Linear elastic design checks tell you whether a structure meets the code at working loads. They do not tell you how much reserve strength it has, how it would fail, or whether a damaged or ageing asset can safely remain in service. BH&C Dynamics® uses advanced nonlinear finite element analysis to answer these questions. We model geometric and material nonlinearity, contact and soil–structure interaction explicitly, so decisions are based on a realistic picture of capacity rather than on conservative assumptions.

When nonlinear analysis adds value

• Life extension and reassessment of existing assets – structures that fail linear code checks often have significant reserve strength. Demonstrating it can avoid or defer costly strengthening.
• Accidental and extreme events – ship collision, dropped objects, explosion, fire, earthquake and extreme storms involve large deformations and yielding by nature.
• Damaged or modified structures – we quantify the effect of dents, corrosion, cracks, missing members or added topsides weight on overall capacity.
• Optimised new design – nonlinear analysis can justify lighter, more economical solutions where conventional methods are overly conservative.
• Stability-critical components – shells, plated structures and slender members where buckling, imperfections and post-buckling behaviour govern.

ULTIMATE STRENGTH AND PUSHOVER ANALYSIS
Incremental collapse analysis of jackets, monopiles, topsides and building frames, giving the reserve strength ratio (RSR), the failure mechanism and the residual strength of damaged structures.

SEISMIC ANALYSIS

• Ductility-level (abnormal level) earthquake assessment
• Nonlinear time-history analysis using recorded or spectrum-matched ground motions
• Performance-based seismic evaluation

BUCKLING AND STABILITY

• Linear eigenvalue buckling to identify critical modes
• Geometrically and materially nonlinear analysis with imperfections (GMNIA) for shells, stiffened panels, cans and cones
• Local–global interaction and post-buckling capacity

SOIL–STRUCTURE INTERACTION

• Nonlinear pile–soil springs (p-y, t-z, Q-z) and continuum soil models
• Pile group effects and cyclic degradation
• Foundation capacity for offshore wind monopiles, jackets and suction buckets

DETAILED COMPONENT AND CONNECTION ANALYSIS

• Tubular joints, grouted connections, clamps and repairs
• Stress concentration factors and hot-spot stresses for fatigue
• Plasticity, contact and bolt pretension in bolted and flanged connections

NONLINEAR DYNAMICS

• Implicit and explicit time-domain analysis
• Impact, vibration and transient response
• Dynamic amplification and coupled structure–equipment response

NONLINEAR DYNAMICS

• Implicit and explicit time-domain analysis
• Impact, vibration and transient response
• Dynamic amplification and coupled structure–equipment response

Industries we serve

• Offshore oil & gas – fixed steel platforms, topsides, risers and subsea structures: reassessment for life extension, ALS studies and damage assessment.
• Offshore wind – monopiles, jackets, transition pieces and offshore substations: design optimisation, ULS/ALS verification and foundation interaction.
• Energy and industrial facilities – machine foundations, equipment supports, pipe racks and process structures.
• Buildings and infrastructure – seismic assessment, progressive collapse and robustness, long-span and stability-critical structures.

Standards and guidance

• Our analyses follow recognized international methods, including:
• ISO 19902 and the ISO 19901 series (fixed steel offshore structures; seismic, metocean and geotechnical requirements)
• API RP 2A, including assessment of existing platforms
• DNV-RP-C208 – determination of structural capacity by nonlinear finite element analysis
• DNV-RP-C204 – structural design against accidental loads and explosions
• NORSOK N-004, including accidental actions
• DNV-ST-0126 and DNV-ST-0145 – offshore wind support structures and offshore substations
• EN 1993-1-5 and EN 1993-1-6 – plated and shell structures
• EN 1998 (Eurocode 8) and TCVN 9386 – seismic design

Software
We use leading general-purpose finite element software, including Abaqus®, ANSYS® and USFOS, together with in-house tools for pre- and post-processing and code checking. Every model is checked against hand calculations, benchmark results and linear analysis. Mesh, material and imperfection sensitivity studies are part of every project, not an optional extra.

How we work

• Define the question – we agree the limit state, acceptance criteria and the decision the analysis must support.
• Choose the right level of model – from beam-element frame models to detailed shell and solid models, matched to the question.
• Calibrate and verify – material models, imperfections, boundary conditions, mesh convergence and benchmark checks.
• Analyse and interpret – failure mechanism, capacity and sensitivity to key assumptions.
• Report for decision-making – clear, auditable reports that engineers, operators and certifying authorities can act on.

What you receive

• A technical report setting out methodology, assumptions, results and recommendations
• Capacity curves, failure-mode visualisations and utilisation plots
• Model files and input data on request
• Support during third-party verification and certification review