ICC-ES AC156 — Acceptance Criteria for Seismic Qualification by Shake-Table Testing of Nonstructural Components — is the controlling test standard for special seismic certification of active equipment in the United States. Every OSHPD OSP, every Special Seismic Certification Label on a chiller or air handler in a California hospital, and every ASCE 7-22 §13.2.2 Designated Seismic System owes its compliance to AC156. This article walks through the test program from RRS to certificate.

When AC156 is required

Per ASCE 7-22 §13.2.2, components with importance factor Ip= 1.5 that are "active" — meaning they must function during or after the design earthquake — require certification by approved shake table testing. This includes:

  • Generators, ATSs, switchgear, UPSs.
  • Chillers, air handlers, fan coils on essential MEP systems.
  • Fire pumps, jockey pumps, control panels for life-safety.
  • Medical gas equipment in hospitals and surgery centers.

The Required Response Spectrum (RRS)

AC156 §6.3 derives the RRS from the project's SDS, the component's importance factor Ip, and the elevation ratio z/h:

  • AFLX-H = SDS · (1 + 2 z/h) — horizontal flexible-component peak.
  • ARIG-H = 0.4 · SDS · (1 + 2 z/h) — horizontal rigid-component peak.
  • AFLX-V = 2/3 · AFLX-H — vertical flexible peak.
  • ARIG-V = 2/3 · ARIG-H — vertical rigid peak.

The test laboratory bands these into a tri-axial input motion that envelopes the RRS at 5% damping. Most California hospital projects target SDS = 1.5 g and z/h = 1.0 (roof) — that yields a flexible horizontal peak of 4.5 g, an envelope that almost no untested equipment will pass without retrofit.

The test plan — what HCAI/OSHPD reviewers want to see

  • Component description with weight, dimensions, center of gravity, and a unique part number.
  • Mounting configuration: free-standing on isolators, hard-mounted, wall-mounted, or suspended — each is its own test.
  • Operating configurations: powered on, doors open/closed, fluid filled, pressure on. Per AC156 §4.5.4 each must be simulated.
  • Instrumentation plan: tri-axial accelerometers on the table, on the equipment frame, and on critical sub-components (boards, displays, pumps).
  • Pre/post functional test scope — what proves "operability."

Mounting — the most common cause of test failure

AC156 §6.4 requires the test fixture to replicate the in-service mounting stiffness. If you bolt your generator to the shake table through a 2-inch steel plate when the field installation is on a 4-inch concrete pad with neoprene isolators, the test result is invalid. The fixture must reproduce the lowest-frequency support path that the equipment will see in service.

The 45° supplemental test (AC156 §6.4.1)

If your shake table is uniaxial or biaxial, an additional test at 45° to the principal axes is required to capture the worst-case directional response. Triaxial tables can skip this. Most modern California labs are triaxial.

Pass/fail criteria

  • The input motion must envelope the RRS at 5% damping in all three axes simultaneously.
  • The equipment must remain anchored (no anchor failure, no fixture displacement > published limit).
  • Post-test functional check must pass — the equipment must operate within manufacturer specifications.
  • No structural damage that would impair function (cracked welds on internal frames, leaks, unseated boards).

What goes in the AC156 test report

  1. Identification of the equipment, the test plan, and the lab (ISO/IEC 17025).
  2. RRS derivation and the achieved Test Response Spectrum (TRS) overlay.
  3. Instrumentation plan with as-installed photos.
  4. Time histories of input motion and key accelerations.
  5. Functional test results, pre and post.
  6. Any failures and the resolution (re-test after retrofit).
  7. Sealed by the lab and reviewed by an independent California-licensed structural engineer (per HCAI PIN 55).

From AC156 to the Certificate of Compliance

The AC156 report is the technical backbone, but the deliverable that gets stamped onto the equipment is the Certificate of Compliance — for HCAI submittals this means an OSHPD OSP. See our OSHPD OSP guide and the latest HCAI PIN 55 update for the certificate's contents and validity.

Common AC156 mistakes by manufacturers

  • Designing the equipment for the wrong RRS (using a 0.5 g project when the typical California hospital is 1.5 g).
  • Single test on one configuration and assuming it covers all SKUs (ISO 9001 single-test exception is narrow).
  • Skipping the post-test functional check.
  • Mounting fixture too stiff — passes but does not represent field conditions.
  • Test report without a California-licensed structural engineer review.

How PANACHE ENGINEERING helps manufacturers through AC156

We design the test plan, run the shake-table-side analysis, attend the test, and prepare the OSP submittal. See our Shake Table Testing service page or contact our certification engineers.