YOUR GUIDE TO SEISMIC CERTIFICATION
A well developed special seismic certification program requires detailed evaluation of products to be certified along with their intended use and installation. Critical items must be considered in a certification and appropriately documented so that users understand limitations and ensure proper application of a certified product. In order to properly develop a program, certain key elements must be considered, including:
- Product options and subcomponents
- Materials and details of construction
- Mounting Details
- Attached elements
- Seismic demand
- Certificate of compliance and seismic label
YOUR GUIDE TO SEISMIC CERTIFICATION
Variations in product options and internal subcomponents must be explicitly considered and documented during seismic certification. Special seismic certification is only valid for components with the same design, construction and quality assurance as those considered during testing or analysis. Rigorous consideration of the parts and pieces of a component must be documented and considered to ensure proper compliance with code requirements.
Product options include internal subcomponents, additional features or other potential variations in actual products. The manufacturer and model line of subcomponents must be considered and documented with adequate testing of elements for compliance. When developing programs for HCAI compliance, a minimum of two tests per product type, per manufacturer, per product line are required for active or energized subcomponents.
MATERIALS OF CONSTRUCTION
Construction of components and subcomponents built with different materials must be considered due to variations in physical properties. Variations include carbon steel, stainless steel, aluminum, composite materials, etc. The material of construction of nonactive housings, NEMA ratings, etc. must be documented and considered in the SSC either through testing or other engineering justification.
For active or energized components, it is essential to test the varying materials of construction to properly consider the implications on dynamic response and potential force redistribution. When developing programs for HCAI, each material for nonactive components must be tested at least once and for active components at least two tests are required per material.
Seismic certification is only valid for the manner of attachment considered in the performance of the analysis or testing. The manner in which a component is attached to the main structure can play a significant role in the transmission of seismic demands onto the component. In performing a seismic certification test, the mounting hardware and arrangement must replicate the proposed manner of installation in practice. For instance, systems mounted on vibration isolators must be tested on vibration isolators in order to be applicable.
Shake table testing is regularly performed in a variety of arrangements including base mounted, isolated, wall mounted and ceiling suspended.
Most times, shake table testing is performed on components with little to no connected elements, such as piping, ducting, conduit, etc. These elements can significantly affect the response of a unit and need to be addressed during the certification and installation process. While it is possible to simulate connected elements, many times this is ignored in test programs and put as a condition of installation.
ASCE 7 Section 13.2.3 has explicit requirements to consider the interaction between components and their attachments. It is essential to ensure that components are connected in a manner representative of what was considered during testing. It is important to document and properly address connections including the need to provide flexible connections when loading was not addressed during certification.
Any seismic certification program is limited to a specific level of earthquake demand. For IBC compliance, the typical areas of concern are the short period design acceleration (SDS), installation height factor (z/h) and importance factor (Ip). For generic certification, these numbers are documented and must be less than site-specific demands for a given installation.
For other programs, such as IEEE 693 certification programs, the seismic level is defined based on predetermined seismic levels, such as moderate and high seismic loading. Whereas, in the nuclear industry certification levels are typically presented as specified in structure response spectra outlining the anticipated demands at the exact component level.
Recent updates to the seismic hazard for IBC applications have increased the maximum short period design acceleration to 2.49g in California. However, ASCE 7 has placed a cap on required seismic certification levels by testing equal to 3.2g which is the equivalent of 2.0g short period design acceleration at the roof level.
CERTIFICATES AND LABELS
Building codes require that systems and components which have seismic certification be properly documented and labeled. When proposing to provide nonstructural components for a given project, the manufacturer must provide the project team with project submittals including a Certificate of Compliance (CoC) for seismic certification. This CoC should properly document the limitations of the certification, mounting restrictions and attachment considerations.
In addition, certified components must be provided to projects with a Seismic Label to show the certification limits and mounting restrictions for IOR and SEOR to review.