Cable Hangers: An Established Method for Suspending MEP Systems
Part 1: Tackling the Technical Aspects and Overcoming the Traditional Mindset
1. Rigidity and Sway - That is not a concern, for the following reasons:
I. Absence of reasons for sway
In a typical application, where building service systems such as ductwork, piping, electrical distribution systems, etc. are hung using cable hangers, such systems impose purely static gravity loads on the hangers and there are no lateral loads present on such systems. Hence there are absolutely no effects creating any type of sway once these systems are installed.
There are some special situations where there is indeed a presence of lateral loads, such as the possibility of seismic forces during an earthquake, or systems that are directly exposed to wind where wind creates a lateral force on the systems. However, in such scenarios building codes mandate the requirements for bracing of the building services, irrespective of the type of hanger used - cable or not. These bracing requirements are applicable even if the systems are hung using conventional hangers such as threaded rod. For example, in buildings classified as Seismic Design Categories C, D, E & F, suspended services are required to be seismically braced per requirements of ASCE 7, even if they are suspended with threaded rod. Such systems are then protected against lateral forces via the seismic bracing, and cable hangers can then be used at the support locations other than where seismic braces are installed.
II. Threaded rod is not completely rigid either
Although threaded rod may seem rigid when compared to a cable hanger, its rigidity is not
significant, especially when analyzed in the context of long drop lengths that are seen in a typical
building services installation. Rather, at such drop lengths, threaded rod ends up in an interesting
state that is neither flexible nor effectively rigid, and this becomes a weak point in a lateral loading
scenario. On longer drops (typically longer than 1 ft) threaded rod is highly susceptible to the lateral
forces, which can cause them to move and bend permanently. This can be disastrous and lead to
the failure, or even collapse, of the suspended systems. For the same reason, it is recommended
by the code to brace the systems hung by threaded rods where lateral forces are expected, such
as in seismic design categories C and above.
In comparison, cable hangers are flexible and lateral forces don’t cause them to bend. Hence,
they are relatively safer against the bending-inducing lateral loads. However, seismic bracing is still
required on systems hung with cable hangers, as in systems hung with threaded rod per ASCE 7
2. Cable Hangers Can Stretch - This is normal but negligible, as explained below:
Cable (a.k.a. Wire Rope) does exhibit a property called stretch, which basically means a small change in the cable length after it is subjected to the load. This happens for two reasons:
1.) Compacting of the wires and strands under load leads to slight reduction in diameter and increase in length (Constructional Stretch), and 2.) There’s also a small amount of stretch due to the elastic elongation of the rope (Elastic Stretch). The net effect of this stretching is very small, typically around 1% to 2% of the cable length. Also, this effect is observable only until cables are subjected to the loads. Once the cables are loaded and achieve a certain increase in length due to above explained effects, there’s no further stretching for the full lifetime of the cable. Once the systems are suspended on the cables, hangers can be adjusted using adjustable locking devices and there’s no need to worry about any future stretching of the cable.
Part 2: Code Compliance
A great deal of assurance regarding cable hangers as an established method of suspending MEP services comes from the approvals and listings that establish compliance of cable hangers with US Building Codes and other prominent standards used in construction industry.
For example, Gripple cable hangers are listed with International Code Council – Evaluation Services (ICC-ES) through a listing report, PMG-1408, which established compliance of Gripple hangers with following codes and standards:
• International Building Code (IBC) through compliance with:
• International Mechanical Code (IMC)
• International Plumbing Code (IPC)
• MSS SP-58 Standard for Pipe Hangers and Supports
• SMACNA Duct Construction Standards
• ASME B31.9 Standard for Building Services Piping
3. Compliance with IBC and State building codes is a must, and Gripple hangers meet this requirement through ICC-ES Certification.
From the contractor’s perspective, using cable hangers instead of threaded rod comes with
some distinct advantages. Some of these are summarized below.
Time & Material
- Reduced Loading of Interior Structure: 150 lbs of cable hangers (1,000 hangers) replace over
3,000 lbs of rod and strut.
- Reduced Transporting Costs: 100 cable hangers are packaged in a single small box, easily carried under one arm. Avoids transporting and moving heavy material five or six times prior to hanging.
- Adjustable: Contrary to threaded rod, cable hangers allow easy height and leveling adjustment of the suspended service, during and after installation.
- Versatile: The variety of end fitting and fastener options for cable hangers ensure an attachment solution for every structure, service, or ceiling type.
Health & Safety
No More Tools: In contrast to the manpower required to measure and cut threaded rod and grind the
edges smooth, cable hangers come in pre-cut, ready-to-use lengths with your choice of end fitting
The advantages of cable hangers covered under Time & Material and Health & Safety also make cable hangers the most sustainable MEP hanging solution that exists today. With reduced requirements of materials, tools, and transportation compared to other conventional hanging methods, cable hangers result in a sustainable hanging method reducing the overall carbon footprint of the project.
Cable hangers are less visually invasive than threaded rod and are virtually invisible from the ground, and therefore don’t require painting to match the ceiling.
In summary, cable hangers provide:
- Industry Accepted Code Compliance
- Time & Material Savings
- Health & Safety Benefits
- Sustainability Advantages
- Aesthetic Improvements
Considering all the advantages of using cable hangers, it’s clear to see why this has become a well established method of suspending MEP services for the contractor.
Why use Gripple?
- Significant time and cost savings on your project
- Complete, off-site solutions which minimize health and safety concerns
- Innovative, patented solutions designed by an in-house team of engineers
- Considerable reductions in packaging, vehicle movements, and embodied CO2
- A range of support services at every stage of your project, provided by our technical team.