Seismic application of fillet and partial penetration butt welds

The paper presents a review of the research works conducted by HERA Seismic Research Programme to address both the cost-effective and reliable design of fillet and partial penetration butt welds in the steel construction industry of New Zealand. The authors of paper are Dr Hafez Taheri and Dr Michail Karpenko from HERA together with Prof. Charles Clifton, Prof. James Lim, Dr Shahab Ramhormozian, Dr Kris Roy and Prof. Pingsha Dong from different national and international universities.

Designing economical welds that can be easily fabricated and inspected is very important to improve the productivity and efficiency of steel construction. With the significant use of structural steel in multi-storey commercial and residential buildings, steel fabricators are seeking ways to implement the most cost-effective fabrication. It starts with the use of fabrication-optimised design solutions, including weld details such as fillet welds.

Fillet and partial (incomplete) penetration butt welds are often the most cost-effective weld details for structural steel connections in seismic-resisting systems. Appropriately 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 explained in NZS 3404 standard, including for use in seismic connections between members in ductile responding systems.

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. The paper presents literature review and test results achieved as a part of HERA 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 used in the seismic connections currently included in NZS 3404 is conservative, especially the use of the over strength 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.

The authors would like to acknowledge HERA Foundation for providing scholarships for the PhD students and the following HERA member companies for their support: John Jones Steel Ltd, D&H Steel Construction Ltd and Grayson Engineering Ltd.

For more information about the paper, please contact:

Hafez Taheri – Research Engineer