Source: Whole Trees, LLC submitted to
STRUCTURAL TESTING OF BRANCHED TIMBER AND TRUSS ASSEMBLIES
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
NEW
Funding Source
Reporting Frequency
Annual
Accession No.
0230053
Grant No.
2012-33610-19933
Project No.
WISW-2012-02128
Proposal No.
2012-02128
Multistate No.
(N/A)
Program Code
8.1
Project Start Date
Sep 1, 2012
Project End Date
Aug 31, 2014
Grant Year
2012
Project Director
Gundersen, R.
Recipient Organization
Whole Trees, LLC
e2890 Lorenz Rd
Stoddard,WI 54658
Performing Department
(N/A)
Non Technical Summary
USDA secretary, Tom Vilsack, has urged the Forest to prioritize "protecting and maintaining all American Forests, including state and private lands. ... The Forest Service must play a significant role in the development of new markets and ensure their integrity." Small-diameter round timber is a vast and under-used waste product of well-managed forests. At the same time, the structural building systems market is currently dominated by steel and concrete structural systems. Round timber can substitute for steel and concrete in medium and large scale construction under Type IV: "Heavy Timber Framing." Round timber can qualify for up to eight US Green Building Council Leadership in Energy and Environmental Design (LEED) credits, more than triple any other "green" structural material and almost a third of the credits necessary to achieve LEED Silver rating, now the standard for new federal buildings. This convergence of factors will benefit WT's efforts to build an industry. Research conducted at the FPL indicates the superior strength of round wood timbers. Small-diameter round timbers are 50% stronger in bending than an equivalent square section of milled timber. WHOLETREES ARCHITECTURE AND STRUCTURES (WT), a leader in round timber design and construction, has conducted Phase I research into the strength of the branched connection between tree limbs and trunk. Structural tests, conducted at the Forest Products Laboratory in Madison, WI, applied lateral or axial force to a variety of branching Ash tree specimens and found the strength of the branched connection to be significant. Phase I testing demonstrated that out-of-plane bending of tributary branches or stem is critical to overall timber load capacity. Optical metrics of branched timbers along with structural analysis can be effective predictors of load capacities. A combination of slenderness ratio, branched geometry, and out-of-plane curvature seem to be a strong estimator of the load capacities. WT will, in Phase II, conduct focused testing to refine the selection criteria for specimens - a combination of slenderness ratio, branched angle and out-of-plane curvature - and develop the best visual parameters for selection. These selection criteria will be used for in-field sorting, and to develop proprietary grading software. Designing and testing original connection subassemblies will be crucial to bringing the strength of the branched timber to market. WT will build successful connection designs into full-scale branched column-truss assemblies.
Animal Health Component
60%
Research Effort Categories
Basic
(N/A)
Applied
60%
Developmental
40%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1230650202025%
1230650311045%
4040650202020%
4040650311010%
Goals / Objectives
The GOAL of this Phase II SBIR-funded research is to make round timber structures a viable alternative to steel and concrete framing systems by developing cost effective selection, grading, and manufacturing techniques, and establishing the design capacity of round timber assemblies. Phase II results will allow for the scaling of round timber manufacturing. They will also respond to building officials concerned with the structural quality and performance of branched timbers, while introducing to the construction market a viable branched column-truss assembly using both branched and straight timbers. Phase II technical OBJECTIVES are to: 1) Continue axial mechanical testing of branched timbers in Ash and in White Oak. 2) Develop a prototype grading system focused on optical NDE data and branched timber geometry. Further develop and test novel sub-assembly connection methods for branched column-truss assemblies to best utilize the strength of branched timbers. 3) Test prototype column-truss assemblies for axial loading the field. 4) Use test data to establish design values for the connections, the Y-branched columns and trusses to assist in grading timbers and engineered framing systems for Phase III commercialization. EXPECTED OUTPUTS are: 1)Structural axial load capacity tables for Y-branched timbers: For round timber to penetrate mainstream structural systems markets, structural engineers in the industry will need key data on the axial load capacity of Y-branched timbers. 2) Structural load tables for branched column-truss assemblies. 3) Steel connections that leverage the powerful axial and lateral loading capacity of Y-branched timbers. 4) Cost effective and efficient selection and inventory of raw material from the by-product of healthy timber management.
