Brief
Seismic retrofit at Skyline College in California combines innovation and engineering excellence to enhance earthquake resilience.
Insight
The seismic retrofit of Skyline College in San Bruno, California, stands as a showcase of engineering ingenuity and resilience planning. Located just one mile from the San Andreas Fault, the campus consists of reinforced concrete buildings from the late 1960s, constructed in a style typical of the era. Among these, Building 2—a three-storey, 53,000-square-foot structure with complex slab systems and substantial gravity loads—presented unique seismic challenges due to its heavy mass, non-ductile precast walls, and discontinuous shear systems.
The seismic retrofit California project addressed these vulnerabilities using the Tier 3 methodology of ASCE 41-17, applicable to Risk Category III structures. This rigorous approach combined detailed analysis with targeted strengthening. New shotcrete overlay walls and interior concrete infills were added to improve continuity in the lateral system. A redesigned grade beam network allowed for even distribution of seismic forces to the building’s caisson foundations, eliminating the need for new deep foundations in a site with limited access.
One of the most innovative solutions involved the development of “grippers”—wide-flange steel beams clamped to all four faces of concrete columns to transfer heavy loads during construction. This replaced more conventional but less practical shoring methods, such as stacked spreader beams or post shores, which were deemed costly, risky, or space-prohibitive. The gripper system was tested on full-scale mock-ups to verify load transfer capacity and minimise the risk of slippage, ultimately proving effective in the field.
The construction sequence was carefully phased to maintain stability, control costs, and allow for waterproofing works. Temporary wind loads surprisingly governed the design of the shoring system, despite the site’s seismic proximity. Advanced monitoring systems were used to track column movements in real time, ensuring safety throughout the project.
By completion in March 2025, the retrofit had successfully transformed Building 2 into a more resilient, code-compliant structure without compromising its architectural character. This seismic retrofit California case illustrates how creative engineering, rigorous testing, and collaboration between designers and contractors can deliver a cost-effective and technically sound solution to complex seismic challenges, setting a benchmark for future retrofits in earthquake-prone regions.
Highlight
- The seismic retrofit California project addressed these vulnerabilities using the Tier 3 methodology of ASCE 41-17, applicable to Risk Category III structures.
- This rigorous approach combined detailed analysis with targeted strengthening. New shotcrete overlay walls and interior concrete infills were added to improve continuity in the lateral system. A redesigned grade beam network allowed for even distribution of seismic forces to the building’s caisson foundations, eliminating the need for new deep foundations in a site with limited access.
- One of the most innovative solutions involved the development of “grippers”—wide-flange steel beams clamped to all four faces of concrete columns to transfer heavy loads during construction.
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