How California’s Retrofit Ordinances Are Reshaping Seismic Engineering

It’s one thing to follow a checklist. It’s another to deeply understand how a structure behaves when the ground begins to shake. California’s seismic story is full of lessons—from collapsed unreinforced masonry to dangerously fragile soft-story apartments. For decades, building codes evolved in response to disaster, often applying force-based, prescriptive rules to try and reduce future damage. Yet engineers today are realizing that these rules—while improving safety—don’t always hit the mark.

What we truly need is a shift in mindset. Not just what’s required by the code, but what a building should do in an earthquake. This is where performance-based seismic design steps in: an approach that first defines a building’s intended performance goal (like life safety or collapse prevention) and then tailors the design to meet that outcome. It’s not about checking boxes—it’s about intelligent, customized solutions rooted in behavior, not just formulas.

This need is even more pressing when it comes to retrofitting existing structures. Many of California’s older buildings—from charming brick façades to vast concrete tilt-ups—were never designed with today’s seismic knowledge. Applying a one-size-fits-all code to them may tick the compliance box, but it doesn’t guarantee actual performance.

California has implemented various seismic retrofit ordinances over the years, each one driven by hard-earned lessons from past earthquakes. But each also reveals the limitations of relying solely on minimum standards:

In each case, the story is the same: the building code improved performance, but only after repeated failures. It fixed what had already gone wrong, rather than anticipating what could. This is why performance-based design is so powerful—it allows engineers to tailor solutions based on how a building actually behaves.

Seismic design isn’t just about preventing collapse—it’s about ensuring buildings behave predictably. The code tries to achieve this, but it does so by prescribing rules rather than evaluating outcomes. Performance-based design flips this script.

In essence, performance-based design asks: How do we want this building to perform in a major earthquake? Should it remain operational, allow safe exit, or just avoid collapse? Once the target is set, engineers can back-calculate the forces and configurations needed—not the other way around.

For example, a flexible roof diaphragm in a tilt-up building is usually the weak link, not the rigid concrete walls. Yet prescriptive codes often focus on wall details, ignoring the diaphragm altogether. Performance-based design, however, looks at the entire system—how walls, diaphragms, and connections behave together. It leads to smarter, more holistic retrofits.

Engineers also need to factor in geotechnical effects—soil liquefaction, settlement, fault rupture, and landsliding. In performance-based retrofits, these aren’t afterthoughts—they’re central to the design strategy. For soft-story retrofits, understanding how seismic loads travel through irregular framing to a potentially weak foundation is crucial. For URM retrofits, knowing how soil amplifies shaking can influence whether additional bracing or anchorage is sufficient.

Yes, performance-based design is more complex. But it is also more precise, more adaptable, and more realistic. It encourages engineers to think like investigators and strategists, not just coders. And that’s exactly what we need when preparing buildings for earthquakes that haven’t happened yet.

It’s tempting to see the building code as a safety net. But as California’s long history of retrofit ordinances shows, that net can have holes. The code is a baseline—not a guarantee. If we want to build structures that stand the test of time (and tremors), we must go further.

Performance-based design is not just a technical upgrade—it’s a philosophical shift. It means trusting engineers to analyze, understand, and anticipate—not just comply. And it means making design decisions based on real-world performance, not hypothetical numbers.

For geotechnical engineers especially, the soil is where it all begins. Ground behavior affects everything from wall anchorage to diaphragm response to seismic loads. A performance-based mindset ensures that those behaviors are front and center, not buried in assumptions.

As we face more frequent seismic events and a growing backlog of vulnerable buildings, California—and the rest of the seismic world—must embrace this smarter, more thoughtful approach. Because in the end, it’s not about building to code. It’s about building for the quake.