ASCE 7-22 Chapter 13: Seismic Anchorage & Anchor Bolt Design Guide

ASCE/SEI 7-22 Chapter 13 is the controlling code provision for the seismic design of nonstructural components in the United States. Adopted by the 2024 IBC and the 2025 California Building Code (CBC), Chapter 13 governs every piece of architectural, mechanical, electrical, and plumbing (MEP) equipment that must be anchored, braced, or restrained against earthquake forces. Whether you are sizing post-installed anchors for a 5,000 lb chiller, designing seismic bracing for a hospital fire-water main, or preparing an HCAI/OSHPD seismic anchor calculation package, every number on your submittal traces back to Chapter 13.

1. Scope: what Chapter 13 covers

Chapter 13 applies to permanently attached nonstructural components, their supports, and their attachments to the structure. The scope explicitly includes:

• Architectural components — partitions, ceilings, cladding, glass, parapets, signs.
• Mechanical and electrical components — HVAC equipment, generators, transformers, pumps, switchgear, batteries.
• Distribution systems — piping, ductwork, electrical conduit, cable tray, and busway.
• Their supports (frames, skids, hangers, trapezes) and attachments (anchors, welds, bolts).

Chapter 13 does not cover non-building structures — those are governed by ASCE 7 Chapter 15. See our companion page on equipment anchorage design for the project-side workflow.

2. The new Fp equation (ASCE 7-22 Eq. 13.3-1)

The biggest change from ASCE 7-16 is the structure of the horizontal seismic design force. The familiar 0.4 a_p S_DS W_p (1+2z/h) / (R_p/I_p) equation has been replaced with one that explicitly captures the building's lateral system and the component's dynamic behavior:

The upper and lower bounds carry over unchanged:

2.1 H_f — height amplification factor

H_f replaces the old (1 + 2z/h) term and accounts more accurately for floor acceleration up the building height. It is calculated from the building's approximate fundamental period T_a per Eq. 13.3-4. For most rigid podium-mounted equipment near grade, H_f ≈ 1.0; at the roof of a tall flexible building it can exceed 2.5. This is the term that punishes upper-floor MEP installations.If you need a fast pre-design check for S_DS, I_p, z/h, and Chapter 13 table selections, use our SDS, I_p & z/h calculator.

2.2 R_μ — structure ductility reduction factor

R_μ is tied to the host building's Seismic Force-Resisting System (SFRS) per Table 13.3-1. Stiffer, less ductile systems push R_μ toward 1.0 (forces go up); ductile special moment frames go to ~1.5 (forces come down). This is why the same chiller on the same floor of two buildings with different SFRS yields two different F_p values — and why an OPM/OSP capacity table indexed only by S_DS and z/h is no longer sufficient under ASCE 7-22.

2.3 C_AR — component resonance amplification

C_AR captures how the component itself responds to floor motion. It comes from Tables 13.5-1 (architectural) and 13.6-1 (mechanical and electrical). Rigid components have C_AR = 1.0; flexible components (long pipe runs, slender stacks, tall cable trays) carry coefficients up to 4.0.

2.4 R_po — component over-strength factor

R_po replaces the lumped R_p from ASCE 7-16. It separates the component's strength from its over-strength so that anchorage to concrete (which by ACI 318 Chapter 17 is designed for amplified forces) can be sized rationally. For most mechanical and electrical equipment R_po = 1.5.

3. The Importance Factor I_p

Per ASCE 7-22 §13.1.3, I_p = 1.5 if any of the following apply:

• The component is required to function for life-safety after the earthquake (fire pumps, smoke control, emergency power).
• The component contains hazardous materials in excess of code thresholds.
• The component is in or attached to a Risk Category IV structure (hospitals, fire stations, EOCs) and is needed for continued operation.

Otherwise I_p = 1.0. The factor scales F_p, F_p,min, and F_p,max linearly.

