Session: MF-15-01 Fatigue and Fracture of Welds and Heat Affected Zones-1

Paper Number: 155420

155420 - Study on Fatigue Assessment for Welded In-Plane Gusset Joints 

Abstract: 

Welded in-plane gusset joints have been widely used for various structures, including steel bridges and offshore structures. The traditional fatigue design and evaluation procedures of welded in-plane gusset joints are available through codes and standards using nominal and hot spot stress. However, multiple codes and standards simply provide the categorized S-N curves based on gusset length and weld toe grinding radius size. Even though the fatigue S-N behaviors for single-sided gusset joints are different from those for double-sided gusset joints, the codes and standards seem not to consider the differences clearly.

This study proposed fatigue failure criteria and investigated its effectiveness to both single-sided and double-sided gusset joints through three different fatigue assessment methods: the first one is the nominal stress method; the second method is the hot spot stress method, which requires stress calculation using FEA; and the third method is the master S-N curve using the equilibrium-based structural stress method adopted by ASME BPVC VIII-2 and API 579-1/ASME FFS-1, which requires structural stress calculation using FEA.

The fatigue crack behavior of the subject joint types is different from that of conventional welded plate joints. The crack starts from the weld toe of one edge and grows into the base plate width direction for welded in-plane gussets, while the crack starts from the weld toe and grows in plate thickness and along the weld for conventional welded joints.

The failure criteria for welded in-plane gusset joints were proposed based on loading and geometry conditions to apply the equilibrium-based structural stress method. When the failure criteria were applied, all fatigue data sets were consolidated within the master S-N curve, and the design S-N curve was appropriately conservative. However, nominal and/or hot spot stress-based approaches showed inconsistent trends compared to the fatigue data sets.

Some applications can use rigorous failure criteria, such as finite crack sizes, rather than complete failures. The modified equilibrium-based structural stress procedure was proposed for partial failure cases. Once the modified procedure was applied, the partial failure data sets were mingled with the full failure data sets, and therefore, the design S-N curve shows excellent conservatism regardless of complete failure and partial failure.

From this study, when the failure criteria for welded in-plane gussets were applied, the master S-N curve approach using the equilibrium-based structural stress method shows great data collapse and proper conservatism regardless of the geometry conditions and failure criteria.

Presenting Author: Jeong Hong Thornton Tomasetti

Presenting Author Biography: Dr. Jeong K. (J.K.) Hong joined Thornton Tomasetti as a Vice President in 2022. He used to work at Battelle Memorial Institute and Engineering Mechanics Corporation of Columbus.
Dr. Hong has extensive experience directing and managing engineering research and development programs in the Offshore, Oil & Gas, Nuclear, Heavy Machinery, and Automotive industries for more than 25 years.
His main research interest areas are advanced design methods and analysis procedure development for welded structures using computational and analytical methods. He has developed unique analysis tools for characterizing residual stresses, distortions, fatigue, fracture, and failure analysis in welded structures.
As a co-inventor of Verity® mesh-insensitive structural stress procedures, Dr. Hong holds multiple patents on weld fatigue design and evaluation.
Dr. Hong holds a doctorate in welding engineering from The Ohio State University, Columbus, OH, and a Master and a Bachelor of Science from Yonsei University, Seoul, Korea.

Authors:

Jeong K. Hong Thornton Tomasetti
Yuan Tian Thornton Tomasetti
Vahid Barzegar Thornton Tomasetti
Xin Chu Thornton Tomasetti
Zhi Zhang Thornton Tomasetti