ICC-ES AC156 — Acceptance Criteria for Seismic Qualification by Shake-Table Testing of Nonstructural Components — defines the acceptance criteria used to qualify nonstructural components and equipment through shake-table testing. Before committing a product to the table, a manufacturer should understand how the Required Response Spectrum (RRS) is derived, how the specimen must be mounted, which operating configurations must be represented, what instrumentation is expected, how a product family is represented by test units, and what the pass/fail criteria are. This guide walks through each of those requirements.

Need an engineering team to manage the actual qualification? See our Shake Table Testing Services for test planning, fixture engineering, laboratory coordination, witness testing, remediation, and seismic certification.

When AC156 is used

The certification pathway for a given component depends on the adopted building code, the component type, its performance requirement, and the authority having jurisdiction. AC156 is the primary shake-table acceptance criterion used for many special seismic certification programs — including HCAI's OSP preapproval program for California healthcare construction. Components commonly qualified under AC156 programs include:

  • 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.

Code-edition note: for 2025 CBC/HCAI OSP work, HCAI's current PIN 55 identifies the special seismic certification provisions at ASCE 7-22 §13.2.3; older documents may reference §13.2.2 under earlier code editions.

The Required Response Spectrum (RRS)

AC156 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.

AC156 applies upper limits to the computed spectral demands, so the governing edition should be checked for the exact values used in the test plan. The test laboratory bands the demands into a tri-axial input motion that envelopes the RRS at 5% damping. Most California hospital OSP programs target SDS = 1.5 g with z/h = 1.0 (roof) — a demand envelope severe enough that little untested equipment passes without deliberate seismic design attention.

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. Each configuration relied on for certification must be represented in the program.
  • 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 requires the test mounting to be representative of the in-service installation. 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.

Multi-axis input and supplemental orientations

The qualification input is applied tri-axially — both horizontal axes plus vertical, simultaneously, on a triaxial table. When a table cannot apply the required input simultaneously along all axes, AC156 prescribes supplemental test runs, including input oriented at 45° to the principal axes, to capture worst-case directional response. Most modern California labs operate triaxial tables.

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, for HCAI OSP submittals, reviewed by a 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 travels with the equipment is the Certificate of Compliance — and for manufacturers pursuing HCAI preapproval, the program culminates in an OSP listing. 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 demand when the typical California hospital program targets 1.5 g).
  • Testing a single configuration and assuming it covers all SKUs — product-family coverage rules are specific about which units must be tested.
  • Skipping the post-test functional check.
  • Mounting fixture too stiff — passes but does not represent field conditions.
  • For HCAI OSP submittals, omitting the required California-licensed structural engineer review.

How PANACHE ENGINEERING helps manufacturers through AC156

This article is an informational guide to the AC156 criteria. When you need the qualification managed end to end — test planning, shake-table-side analysis, witness testing, and the certification submittal, including pre-test modal and response spectrum analysis through our finite element analysis services — our commercial Shake Table Testing Services page covers the full program, or contact our certification engineers directly.