Welded Connections: Key Design Considerations & Best Practices

Connections are a key part of a steel structure and it is critical to achieve a safe and economical structure. Most major structural failures have been due to some form of connection failure. In this chapter, we are going to learn about essential considerations for weld design.

ROLE OF WELDS

The versatility of welding gives the designer greater freedom than any other method of joining. Today, welding is used to construct members such as plate girders and box sections as well as to connect structural members

WELDING CODES

AISC standards address the design requirements for the structure, while AWS standards typically focus on welding issues. Of necessity, there is some overlap between the coverage of AISC and AWS standards, and these standards have been produced by ANSI consensus committees that are responsible for each standard.

WHAT MAKES FOR A GOOD WELDED CONNECTIONS?

General guidelines for good welded connection. In some cases, the AISC Specification provides design rules. The following principles are not codified rules,

A good welded connection is strong enough to transfer all the applied loads.
A good welded connection has a clear and direct load path.
A good welded connection protects the toes and roots of the welds.
A good welded connection is aesthetically pleasing.
A good welded connection recognizes material properties.

HOW TO READ WELD SYMBOL?

THINGS TO KNOW WHILE DESIGNING WELDS:

The shelf dimension should be a minimum of 1/4 in. (6 mm) larger than the fillet weld leg size as per AISC Manual Part 8 (AISC, 2017). An inadequate shelf dimension may lead to undesirable melting of the edge.

Boxing is nothing but end returns. End returns are used to ensure quality terminations to welds and to provide some resistance to prying of the weld roots. End returns is determining the total weld length according to AWS D.1.1. In general, end returns are neither prohibited nor required. When they are used, AISC Commentary J2.2b places certain restrictions on their length.
Intermittent welds are options for lightly loaded connections. The minimum weld length discussed in AISC Specification Section J2.2b also applies to intermittent fillet welds, but in addition to that the minimum length is not permitted to be shorter than 1 1/2 in. (38 mm).
AISC Specification Table J2.4 specifies minimum weld sizes that are a function of plate thickness. The fillet weld size need not exceed the thickness of the thinner part being joined. These are not only design related requirements but also used to address welding-related concerns that involve fusion and cracking.

The maximum fillet weld leg size is restricted to the thickness of the material, less 1/16 in. (2 mm) when welded on the edge of material greater than 1/4 in. (6 mm) thick. It is possible to confirm that the edge has not been melted and therefore, a weld with a proper throat dimension is achieved. It’s not applicable for T-joints & HSS connections.

Most T-joints intersect at 90° angles. When the T-joint is skewed, special consideration must be given to both the acute and the obtuse sides of the joint. Table 10-14c provide weld clearances & dimensions for skewed plate shear connections. PJP groove welds become a more economical choice when the fillet weld throat becomes disproportionately small for the weld leg size in obtuse.

REFERANCES:

AISC STEEL CONSTRUCTION MANUAL 14TH EDITION
AISC STEEL CONSTRUCTION MANUAL 15TH EDITION
AISC DESIGN GUIDE 21- Welded Connections – A Primer for Engineers

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