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The significance of supports and fixings in the design and installation of building services engineering is often underestimated. These components are commonly treated as commodity items, with procurement decisions based solely on cost, or worse, altered on-site without proper understanding of the consequences. Furthermore, they are frequently installed by individuals lacking the necessary skills and proper tools.
This flawed approach makes it challenging to demonstrate the correct design and installation of supports and fixings, rendering them unfit for their intended purpose. Instances of suspended services collapsing due to failures in design, procurement, or installation are not uncommon. Failures in supports for roof-mounted equipment also occur when factors such as wind or snow loading are not considered during the design phase.
To address issues related to fixings into concrete, 'BS 8539:2012+A1:2021 Code of practice for the selection and installation of post-installed anchors in concrete and masonry' was introduced in 2012. This code provides a structured framework for managing the concrete anchor design, specification, installation, and testing process. Despite its wide circulation, the adoption of this code has been slow. This is because the fundamental principles of BS 8539 emphasize the necessity of considering best practices for supports and fixings during the design phase, as well as ensuring accurate specification during procurement and competent installation. However, the BS 8539 doesn’t really provide clear guidance on how (or how not) to implement these best practices, with real-life examples and detailed guidance on what good versus bad practice might look like.
So, then what does the BESA TR50 do?
The BESA TR50 offers technical assistance to address these deficiencies by providing recommended practices for designing, specifying, installing, and testing supports and fixings in building mechanical service systems. Additionally, it highlights instances of common errors and neglected aspects in supports and fixings as instructive examples of what to avoid.
What is BESA?
BESA, short for Building Engineering Services Association, is a professional organization dedicated to serving the needs of contractors engaged in the design, installation, commissioning, maintenance, control, and management of engineering systems and services within buildings. Established in 1904 under the name National Association of Master Heating and Domestic Engineers, it underwent several name changes, including Heating and Ventilating Contractors' Association (HVCA). Since 2012, it has been known as the Building and Engineering Services Association (BESA).
The association, in existence for over a century, seeks to enhance industry knowledge by addressing informational gaps related to fixings within the sector through the provided guide.
This article delves into all the points that the BS 8539 Code of Practice missed that the BESA TR50 aims to address with regards to best practice for supports and fixings.
What are the problems addressed in BESA TR50?
The BESA TR50 guide places particular emphasis on rectifying prevalent errors made by contractors during the installation of supports and fixings. While the BS 8539 Code of Practice outlines "best practices," it is equally valuable to delve into the underlying reasons for implementing these practices. Many individuals may not fully comprehend where traditional approaches falter, making it essential to scrutinize the nuances of these guidelines for a more comprehensive understanding.
Viewing fixings as commodity items
According to BESA TR50, contractors and design professionals need to reassess their approach to supports and fixings to mitigate the risks associated with unsafe building services installations.
BESA TR50 emphasizes the critical importance of supports and fixings in M&E installations within buildings, often overlooked elements that, when improperly addressed, can lead to catastrophic consequences. Recent high-profile failures underscore the necessity of considering these issues thoroughly during design, procurement, installation, and testing phases.
Mr Pitt, the chair of BESA’s Technical Committee stated: “Fixings are not commodity items – they should be properly considered and specified.”
BESA TR50 raises concerns about structures constructed with lightweight steel frames, noting that wind loading is frequently neglected early in the design process. It also points out that wind can significantly impact loads, citing instances of rooftop air handling units moving when not properly restrained. This underscores the vital need for comprehensive design and early engagement, leading to the subsequent point of discussion.
Lack of Early Engagement
Many of these issues can find solutions through proactive early engagement and thorough design consideration.
According to BESA TR50, the weight of services should be contemplated much earlier in the design process, ideally at RIBA Stage 2 (or no later than Stage 3). It emphasizes the necessity of incorporating details about brackets and other fixings in installation drawings.
Mr. Pitt said: “This requires a completely new mindset for the industry that involves opening up a dialogue with structural engineers and fixings manufacturers much earlier.” Thus, highlighting the significance of early engagement.
Site Teams Making Uninformed Decisions
Industry practices that delegate crucial decisions to on-site teams without the requisite knowledge, skills, or experience pose a serious threat to installation safety.
According to BESA, the industry's tendency to entrust critical decisions to on-site teams. This approach undermines safety, as these teams often work with incomplete information and rarely consult structural engineers.
Consequently, the inability to verify the appropriateness of selected supports and fixing systems for their intended purpose arises. To address this issue, it is strongly recommended to engage an independent structural engineer for advice on specialized and non-standard support and fixing designs. Specific areas of concern include point loads, cantilever bracket arrangements, assessment of wind loadings for external MEP services in exposed locations, and evaluation of snow loadings.
Mixing and Matching Components
Mixing and matching components within a system, especially without a comprehensive understanding of their compatibility, can introduce a range of hazards and complications. This practice, though seemingly frequent in the M&E industry, poses significant risks that can compromise the overall functionality, safety, and longevity of installations.
