How much consideration have you given to the use of steel backing for welds in seismic applications on your recent structural design jobs? Do you consider it more of a contractor’s means and methods, or do you investigate each application to be sure it meets the requirements of AWS D1.1?
In the February 2017 SEU Core Session, Duane Miller, PE, from The Lincoln Electric Company, presented Welding Myths that Structural Engineers Need to Know About. Duane covered a variety of topics that are often misunderstood by structural engineers in regard to the design and detail of welded connections. As he pointed out, many of these myths have some roots in truth, but some are only partly true or can be completely false.
For example, Duane spoke about the myth that “Weld backing is simply a construction aid or part of the contractor’s means and methods.” Although it is true that weld backing can be a part of the contractor’s responsibility when it comes to means and methods during the construction process, it is not a topic to which the structural engineer can turn a blind eye. Duane explained many of the findings from the Northridge earthquake and the reasoning for some of the requirements in AWS D1.8 and AISC 358 as far as the removal of weld backing in seismic zones. Left in place steel backing may create stress concentrations at the root, or in discontinuous backing, and whether this happens or not depends on several factors including joint type, direction and type of loading, among other things. Click here to watch a short 3 minute video explaining some findings from the Northridge earthquake, and why it is important for structural engineers to be aware of the issues that can arise from left in place weld backing.