Performance tests of small barn frame constructed with round mortise and tenon joints

Structural tests were conducted to determine the strength and deflection characteristics of an 8 by 10 foot light-timber barn frame constructed with 3.5-inch square Douglas-fir members and round mortise and tenon joints. Structural analyses of the frame were also conducted using finite element methods and predicted deflections compared with test values. Results of the tests indicated that the roof and frame system could withstand positive and negative roof loads of 10,000 pounds, or 125 psf. Diagonal bracing or shear resistant siding likely would be needed to resist high lateral loads, however. Relatively close agreement was obtained between predicted and test deflections, after taking the semi-rigid behavior of the joints into account. Overall, results of the study indicate that high strength, ease and simplicity of construction, and the fact that members can be machined from small-diameter tree stems makes round mortise and tenon light timber frame construction well-suited for relieving both longand short-term shelter problems, particularly in less-developed countries. The use of round mortise and tenon joints in light-timber frame construction provides the opportunity for high-speed processing of standardized components that can easily be assembled to form a wide variety of modular frame constructions with a multitude of potential end uses. These frames provide potential outlets for square or round timbers cut from small-diameter tree stems and can thus lead to better utilization of underutilized timber resources. These frames also provide the means for constructing frames from local resources in less developed regions of the world and can thus lead to significant improvements in quality of life. In addition, the quick and easy assembly characteristics of these frames make them potentially useful for disaster relief in many parts of the world. In this respect, it is anticipated that these frames can be constructed to have high resistance to wind and other racking forces. The construction of a small backyard barn frame using round mortise and tenon joints and squared members fabricated from small-diameter yellow-poplar stems was discussed in a previous paper (Eckelman et al. 2002). The purpose of that study was to investigate the feasibility of round mortise and tenon light-timber frame construction from a machining and assembly viewpoint. Parallel cooperative research with similar structures is also underway at the Institute of Technology of Costa Rica. Marketing of such structures was treated by Morgan (2003). This method of construction has also been incorporated into commercially available structures (Round-Peg 2005). In addition, the strength of smalldiameter timbers as well as the strength of members cut from them has been addressed (Wolfe 2000, Wolfe and Moseley 2000, Wolfe and Murphy 2005). This paper provides additional information about the structural behavior and loadcarrying characteristics of this type of construction.