Project Methods
Technical objectives will be addressed through the following major tasks: 1) Specimen Selection: Branched members will be selected, harvested and prepared by WT crew. Selection will be based on geometric criteria including length, branch diameter, and angle between branches. Each specimen will be completely stripped of bark and kiln dried in order to ensure consistent moisture characteristics. 2) Collect Physical and Optical NDE: Each timber will be measured, photographed and documented (data will include: found location, visual marks, slenderness ratio, branched angle, out-of-plane ratio, etc). Parametric optical data will be collected using calibrated high resolution digital cameras; parallel and perpendicular to the branch direction. Using image analysis edge detection routines in MATLAB, the branch edges, branched angle and diameters will be established for key points. 3) Compressive axial testing of individual specimens: Specimens will be oriented with branched ends to the floor and loaded with an hydraulic actuator capable of applying 300,000 lb. Branched ends will be held by supports that restrain lateral movement while allowing for limited end rotation. All testing will be conducted in deformation control, so that failure of the specimen will occur between five and ten minutes (ASTM D198). Out-of-plane displacements will be measured using three calibrated digital cameras. 3D digital image correlation (DIC) techniques will determine out-of-plane deformation and document the failure modes. 4) Design and testing of sub assembly connections: WT architects, structural engineer and machinist will collaborate with FPL engineers to develop two to three connection designs for round wood elements necessary for the construction of the branched column truss system. Once the initial designs have been fabricated, they will be evaluated using sub-assembly connection tests (five tests per connection). 5) Testing of Branched Truss assemblies: Three independently observed tests will be conducted on branched column-truss assemblies to assess the ability of branched columns to reduce effective truss spans and develop structural frame behavior under typical roof load conditions. 6) Frame analysis: WT structural engineer will perform structural analysis of the branched column-truss assembly to determine test loading, connection forces and expected deflections using geometry of the branched columns provided by NDE and optical analysis methods described above. The loads to be placed on the test frame and the forces in the connections will be determined along with estimated deflections of the frame timbers. 7) Correlation of destructive tests to NDE data: Optical measurements determined via image analysis will be compared to physical measurement. Image analysis measurements will be used to generate structural models of each Y-branched axial specimen to determine the regions and values of maximum stress. In Phase II, the structural analysis model will include the effect of geometric non-linearites. Setting the limits for out-of-plane specimens imperfections is critical to this development. 8) Development of a prototype grading system.

Progress 09/01/12 to 08/31/13

Outputs
Target Audience: Phase II results will allow for the scaling of round timber manufacturing through the following Technical Objectives: 1) Continue axial mechanical testing of branched timbers in Ash and in Aspen. 2) Further develop and test novel sub-assembly connection methods for branched column-truss assemblies to best utilize the strength of branched timbers. 3) Test prototype column-truss assemblies for axial loading the field. 4) Use test data to establish design values for the connections, the Y-branched columns and trusses to assist in grading timbers and engineered framing systems for Phase III commercialization. In its first year's efforts toward these technical objectives, the project team reached the following target audiences: Construction Industry Leaders: In order to eventually commercialize the products developed under this grant, WholeTrees has engaged leaders in commercial construction through out the development of this truss system, its branched tree members, its steel connections, and its assemblies. Market research has occured during the development of these tests and products to establish what building dimensions will allow for these products, which early adopters in the industry will likely purchase these products, and for what types of commercial construction. Forestry Operations: By seeking convenient sources for its branched timbers destined for testing, WholeTrees reached out to forest owners, municipalities and rural land owners, to connect with their foresters, their timber cruisers, and the end-users for small diameter branched timbers (pulp mills, urban stagin grounds and chipping centers, as well as occassional structural timber builders). This outreach built awareness for the growing use of timber as structural members. WholeTrees is now a central connector and leader for Upper Midwest forest stakeholders seeking higher value markets for their management thinnings. Timber Engineers: The increased use of small diameter round timber in construction implies a larger network of structural engineers comfortable with timber. As WholeTrees drew together experts on structural steel connections and timber assemblies for this project, we began to create a database of structural engineers accross the country interested in increasing the use of timber in construction, and willing to innovate and advocate for this. Changes/Problems: The problems and challenges encountered in our first year fell under the following project tasks: TASK Complete Structural Engineering of 36’ long column-truss assembly, as well as second, pre-tensioned truss assembly: PROBLEM: These values are for a normal duration and wet service condition. If dry condition is required, the following increases ASTM D245 increases to 19% MC. WholeTrees needed to decide whether the testing of this assembly