Fatigue life is the number of loading cycles that a structure or component sustains before failure occurs. Because fatigue failure can occur at very low stresses with little warning, this mode of failure is often overlooked in the design and the consequences are frequently catastrophic.
Traditionally, fatigue failures have been fixed by overdesign. Not anymore.
SFAT is a fatigue life analysis software for steel structures, components, as well as welded and bolted connections in bridges, cranes, offshore platforms, offshore wind structures, and other structures subjected to cyclic loading. SFAT is a design code compliance software. Fatigue failure involves complex phenomena and mechanism, and the design codes constantly change as researches, practices and experiences evolve. Using SFAT the user can minimize risk of failure from cyclic loading and ensure design code compliance by applying automated fatigue life analysis, making the complicated fatigue life calculations and prediction easy. Increase your design productivity with streamlined workflows to reduce unnecessary repetition of work and effectively eliminate human errors.
Features of SFAT Software
SFAT can handle cyclic loading from as simple as a single stress value, to component stresses of large number of nodes/elements in large number of loading steps generated by ANSYS, with the computer hardware limit being the ceiling. Stress history files generated by other FEA packages can also be imported and processed. Data input can be generated by manual entry, by importing ANSYS .rst files, or by importing stress history files. The loading can be of constant amplitude or variable amplitude, proportional or non-proportional. For non-proportional loading conditions, the program scans for critical plane that generates the highest fatigue damage ratio.
SFAT calculates fatigue damage ratios for each loading cycle, sums cumulative damage ratios using Miner’s Rule, and counts the number of loading cycles using rainflow counting algorithm following ASTM 1049 procedure. In addition to reporting calculations, the graphical charts of stress range time history, stress range histogram and fatigue damage ratios are also generated.
Modules of SFAT Software
SFAT consists of different modules for different design codes, including the following:
- ANSI/AISC 360, Specification for Structural Steel Buildings.
- ASME BTH-1, Design of Below-the-Hook Lifting Devices.
- EN 1993-1-9, Design of steel structures – Part 1-9: Fatigue.
- DNVGL-RP-C203, Fatigue design of offshore steel structures.
- API-2A-WSD, API Recommended Practice 2A-WSD: Planning, Designing, and Constructing Fixed Offshore Platforms — Working Stress Design.
- ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures.
ANSI/AISC 360, Specification for Structural Steel Buildings
This design code covers industrial building sector with highly cyclic live loading, such as bridge cranes, crane runways, monorails, lifting beams, lifting lugs (lifting eyes), manufacturing equipment, etc. AISC 360 also covers highway bridges, railway bridges and pedestrian bridges in transportation sector.
AISC 360 deals with steel members, welded components, bolts and threaded parts.
ASME BTH-1, Design of Below-the-Hook Lifting Devices
ASME BTH-1 deals with steel members, welded components, bolts and threaded parts of below-the-hook lifting devices, such as lifting beams, spreader beams, lifting lugs (lifting eyes), hooks, slings and rigging hardware, etc.
EN 1993-1-9, Design of steel structures – Part 1-9: Fatigue
EN 1993-1-9 gives methods for the assessment of fatigue resistance of members, connections and joints subjected to fatigue loading. These methods are derived from fatigue tests with large scale specimens, that include effects of geometrical and structural imperfections from material production and execution. Fatigue strengths are determined by considering the structural detail together with its metallurgical and geometric notch effects. In the fatigue details presented in this design code the probable site of crack initiation is also indicated. The assessment methods presented in this code use fatigue resistance in terms of fatigue strength curves for (1) standard details applicable to nominal stresses; (2) reference weld configurations applicable to geometric stresses.
DNVGL-RP-C203, Fatigue design of offshore steel structures
This recommended practice presents recommendations in relation to fatigue analysis based on fatigue tests (S-N data) and fracture mechanics. DNVGL-RP-C203 is valid for carbon manganese steel (C-Mn) in air with yield strength less than 960 MPa. For carbon and low alloy machined forgings for subsea applications, the S-N curves are valid for steels with tensile strength up to 862 MPa in air environment. For steel (C-Mn) materials in seawater with cathodic protection or steel with free corrosion, the recommended practice is valid up to 690 MPa. This limit applies also to the carbon and low alloy machined forgings for subsea applications. This recommended practice is also valid for bolts in air environment or with protection corresponding to that condition of grades up to 10.9, ASTM A490 or equivalent. This recommended practice may be used for stainless steel.
API-2A-WSD, API Recommended Practice 2A-WSD: Planning, Designing, and Constructing Fixed Offshore Platforms — Working Stress Design
This recommended practice is based on global industry best practices and serves as a guide for those who are concerned with the design and construction of new fixed offshore platforms and for the relocation of existing platforms used for the drilling, development, production, and storage of hydrocarbons in offshore areas.
Nontubular members and connections in deck structures, appurtenances and equipment; and tubular members and attachments to them, including ring stiffeners, may be subject to variations of stress due to environmental loads or operational loads. Where variations of stress are applied to conventional weld details, the associated S-N curves provided in AWS D1.1 are used. For service conditions where details may be exposed to random variable loads, seawater corrosion, or submerged service with effective cathodic protection, the fatigue life reduction factors are applied accordingly.
For tubular connections, this recommended practice provides S-N curves for welded joints (WJ) and cast joints (CJ) in air environment, seawater with cathodic protection, and seawater free corrosion conditions.
ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
This International Standard specifies requirements and provides recommendations applicable to the following types of fixed steel offshore structures for the petroleum and natural gas industries:
- caissons, free-standing and braced;
In addition, it is applicable to compliant bottom founded structures, steel gravity structures, jack-ups, other bottom founded structures and other structures related to offshore structures (such as underwater oil storage tanks, bridges and connecting structures), to the extent to which its requirements are relevant.
ISO 19902 provides S-N curves for tubular joints (TJ), cast joints (CJ) and other joints (OJ) in air environment, seawater with cathodic protection, and seawater free corrosion conditions.
User Interface of SFAT Software
The user interface and workflow of SFAT is straightforward. SFAT is by far the most intuitive and easy-to-use fatigue life analysis software for structural engineers and stress analysts.
Screen Shot of SFAT Interface
Screen Shots of SFAT Results