How detailed should a model be? Pierre Hoogenboom Delft University of Technology
Modeling Objectives Gain fundamental understanding Validate design rules in codes of practice Check a completed design Design a structure
Performance-Based Design Virtual prototyping Simulation-based design Design trough simulation Using simulation software in a cyclic design process.
Example of Performance Criteria Load ReliabilityLimit State Small earthquake 0.50 No significant damage to the structure. It retains nearly al its strength and stiffness. Most non-structural components function. Building use impaired. Medium earthquake 0.90 Significant damage to structural elements, with substantial reduction in stiffness. Non-structural elements may not function. Use prevented until repair. Maximum credible earthquake 0.98 Near collapse. Substantial structural and non-structural damage. Some falling debris.
Types of Models Structure & Components Component & Continua Continuum & Materials
Model Hierarchy Structural level Component level Continuum level Material level Structural model Finite element model Continuum model MM FF FF
A model should not include all levels. A unrealistic model can be better. Design process
Example 1. RC Frame Buildings Earthquake loading Accept beam flexural failure only Needed strength Needed ductility
Example 2. Development Length Slipping reinforcing bars Often designers do not want slip. No slip but interface stress Anchorages in one sweep
Example 3. Safety Safe material parameters Redistribution of force flow Average stiffness and small strength Bi-linear stress strain
Example 4. Fictitious Materials stress strain realstrengthening linear When a material breaks we cannot see what forces would have developed.
Timetable for Progress Moore’s Law of PC computation costs t o Current computation time t Future – acceptable – computation time n Number of years into the future n
Timetable for Progress Nonlinear simulations Reliability-based design Design optimisation Reliability-based optimisation Live cycle cost optimisation in 0 years in 6 years in 8 years …. Innovation Introduction in practice
Do's & Don'ts for Model Development Do include … multiple material relations fictitious materials Don’t include... more than two scales more than one component
Conclusions Advanced models can be used efficiently in a design process. A design model needs to fit in the hierarchy. An unrealistic model can be better for design. The design process is key.