Introduction to Seismic Bracing Systems
EARTHQUAKE SWAY BRACE SYSTEMS FOR CABLE TRAYS
Legrand®/Cablofil has joined with Loos and Company, the industry's top manufacturer of Seismic Wire Rope/CableTM Bracing, to provide a comprehensive and unique line of seismic protection products specifically designed for electrical cable tray applications. All our seismic Wire Rope/CableTM bracing, complies with model building codes, and installs in just one-third the time needed for more conventional pipe, angle, and strut bracing systems. Our exclusive systems have no length limitation and are UL listed.
Loos & Company's
Seismic Wire Rope/Cable Bracing
Our standard braces are constructed of a splayed assembly of
either 49 or 133 high-strength, zinc coated, steel wires, configured
into Wire Rope/CableTM. This type is similar to that successfully utilized
for over 30 years to satisfy the aircraft industry's own stringent
requirements. For the building industry's seismic bracing needs, we
have made various unique improvements and developed special
design&installation features in our brace assemblies.
Special Design & Installation Features
The breaking strengths of the standard braces have been specially
redesigned to accommodate the magnitude of earthquake loads
prescribed by Codes and Standards for typically used building
components. In addition, the specifications take into account the
ability of these components to transfer loads between braces.
Furthermore, the new design meets the practical load resistance
limits of generally available fasteners as well as the ability of
secondary structural framing members to resist the concentrated
loads imparted by bracing.
Every brace is designed to resist earthquake loads in tension; they
are not restricted in length as are compression braces, thanks to
their "least radius of gyration" limitations.
These features allow designers and installers to satisfy code
requirements in a cost effective manner, while being able to easily
adapt the braces to fit a wider range of design and field installation
conditions.
Standard braces are extremely flexible and lightweight. They are
offered in precut lengths, with or without fixed end fastener fittings,
as described on the following pages. These features facilitate
efficient installation and reduce construction costs.
Quality Assurance & Certified Break Strength
Loos & Co. maintains a fully staffed quality control department
which conducts a rigorous in-plant program of inspection, testing,
and retesting of all its seismic wire rope/cable products to meet code
and industry standards. Loos & Co.'s Certificate of Minimum
Breaking Strength, included with each shipment, further assures
the quality of all assemblies.
Pre-Stretched Assembly
Dampens Seismic Loads
Our Wire Rope/CableTM is pre-stretched to its maximum
recommended working load. This pre-stretching eliminates the
permanent stretch which would otherwise result from the wire
rope's construction. Pre-stretching allows our cable to act in its
elastic range; in essence, it behaves like a shock absorber. Our
braces elongate to an additional 1% of their length under the
maximum recommended working load, and then reset to their
original length once the load is removed. This elongation is well
within the tolerable limits of components and systems and offers the
advantage of dampening the effects of earthquake loads on
components, connections, and structural elements.
Three Standard Color-Coded Sizes
Our standard braces are offered in three basic sizes, with
minimum breaking strengths of 900, 1650, and 4000 Lbs. Each is
respectively tinted in red, white, or blue, insuring proper
designation on plans and specifications. In addition, proper field
installation can be easily confirmed.
Quality Assurance & Certified Break Strength
Loos & Co. maintains a fully staffed quality control department
which conducts a rigorous in-plant program of inspection, testing,
and retesting of all its seismic wire rope/cable products to meet code
and industry standards. Loos & Co.'s Certificate of Minimum
Breaking Strength, included with each shipment, further assures
the quality of all assemblies.
Code & Industry Material Standards
Loos & Co.'s Seismic Wire Rope/Cable is manufactured and
tested to equal or exceed the minimum materials standard
requirements of:
- The Manual for Structural Applications of Steel Cables as published by the American Iron and Steel Institute (AISI) and as referenced by or contained in theBOCANational Building Codes.
- the ICBO Uniform Building Codes and Standards.
- The SBCCI Standard Building Codes and the National Earthquake Hazards Reduction Program (NEHRP) Standards.
- The mechanical strength requirements of ASTM A603 as referenced within the above AISI manual.
- Breaking strength failure testing under ASTME-8 procedures.
- The Wire Rope Users Manual of the Wire Rope Technical Board as published by the American Iron & Steel Institute (AISI) and the American Society of Civil Engineers (ASCE 19-96).
THE SEISMIC BRACING SYSTEM
Our seismic brace consists of four basic components: the Wire Rope/CableTM, a factory-attached stake eye end treatment, an oval sleeve used to secure the cable loop, and a universal restraint clip (URC). The seismic braces are pre-packaged with all of the parts needed to make a single 4-way sway brace. Hardware required to connect the cable tray to the braced component and to the building structure are not included in the brace packages.
DESIGNING A SEISMIC BRACING SYSTEM
The following guidelines have been developed to aid in the process of designing seismic bracing systems for cable tray installations. This information is intended to serve as a recommendation only and users are cautioned to modify each installation as required to meet all federal, state, and local laws and regulations, which may supercede these recommendations. The design professional responsible for each project on which these braces are used must approve the bracing layout, the capability of the structural elements to which the braces are attached, and the use of the braces themselves along with their fasteners.
1. Calculate the Horizontal Load Factor (HLF) for the installation.
Each earthquake sway brace must be designed to resist the horizontal earthquake load/force within the brace zone of influence. The Horizontal Load Factor is the minimum portion or percentage of the cable tray system's total weight within the brace zone of influence, which must be resisted by the brace as applied in any horizontal direction.
2. Calculate the cable tray total linear weight.
The loads that must be resisted by the seismic brace include the weight of the cable tray system and its contents. To do this, the total tray weight must be calculated and expressed in total pounds per linear foot. For multi-tier tray installations where only the bottom level of the tray is braced, the total weight of all tiers should be included in the calculation.
3. Use the bracing tables to determine the brace sizes and spacing.
We have developed a series of bracing tables to simplify the selection of the correct brace size, brace spacing, and minimum fastener sizes. These tables tabulate this information according to the cable tray total linear weight versus the brace spacing for a given horizontal load factor and a minimum brace angle of 45 degrees from vertical. There are four bracing tables, each based on horizontal load factors of 0.25, 0.50 (shown at the bottom of this page), 0.75, and 1.00 respectively. Go to www.legrand.us/cablofil to find the bracing table that contains an HLF that meets or exceeds the HLF required for your application. Contact Legrand®/Cablofil for a more precise calculation of your bracing needs.
4. Specify Components and Catalog Numbers
Refer to the Seismic Bracing Systems catalog on our website to generate component specifications, material lists and part numbers specific for the project. There are many important installation-specific factors to consider which include, but are not limited to, the following conditions:
- The distance between the cable tray support and the various building structure components.
- The type of cable tray to be installed
- The type of cable tray supports to be installed.
- Fastener types and attachment methods for making seismic brace-to-structure connections.
- Whether or not the installation of the seismic braces will be concurrent with the installation of the cable tray supports, or retrofitted at a later time.