This is why tested channel systems such as the MX Channel System is a safe and compliant option for your bracket assemblies. The MX Channel System has undergone extensive physical testing to evidence that the final installation, not just the individual components, is fit-for-purpose and can withstand the designated load applied to it,
Lack of Installation Training
According to the BESA TR50, Installers should undergo manufacturer-specific installation training, and anchors into concrete must be installed by trained individuals under competent supervision. A competent supervisor should have completed a relevant course, such as the one offered by the Construction Fixings Association.
Many systems require torque control, and torque settings specified by the manufacturer must be strictly adhered to. Calibration-certified torque wrenches should be used, and certain anchor types may require impact drivers.
Parasitic Loading
Parasitic loading in the building services sector poses a significant danger, as highlighted by BESA TR50. It is crucial for professionals to avoid assumptions when adding new services to existing supports in a project. BESA technical consultant, Peter Rogers, emphasizes that blindly integrating one's systems onto someone else's supports without a thorough understanding of their intended design can lead to perilous consequences.
The danger escalates when considering the assumption that existing supports can bear additional weight, particularly that of a person seeking access for maintenance purposes. Such assumptions can result in what is known as parasitic loading, where the original supports may be compromised, leading to structural failures or, at the very least, diminished safety margins. BESA TR50 underscores the importance of precise knowledge about the design and intended load-bearing capacity of existing supports before incorporating new systems. This cautionary approach is vital to mitigate the risks associated with parasitic loading, ensuring the integrity and safety of building service installations.
Lack of Attention to Fire Safety
In certain applications, it is crucial to ensure that support and fixing systems are specified to endure a designated period or rating of exposure to fire. Presently, there is no established UK test standard or corresponding industry guidance for the fire rating of supports and fixings as an integrated system.
Here are some best practices outlined in the BESA TR50 to ensure fire safety:
- Multi-Service Supports Carrying Critical Applications: In large commercial buildings, where mechanical and electrical services share a common support system (trapeze arrangement), specific attention is given to power supplies for life safety, fire-fighting, and other critical applications.
- Designated Fire Escape Routes: Supports and fixings within designated means of escape, as per the fire strategy, must provide the same level of fire performance as the escape route itself. This ensures consistency in fire performance throughout the escape route, emphasizing safety.
- Fire Stopping of Service Penetrations: Supports and fixings play a crucial role in maintaining fire performance when services pass through compartment walls. Fire stopping of service penetrations is a critical aspect and supports must adhere to manufacturer-tested and approved fire stopping solutions. The distance between supports on either side of penetration seals must align with fire test or certification evidence provided by the manufacturer.
- Fire-Rated Fixings into Concrete: Specific applications may demand supports and fixings with the ability to withstand a prescribed fire exposure period.
- Load De-Rating Under Fire Conditions: It's essential to note that most fixings into concrete experience significant load de-rating under fire conditions. Engineers must consider these de-rating factors in the design and specification process to ensure the supports and fixings maintain their structural integrity during a fire event.
Examples of good vs bad fixing practices
Presented below are specific scenarios outlined in the BESA TR50, along with guidance distinguishing between practices deemed favourable and those considered unfavourable.
Connections to Purlin Flanges
Purlin clips should be avoided for load application unless explicit permission is granted by both the purlin manufacturer and the structural engineer. In cases where approval is obtained, the preferred fixing method typically involves drilling through the web. Fixing to purlin lips is generally discouraged.
Window Brackets
When utilizing window brackets to attach support systems to main structural steelwork, it is crucial to employ them in pairs, with one bracket on each side of the beam.
When clamping strutted steel or metal channel to intumescent-coated steel beams, careful adherence to the manufacturer's guidance is essential to allow for proper expansion during the intumescent process.
Overloading of Fixings
Fixings may inadvertently face overloading when additional brackets and supports are installed by follow-on sub-contractors.
Complex Load Paths
Services should be distributed as evenly as possible across all supports and fixings. Hanging services from other services should be minimized, as complex load paths may lead to cantilevers and multiple forces affecting the fixing.
Channel Header Rails
When fixing to channel header rails, ensure an even distribution of load across the header. Additionally, be mindful of the distance between supports to prevent excessive lengths.
Cantilever Loads
Cantilever brackets, which introduce significant additional force through the support and fixing, should only be used after thorough verification by a structural engineer.
Conclusion
In conclusion, the BESA TR50 guide provides comprehensive guidance on supports and fixings in commercial/non-domestic premises, emphasizing the importance of proper design, specification, installation, and testing. Professionals in building services engineering should adhere to the principles outlined in the guide to ensure the safety, reliability, and compliance of mechanical service systems. As building services continue to evolve, adherence to the BESA TR50 guide remains crucial for maintaining the integrity of supports and fixings in diverse environments.
