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Design structures to stand the test of time

While offshore structures are typically designed to last around 20 years, many factors contribute to their actual lifetime. On one hand, time degradation, environmental and accidental loads may reduce structural integrity and the asset's service time. On the other, structural modifications and modern re-qualification methodologies can extend the operational life beyond the original design. For both scenarios, Sesam’s Usfos has you covered.

Sesam - Usfos - Ranhill Worley

One of the best structural software in the market, coupled with good technical support from DNV and training plan to suit our requirement.

  • Zahari A Razak ,
  • HOD Civil/Structural ,
  • Ranhill Worley (Malaysia)


Life extension: see that your offshore asset operates safely beyond design life

Assess older structures for reserve strength and design modifications to extend life safely. Identify the fatigue for the remaining life estimation using modern approaches, and develop a safe operational strategy.

Accident analyses: demonstrate that your offshore asset can operate safely through extreme scenarios

Predict progressive collapse behavior and run accident analyses of space-frame structures - jackets in intact and damaged conditions, for example. Usfos covers extreme and accidental scenarios such as earthquakes, explosions, fires, ship collisions, and dropped objects. 

Be Ready for the Unexpected

Calculate the risk for your existing offshore structures, and find out how risks can impact your structure such as: 


Sesam's Usfos employs single-degree-of-freedom (SDOF) analysis to simulate the response of offshore structures to earthquake loads. This method models the dynamic response by subjecting a simplified SDOF system to historical earthquake data. The maximum responses, including acceleration, velocity, and displacement, are recorded and used to assess the structure’s behavior under seismic conditions. USFOS allows for repeated analyses with varying natural periods to capture the range of vibration modes excited by earthquakes, providing a comprehensive understanding of the structure's resilience to seismic events.


Usfos uses a method that focuses on the dominant mode of response to analyze the effects of explosions on offshore structures. This involves modeling the explosion pressure's temporal variation and adjusting the magnitude and duration of the pressure. The analysis assumes that the structural response is dominated by a single mode, combining elastic and plastic deformation. This approach helps in understanding how structures behave under explosion loads and ensures that they can withstand such extreme conditions without catastrophic failure.


Sesam's Usfos addresses accidental fires through comprehensive analysis of different fire scenarios, such as pool fires, fireballs, and jet fires. The design philosophy incorporates performance criteria to ensure functional requirements are met during fire incidents. Fire process analysis involves studying heat transfer via conduction, convection, and radiation. The approach ensures that structures maintain their integrity for sufficient time to allow for safe evacuation and rescue. Advanced numerical methods and information from recent research are utilized to accurately model and assess the impact of fires on offshore structures.

Ship Collisions 

A ship could collide with the offshore structures (i.e. bridges, rigs, windmills, etc.) causing damage to the base, which could cause the structure to collapse. Usfos is utilized to simulate ship collisions with offshore platforms, focusing on the dynamic response and structural integrity under impact. The analysis models the ship as a mass connected through a nonlinear spring, representing the collision force. This approach helps in understanding the energy absorption and deformation characteristics of both the ship and the platform. Case studies include impacts on jack-up rigs and jackets, evaluating different scenarios such as beam and bow impacts. The method incorporates local buckling, nonlinear joint behavior, and potential fractures to provide comprehensive collision response analysis.

Dropped Objects

Sesam's Usfos analyzes the impact of dropped objects on offshore structures by modeling the dynamic response and potential damage. The analysis incorporates the weight, drop height, and velocity of the object to simulate the impact forces and resultant structural deformations. Nonlinear finite element methods are employed to accurately predict local buckling, plastic deformation, and potential fractures. This comprehensive approach ensures that the structural integrity is maintained, or appropriate reinforcements are designed to mitigate the risk of failure due to accidental drops.

With Usfos, you perform 

  • Non-linear analysis on subsea template during installation 
  • Wave-in deck analysis on jackets 
  • Progressive collapse analysis of jacket structures with pile-soil interaction 
  • Redundancy analysis of jacket structures 
  • Contact analysis 
  • Ship impact analysis 
  • Blast and fire analysis 
  • Time domain earthquake analysis 
  • Re-assessment of as-built / modified structural design / re-design




Get it done, hassle-free  

  • Simplify complex analyses: with built-in formulations, Usfos is the only expert in non-linear beam behavior you'll need 
  • Easy to use and easy to verify: set up the analysis in Sesam and visualize the results in a 3D design-oriented, graphical user interface 
  • Skip tedious work: go straight into non-linear analysis using models built in Sesam, or converted from third-party software into Sesam 
  • Combine powerful tools: save time using the time domain temperature loads from KFX when performing non-linear fire analysis 
  • Lower costs: non-linear theories provide a clear picture of structural resistance and residual strength of structures. This enables savings in areas such as inspection planning, life extension, reassessment of ageing structures, boat impact, accidents and fire protection assessments 
  • Optimize new design of OWT and Oil & Gas assets: plastic limit state design allows taking advantage of reserve capacity in the structure 

Offshore structures are engineered constructions located in marine environments, primarily used for various purposes such as oil and gas extraction, wind energy production, and scientific research. These structures are designed to withstand harsh oceanic conditions including waves, wind, and currents. Some of the well-known structures include offshore platforms, wind turbine structures, ships and oil rigs.

Yes, Sesam Usfos can be employed to assess the risk of bridge collapse. By analyzing structural behavior under extreme scenarios, it predicts progressive collapse and evaluates reserve strength. Its non-linear analysis capabilities provide insights into structural resistance and reserve strength of existing structures.

Yes, Sesam's Usfos can be used for risk assessment of oil rigs. It provides nonlinear structural analysis, crucial for understanding how oil rigs respond to extreme loading conditions. Sesam's Usfos simulates progressive collapse, accidental impacts, and fatigue, which helps assess the risk of partial or total failure. It also models extreme environmental conditions like wind, waves, and currents. By identifying critical failure points, Sesam's Usfos aids in planning cost-effective risk mitigation strategies, ensuring the safety and reliability of offshore oil rigs through detailed simulations and comprehensive analysis.

Customers can import their bridge design drawings, data, and analysis results into Sesam using Sesam GeniE, the structural modeler. Various CAD formats are supported, including Intergraph PDS (SDNF File), CadCentre PDMS (SDNF File), and DXF File. This capability ensures that bridge designs from different software can be seamlessly integrated into Sesam for further analysis.

Sesam supports the analysis of different bridge types. Once the structural components are imported, users can perform static, dynamic, and non-linear analysis to check the integrity and performance of the bridge designs, ensuring comprehensive evaluation and reliability.

Every risk calculation is different and cannot account for all factors. Talk to a DNV subject matter expert to learn more.

What can Sesam's Usfos do for your company?

Contact us