Mar Structural Design
Casa Adelante - Delivering Affordable Seismic Resilience
Casa Adelante is a new nine-story Type I affordable senior housing project that was developed by the Chinatown Community Development Center and the Mission Economic Development Agency. 20% of the units are designated for people who are formerly unhoused. Recognizing that the residents are a potentially vulnerable population, we developed a resilient seismic system to enable shelter-in-place building performance after a major earthquake. The design objective was to have manageable structural damage after a major earthquake, and have the building return to plumb. The damage would be mostly limited to architectural finishes, which are easier to repair than structural elements. The seismic system is a foundation rocking and re-centering wall system. The system relies on the intrinsic capacity of the mat slab and the concrete floors for energy absorption, in combination with stable rocking under seismic loads. Economic life-cycle cost modeling using FEMA P-58 and SP3 showed the improved value of the high-performance design, which we were able to achieve at a near-zero construction cost premium (.24%).
Our collaboration with Central Concrete Supply was integral to achieving high performance and low embodied energy materials including low carbon concrete. This resulted in a structural design that was cost neutral on seismic design and absolutely cost neutral on the low carbon concrete. Our philosophy for successful projects recognizes the synergistic benefits of collaboration between designers and builders. A prime example of this is the low-cement concrete design at Casa Adelante. We worked directly with Central Concrete to tailor our performance specification for concrete to have the lowest carbon footprint practicable. The mixes needed to be cost-neutral, suitable for an open bid environment, and have no negative construction impacts. The result of the collaboration met the criteria above and achieved over a 50% reduction of CO2, against the benchmark designs. The lessons we take from this example are several. First is that we see the power of open communication and shared goals. We see the benefits of listening to outside expertise. We see that we are a team and silos are detrimental to shared successes.
Awards and Certifications for Casa Adelante:
2020 NCSEA Excellence in Structural Engineering
2021 SEAONC Award of Excellence
2021 SEAOC Excellence in Structural Engineering Award
U.S. Resiliency Council Gold Rating
Green Point Rated Platinum
Once Casa Adelante was designed and performing well, the team reached out to the US Resilience Council and got them excited about the project. The USRC waived their fees and after a detailed evaluation, they awarded the project a Gold Rating for resilience. Case Adelante is the first multi-unit housing project to be rated by the USRC. The project may be one of the first high-performance designs for under-resourced occupants constructed in the US. The San Francisco Office of Resilience and Recovery promotes resilient design and targets 40 days of repair and loss-of-use for buildings after a major earthquake. Casa Adelante is rated to have zero days of loss-of-use.
Cost and Value Verification –
The high-performance and conventional schemes were evaluated for economic losses, using FEMA P-58 and the SP3 software. The high-performance scheme was found to be more valuable, yielding $500,000 (net present value) savings from earthquake losses. Finally, the contractor performed a post-construction cost evaluation of the as-built structure against the conventionally designed benchmark. The results were an additional cost of $100,000 for the high-performance design for the $42 million project – a 0.24% overage. Although the project slightly missed the cost neutral target, the team was pleased with how close it was. The result is resilient performance for affordable senior housing at a great value.
Mar Structural Design has been working with Central Concrete Supply for over a decade to refine our mixes and learn from their design research and understanding of market conditions. Without them as a partner innovating on this project the result would not have been an exemplar in both sustainability and resilience due to its seismic performance strategy and embodied energy strategy.