FATIGUE OF HYDRAULIC STEEL STRUCTURES: BACKGROUNDS AND OBJECTIVES OF PIANC WG-189, presentation on online PIANC UK - ICE Seminar, London March 29, 2021 (original) (raw)

Control of Fatigue in Hydraulic Steel Structures

IABSE Symposium, Prague 2022: Challenges for Existing and Oncoming Structures

Hydraulic Structures, like lock gates, movable river weirs, tide and flood barriers, are subject to varying loads that may lead to fatigue damage. These loads are primarily generated by differential water heads, but also by waves, gate drive forces, vibrations in flow and other actions. The existing guidelines in the field of fatigue did not sufficiently cover the specific operation conditions and demands that apply to hydraulic structures. An improvement in this matter was the investigation report by a Working Group of PIANC, the International Association for Waterborne Infrastructure. The intention of this paper is to describe the practices followed by designers, constructors and maintenance crews of hydraulic structures with respect to fatigue control; and to evaluate the applicability of existing codes and regulations in this regard. The discussed subject constitutes a challenge for both existing and prospective hydraulic steel structures.

Fitness-for-Purpose Evaluation of Hydraulic Steel Structures

Hydraulic structures such as locks, spillway gates, and maintenance closure structures may have fabrication defects and flaws that can be large enough to threaten the integrity of the structure. In addition, some defects that are not allowed based on stringent specifications are not at all harmful to the structure. "Fitness-for-purpose" evaluation is a method for determining a factor of safety against fracture and the risk of collapse in existing structures. This report discusses the different types of hydraulic steel structures, typical fatigue cracks that could exist in such structures and details that could lead to brittle fracture. Using steps developed by the British Standards Institute, the report describes a fitness-for-purpose evaluation procedure for hydraulic control structures under Mode I loading, including how large a crack-like discontinuity would have to be before it could lead to fracture in a typical steel member. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

Fatigue Life Prediction Of The Marine Steel Gates

WIT Transactions on the Built Environment, 1970

The maritime structures are subjected to the effects of nonbreaking, breaking and broken waves. Quaywalls are designed by the hydrostatic pressures and dynamical forces of the wave motions; and Morison's forces to the legs are also taken into account if their combinations cause greater stresses. Members and fasteners of the quaywalls in harbour which are subjected to repeated variations and reversals of stresses shall be designed so that the maximum stress does not exceed the given allowable stresses, and the actual range of stress does not exceed the allowable fatigue stress range. The main objective of the paper is to present a procedure to calculate effective stress range for quaywall members under variable-amplitude randomsequence stress spectrums and to give analytical method for predicting fatigue life under variable amplitude stress spectrums from constant amplitude fatigue stress.

Background for New Revision of DNV-RP-C203 Fatigue Design of Offshore Steel Structures

