A Fracture Mechanics Approach to Estimate Fracture-Induced Unstable Failure in Steel Structures

2020 ◽  
pp. 1063-1073
Author(s):  
X. Qian ◽  
T. Liu
Keyword(s):  
Fracture Mechanics ◽  
Steel Structures ◽  
Unstable Failure

Application of Fracture Mechanics to Steel Connections in Moment Frames under Seismic Loading

1997 ◽  
Vol 1 (1) ◽  
pp. 23-37 ◽  
Author(s):  
C. Joh ◽  
W.F. Chen
Keyword(s):  
Fracture Mechanics ◽  
Steel Structures ◽  
Northridge Earthquake ◽  
Moment Frames ◽  
Moment Connections ◽  
Related Factors ◽  
Steel Connections ◽  
Moment Connection ◽  
San Fernando ◽  
The Moment

The 6.8 magnitude Northridge earthquake that shook California's San Fernando Valley on January 17 in 1994, did not cause the collapse of any steel structures but connections, confidently designed and constructed in the past with traditional code simplification and common site welding techniques, were discovered not to meet our expectations. This paper reviews connection failures during the 1994 Northridge earthquake and the design philosophy and examines the post-Northridge earthquake experimental and analytical researches. Possible causes of the moment connections damage are categorized into three classes; welding-related factors, design-related factors, and material-related factors. For the analyses, the idealizations of the moment connection considering each factor are studied. From the idealization of the moment connection, the five-plate model is analyzed to investigate the stress concentration and stress state of the connection. The equivalent design crack models are investigated using the fracture mechanics approach.

Applications of Probabilistic Fracture Mechanics to Offshore Structures

1988 ◽  
Vol 41 (2) ◽  
pp. 61-84 ◽  
Author(s):  
Finn Kirkemo
Keyword(s):  
Fracture Mechanics ◽  
Model Updating ◽  
Fatigue Cracks ◽  
Limit State ◽  
Steel Structures ◽  
Local Stress ◽  
Offshore Structures ◽  
And Performance ◽  
Fatigue Limit State ◽  
Life Predictions

For offshore structures the fatigue limit state is governing the structural dimensions of several members and joint connections. Safety against fatigue failure is achieved through a combination of design requirements and performance of in-service inspections with repair of detected fatigue cracks. A review of uncertainties involved in fatigue life predictions by fracture mechanics is presented with particular reference to steel structures. Sources of uncertainties considered are: environmental conditions, hydrodynamic loading, global structural analysis, local stress calculation at fatigue sensitive points, and fatigue crack growth modeling by fracture mechanics. A probabilistic model using the fracture mechanics in probabilistic form is presented. This model accounts for uncertainties in loading, initial and critical defect sizes, material parameters, and in the uncertainty related to computation of the stress intensity factor. Failure probabilities are computed by first-order reliability methods and sensitivity factors are determined. Model updating based on in-service inspection results is formulated. Uncertainties with respect to detecting a crack and to correctly sizing a crack are included. Experience on application of the analysis method is presented.

Bi-Linear Fatigue and Fracture Approach for Safety Analysis of an Offshore Structure

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Parameters ◽  
Limit State ◽  
Steel Structures ◽  
Published Data ◽  
Offshore Structure ◽  
Structure Degradation

The design of welded structures for the fatigue limit state is normally carried out by means of either linear or bilinear S-N curves, which have been found adequate to predict crack initiation only. To properly assess the effects of the design, fabrication, inspection, and repair strategy for structure degradation due to crack growth, fracture mechanics (FM) models need to be applied. In this paper, alternative S-N and FM formulations of fatigue are investigated. The probabilistic fracture mechanics approach predicts the fatigue life of welded steel structures in the presence of cracks under random spectrum loading. It is based on a recently proposed bi-linear relationship to model fatigue crack growth. Uncertainty modeling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bilinear crack growth relationship. Results pertaining to the fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo simulation technique and the emphasis is placed on a comparison between the linear and bilinear crack growth models. Variations in the system configuration, service life, and coefficients of crack growth laws have been studied on the parametric basis

The Fatigue Behavior of Steel Structures under Random Loading

2008 ◽  
Vol 378-379 ◽  
pp. 3-16
Author(s):  
Henning Agerskov
Keyword(s):  
Fracture Mechanics ◽  
Fatigue Test ◽  
Steel Structures ◽  
Fatigue Tests ◽  
Test Series ◽  
Test Results ◽  
Random Loading ◽  
Mechanics Analysis ◽  
Miner’S Rule ◽  
Miner's Rule

Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part of the investigation, fatigue test series with a total of 540 fatigue tests have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel or high-strength steel. The fatigue tests and the fracture mechanics analyses have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude and variable amplitude fatigue test results. Both the fracture mechanics analysis and the fatigue test results indicate that Miner’s rule, which is normally used in the design against fatigue in steel structures, may give results, which are unconservative, and that the validity of the results obtained from Miner’s rule will depend on the distribution of the load history in tension and compression.

The Potential for Non-Conservative Results From the Probabilistic Fracture Mechanics Analyses Is Assessed Based on the Collected Observation of Fatigue Cracks in Offshore Steel Structures

2017 ◽  
Author(s):  
Ole Tom Vårdal
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Lessons Learned ◽  
Probabilistic Methods ◽  
Growth Potential

In structural integrity management, it is essential to know the fatigue crack growth potential. The lessons learned from use of refined fatigue analyses, fracture mechanics and probabilistic methods for platforms in-service are presented. For ageing offshore units of semi-submersible design, the inspection history of more than 20 000 NDT inspections and detection of close to 1000 fatigue cracks, are used in this study. These experience data are used to assess the potential for Non-conservative estimate for the fatigue crack growth potential.

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