Use In-Place Tab Welds for Seismic Bracing?

12/26/2024

NFPA 13 9.3.5.11.6 states 'For longitudinal braces only, the brace shall be permitted to be connected to a tab welded to the pipe in conformance to 6.5.2' 6.5.2.2.3 specifies that 'Tabs for longitudinal earthquake bracing shall be permitted to be welded to in-place piping where the welding process is performed in accordance with NFPA 51B.'

Section 6.5.2.4.7 states ' Tabs for longitudinal earthquake bracing shall have minimum throat weld thickness not less than 1.25 times the pipe wall thickness and welded on both sides of the longest dimension.'

My questions are: Is anybody using this method for longitudinal bracing?

How do you calculate a brace using this configuration?

Is there a tab on the market specifically for this application?

Additionally, is Section 6.5.2.2.3 suggesting that tabs are only permitted to be welded in field?

We do giant open warehouses where bracing typically can go exactly where the plan shows it. We fab 90% of our pipe in-house, and if we could specify the tab's location on the fab listings, we could potentially get rid of 212 pipe clamps for all longitudinal bracing.

Besides the obvious install issue of 'it might not work in the exact location it's welded' - am I missing something...?

Thanks in advance.

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4 Comments

Jose Figueroa

12/26/2024 12:19:44 pm

Given my background in the insurance sector, I would like to share some insights on this topic that may be relevant to discussions originating from California, Oregon, or Washington.

I understand that the discussion is centered on NFPA standards. However, I suggest also considering the guidelines from FM Data Sheet 2-8, titled “Earthquake Protection for Water-Based Fire Protection Systems” (https://drive.google.com/file/d/1LS0qz7M3OcbBSQkD2XQLlqQ6YoIMqo3Z/view?usp=drivesdk).

A crucial aspect of the installation and design of sway bracing is ensuring that all mechanical components are FM-approved. Fortunately, all relevant information, including FM Data Sheets, is readily available.

According to NFPA 13, using tabs welded to the pipe for longitudinal earthquake bracing is permissible, provided we comply with the welding standard specified in NFPA 51B. These standards state that the throat weld thickness must be at least 1.25 times the thickness of the pipe wall, with tabs welded on both sides of the longest dimension.

However, when comparing this with FM Data Sheet 2-8, it is evident that FM Global often imposes more stringent requirements than NFPA standards.

Therefore, while NFPA 13 allows for welded tabs for longitudinal bracing under certain conditions, I recommend thoroughly reviewing the requirements and suggestions outlined by FM Global (FM Data Sheet 2-8). Doing so will help ensure compliance with both standards while maximizing safety. Additionally, the graphics and schematics included in FM Data Sheet 2-8 can assist designers and installers.

Now, let’s address the two questions separately:

1. Calculating a Brace Using Welded Tabs for Longitudinal Bracing. To calculate a brace using welded tabs, consider several factors:

1.1 Load Requirements. Determine the seismic forces expected in your area using local building codes or standards such as ASCE 7.

1.2 Pipe Specifications. Know the pipe diameter, wall thickness, and material that will affect the brace design.

1.3 Tab Specifications.

1.3.1 Material and Dimensions. Ensure the tab material is compatible with the pipe material. The size and shape of the tab should align with the seismic forces it needs to resist.
1.3.2 Weld Specifications. Calculate the throat weld thickness, which must be at least 1.25 times the pipe wall thickness per NFPA 13. Ensure welds are on both sides of the tab's longest dimension.
1.3.3 Structural Analysis. Conduct a structural analysis to ensure the brace can withstand expected seismic loads. It includes evaluating the capacity of both the pipe and the brace assembly. Using engineering software or consulting a structural engineer for precise calculations is advisable, as this process involves complex load analysis and safety considerations.

2. Availability of Tabs for This Application. Companies manufacture tabs and brackets specifically for seismic bracing of pipes. These companies often provide ready-to-use solutions tailored for such applications, per NFPA 13.

2.1 Manufacturers and Suppliers. Companies like Hilti, Anvil International, and others specialize in seismic bracing components. They offer various pre-engineered products designed for pipe bracing, including tabs that comply with relevant standards.
2.2 Custom Fabrication. Custom fabrication could be an option if standard products do not meet your specific requirements. Local fabricators might produce tabs that meet your project's precise specifications.

If comparing it with FM Data Sheet 2-8 is unacceptable, please disregard my post.

Glenn Berger

12/26/2024 03:13:11 pm

Very thoughtful response. Thanks for providing.

Dave L.

12/27/2024 04:56:00 pm

Interesting. “IS” anybody using this method? I am curious, too. Because I remember for a short time (80’s or 90’s) we sometimes did this, but I don’t remember continuing the practice. Especially after bracing-specific attachments came around. I happen to have the 1987 edition on my desk and is specifically says in the Annex, “The brace should not be connected to a tab welded on the pipe.” But I see at least by the 1996 edition it is mentioned in the main body, and in modified form, remains allowed in the 2025 edition.

Joe. W

1/2/2025 07:58:35 am

I don't believe welding tabs on the pipe would be advantageous unless you are operating your own fab shop. Also handling the pipe in the field would be more complicated with tabs welded on. The tabs would also need to line up with structural members whereas bolt on braces are adjustable in the field.

Use In-Place Tab Welds for Seismic Bracing?

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