demanded kiln drying, or whether strength values for seasoned wood might be suffi cient. Certainly, on our path to commercialization, seasoning is far more cost effective than kiln drying. The team has yet to conclude the best method moving forward, so WholeTrees assumes its Red Pine cords will be kiln dried. TASK Complete analysis of structural forces for each connection point on truss: PROBLEM: The forces transferring from steel web to steel and wood connection are very high at the edges of each girder truss (less in the middle), and the design solution for a connection that can withstand such high tension and compression loads is very challenging. The team has spent many iterations of connections exploring this problem, and one is certain yet whether the proposed designs will handles the necessary force during sub-assembly tests. TASK A brainstorm of connection ideas are shared by the project team, and three distinct connection concepts are chosen. PROBLEM: The performance to cost analysis ratio of each proposed connection type is proving more relevant than originally assumed, and needs exploration prior to proceeding-- an unfunded cost to WholeTrees. This is slowing down the eventual sub assembly tests. TASK Final selection criteria established for columns to-be-tested, as well as for column-truss assembly sizes, lengths, geometry, and moisture level. PROBLEM: Harvest criteria was established in Autumn, which is a less ideal season for peeling timber, and added time and money to the acquisition of text-specimens. Then, the South West Wisconsin forest floor did not freeze until late in winter, delaying the harvest of felled and peeled trees to a landing ground for further seasoning. TASK Harvest, peeling and storage of 60 columns for destructive testing (25 Ash, 35 Aspen); and 10 red pine cutoffs for sub assembly connections. PROBLEM: Matching the established chord size for red pine (14” width at mid span for lower chord, and 12” width at mid span for upper chord) proved more challenging than expected. This width, though abundant in larger scale production, is less available in quantities of 15 or 20, as this research project requires. WholeTrees finally located two sources for this size of red pine thinning, but the search was time consuming. What opportunities for training and professional development has the project provided? The first year of this project has allowed WholeTrees staff training and professional development in the following areas: Collaboration and Mentoring by Structural Engineers nationally: The work plan required WholeTrees to network with the nation's most experienced timber structural engineers. Sharing our research problems with this cohort, under NDA's, WholeTrees was able to develop a much more substantial body of knowledge regarding existing engineering for timber structures, as well as undeveloped research. This collaboration also helped WholeTrees identify entire areas of research required to scale up the use of small diameter timber internationally. Non-Destructive Evaluation (NDE) collaborations: The USDA Forest Products Laboratory hosted an international NDE convention, which WholeTrees partipated in as a sponsor. This network of researchers has built our staff's understanding of what is already possible in non-destructive evaluation of round timber, and what areas of research need further pursuit. How have the results been disseminated to communities of interest? Year two of this project has and will include dissemination of project results. WholeTrees will be sure to report on these events in its final report. What do you plan to do during the next reporting period to accomplish the goals? The work thus far accomplished within this Phase 2 research project prepares the team for destructive testing of a) subassembly connection tests, b) branched column axial load tests; c)full assembly load tests of column/truss prototype. These tests are scheduled at the Forest Products Laboratory for Spring-Summer 2014. Prior to these destructive tests, all branched columns will undergo a 30-dimensional scan with appropriate laser devices to collect digital point clouds that will later be paired with information on breakage, strength, and structural failure. This process is scheduled for August-September, 2013, and WholeTrees has connected to researchers at MIT and internationally involved in tangential uses of lasers in forest products metrics. Finally, all data from destructive testing will be analyzed, and correlations will be drawn between structural failure and 3-dimensional geometric characteristics of branched timber columns.

Impacts
What was accomplished under these goals? WholeTrees has reached its mid-phase goals for three of the four stated objectives, with the fourth objective scheduled for Year Two of this project. All specimens for continued axial mechanical testing have been harvested and are seasoning until Spring, 2014; and axial tests have been designed, with preparations made at the USDA Forest Products Laboratory, Madison, WI. Data from Phase 1 has infl uenced the selection criteria for these specimens, as has ongoing dialogue about ideal product heights, lengths, and load capacity for commercialization. A diverse team of architects, engineers, and business professionals have brainstormed innovative steel connections that will enable the cost-effective use of branched timber in commercial construction settings, and the top three designs have been fabricated by a steel fabricator, in preparationg for sub assembly load tests in May-June, 2013. Extensive structural analysis has been completed for the prototype column-truss assembly described in this grant proposal, with load requirements influencing the design of steel connections and webbing, as well as the species of round timber selected for the project. All inventory for assembling these prototypes has been harvested and is seasoning through Summer, 2013. If need be, all inventory will be kiln dried in September, 2013.

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