Hilti Mechanical Anchors for Seismic Bracing

Hilti Mechanical Anchors and Cast-in Anchors for Seismic Bracing in Accordance with NFPA 13

Hilti post-installed mechanical anchors and single point cast-in-place anchors are common, cost-effective methods for attaching both structural and non-structural elements to concrete base materials. Non-structural elements, such as fire sprinkler pipes; electrical conduit and cable trays; heating, ventilation and air conditioning (HVAC) equipment and ductwork are especially suited for Hilti anchoring systems.

For fire sprinkler pipe applications, Hilti anchors have been effectively used for many years to support the gravity loaded hangers as well as the sway bracing for resisting the lateral and vertical motion resulting from seismic loads.

While Hilti anchors can be designed and installed to support gravity loads of the pipe through the attachment of the hanger to the concrete, this document will focus on the design of the anchorage to attach the sway brace assembly to the concrete structure. Contact Hilti for more information related to Hilti anchors to support the vertical pipe hanger.

In a seismic event, earthquake forces are resisted by transverse and longitudinal sway bracing. The sway braces transfer loads through a fastener attached to the concrete. The capacity of the fastener in concrete is dictated by ACI 318-19 Chapter 17, and the design of sway brace components is dictated by NFPA 13-16 Section 9.3.5 (referencing ACI 318-11) and NFPA 13-19 Section 18.5 (referencing ACI 318-14). This document references the 2016 and 2019 NFPA-13 sections.

This document will not cover the design of pipe support hangers or sway bracing components. Instead, it provides the maximum horizontal load (Fpw) applicable to the sway brace, based on Hilti fastener type, embedment depth, load capacity, concrete strength, seismic hinge geometry, and brace angle. Fpw does not consider the adequacy of the seismic hinge or other bracing components. The design engineer of record must ensure all components are suitable for the application and design loads.

This document is a supplement to the Hilti North American Product Technical Guide, Volume 2, Anchor Fastening Technical Guide, Edition 21. It is available at www.hilti.com or www.hilti.ca.

Horizontal Earthquake Load Design per NFPA-13

The maximum horizontal earthquake load, Fpw, derived from NFPA 13-16 Eq. A.9.3.5.12.2a and NFPA 13-19 Eq. A18.5.12.2a, is calculated as follows:

$$ \left( \frac{T}{T_{allow}} \right) + \left( \frac{V}{V_{allow}} \right)^{1.2} $$

Variables:

• T: Applied service tension load, including the effect of prying = Fpw x Pr for all Angle Categories
• Fpw: Horizontal earthquake load
• Pr: Prying factor based on fitting geometry and brace angle (from NFPA 13-16 A.9.3.5.12.2 and NFPA 13-19 A18.5.12.2)
• Tallow: Allowable service tension load
• V: Applied service shear load
• θ: Brace angle (see Figure 2)
• Vallow: Allowable service shear load

Service Shear Load Calculation:

• Angle Category A, B, and C: V = Fpw
• Angle Category D, E, and F: V = Fpw / tan(θ)
• Angle Category G, H, and I: V = Fpw / sin(θ)

Note: T/Tallow ≤ 1.0 and V/Vallow ≤ 1.0

Formulas for Angle Categories:

Angle Category A, B, and C:

$$ \left( \frac{F_{pw} \cdot P_{r}}{T_{allow}} \right) + \left( \frac{F_{pw}}{V_{allow}} \right)^{1.2} $$

where: Fpw · Pr / Tallow ≤ 1.0 and Fpw / Vallow ≤ 1.0

Angle Category D, E, and F:

$$ \left( \frac{F_{pw} \cdot P_{r}}{T_{allow}} \right) + \left( \frac{F_{pw} / \tan(\theta)}{V_{allow}} \right)^{1.2} $$

where: Fpw · Pr / Tallow ≤ 1.0 and (Fpw / tan(θ)) / Vallow ≤ 1.0

Angle Category G, H, and I:

$$ \left( \frac{F_{pw} \cdot P_{r}}{T_{allow}} \right) + \left( \frac{F_{pw} / \sin(\theta)}{V_{allow}} \right)^{1.2} $$

where: Fpw · Pr / Tallow ≤ 1.0 and (Fpw / sin(θ)) / Vallow ≤ 1.0

Design Tables for Pre-calculated Horizontal Earthquake Load

The design tables provide the maximum horizontal load, Fpw, for various Hilti post-installed and cast-in anchors used with seismic brace swivel attachments. These tables are based on NFPA 13-16 Eq. A.9.3.5.12.2a and NFPA 13-19 Eq. A18.5.12.2a.

