This project’s goals are to evaluate the structure and strength design of Schnadig three-seat sofa frames, summarize current available information on engineering design, derive cyclic schedules for durability evaluation of frame components, and improve the design to meet product performance requirement specified by Schnadig. The target goal of medium or above acceptance level of General Service Administration (GSA) performance test was expected for the improved design. The design procedures and testing results in the study are also applicable to other frames, and can be used as a guideline for product engineering and reengineering. In this study, the mechanical and strength properties of frames, and members and joints, were evaluated. Schnadig three-seat sofa frames were evaluated by the performance tests. Six sets of tests were conducted with three replicates for each test. The critical joints and members were identified. Generally the frames did not reach the anticipated medium acceptance level except for the arm vertical test, where all the tested frames passed heavy duty. The inadequate connection of joints and the weak member were the major cause of failure. Next, the static and fatigue properties of selected plywood, oriented strand board (OSB) and particle board (PB) were investigated. The regression equations of S-N (stress versus number of cycles to failure) through low 5% points (i.e., the 5th percentile) were derived for all selected wood composite materials and proposed as design equations for achieving a conservative design of furniture frame structural members considering fatigue effects. It was found that the fitting constant E in the S-N equation at low 5% data was 0.85, and the constant H values were 0.06, 0.08, and 0.10, for plywood, OSB, and PB, respectively. Analysis results indicted that when cyclic stepped load effects were considered, the allowable design stress for plywood, OSB, and PB should not exceed respectively, 54%, 64%, and 68% of their MOR. Experiments were also designed to investigate the lateral shear and direct withdraw load resistances of face-toace and end-toace joints. Two types of connection, glue and single staple, were studied. Load direction relative to grain direction was considered. Statistical analyses were implemented to study the effect on the load resistance of the joints. Lastly, a solid 3D frame model was developed in I-DEAS to obtain the internal forces on critical components. Suggestions on the constructions of critical components were made based on internal forces obtained from computer modeling, as well as the laboratory results of frames, members, joints. One result of this study is the recommendations for improved construction details.

This study investigated the lateral shear resistance of multi-staple joints, static and fatigue bending moment resistances of stapled gusset-plate joints, and fatigue bending performance of full size sofa structural members in three oriented strandboard (OSB) materials. It is concluded that the lateral shear resistance capacity of multi-staple joints in OSB can be predicted with power equations including single-staple lateral resistance capacity, number of staples, and material density. The bending moment resistance of stapled gusset plate joints in OSB can be predicted by mechanical models including the lateral resistance property of multi-staple joints. The static moment capacity study of a gusset-plate joint concluded that its maximum moment resistance is 2 times of its corresponding proportional limit moment resistance. Experimental results indicated that there was no significant difference in lateral shear resistance among vertically-aligned multi-staple joints constructed of three OSB materials even though there were significant differences in lateral resistance among single-staple joints in these three materials. However, there were significant differences in lateral resistances among horizontally-aligned multi-staple joints in three OSB materials. Fatigue test results concluded that the ratio of static to passed fatigue moment capacity of gusset-plate joints was 2.6. The proposed equations reasonably estimated fatigue life of less brittle OSB materials subjected to cyclic stepped and constant fatigue loads but underestimated the brittle OSB material. The ratios of material modulus of rupture to passed fatigue stress were 2.17 and 2.25 for cyclic stepped and constant cyclic tests, respectively.