Vulnerable Steel-Framed Skyscrapers Still Ignored Under LA’s Mandatory Retrofits
Many of Los Angeles’s steel-framed skyscrapers were built far before the devastating Northridge earthquake of ’94. The same earthquake that saw the destruction of apartment buildings, commercial buildings, freeways and homes throughout Los Angeles.
“Us engineers, we wish we could go back in time and build our buildings with the knowledge we have now,” structural engineer Daniel Zepeda told Curbed Los Angeles.
The Northridge earthquake highlighted how fragile many of downtown Los Angeles’s skyscrapers really are, and how brittle the welded steel moment frames have become over the years.
Though the 6.7 magnitude Northridge quake lasted less than a minute, many of the towers (roughly 100+ L.A. buildings) were left with fractured connections after the shaking.
Of course, technology has changed greatly over the years, which is why many of these steel moment frames need earthquake retrofitting – especially since many of L.A.’s skyscrapers were built in the mid 60s-80s.
After the Northridge earthquake, it became apparent to structural engineers that if a larger earthquake were to occur these buildings could completely collapse.
Los Angeles has made strides in earthquake safety, though. The city has mandated the retrofit of all vulnerable non-ductile concrete (otherwise known as soft story) buildings throughout the region that were built before 1977.
Building codes have also changed since the Northridge earthquake, now requiring all new constructions to use stronger connections to the building’s beams.
But, unfortunately, the same retrofit requirements have not been mandated to all vulnerable buildings with steel moment frames that were built before the Northridge earthquake.
“We wish we could convince the public that we should look at every building out there and analyze and it make it stronger,” Zepeda added. “But we have to be realistic. It’s probably not feasible.”
While retrofitting these structures would be nothing short of a massive undertaking, it is something Los Angeles and its neighboring cities should consider.
The Northridge earthquake struck early in the morning (around 4:30 a.m.) which meant that most people were home when it happened. Yet, if a larger earthquake occurred during normal business hours, what would this mean for all the individuals working in these vulnerable skyscrapers?
Cities like Santa Monica and West Hollywood have taken their required retrofits one step further than Los Angeles, and have assigned owners of these vulnerable steel moment frame buildings 20 years to finish their retrofits.
Now, more than ever, it’s important to be proactive about earthquake preparation and safety.
Julian De La Torre is an expert in Los Angeles foundation inspection, foundation contractors and foundation repair. Julian’s company, Julian Construction, has inspected over 15,000 structures, working with engineering firms and local departments of building & safety. The company has done more foundation repair in Los Angeles than any other company in the area over the last five years.