Key Notes for Table Usage:

• Allowable tension (Tallow) and shear (Vallow) values are derived from ACI 318-19 strength design calculations and converted per NFPA 13.
• Calculations assume cracked concrete and seismic design categories C through F.
• Minimum edge and spacing distances are specified. For corner conditions, edge distance requirements may increase.
• Prying factors (Pr) for seismic brace swivel attachments are based on manufacturer data.
• The tables do not assess the adequacy of the seismic hinge or other brace components; the design engineer is responsible for ensuring suitability.
• Values are applicable for specified concrete strengths and higher.

Design Example

This example demonstrates calculating the maximum allowable pipe horizontal load (Fpw) for a Hilti KWIK Bolt TZ2 (KB-TZ2) expansion anchor used with a Hilti MQS-SP-L-1/2" seismic hinge (Angle B, Pr = 1.580) in 3,000 psi cracked concrete.

LRFD capacities for KB-TZ2: TLRFD = 2,660 lb., VLRFD = 4,471 lb.

ASD values (using 0.43 factor): Tallow = 1,144 lb., Vallow = 1,923 lb.

Calculation for Fpw (using Angle B formula):

$$ \left( \frac{631 \cdot 1.580}{1144} \right) + \left( \frac{631}{1923} \right)^{1.2} = 0.87 + 0.33 = 1.20 \text{ (OK)} $$

Check conditions: Fpw · Pr / Tallow = 0.87 ≤ 1.0 (OK); Fpw / Vallow = 0.33 ≤ 1.0 (OK).

Maximum horizontal load, Fpw = 631 lb.

Sample Load Table Snippet:

Hilti Anchors for Seismic Bracing

• Carbon Steel KWIK Bolt TZ2

  Versatile anchor for pipe supports in seismic areas, available in 3/8-in. to 3/4-in. diameters. Supported by ICC-ES ESR-4266 and has FM/UL listings.

• KB1

  Cost-effective wedge anchor for seismic areas, available in 3/8-in to 3/4-in diameters. Supported by IAPMO ER 678 and has FM/UL listings.

• KCM-WF/-PD

  Cast-in anchor with internal threads for flexibility, intended for flat concrete slabs. Available in 1/4-in. to 3/4-in. inner thread diameters (3/8-in to 3/4-in. for seismic bracing). Supported by ICC-ES ESR-4145 and has FM/UL listings.

• KCM-MD

  Cast-in anchor optimized for concrete over metal deck applications, offering flexibility with short or long plate options. Supported by ICC-ES ESR-4145 and has FM/UL listings.

• KCC-WF

  Quick push-to-connect anchor for flat concrete slabs, available in 3/8-in. and 1/2-in. diameters. Supported by ICC-ES ESR-4145 and has FM/UL listings.

• KCC-MD

  Anchor with pre-assembled self-tapping screws and color-coded plugs. Available in 3/8-in. and 1/2-in. diameters. Supported by ICC-ES ESR-4145 and has FM/UL listings.

• HILTI MQS-SP-L-1/2" AND MQS-SP-T/1/2" (Seismic Hinge)

  Versatile and quick connect solution for seismic bracing attachments. FM rated for seismic solutions.

Load Tables

Detailed load tables are provided in the original document, covering various Hilti anchors, concrete strengths (3,000 psi to 6,000 psi), and configurations (flat slab, lightweight concrete over metal deck). These tables allow engineers to determine the maximum allowable pipe horizontal load (Fpw) for specific applications.

Contact Information and Legal Notices

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Customer Service: 1-800-879-8000 | en español: 1-800-879-5000 | Fax: 1-800-879-7000

www.hilti.com

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Customer Service: 1-800-363-4458 | Fax: 1-800-363-4459

www.hilti.ca

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The data in this literature is current as of publication. Updates may occur. For verification, contact Hilti Technical Support Specialists. Published load values represent Hilti testing results; on-site testing may be necessary due to material variations. Printed in the United States.