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Publication date: 10 June 2019

Chien-Yuan Hou

The purpose of this paper is to complete fatigue analysis of welded joints considering both the crack initiation sites and crack coalescence, and to generate virtual welded…

130

Abstract

Purpose

The purpose of this paper is to complete fatigue analysis of welded joints considering both the crack initiation sites and crack coalescence, and to generate virtual welded specimens for computer simulation of fatigue life on a specimen-by-specimen basis; knowledge regarding the weld toe stress concentration factor (SCF) sequence is essential. In this study, attempts were made to analyze the sequence and to find a simple method to generate the sequence using computers.

Design/methodology/approach

Laser scanning technique was used to acquire the real three-dimensional weld toe geometry of welded specimens. The scanned geometry was digitally sectioned, and three-dimensional finite element (FE) models of the scanned specimens were constructed and the weld toe SCF sequence was calculated. The numbers in the sequence were analyzed using a simple autoregression model and the statistical properties of the sequence were acquired.

Findings

The autoregression analysis showed the value of a weld toe SCF is linearly related to its neighboring factor with a high correlation. When a factor value at a toe location is known, the neighboring factor can be simulated by a simple linear equation with a random residual. The weld toe factor sequence can thus be formed by repeatedly using the linear equation with a residual. The generated sequence exhibits close statistical properties to those of the real sequence obtained from FE results.

Practical implications

When the weld toe SCF sequence is known, it is possible to foresee potential crack locations and the subsequent crack coalescence. The results of the current study will be the foundation for the future work on fatigue analysis of welded joints considering the effects of crack initiation site and crack coalescence.

Originality/value

The weld toe SCF sequence was rarely discussed previously because of a lack of the available data. The current study is the first work to investigate the statistical properties of the sequence and found that a simple autoregression equation can be used to perform the analysis. This study is also the first work that successfully generates a weld toe SCF sequence, which can be used to simulate virtual welded specimens.

Details

International Journal of Structural Integrity, vol. 10 no. 6
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 25 January 2019

Chien-Yuan Hou, Yung-Feng Lee and Yen-Hao Peng

Examination of steel moment resisting frames after the 1994 Northridge earthquake showed fatigue cracks presented in the beam–column connections of the frames. These observations…

148

Abstract

Purpose

Examination of steel moment resisting frames after the 1994 Northridge earthquake showed fatigue cracks presented in the beam–column connections of the frames. These observations indicate that fatigue failure may occur in the steel components of building structures in an earthquake event. To apply the fatigue design approach using the Palmgren–Miner’s rule for steel components of the moment resisting frames requires the knowledge regarding the damage index value at fatigue failure. The purpose of this paper is to perform fatigue tests to give the first damage values of steel components subjected to real earthquake-induced loadings.

Design/methodology/approach

The added-damping-and-stiffness steel plates which are used in building structures for earthquake mitigation were fabricated and tested by constant amplitude, SAC block and earthquake-induced loadings to failure. The earthquake loadings were obtained from the dynamic analysis of a steel frame with the mentioned plates. The load cycles of the SAC block and the calculated earthquake loadings were counted using the rainflow-counting method, and the damage index value of each specimen were calculated using the Palmgren–Miner’s rule.

Findings

Reverse stiffness obtained from cyclic load-displacement loops is a robust and consistent parameter that can be used for determining fatigue failure of tested components. The Palmgren–Miner’s damage values at failure, caused by earthquake loadings, are smaller than 1, and in addition, are also smaller than those obtained from the tests of the SAC block loading. The large-amplitude cycles in the earthquake loading produce large damage on the specimens, and intermediate range cycles also produce damage that should not be neglected in the fatigue analysis.

Originality/value

Today’s building design code allows large plastic deformation to occur in steel frames during an earthquake. However, the pre-Northridge earthquake steel frames showed fatigue cracks without the expected substantial plastic deformation at beam flanges. Proposed solutions to this problem were the reduced beam section neglecting the existence of the cracks at beam–column connections. This study considered the fatigue phenomenon in steel frames and provided the first set of tested fatigue damage values for steel components subjected to realistic earthquake loadings, which offered a possible method of dealing with fatigue cracks in the steel components of a building structure.

Details

International Journal of Structural Integrity, vol. 10 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

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