Colombian Earthquake Highlights Non-Ductile Concrete Risks in Los Angeles

In the aftermath of the recent 7.4-magnitude earthquake that struck western Colombia, awareness of seismic vulnerabilities in older structures has intensified, particularly in Los Angeles. This earthquake affected over 225,000 buildings, resulting in an estimated $13.28 billion in damages, serving as a stark reminder of the catastrophic potential of unprepared structures. It comes as a crucial time for Los Angeles, where the risk of similar vulnerabilities in non-ductile concrete buildings is considerable.

For over a decade, Los Angeles has mandated retrofitting for certain non-ductile concrete buildings, yet reports indicate that less than 15% of these structures have submitted plans for necessary upgrades. This is alarming, especially in light of findings from the journal Earthquake Spectra that identified financial concerns, along with technical and governance hurdles, as major impediments for property owners.

Kyle Tourjé, Executive Vice President of Alpha Structural, underscores the criticality of understanding how older concrete buildings will perform in significant seismic events before undertaking retrofit initiatives. According to Tourjé, “Once a potential seismic vulnerability is identified, the most vital next step is developing a clear engineering understanding of existing conditions.” This insight is essential for property owners to gauge the scope, cost, and timing of necessary retrofits.

Understanding Non-Ductile Concrete Structures

Non-ductile concrete buildings are those that were constructed without adequate seismic detailing, meaning they lack the necessary design features to absorb and dissipate earthquake energy effectively. While reinforcing steel is integral to concrete structures, Tourjé points out that having more of it does not automatically enhance earthquake performance. “A building can contain significant amounts of reinforcing steel and still perform poorly,” he explains.

Many older buildings face significant vulnerabilities due to various structural irregularities, and their concrete elements may not possess the necessary resilience due to changes in engineering standards over the years. For instance, insufficient lap-splice lengths in reinforcing steel or inadequate spacing of ties within columns could leave them susceptible during intense shaking events. Tourjé emphasizes that some older structures weren't designed to endure the forces considered in modern seismic design practices.

Los Angeles' retrofit program specifically targets concrete buildings built before January 13, 1977—before significant changes were introduced in seismic codes. However, not all buildings from this era inherently perform poorly. Engineers might start evaluations by examining original construction drawings, but field investigations are often required for a comprehensive understanding of current structural integrity.

The Complexity of Retrofitting Non-Ductile Buildings

Non-ductile concrete retrofits involve a complex array of evaluations and enhancements, often requiring a multilevel approach rather than fixing a single weak point, like a soft-story issue. Retrofits may call for reinforcing columns and beams, adding shear walls, or implementing various steel bracing systems, which accommodate the building's structural dynamics.

Importantly, Project leads can prioritize enhancements based on urgency and risk evaluation, considering financial constraints. The Los Angeles Department of Building and Safety also advocates for financing solutions, such as Property Assessed Clean Energy (PACE), to facilitate eligible seismic improvements.

Tourjé cautions that delaying evaluations until after an earthquake can lead property owners to grapple with difficult financial and logistical decisions under extreme pressure. He states, “Meeting compliance requirements doesn’t eliminate the pre-existing structural vulnerabilities.”