D.E.N.
Structural
- Apr 22, 2021
- 31
TL;DR:
A shear wall hardware product manufacturer is claiming a steel threaded rod with epoxy anchored to concrete does not need to comply with ACI 318 anchorage provisions. I disagree. If ACI equations are used to check the anchor’s capacity, the product would have a reduced capacity and wouldn’t work as they have designed.
Full explanation:
I am the EOR on a large 5-story light-framed wood apartment building. I designed and detailed all of the shear walls using “typical” hardware, such as coil straps floor-to-floor and holdowns with threaded rods in epoxy at the base. Recently, I received a hardware substitution request from the GC, proposing a different product. Initially, I assumed this was a request to substitute hardware directly from a different manufacturer. However, the submittal proposes a completely different shear wall system.
The proposed system is a proprietary continuous hold-down assembly that connects to the building at the roof level only and anchors to the concrete at the bottom. Its tension capacity is based on testing and comes with a “code approval” report from a certified testing agency. This report, a Technical Evaluation Report (TER), is similar to an Evaluation Service Report (ESR) from other agencies. Due to the proprietary nature of the assembly, no published calculations or test result data are available; only a single allowable tension capacity is provided. The TER specifies installation conditions that must be followed to achieve the published tension capacity.
I have several concerns about this proposed system's ability to resist the required shear wall overturning forces and the proposed load path. Although I have been working with the manufacturer to address these concerns, one aspect of the design remains problematic. Both the manufacturer and the testing agency assert that the system's anchorage into the concrete does not need to be checked using ACI 318 anchorage provisions. The proposed shear wall system consists of a steel cable assembly with steel threaded rods at each end, with the bottom rod embedded in an epoxy-filled hole in the concrete. In my opinion, this anchorage design is not proprietary since it involves a steel threaded rod with epoxy in concrete, which is clearly defined in ACI 318. I would understand the argument if we were talking about a Simpson “LSTHD” Strap-Tie Holdown or MiTek “LSTAD” Foundation Strap, which is a truly proprietary anchorage design since it is just bent steel embedded in the concrete. But this is a steel threaded rod embedded in epoxy that just happens to be attached to the end of a proprietary cable assembly.
The manufacturer has a proprietary epoxy with an ESR report, stating to follow ACI 318-14 Chapter 17. However, the testing agency and manufacturer claim that the ESR for the epoxy is not valid when used with the cable hold-down system. They argue that the ESR only applies when the epoxy anchors steel threaded rods to concrete. It just so happens that the bottom of the cable hold-down system has a steel threaded rod attached to it…
Problem:
Using ACI 318 equations to check the anchorage capacity, I find that the assembly's allowable tension capacity is about 60% less than the manufacturer’s published values, primarily due to concrete breakout. This calculation includes product-specific variables and factors from ACI 355.4 tests, accounting for any proprietary epoxy behavior, which are published in the ESR.
I believe the proposed system’s anchorage must be checked using ACI 318 provisions, as the design closely matches the scenarios covered in the standard. The difference between the published assembly capacity and calculated anchorage capacity is a significant concern that I want to resolve before allowing the product to be used in my building. The testing agency and the manufacturer are telling me not to worry about it since the submittal and the TER are both sealed by PEs in the project state. They claim that since it is a delegated design, I don’t need to worry about how it interacts with my building. I would like to reject the entire system and stick with the original design, but the contractor really wants to use the cable system.
Question:
Have you ever dealt with something like this before? I don’t see how I can allow this anchorage “design” to bypass the ACI 318 requirements just because they are calling a standard anchorage method “proprietary.”
A shear wall hardware product manufacturer is claiming a steel threaded rod with epoxy anchored to concrete does not need to comply with ACI 318 anchorage provisions. I disagree. If ACI equations are used to check the anchor’s capacity, the product would have a reduced capacity and wouldn’t work as they have designed.
Full explanation:
I am the EOR on a large 5-story light-framed wood apartment building. I designed and detailed all of the shear walls using “typical” hardware, such as coil straps floor-to-floor and holdowns with threaded rods in epoxy at the base. Recently, I received a hardware substitution request from the GC, proposing a different product. Initially, I assumed this was a request to substitute hardware directly from a different manufacturer. However, the submittal proposes a completely different shear wall system.
The proposed system is a proprietary continuous hold-down assembly that connects to the building at the roof level only and anchors to the concrete at the bottom. Its tension capacity is based on testing and comes with a “code approval” report from a certified testing agency. This report, a Technical Evaluation Report (TER), is similar to an Evaluation Service Report (ESR) from other agencies. Due to the proprietary nature of the assembly, no published calculations or test result data are available; only a single allowable tension capacity is provided. The TER specifies installation conditions that must be followed to achieve the published tension capacity.
I have several concerns about this proposed system's ability to resist the required shear wall overturning forces and the proposed load path. Although I have been working with the manufacturer to address these concerns, one aspect of the design remains problematic. Both the manufacturer and the testing agency assert that the system's anchorage into the concrete does not need to be checked using ACI 318 anchorage provisions. The proposed shear wall system consists of a steel cable assembly with steel threaded rods at each end, with the bottom rod embedded in an epoxy-filled hole in the concrete. In my opinion, this anchorage design is not proprietary since it involves a steel threaded rod with epoxy in concrete, which is clearly defined in ACI 318. I would understand the argument if we were talking about a Simpson “LSTHD” Strap-Tie Holdown or MiTek “LSTAD” Foundation Strap, which is a truly proprietary anchorage design since it is just bent steel embedded in the concrete. But this is a steel threaded rod embedded in epoxy that just happens to be attached to the end of a proprietary cable assembly.
The manufacturer has a proprietary epoxy with an ESR report, stating to follow ACI 318-14 Chapter 17. However, the testing agency and manufacturer claim that the ESR for the epoxy is not valid when used with the cable hold-down system. They argue that the ESR only applies when the epoxy anchors steel threaded rods to concrete. It just so happens that the bottom of the cable hold-down system has a steel threaded rod attached to it…
Problem:
Using ACI 318 equations to check the anchorage capacity, I find that the assembly's allowable tension capacity is about 60% less than the manufacturer’s published values, primarily due to concrete breakout. This calculation includes product-specific variables and factors from ACI 355.4 tests, accounting for any proprietary epoxy behavior, which are published in the ESR.
I believe the proposed system’s anchorage must be checked using ACI 318 provisions, as the design closely matches the scenarios covered in the standard. The difference between the published assembly capacity and calculated anchorage capacity is a significant concern that I want to resolve before allowing the product to be used in my building. The testing agency and the manufacturer are telling me not to worry about it since the submittal and the TER are both sealed by PEs in the project state. They claim that since it is a delegated design, I don’t need to worry about how it interacts with my building. I would like to reject the entire system and stick with the original design, but the contractor really wants to use the cable system.
Question:
Have you ever dealt with something like this before? I don’t see how I can allow this anchorage “design” to bypass the ACI 318 requirements just because they are calling a standard anchorage method “proprietary.”
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