5.16.1. Performance-Based Design

Each performance level (Immediate Occupancy, Life Safety, Collapse Prevention) is linked to SDOF demand using capacity spectrum method.

In performance-based design, structures are assessed for their expected performance during an earthquake. There are three key performance levels: Immediate Occupancy, Life Safety, and Collapse Prevention. Each of these levels indicates how well a building will perform under seismic loads. The capacity spectrum method links these performance levels to the demands experienced by Single Degree of Freedom (SDOF) models, which simplifies the analysis of complex structures. The SDOF demand helps engineers ensure that structures meet specific safety and functionality criteria after an earthquake.

Imagine you are planning a trip to a theme park. You might want to ensure that your favorite ride is open (Immediate Occupancy) and that it is safe to ride, even if it experiences some bumps along the way (Life Safety). However, you would not want to risk it falling apart entirely (Collapse Prevention). Just like planning for your day at the park, engineers need to plan how a building will handle earthquakes, ensuring it can withstand different levels of stress.

Focuses on displacement rather than force. Uses equivalent SDOF systems to match demand and capacity spectra.

Displacement-based seismic design emphasizes the actual movement of a structure under seismic action, rather than focusing solely on the forces involved. This method helps to better predict when a building will reach its limits. By using equivalent SDOF systems, engineers can match the seismic demands (what the structure will experience during an earthquake) with the building's capacity (how much it can withstand) through the use of demand and capacity spectra.

Think of riding a bike down a hill. You can feel how much you lean to handle the slope and avoid falling. Just like how the rider's lean corresponds to the bike's ability to stay upright under different conditions, displacement-based design helps ensure that buildings appropriately adjust to ground movements, staying safe instead of toppling over.

The non-linear static analysis method. Load applied incrementally until target displacement (SDOF-based). Converts actual structure to a capacity curve of an equivalent SDOF system.

Pushover analysis is a static method used to evaluate a structure's strength and performance under seismic loads by applying an incremental lateral force until a target displacement is reached. This method helps to create a 'capacity curve' for the building, representing the relationship between the applied load and how much the structure can deform. By converting the actual multi-degree-of-freedom system into an equivalent SDOF system, engineers gain insights into the building's potential performance and safety during an earthquake.

Imagine testing a flexible rubber band. If you slowly pull it, you can see how far it stretches until it finally snaps—it gives you an idea of its limits. In a similar way, pushover analysis helps engineers see how much a building can bend (or deform) before it fails, helping to ensure it will remain safe during seismic events.

--