Selected provisions of the AISC specifications for the Design, Fabrication and Erection of Steel for Buildings, 1999, and the American Welding Society D1.1 Structural Welding Code – Steel, 1998, have been implemented.

STAAD.Pro is able to select weld thickness for connections and tabulate the various stresses. The weld design is limited to the members having properties from wide flange, tee, single angle, single channel, pipe and tube section tables only. The parameters WELD, WMAX, WMIN, and WSTR (as explained in D1.B.1.2 Design Parameters) govern the weld design.

Since the thickness of a weld is very small in comparison to its length, the properties of the weld can be calculated as line member. Therefore, the cross-sectional area (AZ) of the weld will actually be the length of the weld. Similarly, the units for the section moduli (SY and SZ) will be length-squared and for the polar moments of inertia (JW) will be length-cubed. The following table shows the different available weld lines, their type and their coordinate axes.

Table 1. WELD Parameter Values

Weld Type	Angle	Wide Flange	Tee	Channel	Pipe	Tube
1
2					n/a	n/a

Actual stresses, calculated from the member forces, can be specified by three names, based on their directions.

Horizontal Stress

as produced by the local z-shear force and torsional moment.

$F_h=\frac{VZ}{AX}+\frac{CH\times MX}{JW}$

where

VZ	=	Shear in local z-axis
MX	=	Torsional moment
CH	=	Distance of the extreme fiber for horizontal (local z) forces
AX	=	Area of the weld as the line member
JW	=	Polar moment of inertia

Vertical Stress

as produced by the axial y-shear force and torsional moment.

$F_v=\frac{VY}{AX}+\frac{CV\times MX}{JW}$

where

VY	=	Shear in local y-axis
MX	=	Torsional moment
CY	=	Distance of the extreme fiber for vertical (local y) forces
AX	=	Area of the weld as the line member
JW	=	Polar moment of inertia

Direct Stress

as produced by the axial force and bending moments in the local y and z directions.

$F_d=\frac{FX}{AX}+\frac{\left|MZ\right|}{SZ}+\frac{\left|MY\right|}{SY}$

where

FX	=	Axial force
MY	=	Bending in local y-axis
MZ	=	Bending in local z-axis
CH	=	Distance of the extreme fiber for horizontal (local z) forces
AX	=	Area of the weld as the line member
SY	=	= Section modulus around local y-axis
SZ	=	= Section modulus around local z-axis

Note: The moments MY and MZ are taken as absolute values, which may result in some conservative results for asymmetrical sections like angle, tee and channel.

Combined Stress

calculated by the square root of the summation of the squares of the above three principal stresses.

$F_{comb}=\sqrt{F_h^2+F_v^2+F_d^2}$

The weld thickness required is then calculated by:

The thickness, t_w, is rounded up to the nearest 1/16th of an inch and all the stresses are recalculated. The tabulated output prints the latter stresses. If the parameter TRACK is set to 1.0, the output will include the weld properties. The program does not calculate the minimum weld thickness as needed by some codes, but checks only against the minimum thickness as provided by the user (or 1/16th inch if not provided).

When the TRUSS qualifier is used with SELECT WELD command, the program will design the welds required for truss angle and double angle members that are attached to gusset plates. The program reports the number of welds (two for single angles, four for double angles), and the length required for each weld. The thickness of the weld is taken as 1/4 inch (6 mm) for members up to 1/4 inch (6 mm) thick, and 1/16 inch (1.5 mm) less than the angle thickness for members greater than 1/4 inch (6 mm) thick. The minimum weld length is taken as four times the weld thickness.

Weld design for SELECT WELD TRUSS