roof framing connections in conventional residential construction

Uplift tests were conducted on toe-nailed roof framing-to-wall connections and on modifiedconnections. The modifications were chosen to represent retrofitting alternatives available forhomeowners to improve the wind resistance of roof framing-to-wall connections. Three testswere conducted on rafter-to-wall connections using three 16d box toe-nails. It should be notedthat this configuration is stronger than the three 8d common toe-nails required by current code[27]. The framing lumber species was Douglas-fir having an average tested specific gravity of0.45. A mean value of 668 lb with a standard deviation of 63 lb was recorded for the upliftcapacity of the connection.Reed et al. [28] investigated the uplift capacity of rafter-to-top plate connections in light-framewood construction. The results were used to evaluate the resistance of individual connections touplift loads caused by severe wind events. Connections fastened with hurricane straps, toe nails,and adhesives were tested. Over 350 tests were performed on 28 different roof-to-wallconnection details. A total of 13 tests were conducted on the standard toe-nail connection usingSPF lumber and three 8d common toe-nails per joint. This connection had an average withdrawalcapacity of 410 lb and a standard deviation of 139 lb (COV = 0.34) in the assembly tests. Forcomparison, Equation 1 predicts an ultimate uplift capacity of about 200 lb to 280 lb, assuming aframing lumber specific gravity of 0.37 to 0.42, a nail penetration of about 1 inch, and no toenailreduction factor as required by NDS-97. The mode of failure reported for the toe-nailedconnections was nail withdrawal.2.3 CONCLUSIONS ON LITERATURE SURVEYResults of the literature survey of research information relevant to the performance and methodsof analysis of nailed wood connections in residential roof construction indicate that a voluminousbody of knowledge is accumulated in this field. However, there is a disparity in bothunderstanding the response and the state-of-the-art of the engineering design methods betweenvarious connection configurations, failure modes, and design applications. While a soundmethodology exists for analysis of withdrawal resistance of individual nail connections andmultiple nail connections within roof systems, there is a lack of rational application of the designmethodologies for lateral analysis of nail connections. The capacity-based design philosophy forwood shear connections is advocated and analytical methods for determination of connectioncapacity are proposed [2], yet little experimental data is compiled to substantiate theimplementation of capacity-based design into the engineering design procedures. As an integralpart of capacity-based design, a practical method for modeling the nail load-slip relationshipshould be adopted. Moreover, current design methods ignore systematic aspects of theperformance of the nail shear connections within multiple nail joints and structural systems thatuse a cumulative resistance of multiple joints with the exception of the nail diaphragm factor [1].Determination of these system effects for conventional construction is the key for understandingthe generally successful historic performance of conventional light-frame wood construction andis necessary for development of methodologies that accurately predict the response ofconventional systems for efficient design of houses.An experimental research program was developed to begin addressing some of the identifieddeficiencies and inequities in the current design methodologies relevant to the objectives of thisstudy. The purpose of this program was to investigate the response parameters including capacityand stiffness of conventional roof connections with the focus on the system performance9