In short: AC156 shake table testing is the ICC-ES procedure for seismically certifying nonstructural components such as HVAC units, piping, electrical panels and medical equipment. The component is mounted on a shake table driven by a time history matched to the ASCE 7-22 or IBC design response spectrum, preferably biaxially, and must pass three criteria: functional performance, structural integrity and safety. Accelerometers, displacement sensors and load cells record the response.
Comprehensive Guide to AC156 Non-Structural Seismic Testing: Key Technical Insights
Non-structural seismic testing plays a crucial role in ensuring that building components, such as HVAC systems, piping, electrical infrastructure, and essential fixtures, are capable of withstanding seismic events. The widely adopted AC156 standard (Acceptance Criteria for Seismic Certification by Shake-Table Testing of Nonstructural Components) sets forth a technical framework for qualifying non-structural components to ensure their seismic resilience.
This guide aims to provide a deep dive into the technical details of AC156 testing, the steps for generating seismic profiles, and considerations for creating a test plan.
Technical Overview of AC156 Testing
The AC156 standard, developed by the International Code Council Evaluation Service (ICC-ES), outlines the required procedures for assessing non-structural components using shake tables to replicate earthquake ground motion. This ensures that critical building elements remain functional during and after an earthquake, minimizing the potential for failure or dislodgement that could cause hazards.
Key Components of AC156 Testing
Scope of Testing:
- AC156 covers components that are affixed to buildings and critical infrastructures, such as:
- Mechanical systems (e.g., HVAC units, piping systems).
- Electrical systems (e.g., emergency power supplies, control panels, lighting fixtures).
- Safety and medical equipment (e.g., elevators, emergency medical devices).
- These components are tested to verify that they either maintain functionality or remain securely fastened after exposure to seismic forces.
Shake Table Testing Methodology:
- The shake table test is at the heart of AC156, where components are subjected to controlled seismic motion. The shake table simulates the ground motions of an earthquake, applying forces along multiple axes to reproduce real-world earthquake dynamics.
- Biaxial shaking (testing along two orthogonal axes simultaneously) is the preferred method, as it better simulates real-world conditions. However, uniaxial testing is also acceptable for simpler cases, depending on the component’s design.
- Shake table inputs are derived from response spectra, ensuring that ground motions are generated based on regional seismic risks and building codes.
- Seismic Profile Generation:
- A critical part of the test is the generation of a seismic profile, which reflects the seismic demand based on the design response spectrum. The response spectrum is defined by the ASCE 7-22 standard or the International Building Code (IBC) (or California Building Code) for the region where the component will be installed.
- Seismic profile generation can be performed using specialized software tools, which allow for matching a time-history record to the target response spectrum either amplitude scaling or spectral matching. The generated time history ensures that the shake table replicates realistic ground motion for the location.
Testing Criteria:
- Components must meet specific performance criteria based on three key objectives:
- Functional Testing: Verifying that equipment continues to function under and after seismic motion. For example, an HVAC system must maintain operation to avoid disruption to the building’s climate control.
- Structural Integrity: Ensuring that components do not suffer from catastrophic structural failures, which could result in dislodgment, overturning, or breakage.
- Safety: Preventing components from becoming hazards. Even if a component ceases to function, it should not pose additional risks (e.g., falling debris or electrical shock).
Data Collection and Instrumentation
Instrumentation plays a vital role in seismic testing, providing precise data to evaluate the performance of the tested components. Commonly used instruments in AC156 testing include:
- Accelerometers: These measure the acceleration response of the component, capturing how it reacts to seismic forces.
- Displacement Sensors: These measure the movement of the component relative to its original position, essential for assessing whether components remain securely anchored.
- Load Cells: These can be used to measure the forces exerted on the mounting system during the seismic event.
The data from these instruments allow engineers to identify potential failure modes and provide insights into how to improve component design.
