Ask the Expert: Masonry Support Systems

Jonathan Vaughan, Technical Manager and Jeff Edwards, Engineering Manager for Leviat’s Masonry division discuss masonry support systems.

What are the main types of masonry support systems available, where are they typically used, and how are they commonly fixed?

Masonry support systems are available in various configurations to provide loadbearing support for external masonry facades at horizontal movement joints (HMJs). They are also used above large openings, ribbon windows or at undercrofts. Ancon MDC systems are “bespoke as standard” and enable architects to be creative in their design choices, rather than being limited by standardised options. The system comprises a continuous shelf angle with brackets welded to the rear which span the cavity and fix to the structure. The bracket spacing and geometry varies depending on the cavity size, support level, load to be carried and type of structure. Ancon CFA systems are generally used for smaller cavities but are less versatile in terms of achievable geometries due to the lack of bracket.

Systems are fixed to concrete using Ancon Cast-in Channels or post-fixed anchors. Cast-in channels are recommended (where suitable) to ensure maximum adjustment and to minimise on-site drilling operations. At external corners, post-fixed anchors are sometimes used where channels are not able to carry the concentrated load.

When fixing to steelwork, isolated set screws are used where access to the rear is available (e.g. UB sections). When no rear access is available (e.g. RHS sections) Ancon Steelgrip bolts are used.

What are the main design considerations when specifying masonry support systems?

As designs are often limited by the capacity of the fixings, there is a balance between widening the vertical spacing of the HMJs (increasing the load applied) and the capacity of the fixings and structure. As well as the load to be supported, another factor is the cavity size between structure and masonry. The larger this is, the greater the bending moment and resulting bolt tension.

A combination of large cavities, large masonry loads, fire barriers and thinner slabs create design challenges. Leviat are collaborating with partners in the fire barrier industry to ensure relevant testing is available to demonstrate the performance of fire barriers in conjunction with our systems.

Another consideration is concentrated loading. Lintels are supported by bearing on piers between openings resulting in concentrated loads at piers, corners or close to vertical movement joints, particularly where the system is close to the underside of openings. Bands of stack-bonded soldier bricks underneath windows exacerbate this challenge as this limits the ability of load to spread through the masonry. Other design challenges include post-tension pockets, balcony connectors and vent ducting. These limit the positioning of brackets and can complicate designs. Our latest CPD seminar, Considered Façade Solutions for Complex Applications, further explains such considerations.

Structural integrity, feasibility, cost and efficiency aspects must all be considered. Leviat encourages specifiers to engage with us early in the design process in order to arrive at the most appropriate solutions.

What types of building tolerances need to be accommodated and how do support systems typically achieve these?

Vertical adjustment is provided in all of Leviat’s systems, with +/-20mm provided by serrated slots in the back of the brackets.

Lateral adjustment is available through pushing the brick backwards on the angle or by shimming the system outwards. Loose shims may be used up to 12mm, with greater adjustment available by use of prefabricated solid shim packs.

Longitudinal adjustment is almost unlimited when using cast-in channels, however when using post-fixed anchors or fixing to hollow steels, bolt positions must be carefully marked out and holes site-drilled. If reinforcement is encountered while drilling concrete, it is imperative that the site team contact both the Structural Engineer and Leviat’s design team. When fixing to steel UB sections, plates/angles are welded between the flanges to provide a fixing position. Prefabricated horizontal slots in these steels provide longitudinal tolerance.

Leviat encourages specifiers and end-users to consult our installation guides to comprehensively understand adjustment parameters. It is often advisable to provide site survey information to enable us to design systems which minimise the requirement for site adjustment.

How important is corrosion resistance and bi-metallic corrosion when it comes to specifying and detailing support systems and what can be done to mitigate them?

In short, very important! For this reason austenitic stainless steel is typically used for masonry support systems. Grade 1.4301 (304) is most commonly used and is suitable for a broad range of construction applications. However, in more aggressive environments e.g. coastal and industrial locations, the specification of 1.4401 (316) material is recommended to mitigate corrosion. Leviat offers advice on suitable material specifications, but the responsibility for the specification should always rest with the project’s structural engineer. When fixing to steelwork, we recommend an isolation layer between the stainless steel system and the structural steel to eliminate the risk of bi-metallic corrosion. This is normally provided by Leviat with the system along with nylon washers for bolts.

What can be done to minimise the impact of cold bridging when using masonry support systems in terms of products and detailing?

Masonry support systems can be supplied with thermal shims to minimise cold bridging and improve thermal efficiency. However, we always emphasise the importance of the quality of detailing and installation of insulation in and around the masonry support system, as this can make a huge difference to the realised thermal performance. Commissioning a thermal analysis for each specific project is recommended, as systems are bespoke and there is no standard answer for thermal performance – surrounding materials can be highly influential in the resulting ψ-value. Leviat is happy to work alongside consultants to provide the relevant information.

Which types of quality assurance should specifiers look for when choosing masonry support products?

The need for standards to be maintained throughout building projects has never been more relevant and will ensure value for money is being delivered. Leviat factories are EN 1090 accredited, the European Standard that governs the fabrication of structural steelwork.  All fabrications leaving our factory will either have a UKCA, CE-UKNI or CE mark appropriate to the market being supplied. Leviat also has various other approvals from BSI in terms of quality assurance systems and environmental management having achieved ISO 14001 / ISO 9001.

For more information visit our Masonry Support Systems product page, or email tech.ancon.uk@leviat.com.