Analysis of Cracks and Stresses of Welded Attachments on Full-Scale Plate Girder under Fatigue Loading

2006 ◽  
Vol 324-325 ◽  
pp. 459-462 ◽  
Author(s):  
Myung Gu Lee ◽  
Seung Yong Lee ◽  
Cheol Woo Park
Keyword(s):  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Steel Structure ◽  
Fatigue Loading ◽  
Design Criterion ◽  
Full Scale ◽  
Parent Metal ◽  
Girder Bridges ◽  
Fatigue Design ◽  
Plate Girder

In steel structure systems such as plate girder bridges and framed structures, fatigue damage used to occur at welded areas rather than primary structural members. These damages and behaviors of the welded attachments need to be extensively investigated so that the fatigue design criterion can effectively control the fatigue damage of steel structure systems. This study utilized a full-scale plate girder on which various welding attachments were mounted. The welded attachments investigated herein included flange gussets, web gussets, vertical stiffeners, and cover plates. The fatigue cracks initiated at the longitudinal end of joint area of the weld bead and the parent metal where stress was significantly concentrated. The initiated fatigue cracks developed along the weld path and then, propagated to the parent metal in the direction perpendicular to the principal stress. The fatigue cracks developed even under a compressive stress when a significant residual stress was experienced from the welding. The fatigue strengths of the each welded attachment were evaluated and compared with the current fatigue design specifications in AASHTO [1] and JSSC [2].

Fatigue Testing of Full Scale Girth Welded Pipes Under Variable Amplitude Loading

2012 ◽  
Author(s):  
Y.-H. Zhang ◽  
S. J. Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Loading Spectrum

In the fatigue design of steel catenary risers there are concerns regarding the fatigue damage to girth welds from low stresses, below the constant amplitude fatigue limit, in the loading spectrum and the validity of Miner’s cumulative damage rule. In both cases there is increasing evidence that current design methods can be non-conservative. These fundamental issues were addressed in a recent JIP. A key feature was development of the resonance fatigue testing rigs to enable them to test full-scale pipes under variable amplitude loading. Such tests were performed under a loading spectrum representative of that experienced by some risers, with many tests lasting over 100 million cycles to investigate the fatigue damage due to small stresses as well as the validity of Miner’s rule. However, the resonance rigs are only capable of producing spectrum loading by gradually increasing or decreasing the applied load, whereas more ‘spiky’ random load sequences may be relevant in practice. Therefore the programme also included fatigue tests in conventional testing machines on strip specimens cut from pipes to compare the two types of loading sequence. This paper presents the results of these tests, conclusions drawn and recommendations for changes to current fatigue design guidance for girth welded pipes regarding the definition of the fatigue limit, allowance for the damaging effect of low stresses and the validity of Miner’s rule.

Fatigue Performance of Grade R4 and R5 Mooring Chains in Seawater

2014 ◽  
Author(s):  
Jonathan Fernández ◽  
Walther Storesund ◽  
Jesús Navas
Keyword(s):  
Fatigue Test ◽  
Fatigue Damage ◽  
Fatigue Tests ◽  
Design Methods ◽  
Full Scale ◽  
Fatigue Performance ◽  
Test Program ◽  
Gas Industry ◽  
Fatigue Design ◽  
Cumulative Fatigue Damage

With more than 50.000 tons in service to date, the Oil&Gas Industry has the need to understand the tension fatigue performance of grade R5 chains in straight tension, and corroborate the validity of the existing design methods. The chain fatigue design curves in API and DNV are based on fatigue tests obtained in the nineties and early two thousands. However the tests were performed on lower grades such as ORQ, R3 and R4, and small chains, 76 mm diameter being the largest studless chain tested. The industry has moved towards the use of large studless chains, especially in permanent units, where chain diameters above 150 mm are not unusual. This paper gathers information from a full scale fatigue test program on grade R4 and R5 studless chains, performed in seawater and with diameters between 70 mm and 171 mm. The chains being tested are actual production chains supplied for different drilling units and large permanently moored production floating units. The paper analyses the data and determines tension-tension fatigue curves based on API and DNV methods for computation of cumulative fatigue damage, regardless of other damaging mechanisms. Improved fatigue capacity is obtained with respect to the above recommended design methods.

