Performance-Based Design Is a Major Shift from Traditional Structural Design Concepts and Represents the Future of Earthquake Engineering

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La empresa de software Computer &Structures Inc está promocionado seminarios sobre Diseño basado en Desempeño, pero sin aclarar si se trata de un nuevo producto o que relación tiene con el programa PERFORM-3D ( desarrollo comercial del programa DRAIN, del Prof. Graham Powell). Tampoco hay disponibilidad de ejemplos. Por razones didácticas, se recoge la información disponible, subrayando algunos conceptos.

PERFORMANCE-BASED DESIGN BRIDGING THE GAP BETWEEN RESEARCH AND PRACTICE

Performance-based design is a major shift from traditional structural design concepts and represents the future of earthquake engineering. The procedure provides a method for determining acceptable levels of earthquake damage. Also, it is based on the recognition that yielding does not constitute failure and that preplanned yielding of certain members of a structure during an earthquake can actually help to save the rest of the structure. This seminar will present the theory and practical application of nonlinear analysis and performance-based design in terms and analogies that are very familiar to the practicing structural engineer. Performance-Based Design (PBD) is a major shift from traditional structural design concepts and represents the future of earthquake and wind engineering. These new procedures help assure that the design will reliably meet a desired level of performance during a given earthquake or hurricane. The fundamental component of PBD is nonlinear dynamic analysis where an attempt is made to capture the real behavior of the structure by explicitly modeling and evaluating post-yield ductility and energy dissipation when subjected to actual earthquake ground motions. PBD is also being used for the design of structures subjected to extreme wind and hurricane conditions.

Textbooks by Dr. Graham H. Powell : ”Modeling for Structural Analysis"; “Modeling for Structural Analysis – Behavior and Basics”

The seminar will address many basic questions associated with inelastic structural behavior. Such as....

 Why do we even need to talk about nonlinear analysis?  What is a nonlinear material model?  What is the difference between ductile and brittle behavior?  How can a structure have more strength after yielding?  What is a moment, axial and shear plastic hinge?  What is a sacrificial element?  What is a hysteresis loop?  What is a fiber model?  What is a nonlinear event?  What is stiffness and strength degradation?  What is ductility and ductile limit?  What do we mean by element state determination during an analysis?

 What is cyclic stiffness degradation?  What is meant by an unloading event in a nonlinear analysis?  What is Element State Determination?  What is material and geometric nonlinearity?  What is energy dissipation and why is it important?  What is the difference between yield and ductility and why is yielding without ductility useless?  Why is it important to recognize that yielding does not mean failure or collapse?  What is the difference between redundancy and resilience?  What is elastic work and plastic work and how is the difference important for seismic behavior?  What is a time-energy diagram and why is it so important in seismic design?  What is capacity design?  Why is allowing destruction of parts of a structure during an earthquake considered good engineering?  How can we train a structure to follow a predefined path of damage so that the critical components of the structure are spared and preserved?  Why is a nonlinear time history analysis important even for a regular high rise structure?  What is a sustained load and what is a cyclic load?  What is a mechanism and how is it possible that a mechanism that will collapse under a sustained load may not collapse under a cyclic load?  How is the FNA method used for nonlinear analysis if it is a mode-based superposition method considering the fact that any type of superposition is not possible in nonlinear analysis?  What is ASCE 41?  What is a performance measure and performance level and acceptance criteria?  What is a demand/capacity measure and a demand/capacity ratio?  Is a pushover analysis a static analysis or a dynamic analysis?  What is an Acceleration Displacement Response Spectrum (ADRS) and how is it used?

 What is really meant by energy dissipation and why it is important?

 What is a time-energy diagram and why is it so important in seismic design?

 What is deformation capacity and why it is more important than strength capacity?

 What we really mean by ductility and why strength without ductility is useless?

 What is a material model, a fiber model and a hysteresis loop?  Why performance based design? why nonlinear analysis?  Why codes are inadequate for continued functionality  Designing complex buildings requiring code variances  Simulating real earthquakes and real behavior!  Why seismic loads are different from other loads  Why inelastic behavior is important for seismic resistance  Importance of energy dissipation and ductility  Why strength without ductility is useless  The equal displacement concept and implied nonlinear behavior  Comparison of strength-based and deformation-based design  Force is limited by yielding – design is for deformation  Performance-based design and performance levels  Nonlinear force deformation relationships  Performance measures and acceptance criteria  What is capacity design – training the structure to behave!  Steps for a good practical nonlinear analysis

And, elaborate on many interesting observations, for example:

•... that structures can be designed to follow predefined paths of damage to preserve critical components. •... that allowing yielding of parts of a structure during an earthquake can save the rest of the structure. •... that yielding does not mean failure and some structures can have more strength after yielding. •... that the most efficient and accurate nonlinear time history analysis technique is based on mode superposition. •... that most dead load analyses assume that a structure is built weightless and gravity appears instantaneously. •... that a nonlinear time history analysis is important even for a regular high rise

structure.

