roof framing connections in conventional residential construction

1.0 INTRODUCTIONThe NAHB Research Center has been engaged in a multifaceted research program for theNational Association of Home Builders (NAHB) and the U.S. Department of Housing and UrbanDevelopment (HUD) to quantify the structural performance of homes and to develop or refineengineering methods that accurately model conventional wood construction. Previous studieshave focused on the system effects of the whole building performance and specific assembliessuch as built-up headers and shear walls. However, little effort has been made to investigate thesystemic load path with respect to roof framing connections, particularly in the context ofconventional, wood-framed homes. The engineering knowledge needed to cost-effectivelydesign homes or evaluate residential construction guidelines are lacking in this area. In addition,the practice of making connections in conventional wood-frame construction has evolved fromits original use of hand-driven fasteners to the predominant use of pneumatic fasteners. Theprescriptive fastening schedules developed based on historic experience with hand-drivenfasteners need to be verified and updated for use with pneumatic fasteners to ensure consistencywith the intended performance objectives. This problem further extends to the design practice forengineered wood-frame connections.The focus of this project was on connections used with conventional light-frame wood roofconstruction. A literature review was conducted and supplemented with new research on theperformance of conventional roof systems and components including ceiling joist-to-rafterconnections and roof framing-to-wall connections. Individual connections and connectionswithin full-scale roof systems were tested to quantify potential system effects. Hand-driven andpneumatic fasteners were included in the test program. Test results were compared to theprovisions of the National Design Specification for Wood Construction [1] and to predictions ofthe yield theory using the general dowel equations for shear connections [2]. Finally, the resultswere analyzed with respect to an interest in establishing a consistent capacity basis for design ofwood-frame connections.The key objectives for this study were to:1. Survey relevant research on conventional and engineered nailed connections.2. Benchmark the capacity and stiffness of conventional ceiling joist-to-rafter connections(i.e., heel joints) assembled with hand-driven common and pneumatic nails in pairedassembly tests.3. Benchmark the shear capacity of roof-to-wall connections (load direction parallel to wall)assembled with hand-driven common nails, pneumatic nails, and a combination ofpneumatic nails and light-gage steel roof clips using full-scale roof assembly tests andindividual connection tests.4. Better understand system effects in connection behavior in conventional wood-frame roofconstruction.5. Evaluate the applicability of the yield theory methodology for predicting connectioncapacity.This report is organized in seven sections and an appendix. Section 1 formulates the problemstatement, summarizes the major tasks completed under the project, and presents the projectobjectives. In Section 2, background information is provided on the design of nailed connectionsin light-frame wood construction. A summary of relevant research is included with the focus onkey roof framing connections. Properties of materials used in the testing program are reported in1