A Fatigue Design for Large Container Ship Taking Long-Term Environmental Condition Into Account

2011 ◽  
Author(s):  
Masayoshi Oka ◽  
Yoshitaka Ogawa ◽  
Ken Takagi
Keyword(s):  
Fatigue Damage ◽  
Element Model ◽  
Full Scale ◽  
Elastic Model ◽  
Direct Computation ◽  
Wave Condition ◽  
Irregular Wave ◽  
Fatigue Design ◽  
Tank Test

In order to promote the reliable evaluation for the fatigue strength of ships, the validation of a direct load and strength computation was performed based on the tank test and the full scale measurement. The fatigue damage in short term sea state under various operation parameters was indicated quantitatively by the tank test in irregular wave utilizing the elastic model. The long term fatigue damage was evaluated based on the full scale measurement [1]. The fatigue damage inferred from the measured stress on deck structure is quite small compared with the direct computation utilizing a full ship finite element model. That is mainly caused by the difference of environmental wave condition. Moreover, the effect of operational condition through whole life was indicated by the direct computation quantitatively. To make more rational fatigue design, it is important to take the long-term wave condition into account.

Fatigue Testing of Full Scale Girth Welded Pipes Under Variable Amplitude Loading

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Y.-H. Zhang ◽  
S. J. Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Loading Spectrum

In the fatigue design of steel catenary risers, there are concerns regarding the fatigue damage to girth welds from low stresses, below the constant amplitude fatigue limit, in the loading spectrum and the validity of Miner's cumulative damage rule. These fundamental issues were addressed in a recent joint-industrial project (JIP). A key feature was development of the resonance fatigue testing rigs to enable them to test full-scale pipes under variable amplitude loading. Such tests were performed under a loading spectrum representative of that experienced by some risers, with many tests lasting over 100 million cycles to investigate the fatigue damage due to small stresses as well as the validity of Miner's rule. However, the resonance rigs are only capable of producing spectrum loading by gradually increasing or decreasing the applied load whereas more “spiky” random load sequences may be relevant in practice. Therefore, the program also included fatigue tests in conventional testing machines on strip specimens cut from pipes to compare the two types of loading sequence. This paper presents the results of these tests, conclusions drawn, and recommendations for changes to current fatigue design guidance for girth welded pipes regarding the definition of the fatigue limit, allowance for the damaging effect of low stresses, and the validity of Miner's rule.

Deepwater Rigid Spools Slugging Flow Fatigue Design

2010 ◽  
Author(s):  
Tao Zhao ◽  
Philip Cooper ◽  
Joost Brugmans
Keyword(s):  
Fatigue Damage ◽  
Design Criterion ◽  
Resonance Effects ◽  
Simulation Tools ◽  
Fatigue Design ◽  
Detailed Simulation ◽  
Design Software ◽  
Flow Effects ◽  
Nonlinear Normal ◽  
Rainflow Counting

Tie-in spools form an important part of any deepwater flowline system. Successful designs have the potential to deliver significant savings in fabrication, transportation and installation costs, whilst protecting project schedules. For multiphase flowlines, slug-induced fatigue damage has emerged as a governing design criterion in recent projects. Spans have become the focus of attention for slug-induced fatigue damage. These may occur at tie-in spools used to connect flowlines in deepwater developments. Conventional piping design software tools are commonly used for rigid spools design. Limitations/disadvantages of conventional tools were identified by comparison with detailed simulation of critical aspects of the design using more advanced numerical simulation tools. Rigorous 3D numerical dynamic analysis was used to simulate gravity variation of the slugs and bubbles, and the dynamic impact effect due to the passage of slugs through bends. Resonance effects of spools exposed to slugging flow were inspected and the cause of spools resonance was investigated. The consequential fatigue damage was computed using a time-domain FEA and rainflow counting algorithm. While conducting slugging flow fatigue FEA, bespoke pipe-soil interaction models were developed to simulate cyclic lateral and vertical resistances of the very soft seabed soils typically found in deepwater fields. A contact technique with nonlinear normal and decoupled bi-axial tangential interactions was implemented using FORTRAN subroutines. The analysis procedures developed are outlined, and typical spool designs are presented. The paper seeks to understand the slugging flow effects to the deepwater spools fatigue design, fatigue design, especially while the spools resonance can not be mitigated, and provide the optimised spool configuration in which the slugging effects are minimised, taking due account of the complexities outlined above.