Steps for Creating a Test Plan for Shaker-Based Seismic Testing
To ensure comprehensive seismic testing, a well-structured test plan must be developed, accounting for all variables in the testing process:
Component Identification: Begin by identifying the component(s) to be tested, including the type, size, weight, and any specific features that might influence seismic performance.
- Example: A 500-pound HVAC unit mounted on a rooftop requires different testing parameters than a lightweight lighting fixture mounted on a ceiling.
Seismic Profile Development: Utilize the design response spectrum for the region in which the component will be installed. The spectrum provides the basis for generating the seismic profile.
- Example: If testing for installation in a high-seismicity region like California, the profile should replicate severe earthquake conditions, as outlined in ASCE 7-22.
Test Objectives:
- Functional Testing: Determine if the equipment needs to maintain continuous operation after seismic motion. For life-critical systems (e.g., emergency power supplies), functionality is the primary test objective.
- Safety and Integrity: For non-operational components, confirm that they remain safely fastened without causing hazards (e.g., medical gas lines in hospitals).
Testing:
- Instrumentation Setup: Plan the placement of accelerometers, displacement sensors, and load cells to capture detailed data during the test. Data from these instruments will help assess compliance with AC156 standards.
- Execution: Execute the test, applying the seismic profile to the shake table. Ensure proper monitoring throughout the test to capture all relevant performance data.
- Data Analysis: After the test, analyze the collected data to verify that the component meets the performance criteria. If necessary, adjust the design or mounting configurations to ensure compliance.
Applications and Importance of AC156 Testing
AC156 seismic testing is crucial across multiple industries, including:
- Commercial Buildings: HVAC systems, lighting, and electrical panels.
- Healthcare: Seismic compliance for medical equipment, life-support systems, and emergency infrastructure.
- Data Centers: Server racks and backup systems that require uninterrupted functionality during and after seismic events.
- Telecommunication: Ensuring the operational continuity of communication networks during a disaster.
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Key Takeaways
- AC156 is published by ICC-ES and covers mechanical, electrical, safety and medical components affixed to buildings.
- Biaxial shaking on two orthogonal axes is preferred; uniaxial testing is acceptable for simpler components.
- Seismic profiles are time histories matched to the ASCE 7-22 or IBC/CBC design response spectrum by amplitude scaling or spectral matching.
- Three performance criteria: continued function, structural integrity (no dislodgement or overturning) and no new hazards.
- Test plan steps: identify the component, develop the seismic profile, set objectives, instrument, execute and analyze data.
Frequently Asked Questions
AC156 shake table testing is the ICC-ES acceptance criteria for seismic certification of nonstructural components by shake-table testing. Components such as HVAC units, piping, control panels, emergency power supplies, elevators and medical devices are subjected to controlled seismic motion to verify they remain functional or securely fastened after an earthquake. It is used in commercial buildings, hospitals, data centers and telecom facilities.
The seismic profile for an AC156 test is derived from the design response spectrum defined by ASCE 7-22 or the International Building Code (or California Building Code) for the installation region. Software matches a time-history record to that target spectrum using amplitude scaling or spectral matching, producing a shake table input that reproduces realistic ground motion for the site, such as severe California-level demand.
AC156 prefers biaxial shaking, where the shake table moves along two orthogonal axes simultaneously, because it better reproduces real earthquake dynamics. Uniaxial testing is still acceptable for simpler cases depending on the component's design. The choice should be documented in the test plan along with the response-spectrum-based input motions.
Under AC156 a component is judged on three objectives: functional testing (it keeps operating during and after shaking, essential for life-critical systems like emergency power), structural integrity (no catastrophic failure, dislodgement, overturning or breakage) and safety (even if it stops working it must not create hazards such as falling debris or electrical shock).
AC156 shake table tests typically use accelerometers to capture the component's acceleration response, displacement sensors to measure movement relative to its original position and confirm anchorage, and load cells to measure forces on the mounting system. Sensor placement is planned in the test plan, and the recorded data is analyzed afterward to verify compliance and identify failure modes.
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