MASON SEISMIC RESTRAINT GUIDELINES FOR SUSPENDED PIPING, DUCTWORK AND ELECTRICAL SYSTEMS

Mason Seismic Restraint Guidelines for Suspended Piping, Ductwork and Electrical Systems

The Mason SCB/SSB system is featured in a 180 page OSHPD approved guideline that includes layout instructions, restraint requirements and installation  details for a wide variety of projects.  These guidelines provide seismic restraint requirements and details for any seismic horizontal acceleration input up to 2.0g and include conversion factors to be utilized when projects are subject to the new Strength Design based codes such as UBC 1997 and the 2000 IBC.

All other restraint guidelines use bent brackets and generic strut hardware that have been poorly adapted to the purpose of restraining suspended piping, ductwork and electrical systems.  Small brackets and attachments greatly limit the load capacity of the individual braces and require installation of braces at very close intervals, in some cases as close as 5 feet on center!

Mason engineers recognized that larger hardware and attachments, installed at the maximum allowable spacing to reduce the overall quantity of brace locations was a far more cost effective method to achieve proper bracing.

Please contact us for your copy of these guidelines.

Code Requirements

Suspended piping can move through large displacements in a seismic event and damage surrounding building elements.  It has been observed that the pipe itself is very ductile and can withstand a great deal of bending and shaking, however, piping connections to equipment can be easily damaged in earthquakes.  All seismic codes contain provisions for bracing suspended piping for the purpose of life safety. Seismic bracing of piping is not an option and is not left to the judgement of architects, engineers, contractors, owners, or suppliers.

All suspended piping, ductwork, conduit and cable trays (modify to meet scope of engineer's responsibility) shall be provided with seismic sway braces in accordance with the Mason Industries Seismic Restraint Guidelines for Suspended Piping, Ductwork and Electrical Systems and the applicable codes (modify to include all applicable codes).  Seismic sway braces shall consist of galvanized steel aircraft cables or steel angles/channels. Steel aircraft cables shall be prestretched to establish a certified minimum modulus of elasticity. Cables braces shall be designed to resist seismic tension loads and steel braces shall be designed to resist both tension and compression loads with a minimum safety factor of 2. Brace end connections shall be steel assemblies that swivel to the final installation angle. Do not mix cable and steel braces to brace the same system. Steel angles, when required, shall be clamped to the threaded hanger rods at the seismic sway brace locations utilizing a minimum of two ductile iron clamps. The bracing system shall have an Anchorage Preapproval "R" Number from OSHPD in the State of California verifying its capability to resist seismic forces. Cable brace assemblies shall be Type SCB, steel brace assemblies shall be Type SSB, rod clamps shall be Type SRC, pipe clevis braces shall be Type CCB and multiple anchor load distribution brackets shall be type SLDB all as manufactured by Mason Industries, Inc.

SCB/SSB System Components

There are two major types of pipe bracing: solid bracing using steel members or strut and cable bracing using aircraft cable. There are advantages and disadvantages to each system.

	SSB SOLID PIPE BRACING While solid bracing is required on one side of a typical restraint location, the steel members must be sized for compressive loads to resist buckling. Single braces also subject the vertical support rods to added tension loads. These tension loads can be large - up to 5 times the dead load depending on design criteria. Failure to account for these tension loads can result in the catastrophic failure of the support system.
	SCB  CABLE  BRACING Cable bracing is required on both sides of a restraint location, however, cables are tension elements only and length is not a factor. Cable systems do not add tension forces to existing dead load supports and are ideal for retrofits. Cable restraints were originally designed for vibration isolated systems since the cables do not interfere with isolator function but effectively control movement. Because of the Mason SCB cable systems' effectiveness and ease of installation, SCB cable restraints have replaced solid restraints as the preferred restraint system.
	SRC ROD CLAMPS Due to the installation geometry, all bracing systems create a vertical uplift force on the support rod. This force can easily exceed the dead load on the rod, resulting in compression. If the rod is subjected to compression, buckling and uplift of the pipe can result. To better resist these compressive forces, the rods should be braced. The Mason SRC rod clamp allows lengths of standard steel angle to be clamped to the rod quickly and effectively. Where spring isolators are used the hanger box must be attached directly to the overhead support and an uplift prevention washer must be added to prevent unloading of the spring.
	CCB CLEVIS BOLT BRACES When pipe bracing was initially developed, pipe sleeves were added at braced clevis locations. These sleeves are standard on larger clevis sizes and prevent sliding of the clevis sides and collapse of the clevis cross bolt. Sleeves are used on all sizes of braced clevis locations. The addition of these sleeves was practical when the clevis was disassembled to attach restraints to the cross bolt, however, use of the new SCB hooks no longer require disassembly of the clevis and CCB bolt braces can be bolted on the cross bolt to further simplify the installation.

Discussion: Installation Problems and Solutions

The Mason SCB/SSB restraint system has been developed after years of experience and has been specifically designed to solve many installation problems.

When cable bracing was initially used as a method for controlling the sway of suspended piping, cables of various sizes were attached by various size clips and brackets to various connection points. The cable was left slack or installed with sliding loops that allowed large amounts of horizontal motion. The cable was looped around the pipe, looped around the clevis or the clevis crossbolt and attached to the structure by various methods - usually with dramatically undersized expansion anchors. Longitudinal braces, designed to prevent the pipe from moving axially, were installed at clevis locations as if the pipe could somehow slide through the clevis due to thermal growth, but be restrained by the clevis for seismic motion. End connections varied greatly. Standard 45 degree bent clips were utilized regardless of installation angle. Standard 9/16 " holes allowed only 1/2 " bolts for attachment to concrete and required holes to be burned out for attachment to 5/8 " or larger connections.

