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Berkeley architect designs earthquake-resistant, affordable housing
In a world built by structural engineer David Marr, buildings should bend, not break.
California lives with certainty that the big event is coming. In the event of a major earthquake, buildings may not collapse, but they may become unlivable.
While we can all suffer, low-income seniors are most at risk. Even now, affordable apartments are still rare. A major earthquake could exacerbate the crisis for those already suffering.
David Marr, founder of Berkeley-based Mar Structural Design, believes we can do better. Using high-performance design, his firm designed Casa Adelante, a nine-story affordable senior housing project in San Francisco's Mission District, that will resiliate and dissipate energy during a major earthquake. Although they may sustain cosmetic damage, they are designed to remain structurally sound.
And here's the big surprise: This flexible building cost $42 million, and it cost no more than regular designs.
We asked Marr about this major experiment, which has been rated Gold by the US Resilience Council. His comments have been edited for length and clarity.
Q: How did this project come about?
A: I wanted to challenge myself to see how much quality building I could do, without incurring any additional cost. Casa Adelante is a publicly funded affordable housing project. So you set the “zero cost” premium.
Q: Why did this feel so important to you?
A: 25% of its population were previously homeless. They may not have strong family networks. They may not have extra money to go to the hotel. Therefore, they are more likely to be displaced after an earthquake. I thought, “Well, if we can build a better building, these are the people we should be building a better building for.”
Q: What techniques did you use to increase flexibility in this concrete building?
A: The idea I had was to let the building shake on its own foundation.
It is built on a regular concrete slab. But the soil is really bad, and prone to becoming unstable. So we had to reinforce the soil in specific areas under the walls. The contractor drilled holes and mixed a mortar of cement and soil, creating small piers about 20 feet deep in the foundation. This provided additional reinforcement at the ends of the walls to prevent soil failure and ensure swaying in the event of an earthquake.
The foundation is a little thinner than traditional foundation. It's strong, but not too strong. Foundation needs to flex and absorb energy as it flexes. Typically, walls are designed to yield at the base. But the soil is strong enough that the walls can tip over on their edges, without puncturing the foundation.
When a building moves in an earthquake, the columns try to buckle into the slab. So we strengthened against this crooked act.
I knew I needed to supplement (two walls) with dampers, which are large steel pistons that act as shock absorbers. I was at a conference and met Professor Geoff Rogers, from the University of Canterbury, who was looking into very powerful, compact dampers. He donated all his time to our project. There are four of them, basically listed.
Q: How did you test it?
A: Using computers, we simulated major earthquakes — 11 versions of “The Big One” and 11 versions of a larger earthquake, such as a magnitude 7.8, nearby.
We “designed” the performance of all floors, walls and columns. We looked at how it deformed without significant damage. We studied the pressure under the soil. We made sure that the panels would not penetrate the columns, like all the failures we witnessed in the great Turkey earthquake.
Most engineering offices do not take the time or spend the resources necessary to make complex and sophisticated models of buildings. This was a labor of love for us.
Q: If an earthquake occurs, how will it react?
A: When the ground shakes, the walls are initially very stiff and don't move much. Eventually, if the earthquake is large enough, the walls tilt and shake on their foundations. (Because of dampers) When walls vibrate and foundations rise, energy is absorbed. The weight of the walls themselves and the weight of the floor slabs are then used to re-center the building.
Because the San Francisco Department of Building Inspection requires expert peer review when using innovative technologies, Greg Dearlin, a professor at Stanford University, agreed to serve as a reviewer for the project. He volunteered his cash labor for free.
Q: Do you worry about interior walls or other features?
A: The basic strategy was: protect the structure and allow some non-structural features – such as partition walls made of drywall and plaster – to be damaged. These repairs can take place over a period of months. No one has to leave.
Q: How did you manage to cut costs?
A: Compared with the regular version, our flexible building had a lower cost foundation. But it had more expensive soil treatment. The dampers were more expensive to install. So we had offsetting costs. It was basically a tie.
Q: Do you think this is a model that can be replicated in future buildings?
A: I think so. As I look to the future, with greater computational power, our ability to model complex behavior will become commonplace. I think what we will discover is that buildings are “tunable.” I think we'll better understand where the damage is happening. Sometimes we'll know how to prevent it. Sometimes we'll figure out how to live with it, by making the damage non-structural. It keeps the cost low.
Q: Today, how would you rate the overall resilience of buildings in California?
A: It's mixed. Our new buildings are really safe. We have done a good job of protecting life. But there are old buildings that are still dangerous. Cities have done a good job of mitigating the worst criminals. They targeted unreinforced masonry buildings and “soft story” residential buildings.
But I think we are still tolerating too much damage to our cities. Although our new buildings are very safe, most of them could sustain serious damage. It's like a bad car accident – you might be able to walk away, but your car breaks down.
And so we're going to have this huge clean-up mess. People will have to leave their homes. People will not be able to get to work. This will slow down our recovery.
This strategy is integrated into our existing code. But this is something we can improve with more innovative technologies.
David Marr
Organization: Founder, Mar Structural Design, Berkeley Education: University of California, Berkeley; Bachelor's and master's degrees in structural engineering Age: 60 Birthplace: Sacramento City of residence: Berkeley Family: Marr's wife is architect Anne Turney, an expert in mixed multifamily housing and transit-oriented urban housing.
Five things to know about David Marr
After the 1989 Loma Prieta earthquake, he was stuck in San Francisco and unable to return to his home in Berkeley. Since then, he has vowed not to build a bridge between his work and his home. His favorite city to see architecture and design is Kyoto, Japan. His favorite building in California is the Greek Theater at UC Berkeley. To improve the integrity of his house, he modified the “post and nail” system, reinforcing the failing walls with plywood panels and attaching the concrete foundation to the house's frame. To relax, he writes songs and plays the guitar. His albums available on Spotify are Hotel Borealis, Ghost Float, and Blind Eye Cry. He is currently working on the fourth part.
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