The seminar will cover topics related to:

Nonlinear Theory • Material and geometric nonlinearity • Steel and Concrete behavior in the nonlinear range • P-delta and large displacements • Yielding and energy dissipation • History dependence • Ductile and brittle behavior • Ductile limit and strength loss • Elastic and plastic energy • Cyclic stiffness and strength degradation, and fatigue • Hysteresis loops and time-energy diagrams • Redundancy and resilience • Strength based design and deformation based design • Problems of design by analysis • Capacity design and sacrificial elements • Collapse mechanisms • Sustained and cyclic loads

Nonlinear Modeling • Material models :  Details of force deformation relationships  Hysteresis loops and backbone curves  Stiffness and strength degradation  Hysteresis types - degradation paths  Discretized plasticity models and fiber hinge models  Modeling beams, columns and shear walls  Energy dissipation devices – defection-based and velocity-based  Rotation and strains as a performance measure  Steel and concrete – importance of confinement • Moment, axial and shear Fema hinges • Rusty hinge model • Moment axial force interaction • Fiber hinge models for complex shapes • Multi layered nonlinear shell model • Multi linear elastic and plastic behavior • Viscous dampers • Base isolation energy dissipating models • Types of hysteresis loops - kinetic, isotropic, Takeda and pivot • Special considerations for tall building

Nonlinear Analysis Techniques & Performance Based Design Time History Analytical Procedures  Analytical procedures and numerical techniques  Nonlinear time history analysis and pushover analysis  Newton Raphson and constant stiffness iteration

 Step-by-step and event-to-event  Details of time history analysis  Nonlinear step-by-step time history analysis • The fast nonlineal modal time history analisys, FNA; and closed form time integration and the power of Ritz vectors • Step by step nonlinear time history analysis  Advantages and disadvantages of time history analysis  Artificial earthquakes – frequency and time domain • Large-displacement and P-delta effects • Modal and Rayleigh damping • Nonlinear events and element state determination • Unloading events, redistribution and solution complications • Requirements of ASCE 41Pushover analysis and limitations • Force controlled loading and displacement controlled loading • Badly behaved displacements (snap-back and snap-through) • Non-uniqueness of static solutions, uniqueness of dynamics • Acceleration Displacement Response Spectrum (ADRS) • Pushover Analytical Procedures  Pushover theory and correspondence with response spectrum! Pushover curve and target displacement. Equivalent linearization and displacement modification methods  Advantages and disadvantages of pushover analysis  Displacement control load control • Performance measures and performance levels  Demand/Capacity ratio and acceptance criteria  Soil- structure interaction

Nonlinear Applications in Structural Engineering • Buckling restrained braces • Eccentrically braced systems • Base isolation systems • Reduced beam sections • Panel zone plasticity • Foundation uplift and structural pounding • Long term creep and shrinkage • Effects of construction sequence loading • Nonlinear dampers and deflection control • Tension only bracing systems • Cable supported structures

PERFORM-3D NONLINEAR ANALYSIS AND PERFORMANCE ASSESMENT FOR 3-D STRUCTURES Por la mención de los textos del Prof. Powell en el Seminario PBD suponemos el uso de este programa.

Traditionally, earthquake-resistant design has been strength-based, using linear elastic analysis. Since inelastic behavior is usually allowed for strong earthquakes, this is not entirely rational. Strength-based design considers inelastic behavior only implicitly. Displacement-based (or deformation-based) design considers inelastic behavior

6 explicitly, using nonlinear inelastic analysis. Displacement-based design recognizes that in a strong earthquake, inelastic deformation (or ductility) can be more important than strength. PERFORM-3D allows you to use displacement-based design. Procedures for displacement-based design using inelastic analysis are specified in ASCE 41, “Seismic Rehabilitation of Existing Buildings”. ASCE 41 applies to the retrofit of existing buildings, but the procedures can be applied to the design of new buildings. PERFORM-3D implements the procedures in ASCE 41. However, is a general tool for implementing displacement-based design. It is not limited to ASCE 41. The response of a structure to earthquake ground motion, whether elastic or inelastic, is highly uncertain. Capacity design is a rational way to improve the response of a structure in a strong earthquake, by deliberately controlling its behavior. Capacity design controls the inelastic behavior of a structure, by allowing inelastic behavior only in locations chosen by the designer. In these locations the structural components are designed to be ductile. The rest of the structure remains essentially elastic, and can be less ductile. Controlling the behavior in this way improves reliability, reduces the amount of damage, and can reduce construction costs. PERFORM-3D has powerful capabilities for inelastic analysis, but it is not intended for general purpose nonlinear analysis. If you have no idea how your structure will behave when it becomes inelastic in a strong earthquake, PERFORM-3D can probably help you to identify the weak points, and hence can guide you in improving the design. However, is not intended for “design by analysis”, where the engineer expects the analysis to determine exactly how a structure will behave. Is a powerful tool for implementing displacement-based design and capacity design. It will help you to produce better designs, but it will not do the engineering for you.