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Connectors, Anchors and Fasteners
The Role of Pintles in Wall Anchoring
I’ve often said that if something is easy to install, it will tend to be installed correctly. Our goal in selecting a masonry veneer anchoring system will be to design around wind loads specific to the project, yet to keep the installation as efficient and straightforward as possible for the contractor.
It sometimes may seem that masonry anchoring systems are in a perpetual state of transformation. These changes often may occur as a result of meeting new code requirements, building industry trends, energy requirements, or new methodologies of construction.
As an example, we see a change in today’s veneer anchoring needs, since the use of mineral wool as insulation has become more prevalent when looking to comply with NFPA-285 requirements. Because mineral wool has a lower R-value than that of rigid insulations, the wall cavities have to become larger to accommodate more of it. Larger cavities may require heavier anchoring systems in general.
We should examine from where wall anchoring has come, before we delve too far into where it is going. Initially, the anchoring system that integrated into the CMU backup was simply a rectangular tie welded to the cross rods of the wall reinforcing. There was no real adjustability to speak of, and the mason was challenged continually in keeping the masonry coursing in sync.
Often enough, these static anchors were bent and mangled to be made part of the wall or, in some cases, simply bent out of the way and rendered useless. When using this type of anchoring system, wind loads put tremendous stress on the cross wires of the wall reinforcing during compression. This ultimately compromised the integrity of the veneer, which spurred the development of the adjustable pintles we use in integrated wall anchoring today.
The adjustable pintle allowed the mason to work much faster. The coursing was not required to have the same precision as the non-adjustable system, because the mason had 1.25 inches of adjustability within the pintle tie. The secondary operation of installing the pintle anchors into the eyelets of the wire reinforcing was done at the same time the brick veneer was laid. Lateral loads were transferred to the structural backup of the wall much more efficiently, and the hook-and-eye system became the industry standard for decades to come.
Because of its ease of installation, the pintle also works well with anchors often found in steel-stud backup walls. The commonly used back plate anchors or barrel screw anchors both are dependent on pintles to complete the masonry connection. Take, for instance, a barrel anchor modified with a wingnut on the end capable of receiving the pintle’s hooks. The anchor installs with a single drive of the screw gun, and the pintles are installed quickly as the brick is laid into the bed joint, rather than threading the traditional “adjustable” wire tie through the end of the barrel anchor.
What is imperative to the successful use of pintles incorporated in wall anchoring is assuring proper engagement of the hooks to the eyelets. The further the vertical eccentricity is expanded, the weaker the tie becomes. Traditional performance criteria for a pintle between two walls falls under ACI-530, where it allows for the maximum eccentricity for a wire tie of 3/16-inch diameter to be 1.25 inches. That 1.25-inch adjustability can be challenging when laying an economy- or utility-size brick with a height of 3 5/8 inches.
How can you lengthen the allowable adjustability? It’s not uncommon to see the wire thickness go from 3/16 inch to ¼ inch, which, by code, also should change your mortar joints from 3/8 inch to a full ½ inch, though not always executed in the field.
The answer seems simple enough. You need to fit the strength of ¼-inch steel into 3/16-inch wire. And so, we did. We have found that a modification in the pintle leg design achieves a significant increase in strength. By compressing the vertical legs of the pintles, both the strain hardening of the leg and the increased section modulus have increased drastically the working load of the anchor. This reinforcing has shown in testing to be at a minimum of twice the strength of the BIA Tech Note 44, which suggests that a tie have a “maximum deflection of 0.05 inch when tested at an axial load of 100 pound-inches tension or compression.” In cases in which the pintle was fully engaged to the anchor, the strength was more than 10 times the tech note requirement at the maximum deflection.
When the heavier ¼-inch anchoring is required, as we see in the earlier mentioned example of wall cavities becoming wider, or in hurricane-prone areas with greater wind loads, this same principle can apply. Flattening the legs will add strength and adjustability of up to 2.25 inches. If you also compress the back of the anchor that sits in the bed joint, it will allow for a larger wire diameter to sit in a traditional 3/8-inch of mortar. This can be used in conjunction with a high-strength back plate anchor for an engineered high-strength anchoring system.
So, while conventionally thought of as an adjacency to wall reinforcing, the pintle has a beneficial role in today’s masonry wall, due to its ease and speed of installation, adjustability in the field, economical cost, and – now more than ever – its strength. At a minimum of twice the performance standard, an old accessory has been given a second look as an integral part of wall anchoring.
|Last Updated on Friday, 06 September 2013 16:54|