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 6, 2010

A type of loading causing a regular stress fluctuation with constant magnitudes of stress maxima and minima. Crack propagation rate: Amount of crack propagation during one stress cycle. Crack propagation threshold: Limiting value of stress intensity factor range below which the stress cycles are considered to be non-damaging. Eccentricity: Misalignment of plates at welded connections measured transverse to the plates. Effective notch stress: Notch stress calculated for a notch with a certain effective notch radius. Fatigue deterioration of a component caused by crack initiation and/or by the growth of cracks. Fatigue action: Load effect causing fatigue. Fatigue damage ratio: Ratio of fatigue damage at considered number of cycles and the corresponding fatigue life at constant amplitude loading. Fatigue life: Number of stress cycles at a particular magnitude required to cause fatigue failure of the component. Fatigue limit: Fatigue strength under constant amplitude loading corresponding to a high number of cycles large enough to be considered as infinite by a design code. Fatigue resistance: Structural detail's resistance against fatigue actions in terms of S-N curve or crack propagation properties. Fatigue strength: Magnitude of stress range leading to particular fatigue life. Fracture mechanics: A branch of mechanics dealing with the behaviour and strength of components containing cracks. Design Fatigue Factor: Factor on fatigue life to be used for design. Geometric stress: See "hot spot stress". Hot spot: A point in structure where a fatigue crack may initiate due to the combined effect of structural stress fluctuation and the weld geometry or a similar notch. Hot spot stress: The value of structural stress on the surface at the hot spot (also known as geometric stress or structural stress). Local nominal stress: Nominal stress including macro-geometric effects, concentrated load effects and misalignments, disregarding the stress raising effects of the welded joint itself. Local notch: A notch such as the local geometry of the weld toe, including the toe radius and the angle between the base plate surface and weld reinforcement. The local notch does not alter the structural stress but generates non-linear stress peaks. Macro-geometric discontinuity: A global discontinuity, the effect of which is usually not taken into account in the collection of standard structural details, such as large opening, a curved part in a beam, a bend in flange not supported by diaphragms or stiffeners, discontinuities in pressure containing shells, eccentricity in lap joints. Macro-geometric effect: A stress raising effect due to macro-geometry in the vicinity of the welded joint, but not due to the welded joint itself. Membrane stress: Average normal stress across the thickness of a plate or shell. Miner sum: Summation of individual fatigue damage ratios caused by each stress cycle or stress range block according to Palmgren-Miner rule. Misalignment: Axial and angular misalignments caused either by detail design or by fabrication. Nominal stress: A stress in a component, resolved, using general theories such as beam theory. Nonlinear stress peak: The stress component of a notch stress which exceeds the linearly distributed structural stress at a local notch. Notch stress: Total stress at the root of a notch taking into account the stress concentration caused by the local notch. Thus the notch stress consists of the sum of structural stress and non-linear stress peak. Notch stress concentration factor: The ratio of notch stress to structural stress. Paris' law: An experimentally determined relation between crack growth rate and stress intensity factor range. Palmgren-Miner rule: Fatigue failure is expected when the Miner sum reaches unity. Reference is also made to Chapter 9 on uncertainties). Rainflow counting: A standardised procedure for stress range counting.

The effects of fatigue on steel structures

ABSTRACT Fatigue cracks created under repetitive loads are one of the major threats to the structure of steel structures. Overall monitoring is a common method for detecting fatigue cracks but lacks reliability due to its time consuming. Fatigue phenomena in structures are of crucial importance that must be taken into account. Barrier systems that are widely used in structures include: rigid frames, braced frames, framed tubing. One of the effects these factors may have is structural fatigue. Fatigue is usually associated with germination, cracking at the surface of the stress concentration region or areas of propagation in the stress area. Fracture occurs before the material reaches its ultimate resistance, which is known as fatigue failure. Fatigue failure usually occurs in a crisp and sudden type of failure. The purpose of this study is to investigate the effects of fatigue on steel structures that damage many of the urban infrastructure due to the significant loads being widely applied to the structures, so controlling this phenomenon is very important in the design of structures. Keywords: Fatigue estimation, fatigue life, steel structures, fatigue effects.

Fatigue Capacity of Steel Cylindrical Bodies and Conduits Subjected to Cyclic Pressure

Volume 5: High-Pressure Technology; ASME NDE Division; 22nd Scavuzzo Student Paper Symposium and Competition, 2014

This paper presents a code review (API 17G, ASME VIII Div 2 and ASME VIII Div 3) for addressing the fatigue capacity of steel cylindrical bodies and conduits subjected to cyclic pressure only. The fatigue capacity for pipes with a yield strength of 75ksi and 90ksi and with rated working pressures (RWP) ranging from 5ksi to 30ksi have been considered using both the S-N approach and the fracture mechanic approach. The S-N based fatigue lives from API 17G are found to be much longer than the corresponding S-N based fatigue lives from ASME VIII Div 2 and Div 3 and by the fracture mechanic (FM) approach as required in ASME VIII Div 3 for vessels where a leak-before-break condition can not be demonstrated. The S-N predicted fatigue lives are found to decrease with increasing RWP while the FM based fatigue lives are found to be rather independent of the RWP. The S-N based fatigue lives from ASME VIII Div 2 and Div 3 for free corrosion conditions are found to be shorter than the correspondi...