Mason SCB/SSB brackets are available in (4) different sizes to fit 3/8" to 1 1/4" attachment bolt sizes. Attachment of cables to pipe and structure are clearly indicated on installation details. Longitudinal braces are attached to pipe clamps. The SCB/SSB pivots to the exact installation angle,eliminating bracket bending and minimizing prying action on the attachment.

There was a great deal of confusion when cable clamps and bent brackets were used. Cable was often looped over sharp edged holes that had been punched or torched in bent steel brackets. Cable thimbles were required to protect the cable but were not regularly utilized. Cable clamps were installed in various quantities and at various spacings. The u-bolt portion of the clamp, which must be attached to the loose or "dead" end of the cable, was often reversed and attached to the active or "live" length of the cable. Often, clamps on one end were installed properly, and clamps on the other end were reversed. The cable restraint is only as strong as the end connections and leaving the end connection undefined was an extremely dangerous situation.

The Mason SCB bracket was designed to provide a dependable end connection that was easy to install. The cable restraining bolts are included in the SCB and additional cable clamps are not required.


Since cable restraints are installed at an angle, horizontal loads can create compression loads in the support rods. If the rods are allowed to buckle, excessive motion and failure can result.

The Mason SRC clamp was designed to provide easy attachment of steel angles to reinforce the support rods. Three clamps are typically required to adequately attach the brace angle to the rod. This method is a significant labor savings over welded attachment of steel braces. The SRC is available in (3) sizes depending on rod size and loading.


Seismic bracing using solid brace elements wasn't any better. Typical installations included braces that spanned 2' to 20', without the slightest concern for compression loads that would buckle the brace elements. Braces were installed without concern for loads on support rods. Unlike cables, which can only create compressive forces on the support rods, solid braces can also add tension to the support rods depending on the direction of the load. Support rods could either buckle or rod connections could pull out of the structure.

The Mason SSB bracket was designed for solid brace installation. Brace members are engineered to suit a variety of field conditions. Compression loads have been analyzed and braces designed to resist buckling. The Mason SRC clamp was designed to provide easy attachment of steel angles to reinforce the support rods. Support rod connections are certified as part of a solid brace design package.

The initial restraint layout as shown in the 1976 SMACNA guidelines utilized restraints attached to the clevis crossbolt and a brace to prevent the clevis from deforming when subjected to seismic loads. The clevis had to be disassembled and brackets installed at each end. Since the clevis was disassembled, a length of steel pipe could be custom cut to exact length and installed to brace the crossbolt.

With the introduction of Mason SCBH hooks, seismic bracing can be attached to the support rod at the top of the clevis. The clevis no longer has to be disassembled to install the restraints, but would need to be disassembled to install the pipe sleeve crossbolt braces.

Now that SCBH hooks are available, the clevis only has to be disassembled for installation of the pipe sleeve crossbolt braces.

Mason CCB clevis crossbolt braces can be installed without clevis disassembly. These braces are required at all restrained clevis locations, whether restraints are attached directly to the crossbolt or on the support rod at the top of the clevis. Now with the bolt-on CCB, contractors can simply pick a clevis location, install SCBH cables to the support rod at the top of the clevis and install a CCB over the crossbolt. No clevis disassembly is required; this is a very substantial labor savings.

Installation Photos

SCB CABLE RESTRAINTS These all directional restraint locations utilize Mason SCB brackets and aircraft cable. Transverse cables are attached to the clevis cross bolt and longitudinal cables are attached to a riser clamp. Longitudinal restraints should never be attached to pipe clevis supports since longitudinal restraint is not possible. Pipe clamps can be welded to the pipe to increase restraint capacity beyond the clamp's clamping capacity. This picture shows a restraint location where pipe drops into a plenum. Restraints will prevent the pipe from excessively swaying which could damage the plenum roof and fragile coil connections.
A close-up of the SCB cable brace installed at an all directional location. The pipe clamp used for longitudinal restraint is attached within 4" of the clevis to meet SMACNA requirements. In the event of large longitudinal loads, uplift of the pipe would be prevented by contact with the clevis cross bolt. The SCB bracket has been designed using formed steel brackets for attachment to the standard clevis cross bolt without modification or replacement. A longer clevis cross bolt would be required to allow attachment of steel angle brackets that may be as much as 3/8" thick, or thicker.
SCBH  CABLE RESTRAINTS The SCBH restraint hook is used on this pipe to ease installation and avoid insulation conflict. The SCBH brackets are designed to fit over the support rod at the top of the clevis. Since cables are tension devices only, compression forces are not possible and the SCBH hook design can be used to ease installation since clevis disassembly is not required. The SCBH bracket can be stacked for multiple restraints at one location as shown.
SSB SOLID RESTRAINTS The versatility of the SCB/SSB system allows the contractor to properly restrain pipe in a variety of situations. On the left, the SSB is attached to the clevis cross bolt to allow installation of the angle brace under an adjacent valve. On the right, the SSB is attached to the support rod at the top of the clevis to allow installation of the angle brace over an adjacent pipe.
SRC SEISMIC ROD CLAMPS This all-directional restraint location includes an SSB attached to the clevis for transverse restraint and an SSB attached to a pipe clamp for longitudinal restraint. The support rod has been braced with steel angle attached with SRC rod clamps. These restraints are located at a critical point on the piping, at the top of the pipe drop to equipment, where transverse motion could be at its worst. Large motions at this point could impact surrounding pipes or damage weak union fittings on the nearby valve. This picture was taken before the insulation was completed. In order to attach the riser clamps, the hard insert has been moved slightly off center within the clevis.