side timber. This causes the fastener to fail so that its tensile capacity is determined.
• BS EN 409 for yield moment testing of those fasteners where static calculation is not an option. This is a mechanical test that determines the resistance of the fastener to bending.

For screws, while testing is very similar, there are a few key additions:

• BS EN 15737 for torsional resistance to driving in of screws. This test determines how much turning force is required to drive the screw into a selected substrate.
• BS EN ISO 10666 for the torsional strength of the screw itself. This test determines how much torque can be applied to the screw head before the screw snaps. The result should be significantly higher than that of the driving in test.

Usually, C16 grade softwood timber, conditioned at constant humidity and temperature, will be used for withdrawal, head pull through and torque resistance testing. The laboratory will measure the density and moisture content of the timber as part of the test.

It is worth mentioning that every diameter within the fastener range needs to be tested, but not every length. Also, the Approved Laboratory will not test material properties such as the yield strength of the original steel rod, or indeed the effectiveness of any corrosion resistant layers applied on the surface of a fastener. The obligation lies with the manufacturers to declare the necessary performance for these parameters.

Race against time

As the deadline for the implementation of UKCA Marking rapidly approaches, there is plenty for the manufacturers to do to be ready. While it is true that individual tests discussed, in themselves do not need much time to perform, and that each test only needs to be repeated a limited number of times to meet the testing requirement, most manufacturers and suppliers will find that their range of products need careful planning to get tested before the deadline.

As a UKAS accredited Approved Laboratory offering fastener and fixing testing to support UKCA Marking, BM TRADA is expecting a high demand from a wide range of businesses across the UK and around the world. Completion of the accreditation process is imminent.

For business and construction to continue apace come 1^st January 2023 next year, fastener and fixings manufacturers need to prepare products for testing now. In addition to the testing, there must also be adequate planning around preparation of literature, Declaration of Performance certificates and packaging, etc, in time to get the products shipped in a timely manner.