Abstract
To prevent from the brittle fracture accident of steel structure, various fracture assessment methods were irproved. Most of brittle fractures occur from the cracks such as welding defects at the strain concentrated region. The CTOD design curve specified on WES 2805 : 1997 is suitable for the CTOD estimation of such cracks.
However, according to the papers about the fracture analysis of damaged steel structures by large earthquapes, the brittle fracture in the connection zone of the steel structure occurred from small crack sometimes under 1 mm by more than 5% large strain and high strain rate in the order of 0.1/s. And, the strain gradient around the crack is so steep that it is difficult to difine the applied strain for design curve.
In such casen, it is not clear the applicability of the CTOD design curve, and strain difinition is also.
In this paper, the applicability of the CTOD design curve of WES 2805 : 1997 was dincussed for large strain, steep strain gradient and for high strain rate. 3-dimensional EF-models of beam to column welding connections were made and large strain dynamic analyses were conducted. Especially, under dynamic loading condition, as the temperature raise induced by plastic deformation can't be ignored at the strain concentrated zone, the thermal mechanically coupled analyses were conducted.
Based on the rusults of these FE-analyses, new difinition of strain for evaluation was proposed and applicability of CTOD design curve for the crack at the steep strain gradient was confirmed.
From these FE-analyses results, the temperature raise at the strain concentrated zone and the crack tip were also obtained. And it can be said that the crack tip temperature of small crack at the column to beam connection zone is almost same as the temperature of the zone difined by the proposed strain for CTOD evaluation in seismic loading condition.
