NAILED CONSTRUCTION - A COMPARISON OF 1986 AND 1991 NATIONAL DESIGN SPECIFICATION METHODS

The National Design Specification (NDS) for Wood Construction publishe d by the American Forest and Paper Association (AFPA) is the primary g uide used in designing timber structures in the United States. This ar ticle compares the lateral and withdrawal nail design methods in the 1 991 NDS to those in the 1986 NDS. A lateral nail design example is inc luded for illustration. Design method changes from the 1986 to the 199 1 NDS include (a) using a lateral design format that is based on theor etical yield limit equations, (b) reducing annularly threaded nail lat eral design values about 25% from those in the 1986 NDS when threads o ccur at the shear plane, (c) increasing the load duration factor for w ind and earthquake to 1.6 compared to 1.33 in the 1986 NDS, and (d) el iminating the 1986 NDS increases in allowable stress for cold temperat ure conditions.