|
|
|
|
|
Wood Screws
The program includes wood screw fastener modules designed according to CSA O86 12.9.5.1.
Connection Modules
Available Geometries
The program limits the use of wood screws to two-member lapped shear connections, to avoid the complication of overlapping penetration, and because bolts are more commonly used in two-sided connections.
Two member splice, orthogonal, and skew geometries are therefore implemented, for both wood-to-wood and steel-to-wood connection geometries. Wood screws are not available for post-and-beam or ledger connections.
Wood Screw Dimensions
The program uses the wood screw dimensions from Table 12.11.1.
Input parameters
Screw number and length are used as the choices of available input parameters. They can be unknown, but are restricted to the standard wood screw numbers and lengths (it is not possible to type in custom sizes). They are also restricted by connection geometry.
The wood screw numbers available are 6, 8, 10, and 12 ; the lengths depend on screw number and were derived from a number of screw supplier catalogues, taking into account availability, and commonness of use. The lengths range from 1” to 12”. Wood screws greater than 12 gauge are designed as lag screws.
Drawing parameters
The head width is calculated as twice the diameter, and used for drawing only.
Geometric Limitations
The program implements geometric limits at the following times:
upon validating the materials to determine the available methods for the connection;
during input to produce the drop-down lists of available fastener parameters;
during design when resolving unknown values.
Spacing
The program applies spacing requirements for wood screw connections according to O86 Table 12.9.2.1.. These are used to populate the drop-down lists of fastener and row spacing and edge and end conditions.
Protrusion and Minimum Penetration
The program prohibits wood screws from protruding through the main member while ensuring they meet the minimum penetration requirements from O86 Figure 12.9.2.2. These rules are used to populate the drop-down lists of available screw diameters and lengths.
Lateral Design
The program calculates lateral design capacity Nr for wood screw connections according to O86 12.11.4.
Withdrawal Design
As wood screws are implemented for lapped shear connections only, and they are not subject to withdrawal loads, withdrawal design from 12.11.5 is not performed.
Secondary Wood Design Checks
Effective Shear Capacity
Effective shear capacity is required to be calculated for wood screw connections.
Tension Capacity Net Area
Tension capacity, net area is not calculated for wood screw connections..
Group and Row Tear-out Capacity
CSA O86 does not require these checks for wood screws. .
Steel Design
The program does not perform steel design checks for any lapped shear connections, including those fastened with wood screws.
Design
Design Sequence
The order in which the program cycles through unknown input values to achieve a passing design is given below, with items with asterisks representing design checks new to wood screws:
Initial values
In order to avoid impractical connections with numerous small fasteners, if the screw number is unspecified (unknown) the program starts with the initial value specified in the Settings initialization file. If it cannot design using this or a larger value, it tries smaller sizes.
This value can be changed in the Settings initialization as follows
The default value for new installations is screw number 10.