Seismic application of fillet and partial penetration butt welds

Abstract

Fillet and partial (incomplete) penetration butt welds are the most cost-effective weld details for structural steel connections. Correctly sized and executed, double-sided, balanced fillet welds and partial penetration butt welds can offer the same performance as complete penetration butt welds under both semi-static and low cycle fatigue (seismic) loadings. The weld sizing criteria are included in NZS 3404 standard. This standard also allows the use of fillet welds in seismic connections, such as connections with member categories 1 and 2. Despite this, there is a misperception among design engineers about the performance of fillet welds under seismic load. Most overseas design specifications still call for complete penetration butt welds to be used in seismic full-capacity connections. This paper presents literature review and test results achieved as a part of HERA’s Seismic Research Programme in partnership with the Universities of Auckland and Waikato, Auckland University of Technology and the University of Michigan. It demonstrates that the sizing criterion for fillet welds for earthquake currently included in NZS 3404 is conservative, especially the use of the overstrength factor in determining the demand from the principal load path elements in connections results in oversized fillet welds. It also discusses the performance of partial penetration welds as an alternative to fillet welds.