Engineering
Preliminary Design, Detailing, Final Design, and Reliability Analysis

Engineering design carried out using a performance-based format consists of establishing a design which satisfies performance criteria set for very rare, rare and frequent earthquakes.

• Preliminary Design
  - Simple methods to develop structure that performs well.
• Detailing
  - Detail elements, connections of structural elements, attachments of non-structural elements to achieve desired capacities and performance.
• Final Design
  - More refined methods used to fine tune building design to achieve performance goals (physical and economic).
• Reliability Analysis
  - Assess sensitivity of final structure to uncertainties in ground motion and loading.

Preliminary Design

Generally, this is the most important design stage. The focus is on simple methods to develop a structure that performs well. Good performance is attained by providing a design with good proportions, load path completion, stiffness, strength, etc.

Preliminary design is an iterative process:

• Operational Goal: Elastic Analysis, very simple models and elastic spectrum.
• Life Safe Goal: Elastic analysis, and "equivalent elastic" spectrum.
• Near-collapse Goal: Simplified nonlinear analysis, nonlinear design and response spectrum.
• Integrate design requirements
• Evaluate designs
• Re-do if needed

Detailing

Today's prescriptive formats (such as ACI 318 for concrete) say little about expected performance. Currently, there is little attempt to relate details quantitatively to predicted deformation demands. Nominal "ductile" details are typically used that are relatively non-deteriorative and insensitive to loading history effects.

Detailing follows an explicit format, with iteration using estimated demands:

• Operational goal: focus on strength (good stiffness estimates needed to predict demands)
• Life Safe Goal: Focus on triggers for expensive / dangerous behavior (spalling, buckling, etc.)
• Near-Collapse Goal: Focus on ultimate deformation capacity of member, connection or attachment. Difficult with current knowledge.
• Integrate design requirements (contradictory)
• Evaluate details for performance and cost

Final Design

Generally, final design is the most analysis-oriented design stage. The focus is on refined methods to predict / evaluate demands on the nearly complete structural design.

Final design is an iterative process:

• Operational goal: Elastic Analysis, refined models and elastic spectrum, 2D vs. 3D
• Life Safe Goal: Elastic Analysis, and "equivalent elastic" or nonlinear spectrum.
• Near-collapse Goal: Nonlinear analysis (static push-over with nonlinear design response spectrum, or dynamic time history analysis).
• Integrate design requirements
• Evaluate designs (details, goals)
• Re-do if needed

Reliability Analysis

Currently, reliabilitiy analyses are done only infrequently. The focus is on refined methods to assess the reliability of structure and its life cycle costs considering variability of expected earthquakes.

Reliability analysis is an iterative process:

• Operational Goal: Elastic Analysis, refined models and elastic spectrum, 2D vs 3D
• Life Safe Goal: Elastic analysis and "equivalent elastic" or nonlinear spectrum (+1s)
• Near-collapse Goal: Nonlinear analysis such as static push-over with nonlinear response spectrum (+1s), dynamic time history analysis, etc.
• Integrate performance information
• Evaluate performance expectations' costs
• Re-do if needed