scholarly journals Fatigue durability of asphalt-cement mixtures

2015 ◽  
Vol 63 (1) ◽  
pp. 107-111 ◽  
Author(s):  
J. Kuźniewski ◽  
Ł. Skotnicki ◽  
A. Szydło
Keyword(s):  
Fatigue Damage ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Design Criterion ◽  
Asphalt Cement ◽  
Road Pavement ◽  
Fatigue Design ◽  
Fatigue Durability ◽  
Fatigue Design Criterion ◽  
Cement Mixtures

Abstract This paper focuses on examinations of asphalt-cement mixtures (ACM). This is a recycled material which can be used in road pavement layers. In the article stiffness modulus tests and fatigue tests of asphalt-cement mixtures were shown. The authors decided to lead research on fatigue durability of asphalt-cement mixtures to set fatigue characteristics of these materials. So far in research or other works any adequate fatigue criterion for ACM mixtures has not been developed. As a result of the examinations a level of fatigue damage was suggested. For new fatigue damage a strain level in one million load cycle was estimated. Based on that a fatigue design criterion for asphalt-cement mixtures was estimated.

Development of Fatigue Testing of Full-Scale Girth Welded Pipes Under Variable Amplitude Loading

2011 ◽  
Author(s):  
Yan-Hui Zhang ◽  
Stephen Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Cumulative Damage ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Testing Procedures ◽  
Fatigue Design ◽  
Damage Rule

In service the great majority of structures and components are subjected to stresses of variable amplitude (VA). The fatigue design of welded joints in such structures is based on fatigue data obtained under constant amplitude loading, used in conjunction with a cumulative damage rule to estimate the damage introduced by cycles of varying magnitude in the service stress history. There are two major concerns with fatigue design of deepwater steel catenary risers (SCRs): the validity of cumulative damage rule and the damaging effect of stresses below the constant amplitude fatigue limit (CAFL). It is known that SCRs can experience very high numbers of low stress cycles due to vortex induced vibration (VIV) with the result that the choice of method for accounting for the fatigue damage due to stresses below the constant amplitude fatigue limit can be highly significant in terms of the estimated fatigue life. These two fundamental issues have been addressed in a recent group sponsored project. By successfully establishing a loading spectrum representative of that experienced by risers and developing the testing procedures for VA loading using the resonance testing rigs, the fatigue performance of full-scale girth welded pipes under VA loading were investigated. These loading spectra had the same peak/maximum stress histograms but different minimum stresses. Many tests lasted over 108 cycles to investigate the fatigue damage of small stresses in these spectra. This paper describes the development of the method by which fatigue testing of full-scale girth welded pipes under VA loading had been successfully performed.

Fatigue Variation in Ships due to the Variability of Environmental Loads

2012 ◽  
Author(s):  
Wengang Mao ◽  
Zhiyuan Li ◽  
Jonas W. Ringsberg ◽  
Igor Rychlik
Keyword(s):  
Fatigue Damage ◽  
Structural Integrity ◽  
Structural Strength ◽  
Fatigue Cracks ◽  
Maritime Industry ◽  
Fatigue Design ◽  
Routing Design ◽  
Potential Use

The design and analysis of structural strength against fatigue failure always includes large uncertainties. It is crucial to understand and identify the most important uncertainties that affect the performance, functionality and service life of an engineering structure — in particular when it comes to the safety aspect, which may involve the risk of loss of human lives. In maritime industry, it is known that due to various sources of uncertainties in ship fatigue design, some ships may survive (the occurrence of fatigue cracks which may endanger the structural integrity) much longer than their designed life, while other ships develop fatigue cracks far too early. The current investigation presents some of the most important uncertainties and their effects on the accuracy of fatigue assessments in a container vessel. The study emphasizes the analysis of the fatigue damage variation when the ship is sailing on different routings between two ports. A fatigue model developed by the authors for ship fatigue routing application is employed to estimate the long term fatigue damage. In this model, only a few parameters, i.e. the encountered significant wave height and operational profiles, are needed. The procedure of using this model for a ship fatigue routing design is described in detail. Its potential use and benefits are demonstrated in a case study by a 2,800 TEU container ship using both full-scale measurements and hindcast wave data. It is shown that awareness and careful fatigue routing design can reduce fatigue damage significantly by up to 50%!

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