Precision Structural Engineering, Inc.
March 14, 2013
to: Michael Garnier, owner
Out 'n' About Treehouse Treesort,
300 Page Creek Rd
Cave Junction, Oregon 97523
http://www.treehouses.com/
RE: Project Name: Report on GL Bolt test results
Test Location: Out 'n' About Treehouse Treesort, 300 Page Creek Rd
Cave Junction, Oregon 97523
PSE Project Number: KF213-3401
Dear Mr. Garnier:
I witnessed two of the field tests you preformed on GL (Garnier Limb®) bolt connections to Douglas fir trees during the 12th World Treehouse and (1st) Zipline Conference on Columbus Day Weekend 2012, October 5th-7th. Refer to Figures 1-4.
Also, I have the results of 10 tests that were conducted and witnessed by a third party.
The average ultimate, maximum, load of the above tests was 8,200 pounds.
Notes on the test:
1- The load was applied by using a hydraulic pump 2” out from the
cambium layer of the tree.
2- The load was applied parallel to the fibers, length of the tree, mainly
shear load on the bolt.
3- Failure was not sudden or catastrophic. The test was stopped when
the GL bolt failed to take more load.
4- The above results are:
a- Specific to the above location, above tree health, species, wood specific gravity, and test equipment.
b- Method, way and techniques of applying the load.
c- The above results cannot be used, relied on, or applied to
other sites or another tree without written permission from this engineer.
5- We recommend that the user of GL bolt:
a- Hire a Licensed Consulting Arborist to check his/her
tree to make sure the tree is healthy before using the GL bolt.
b- Conduct at least 1-2 tests on a site specific tree he/she is
planning to use under the supervision of a licensed engineer.
c- Use factor of safety of 2. Usable shear load should be one half of the maximum shear load he/she will reach at his/her new tests.
d- No tension or bending moment loads should be applied to the GL bolts unless approved by a local licensed engineer.
e- Hire a local licensed engineer to verify that the tree he/she is planning to use is strong enough, and of enough diameter to support the loads from any attachment.
6- We also used finite element analysis models created using Risa 3D software under my supervision by PSEI staff. This model was created and run with conditions specifically set to make it as similar as possible to the tests above. These conditions are as follows:
a- The bolt and boss in the model were given the same geometric properties of the specifications at the end of this letter. They were also given the material properties of annealed steel including; shear modulus (G) of 11346 ksi, elastic modulus (E) of 29500 ksi, Yield Tensile Stress (Fy) of 55 ksi, and Ultimate Tensile Stress (Fu) of 70 ksi.
b- The model of the wood had the dimensions of a 1 cubic foot 3-dimensional block. The basic finite elements used in analysis were ½ inches3. For elements at the connection of the boss to the wood, where results were most critical, elements were ¼ inches3. The full model can be seen in Figure 5 at the end of this letter.
c- The material of the wood matched the properties of Douglas Fir with a shear modulus (G) of 704 ksi, an elastic modulus (E) of 1242 ksi, and a density of .035. Refer to Appendix A. Comparative analyses were also performed using the material properties of Oak, Pine, and Redwood. For the exact material properties used for these different analyses, please contact Precision Structural Engineering.
d- From Risa 3D, we see that when 8550 lb is placed on the bolt, that wood reaches its maximum compressive stress as listed in Appendix A. This is approximately the ultimate capacity of the bolt. The allowable capacity can be taken as one half this value. This procedure can be seen in Figure 6 at the end of this letter.
e- These analyses further verify the results of the field tests above. To see the full analysis and result report for this model or the models using different wood material properties, please contact PSEI.
7- The GL bolt specifications is included at the end for this letter.
8- See additional limitations below.
We appreciate the opportunity to provide excellent engineering service to you on this project. We sincerely hope that you are very satisfied with our service. If you have any remarks, questions, or if we could assist you in any matter, please contact me.
Sincerely yours,
December 4, 2012
Bill, Nabil, Taha, Ph.D., P.E.
Licensed in 30 States
Precision Structural Engineering, Inc.
250 Main Street, Klamath Falls, Oregon 97601
Tel: 541-850-6300, Fax: 541-850-6322
e-mail:
This email address is being protected from spambots. You need JavaScript enabled to view it.
, Skype: nabil.taha55
Web: http://www.structure1.com
Limitation:
The conclusions presented in this report are professional opinions based solely upon visual observations of the tests and a finite element analysis model. We cannot act as insurers, and no expressed or implied representation of warranty is included or intended in our report, except that our work was performed, within the limits prescribed by our clients, with the customary thoroughness and competence of our profession at the time and place the services were rendered.
Figure 1: GL Bolt
Figure 2: Hydraulic Test
Figure 3: Test Loading Figure 4: Bolt Embedded in Wood
Figure 5: 3D Finite Element Analysis Model in Risa 3D
Figure 6: Maximum Compression Stress in Wood from 8200lb Load
250-A Main Street, Klamath Falls, OR, 97601
Tel. (541) 850-6300 Fax (541)850-6233
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
836 Mason Way, Medford, OR 97501
Tel. (541) 858-8500 Fax(541)282-7689
Click for Treehouse Construction's report on Habitable Treehouses: Building standards July-August 2000.
