Building Constructed with Round Mortise and Tenon Joints from Salvage Materials and Small Diameter Timber

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1 Building Constructed with Round Mortise and Tenon Joints from Salvage Materials and Small Diameter Timber by Carl A. Eckelnam Eva Haviarova Robert Leavitt Huseyin Akcey Department of Forestry and Natural Resource Purdue University

2 Small-Diameter Trees Many forest stands in this country and worldwide are over-stocked with small - diameter trees. They should be selectively thinned. Presently, plantation thinnings have very little market value to justify their removal.

3 Plantation Thinnings Plantations need to be thinned to optimize tree growth. More extensive use of existing timber resources would extend supplies, reduce waste, and slow down deforestation.

4 Potential Material Resource Large quantities of potentially useful but largely unused wood materials presently exist and are available for conversion into value-added wood products.

5 Plantation Thinnings These products must be of sufficient value to justify harvesting costs.

6 Potential Products Structural applications offer a high-potential value-added market for small-diameter stems. Strong, yet cost-effective methods are needed to join the members together. Furniture (especially school furniture) is another valuable product, particularly in underdeveloped countries.

7 Round Mortise and Tenon Round mortise and tenon joints may be quickly and easily constructed and are wellsuited for the fabrication of standardized parts that can be incorporated into modular constructions. Tenons are efficient load carriers and are highly resistant to cyclic loading in bending.

8 Building Frames Building frames must be designed so that internal bending forces are distributed as uniformly as possible to the various members and joints. Sufficient number of members must be included in the design to ensure that the total internal strength of the construction is sufficient to carry the loads imposed on the structure. Building frames should be designed to avoid tension loading of the joints.

9 Building Frames Systems Systems need to be as simple as possible to reduce the need for specialized labor. Acceptance of round mortise and tenon construction requires the standardization of parts and components to ensure that they will fit together when brought to a building site. There is strong need for the rational development of standardized components that can be used to fabricate a wide variety of modular frame systems.

10 Demonstration Building Frame Drawing Simple Frame Drawing Frame measures 6 by 12 feet in cross section by 9 feet tall.

11 Material Used Material was cut from small diameter yellow-poplar logs (plantation thinnings from Purdue University experimental forest.) The structural members measured 3-1/2 inches square. Some of the members were sawn conventionally. Other members were fabricated using the inside /outside technique used by Serrano.

12 Inside/Outside Beams Inside/out beams can be produced economically and are feasible for production in developing countries. 4x4 cants were resawn into 2x4 stock, the faces turned inside out, and glued back together while green.

13 Inside/Outside Beams Inside/outside fabricated beams are straighter, have less or no cracks, and improved strength properties.

14 Round Mortise and Tenon Construction Differs essentially only in the geometry of the joint compared to rectangular mortise and tenon construction -- but information is lacking concerning its suitability for use in building frame construction. Information is needed concerning its basic strength characteristics and adaptability to building construction.

15 Horizontal Drill Press A simple low cost horizontal drill press was built to machine tenons.

16 Machining of Members Tenons for the frame were cut with 2-inch diameter by 12-inch deep hole saws produced by a commercial supplier. The excess material was removed from around the tenon with a saw. Mortises were drilled in the members with 2-1/16 inch diameter Forstner bits.

17 Preservative Treatment Preservative treatment of the wood would be important in areas subject to termite infestation or where the wood might be periodically wetted.

18 Joint Strength - Withdrawal Pilot studies indicate that relatively high levels of withdrawal strength can be obtained with crosspinned tenon joints. A cross-pin of half the diameter of the round tenon is inserted crossways through the tenon so that the tenon and member are locked together.

19 Joint Strength -Bending The bending strength of round mortise and tenon joints is limited by the strength of the tenons themselves. If higher joint strengths are needed, either the diameter of the tenon must be increased or additional members must be used.

20 Frame Design

21 Parts Fabrication Material was first cut to size. Tenons were cut on the ends of the members. Mortises were drilled into the sides of the members.

22 Frame Construction The floor system consisting of floor joists and sills was secured on the foundation.

23 Frame Construction Corner posts, wall studs, and doorpost tenons were inserted into the corresponding sill mortises. Joints were pinned to the sills. Front and back top plates, tie beam, and side rafter plates were slipped in place over the ends of the stud and post tenons.

24 Frame Construction The ridge beam support columns were inserted in place. The wall stud tenons were inserted into the rafter mortises (the rafters were installed over the tops of the wall stud tenons) and the rafter tenons inserted into the ridge beam.

25 Frame Construction The ridge rafter beam along with the side rafter plates were extended in order to provide the fly rafters needed for an overhang. Facia headers were added.

26 Frame Construction The walls and roof were sheathed with standard grades of plywood. The roof was covered with asphalt shingles. The building was floored with salvaged material.

27 Construction Benefits Easy and rapid assembly from a stock of standardized parts. (Disassembly took 15 min, and re-assembly 40 min.) Costly connectors are eliminated. Basic or no tools are necessary. Unskilled labor can be used to erect a frame. High resistance to vertical and lateral loading.

28 Conclusions Round mortise and tenon joints provide a simple and straightforward method of constructing building frames. Standard parts can be manufactured locally by cottage-type industry or regionally by major producers. Standardized parts can be easily incorporated into modular constructions to serve a wide variety of needs: backyard storage sheds, shelters, farm building, light industrial buildings, multipurpose buildings-- in both developed and under-developed countries.