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The program includes lag screw fastener modules designed according to CSA O86 12.6.
Connection Modules
Available Geometries
The program limits the use of lag screws to one-sided post-and-beam connections, to avoid the complication of overlapping penetration, and because bolts are more commonly used in two-sided connections.
One-sided beam-to-beam, one-sided beam-to-column, and sloped beam-to-beam geometries are therefore implemented. Lag screws are not available for column-to-base, beam-to-column top, or lapped shear connections.
Side plates
Lag screws are not used for the side plate design, this being a two-sided connection. Bolts are used for the side plates when lag screws are used for face plates.
Lag Screw Dimensions
The program uses the lag screw dimensions from the USA NDS 2005 Appendix L, Table L2, pg. 166 as follows:
Input parameters
Diameter and length are used as the choices of available input parameters. They can be unknown, but are restricted to the standard diameters and lengths (it is not possible to type in custom sizes). They are also restricted by connection geometry.
The diameters range from ¼" to 1-1/4"; the lengths depend on diameter and range from 1" to 12".
Design parameters
Diameter, length, root diameter, unthreaded shank length, and tip length from Table L2 are used for design.
Drawing parameters
The head width and height are used for drawing only. Threads are not depicted.
Geometric Limitations
The program implements geometric limits at the following times:
Spacing
The program applies end and edge distance, and fastener and row spacing rules for lag screw connections according to O86 12.6.2. These rules are used to populate the drop-down lists of fastener and row spacing and edge and end conditions
Maximum and Minimum Penetration
The program prohibits lag screws from protruding through the main member while ensuring they meet the minimum penetration of 5D into the main member, according to O86 12.6.3.3. The program implements 12.6.3.2 which limits the length of penetration that can be used for withdrawal resistance.
These rules are used to populate the drop-down lists of available screw diameters and lengths.
Lateral Design
Calculation of Z
The program calculates lateral design capacity for lag screw connections according to O86 12.6.6.1:
Withdrawal Design
The program calculates withdrawal capacity for lag screw connections according to O8612.6.5.1 . at the time of calculating lateral design capacity.
Design Routine
The program includes the withdrawal capacity in the search for a passing design, cycling through unknown values if the withdrawal capacity does not exceed the design load.
Combined Lateral and Withdrawal Design
The program calculates combined lateral and withdrawal when there are both X and Y loads on the purlin in the connection geometries that use lag screws using the calculation of combined lateral and withdrawal capacity Nr in O86 12.6.6.1.1. The program compares this value with the resultant load N to determine whether a connection passes.
Secondary Wood Design Checks
Effective Shear Capacity
The program calculates effective shear capacity for perpendicular-to-grain lag screw connections according to NDS 3.4.3. The calculation is the same as for bolts, that is, it uses the worst-case effective depth over the width of the member. The portion of the section where the screws do not penetrate is disregarded.
Tension Capacity Net Area and Group and Row Tear-out Capacity
None of the lag screw geometries contain tension loading parallel to the grain, so these are not performed for lag screws.
Steel Design
The following steel design checks are performed:
Fastener Tension
The fastener tension check is performed using the root diameter Dr of the lag screw and a lag screw steel tension strength that you can modify in Settings initialisation file under the item LagScrewFt = [value in ksi]. Refer to the online help.
Fastener Shear
The fastener shear check is performed using the full diameter D of the lag screw and a lag screw steel shear strength that you can modify in the Settings initialisation file under the item LagScrewFv= [value in ksi]. Refer to the online help.
Fastener Bearing on Steel Plate
The bearing routine currently used for bolts is used for lag screws, using the full diameter D to determine the bearing area.
Plate and Weld Design
All the existing design checks for strength of steel plates and welds that are currently done for plates in bolted connections are also done for lag screws.
Washer Design
The program does not include washers for lag screw connections.
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 lag screws:
Initial values
In order to avoid impractical connections with numerous small fasteners, if the diameter 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 ½".