# D1.B.1.10 Weld Design

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`,
`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.

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
- 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:

_{W} | = | _{y} (where F_{y} =
FYLD parameter value. |

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.