4. Vertical seismic force F_v

Per §13.3.1.2:

F_v combines with F_p using the load combinations of Chapter 2 (with E = ρF_p + 0.2S_DSD acting up or down). For overturning of unanchored floor-mounted equipment, the up-acting case usually controls.

5. Anchorage in concrete and masonry — §13.4

Anchors to concrete are designed per ACI 318 Chapter 17. Section 13.4.2 requires anchor design forces to be amplified by the over-strength factor Ω₀ when:

• The anchor governs over a ductile yield mechanism in the attached part, AND
• Concrete breakout, side-face blowout, or pryout governs the anchor capacity.

In practice, this means most post-installed anchors in seismic design categories C–F must be sized with Ω₀ · F_p for the concrete-controlled limit states. See our worked anchor bolt design examples.

6. Component, support, and attachment — three checks, not one

ASCE 7-22 keeps the three-element decomposition: every nonstructural installation breaks down into a component (the equipment), a support (the frame, skid, or bracket), and an attachment (anchors, welds, bolts). All three must independently satisfy F_p. A signed seismic anchor calculation package shows three checks per component — not one. See the diagram and explanation on our Seismic Anchor Calculations page.

7. Distribution systems — §13.6.5, 13.6.6, 13.6.7

Piping, ductwork, conduit, and cable tray have their own bracing rules with size-based exceptions:

• Piping: bracing required for high-deformability pipes ≥ 1″ NPS in Ip=1.5 systems and ≥ 2½″ NPS otherwise (with exceptions per §13.6.5.1).
• Ductwork: bracing required for ducts larger than 6 ft² cross-section, with hanger and trapeze rules per SMACNA seismic guidelines.
• Conduit and cable tray: bracing per §13.6.6 / §13.6.7 with exceptions for trapeze weights below threshold.

8. Designated seismic systems — §13.2.2

Active mechanical and electrical components with I_p = 1.5 are Designated Seismic Systems and require a Certificate of Compliance proving post-earthquake operability. Per §13.2.2 this can only be obtained by approved shake table testing or qualified experience data — analysis alone is not sufficient.

9. Practical workflow for a Chapter 13 submittal

1. Establish S_DS, Risk Category, and SFRS from the project structural drawings.
2. Compute H_f using building period T_a (Eq. 13.3-4) and component elevation z.
3. Look up R_μ from Table 13.3-1 based on the SFRS.
4. Determine C_AR, R_po, and Ω_0p from Tables 13.5-1 / 13.6-1 by component type.
5. Set I_p per §13.1.3.
6. Compute F_p, then check against F_p,max and F_p,min.
7. Compute F_v and combine per the governing load combinations.
8. Design the component, support, and attachment for the resulting demand — applying Ω₀ to anchorage in concrete where §13.4.2 applies.
9. For Ip=1.5 active equipment, attach the OSP/OPM Certificate of Compliance or commission shake table testing.

10. Common Chapter 13 mistakes

• Using ASCE 7-16 a_p/R_p values on a 2025 CBC project — the tables are entirely different.
• Ignoring SFRS and assuming R_μ = 1.5 for all buildings.
• Forgetting Ω₀ on concrete-controlled anchor checks.
• Treating active Ip=1.5 equipment as analytically certifiable instead of pursuing an OSP.
• Designing only the anchor and skipping the support frame check.
• Missing the F_p,min floor — small components often govern at the minimum.

Need a stamped Chapter 13 calculation? PANACHE ENGINEERING delivers PE/SE-stamped seismic anchor calculations for any nonstructural component, support, or attachment under ASCE 7-22 and the 2025 CBC. Use our equipment anchorage workflow, browse anchor bolt examples, or contact an engineer.

Related engineering resources

• Seismic Anchor Calculations — main service page
• SDS, I_p & z/h Calculator
• Equipment Anchorage Design step-by-step
• Anchor Bolt Design Examples (tension & shear)
• Common Anchorage Design Mistakes
• Engineering Calculation Tools
• ASCE 7-22 vs HCAI OPM/OSP