Treehouse attachment bolts or TABs are specialized bolts engineered for

treehouse A tree house, tree fort or treeshed is a platform or building constructed around, next to or among the trunk or branches of one or more mature trees while above ground level. Tree houses can be used for recreation, work space, habitation, a hang ...

construction.Globe Pequot, "Knack Treehouses: A Step-by-Step Guide to Designing and Building a Safe and Sound Structure", 2010,
p. 66
/ref> Various models and trademarks exist, with names such as Garnier limbs (GLs); tree anchor bolts; artificial limbs; heavy limbs or hyper limbs (HLs); special tree fastener or stud tree fastener (STFs). They may be either of through fastener style (for smaller trees) or side mount type for larger ones.

Description

One of the main features of TABs is their strength, requiring fewer tree penetrations for robust fastening of a treehouse and hence less damage to a live tree. A typical TAB consists of a threaded metal bolt and a larger diameter collar. The latter provides an extra bending strength by bearing upon the

compression strength In mechanics, compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loads tending to elongate). In other words, compres ...

of the tree grain. Since treehouses are subject to frequent load reversal produced by winds, TABs must be made of

spring steel Spring steel is a name given to a wide range of steels used in the manufacture of different products, including swords, saw blades, springs and many more. These steels are generally low-alloy manganese, medium-carbon steel or high-carbon stee ...

The bolts are able to support from between , a much greater load than conventional

lag bolt A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fas ...

s. TABs are commonly used in conjunction with pipe brackets, allowing the treehouse structure to move independently with the tree. TABs are designed so a tree's added girth can further envelop it.

History

The concept of using a collar or large cylindrical object to increase

shear strength In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a mater ...

in wood construction has been around for several centuries in the forms of split rings and shear plates. Shear plates provide a larger load-carrying capacity in shear than can be otherwise achieved by a bolt alone. Because this idea utilized less bolts for equal strength, it transferred well into the use of live trees, as they compartmentalize more efficiently with a single, larger cut than several, smaller cuts. Michael Garnier became involved in treehouse construction beginning in 1990 when he built his first treehouse in

Josephine County Josephine County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 88,090. The county seat is Grants Pass. The county is probably named after a stream in the area called Josephine Creek, which in ...

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idah ...

. Two years later, he was ordered by County official to close the treehouse to the public. He began developing what would become the Garnier limb, a high-strength alloy steel engineered bolt that can be screwed into a bore in the trunk of tree. In 1997 Garnier met Arborist Scott D. Baker who shared his knowledge of tree biology and tree structural responses. By 1998, Garnier had developed a commercial bolt product which he called Artificial Limbs. The Garnier limb was primarily developed to satisfy the safety requirements of the Josephine County Building and Safety

building permit A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and func ...

process.

Engineer Engineers, as practitioners of engineering, are professionals who invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considering the l ...

Charley Greenwood, with the help of Michael Garnier and

machinist A machinist is a tradesperson or trained professional who not only operates machine tools, but also has the knowledge of tooling and materials required to create set ups on machine tools such as milling machines, grinders, lathes, and drilling ...

Michael Birmingham, added a collar onto a hex cap screw to maximize the surface area and minimize compression in the contact area between the tree and the screw. Garnier was initially the sole producer of these bolts under the names, "Artificial Limbs" and "Garnier Limb".

References

{{reflist Screws Threaded fasteners Woodworking

Description

History

See also

References