In a world built by structural engineer David Mar, buildings should bend — not break.
California lives with the certainty that the Big One will come. In a major earthquake, buildings might not collapse, but they could become unlivable.
While all of us could suffer, low-income seniors are at greatest risk. Even now, affordable apartments are scarce. A major earthquake could worsen the crisis for those who are already struggling.
David Mar, founder of Berkeley-based Mar Structural Design, thinks we can do better. Using high-performance design, his company designed Casa Adelante, a nine-story affordable senior housing project in San Francisco’s Mission neighborhood, that will flex and dissipate energy during a major earthquake. While it may endure cosmetic damage, it is designed to stay structurally intact.
And here’s the big surprise: At $42 million, this resilient building didn’t cost more than ordinary designs.
We asked Mar about this grand experiment, which has been awarded a Gold Rating by the U.S. Resilience Council. His comments have been edited for length and clarity.
Q: How did this project come to be?
A: I wanted to challenge myself to figure out how good a building could I make, without having it cost any more. Casa Adelante is an affordable housing project that is publicly funded. So I set a ‘zero cost’ premium.
Q: Why did that feel so important to you?
A: Of its residents, 25% were formerly homeless. They may not have strong family networks. They may not have extra cash to go to a hotel. So they’re more vulnerable to displacement after an earthquake. I thought: “Well, if we could do a better building, these are the folks we should do a better building for.”
Q: What techniques did you use to increase resiliency in this concrete building?
A: The idea I had was to allow the building to rock on its footing.
It’s built on an ordinary concrete mat slab. But the soil is really bad, and is subject to becoming unstable. So we had to strengthen the soil in specific regions under the walls. The contractor drilled holes and mixed a slurry of cement and soil — creating little piers, about 20 feet deep, in the foundation. This provided extra strengthening at the ends of walls to preclude soil failure and ensure rocking, in the event of an earthquake.
The foundation is a little thinner than a traditional foundation. It is strong, but not too strong. The foundation needs to flex, and absorb energy while it’s flexing. Normally, walls are designed to yield at the base. But the soil is strong enough so the walls can tip up on their edges, without punching through the foundation.
When a building moves in an earthquake, the columns try to twist in the slab. So we reinforced against that twisting action.
I knew I needed to supplement (two of the walls) with dampers, which are big steel pistons which act like shock absorbers. I was at a conference and I met Professor Geoff Rogers, from the University of Canterbury, who was researching very compact, very powerful dampers. He donated all his time to our project. There are four of them, inserted in the foundation.
Q: How did you test it?
A: Using computers, we simulated major earthquakes — 11 versions of ‘The Big One” and 11 versions of an even bigger big one, like a magnitude 7.8 nearby.
And we ‘modeled’ the performance of all of the floors, the walls and the columns. We looked at how they deformed without significant damage. We studied the stress under the soil. We made sure that the slabs didn’t punch through the columns, like all the failures seen in Turkey’s great earthquake.
Most engineering offices don’t take the time or expend the resources to do really elaborate, sophisticated modeling of buildings. This was a labor of love for us.
Q: In an earthquake, how will it respond?
A: When the ground shakes, the walls initially are very stiff and don’t move very much. And then eventually, if the earthquake is big enough, the walls tilt and they rock on their foundation. (Because of the dampers,) when the walls rock and the foundation lifts, the energy gets absorbed. Then the weight of the walls themselves, and the weight of the floor plates, is used to re-center the building.
Because San Francisco’s Department of Building Inspection requires an expert peer review when you use innovative technologies, Stanford University professor Greg Deierlein agreed to serve as the project reviewer. He volunteered his critical work for free.
Q: Did you worry about interior walls or other features?
A: The basic strategy was: Protect the structure and allow some of the non-structural features — such as the gypsum-board partition walls and the stucco — to get damaged. These repairs can happen over a period of months. No one has to leave.
Q: How did you keep costs down?
A: Compared to the ordinary version, our resilient building had a less expensive foundation. But it had a more expensive soil treatment. And it was more expensive to put in the dampers. So we had offsetting costs. It was essentially a tie.
Q: Do you think this is a model that could be replicated in future buildings?
A: I think so. When I look into the future, with greater computational power, our ability to model complex behavior will become commonplace. I think what we’ll find is that buildings are ‘tunable.’ I think we’ll better understand where the damage is occurring. Sometimes we’ll know how to prevent it. Sometimes we’ll know how to live with it, by letting damage be non-structural. And it keeps the cost down.
Q: Today, how would you rate the overall resiliency of California’s buildings?
A: It’s mixed. Our new buildings are really safe. We’ve done a good job at protecting life. But there are older buildings that are still dangerous. Cities have done a good job of mitigating the worst offenders. They went after unreinforced masonry buildings and “soft story” apartment buildings.
But I think we’re still tolerating too much damage for our cities. Even though our new buildings are very safe, most could suffer significant damage. It’s like a bad car crash — you may be able to walk away, but your car is totaled.
And so we’re going to have this huge cleanup mess. People are going to have to leave their homes. People will not be able to get to work. That will slow our recovery.
This strategy is built into our existing code. But it’s something we can improve, with more innovative techniques.
David Mar
- Organization: Founder, Mar Structural Design, Berkeley
- Education: University of California, Berkeley; Bachelor’s and Masters degrees in Structural Engineering
- Age: 60
- Birthplace: Sacramento
- Town of Residence: Berkeley
- Family: Mar’s wife is architect Anne Torney, an expert in mixed-income multi-family housing and transit-oriented urban infill.
Five things to know about David Mar
- After the 1989 Loma Prieta earthquake, he was stuck in San Francisco and could not get home to Berkeley. From then on, he vowed to never have a bridge between his work and home.
- His favorite city to view architecture and design is Kyoto, Japan.
- His favorite building in California is UC Berkeley’s Greek Theatre.
- To improve the safety of his home, he’s done a “brace and bolt” retrofit, bracing the cripple walls with sheets of plywood and bolting the concrete foundation to the frame of the house.
- 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 a fourth.