Seismic Bracing: Key Concepts, Components, and Applications for MEP Systems
- thekuljeet
- May 23
- 5 min read
Seismic bracing is a critical design element that protects mechanical, electrical, plumbing, and fire protection (MEP) systems from damage during seismic events. Required by codes such as the International Building Code (IBC), ASCE 7, and NFPA 13, seismic bracing helps non-structural components move safely with the building structure, preventing failures that can lead to substantial losses.
Checking Seismic Design Parameters
The American Society of Civil Engineers developed a hazard tool to view which seismic design category (SDC) your project is located by searching its address. In order to determine the applicable seismic bracing design category, the following steps must be taken,
Determine Building Risk Category (International Building Code Table 1604.5)
The IBC classifies buildings into a roman numeral numbering system based on the nature of occupancy. Occupancies are as follows,
I: Low occupancy, low risk structures (ex. Unoccupied buildings, temporary structures, some storage buildings)
II: Standard occupancy dwellings; most structures (ex. Offices, homes, other businesses)
III: High occupancy buildings (ex. Public gathering areas, public utilities, schools)
IV: Emergency/High risk structures (ex. Hospitals, emergency utilities/control centers)
Where a building may contain multiple different risk categories, the highest risk category shall be applied throughout, unless structurally separated by the Civil/Structural Engineer. This risk category is input into the hazard tool by the user.
Determine Site Soil Class
The categories are dependent upon fault lines, soil structure, and building use/occupancy type. The user inputs a soil class into the hazard tool,
A: Minor ground shaking. Good soils.
B: Moderate ground shaking for Occupancy Groups I, II, and III. Stratified soils.
C: Moderate ground shaking expected with Occupancy Groups IV; Severe ground shaking expected for Occupancy Groups I, II, III.
D: Severe and/or destructive ground shaking, however not located near a fault line. Poor soils.
E: Severe and/or destructive shaking near major active faults. Any soil type. Occupancy Group I, II, and III.
F: Severe and/or destructive shaking near major active faults. Any soil type. Occupancy Group IV.
Seismic Design Category
The newest version of the hazard tool will automatically output the Seismic Design Category (SDC) in the results. A table of spectral response parameters will also be available. The SDC is categorized as letters, A - F. SDC A is the least restrictive, while F is the most restrictive.
The Spectral Response Parameter
The structural response parameter is useful when the SDC is not automatically available. A simplified definition of spectral response is a measurement of the response (movement, e.g. displacement, velocity, acceleration) of a building during an earthquake in a time scale.
For a 1-second period, if the spectral response, S1 is less than 0.75 and the risk category is class I, II, or III, the SDC may be determined from ASCE 7-16 Table 11.6-1. If S1 is greater than 0.75, the SDC shall be Category E. Another version of this method is outlined in the IBC Table 1613.2.5(1).
If S1 is less than 0.75 and the risk category is class IV, the SDC may be determined from ASCE 7-16 Table 11.6-1. If S1 is greater than 0.75, the SDC shall be Category F. Another version of this method is outlined in the IBC Section 1613.2.5(2).
Applying the SDC in Fire Sprinkler Design
If the SDC is C, D, E, or F, seismic design criteria will be required for the project. NFPA 13 has a chapter on seismic bracing that will be applicable for the aforementioned SDC.
Why Seismic Bracing Is Essential
After earthquakes, over half of building-related monetary losses come from non-structural system failures. Seismic bracing mitigates this by preventing MEP systems from detaching or collapsing. Insurance requirements, such as those from FM Global, often reinforce these code mandates.
Bracing is required in two horizontal directions:
Lateral (Transverse): Prevents movement perpendicular to piping or ducts.
Longitudinal (Axial): Prevents movement parallel to the system.
Additionally, vertical movement is addressed by reinforcing hanger assemblies at brace points using rod stiffeners.
Types of Bracing: Rigid vs. Cable
Seismic bracing falls into two primary categories:
Rigid Bracing: Works in both tension and compression, needing only one brace per location. It’s more economical and faster to install, with fewer material and labor costs. However, brace length is limited (typically up to 9'6" using Cooper B-Line B22 strut) and not suitable with vibration isolation systems.
Cable Bracing: Works only in tension, requiring two opposing braces at each location. It is used when long brace lengths or vibration isolation is present. Though more expensive, cable bracing is the only option in certain situations.
Rigid Bracing Components and Applications
Universal Swivel Sway Brace Attachment (Figure 980): Connects brace material (strut, pipe, angle iron) to structural supports. Accommodates materials up to 1/4" thick.
Fast Attach Seismic Brace (Figure 981): Attaches brace to the system being braced via hanger rods. Available in small (3/8"–5/8") and large (3/4"–7/8") sizes.
Fast Clamp (Figure 1000): Clamps directly onto pipe, providing quick, adjustable installations—ideal for sprinkler systems.
Bar Joist Attachments (Figures 825 & 825A): Structural attachments for bracing to bar joists. Figure 825A supports less load and is more cost-effective.
Rigid braces are ideal for systems without vibration isolation and where brace lengths do not exceed the manufacturer’s maximums.
Cable Bracing Components and Applications
Cable bracing systems are designed for easier handling and reliable installation:
Cable Sway Brace Attachment (Figure 990): Facilitates cable threading, even with frayed ends, and includes breakaway nuts for verified torque.
Fast Attach Cable Sway Brace (Figure 991): Connects to hanger rods and shares the same threading and torque verification benefits as Figure 990. Available for three cable sizes (1/8", 3/16", 1/4") to match load requirements.
These braces are used when rigid braces are impractical, particularly in systems requiring long brace spans or vibration control.
Installation Best Practices
Lateral braces are placed perpendicular to pipe or duct runs.
Longitudinal braces attach directly to the system and run parallel to the axis.
Visual verification features (e.g., breakaway bolts and nuts) ensure code-compliant torque and installation.
Conclusion
Seismic bracing is a vital component in protecting MEP systems against earthquake damage. Understanding the differences between lateral/longitudinal and rigid/cable systems allows for better design and installation choices. With proper selection of bracing products and adherence to building codes, facilities can safeguard their infrastructure, reduce risk, and comply with structural safety standards. For any further inquiries regarding this topic, as well as for code consulting and fire engineering design support related to your project, please don’t hesitate to contact us via email at contact@engineeringfireprotection.com.
Application of any information provided, for any use, is at the reader’s risk and without liability to Engineering Fire Protection (EFP). EFP does not warrant the accuracy of any information contained in this blog as applicable codes and standards change over time. The application, enforcement and interpretation of codes and standards may vary between Authorities Having Jurisdiction and for this reason, registered design professionals should be consulted to determine the appropriate application of codes and standards to a specific scope of work.