The International Information Center for Structural Engineers

Non-destructive method to investigate the hardness - plastic strain relationship in cyclically deformed structural steel elements

H. Nashid,W.G. Ferguson,G.C. Clifton,M. Hodgson,M- Battley,C. Seal,J.H. Choi.
Book Title or Journal
New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
Number of pages
A non-destructive hardness testing method is being developed to determine plastic strain in steel elements that have been subjected to inelastic seismic loading. The focus of this study is on the active links of eccentrically braced frames (EBFs). The 2010/2011 Christchurch earthquake series, especially the very intense February 22 shaking, was the first earthquake worldwide to push complete EBF systems into their inelastic state, generating a moderate to high level of plastic strain in EBF active links for a range of buildings from 3 to 23 storeys in height. Plastic deformation was confined to the active links. This raised two important questions: 1) what was the extent of plastic deformation; and 2) what effect does that have on post-earthquake steel properties? To answer these questions a range of actions are being taken. A non-destructive hardness test method is being developed to determine a relationship between hardness and plastic strain in active link beams. Active links from the earthquake affected, 23-storey Pacific Tower building in Christchurch has been hardness and material property tested to determine the changes in the steel, and cyclic testing of active links to defined levels of inelastic demand is underway. Test results to date show clear evidence that the hardness based method is able to give a good relationship between hardness measurements and plastic strain. This paper presents recent significant findings from this project. Principal of these is the discovery that hot rolled steel tested beams, all carry manufacturing induced plastic strains, in regions of the webs, of up to 5%. It is the intention of the overall research project, to establish a robust relationship between measured hardness and plastic strain demand in cyclically deformed steel elements and a comprehensive guideline to assess commonly used seismic-resisting systems will be adopted.
steel elements,non-destructive method