(1994) A Unified Approach for the Design of Steel Structures under Low and/or High Cycle Fatigue

1994

ABS TRACT In this paper, a method is presented trying to unify both design and damage assessment methods for high and low cycle fatigue. In particular it is shown that, by interpreting the stress range A0 as the ideal stress range associated to the real strain range As in an ideal perfectly elastic material, high and low cycle fatigue test data can be interpreted by the same Wohler (S—N) lines usually given in recommendations for (high cycle) fatigue design of steel structures. Furthermore, local buckling can be regarded as a notch eflect, an eflect which is intrinsic to the various shapes, because it is strictly correlated to their geometrical properties (in particular of the slenderness ratios b/t and h/tw of the flanges and the web). It is also shown that, in the case of variable amplitude loading histories reprocessed by the rainflow cycle counting method, a linear damage cumulation rule together with the previously defined S—N curves (a procedure usually adopted in high cycle fatigue) can lead to a reliable collapse criterium for low cycle fatigue also.

Fatigue Evaluation of Offshore Steel Structures Considering Stress Concentration Factor

https://www.ijrrjournal.com/IJRR\_Vol.8\_Issue.10\_Oct2021/IJRR-Abstract041.html, 2021

The installation of offshore structures and facilities in the marine environment, usually for the production and transmission of oil, gas exploration, electricity, and other natural resources is referred to as offshore construction. Since offshore structures are subjected to changing threats to the environment year-round. Fatigue behavior prediction noticed on these structures should be considered during the design stage. Fatigue is one of the failure mechanisms of offshore steel structures, and it must be investigated properly during system design. The fatigue analysis of offshore structures under drag wave force, total wave force, total moment about the sea bed, and other variables are reviewed thoroughly. The structure's dynamic response becomes a critical aspect in the whole design process. The fatigue analysis was carried out using MATLAB software, material properties of the offshore structure, and wave spectrum characteristics in this study. This study shows the JONSWAP spectrum and stress concentration analysis prediction. The offshore support structure that is predicted during the design phase will help to keep the stress concentration factor below the fatigue threshold and anticipate safe life design, according to the results of the fatigue study. The fatigue performances of tripod and jacket steel support structures in intermediate waters depth are compared in this project (20-50 m). The North Atlantic Ocean is used as a reference site, with a sea depth of 45 meters. The tripod and jacket support structures will be designed by using current industry standards.

A Fatigue Analysis of a Hydraulic Francis Turbine Runner

World Journal of Mechanics, 2012

In this work, the estimation of crack initiation life of a hydraulic Francis turbine runner is presented. The life prediction is based on the local strain approach to predict the initiation life. First, the analysis is carried out in air and in water condition and the runner's natural frequencies were calculated using the finite element (FE) method. The analysis in air is compared with experimental analysis in order to have a representative model of real runner and subsequently the numerical analysis was perform in water. In the case of the runner immersed in water, the added mass effect due to the fluid structure interaction (FSI) is considered. Second, the static and dynamic stresses were calculated according to life estimation. For the calculation of static stresses, the pressure distribution of water and the centrifugal forces were applied to the runner. The dynamic stresses were estimated for interactions between the guide vane and the runner. Lastly, the estimation of the crack initiation life of the runner was obtained.

007 High-Cycle Fatigue in a Hydraulic Turbine Runner

Cp2012, 2013

A hydraulic turbine is an equipment where hot-formed blades are welded to band and crown by double-fillet welds. Decades of operating experience have shown that fatigue cracks develop in hydraulic turbine runners where both stress concentrations and material defects can be observed, as often occurs in the welded zones of such runners. In the present paper, a welded joint between the blade and the band or crown of a Francis turbine runner is considered, and the failure mechanism due to high-cycle fatigue loading produced by operational starts and stops is analysed. Such a welded joint can be idealised as a T-joint with a circular-shaped transition zone between blade and band (or crown), subjected to cyclic bending induced by the water action. A semielliptical surface crack is assumed to exist in the above transition zone, and the crack propagation is numerically examined by using the stress-intensity factor values obtained from finite element analyses. Experimental fatigue testing results are employed to substantiate these numerical estimations.