As an authorized distributor of Rehlko (formerly Kohler), Brags & Hayes Generators provides insights for electrical engineers designing and specifying resilient power systems. This article dives into seismic isolation principles, International Building Code (IBC) compliance, and how Rehlko’s engineering ensures operational integrity during seismic events. All information is grounded in the official Rehlko whitepaper “Seismic Isolation and IBC Certification” by Luke Dykstra.
Standby power systems are critical during and after natural disasters, including earthquakes. For engineers, ensuring a generator remains operational during seismic events is not optional—it is essential. Failures can lead to catastrophic consequences in hospitals, data centers, and critical infrastructure.
Seismic Design Strategies in Power Systems
Seismic certification begins at the mechanical interface between the generator and its mounting foundation. The dynamic forces generated during an earthquake can cause unrestrained motion, component failure, or even overturning of equipment. Engineers must carefully evaluate how seismic energy will transfer through the generator skid and into the ground or support structure.
This design challenge is addressed through two principal mounting strategies:
1. Isolated Mount (Integral Vibration Isolators)
Placement: Between engine/alternator and skid.
Material: Typically rubber or neoprene.
Design: Engineered directly into the genset.
Capacity: Common in systems under 1600 kW.
Mounting: Skid is rigidly bolted to a concrete pad.
2. Rigid Mount with Coil Springs
Application: For units over 1600 kW.
Design: Engine and alternator are rigidly attached to the skid.
Seismic Isolation: Certified coil springs placed between skid and foundation.
Understanding these methods ensures correct installation that honors IBC seismic test assumptions.
IBC: The Seismic Standard
Before diving into the specifics of IBC compliance, it’s important to understand what the International Building Code represents. The IBC is a comprehensive model code developed by the International Code Council (ICC) that provides minimum requirements to safeguard public health, safety, and general welfare through structural strength and stability. For standby power systems, seismic provisions in the IBC ensure that critical equipment remains functional and secure during and after an earthquake. These requirements extend beyond structural buildings to include all essential systems, such as generators, which must maintain operability under seismic loading conditions. The code outlines testing and certification protocols such as shake-table simulations and validated modeling techniques, and emphasizes equipment anchorage and proper installation—key concerns for specifying engineers and facility planners.
The International Building Code (IBC) governs building standards across most U.S. states. For power systems:
Emergency systems must meet the same seismic criteria as the facility they support.
Adoption of IBC varies, but FEMA often requires it for funding.
Latest standards include shake-table testing and/or analytical modeling following ICC-ES AC156 protocols.
Certification Process: What It Involves
IBC certification involves two primary methods:
Shake-Table Testing:
Shake-table testing is considered the most direct and empirical method of validating a standby power system’s seismic resilience. By replicating ground motion data from real-world earthquakes, this method subjects the generator set to dynamic forces in three orthogonal axes. The resulting data reveal how the system performs under actual seismic conditions, identifying potential weaknesses in structural design, component integrity, or mounting stability. Testing must be performed at an accredited seismic test facility, and all test parameters must mirror the expected service environment of the equipment.
Simulates seismic events.
Performed at certified labs.
Analytical Modeling:
Analytical modeling leverages computer-based simulations, typically finite element analysis (FEA), to predict the mechanical response of a generator system under seismic loading. This approach allows engineers to evaluate structural stresses, displacements, and failure modes without physical testing. While it offers cost and time advantages, the accuracy of the results depends on the precision of the model, input parameters, and boundary conditions. For IBC certification purposes, this method must be independently validated by a recognized approval agency to ensure the model reflects real-world behavior and complies with ICC-ES AC156 protocols.
Uses finite element simulation.
Must be validated by an independent approval agency.
Group Testing Approach
n seismic certification, especially under the guidelines of ICC-ES AC156, manufacturers often face the logistical challenge of certifying large product families. Testing every configuration of every model would be cost-prohibitive and time-intensive. Instead, a methodology known as “group testing” is used. This approach allows engineers to evaluate a representative unit—typically the model with the highest weight, center of gravity, or dimensional extremity—under seismic conditions. If this worst-case scenario passes the shake-table or analytical tests, other structurally similar units within the same family can inherit the certification, assuming their characteristics fall within the tested envelope. This technique streamlines compliance while maintaining engineering rigor. Manufacturers often certify a family of generators using a worst-case configuration (e.g., heaviest, highest center of gravity).
Key Insight: If a system passes IBC tests using integral isolators, adding additional isolation (like coil springs) is not only redundant but voids the certification.
Mounting and Installation: Critical to Certification
Proper mounting per manufacturer specs is non-negotiable:
Integral isolator systems: Must be rigidly mounted to ground.
Coil spring isolated systems: Must use certified seismic springs.
Improper additions (e.g., placing coil springs under integral isolator systems) can amplify motion during a quake, reducing system stability.
Common Missteps Engineers Should Avoid
Adding isolation to pre-certified integral systems.
Specifying uncertified coil springs on rigid systems.
Assuming installation alone provides certification.
Ignoring anchor and foundation specs provided by OEM.
Real-World Application: Installer Responsibility
Rehlko provides detailed anchor requirements and installation guides. Installers must:
Follow all specs from certification testing.
Ensure hardware matches original test conditions.
Avoid assumptions—consult Rehlko documentation.
Why Brags & Hayes Trusts Rehlko
As a global leader in resilient energy, Rehlko integrates over a century of Kohler expertise with modern design and rigorous seismic testing. Their solutions include:
Industrial gensets (diesel, gaseous, HVO-compatible).
Enclosures, transfer switches, and controls.
Fully IBC-certified models up to and beyond 1600 kW.
References
Dykstra, L. (2025). Seismic Isolation and IBC Certification. Rehlko. Rehlko_G26-14_Seismic_Isolation__IBC_Certification
International Code Council. (2021). ICC-ES AC156: Seismic Testing of Nonstructural Components.
FEMA. (2020). Guidelines for Design of Structures for Earthquake Resistance.
Rehlko Power Systems. (2025). IBC Compliant Generator Brochures. Available at: [https://powersystems.rehlko.com]
