Seismic Assessment & Retrofitting
Vulnerability assessment and strengthening design for existing buildings, including work carried out while the building stays occupied.
A building designed before the current seismic code is not automatically dangerous, and a building designed after it is not automatically safe. What matters is the specific structural configuration — where the stiffness is, where the mass is, and whether the frame can deform without losing its ability to carry gravity.
Our assessment work answers one question: what would actually happen to this building in the design earthquake for its zone, and what is the cheapest intervention that changes the answer.
Assessment, in three levels
Rapid visual screening is a walk-through against a scored checklist. It cannot tell you a building is safe; it can tell you which buildings in a portfolio need attention first. For an owner with twenty assets, this is the right place to spend the first month.
Preliminary evaluation adds a linear analysis, material testing and a review of the original drawings — where they exist. Most of our work begins here.
Detailed evaluation uses non-linear pushover or time-history analysis to find the actual failure sequence: which element yields first, whether the frame has a soft storey, and whether the collapse mechanism is ductile or brittle. This is what justifies a retrofit budget to a board.
Choosing a retrofit strategy
The strategies available differ enormously in cost and disruption, so we compare them explicitly rather than defaulting to the one we last used:
- Concrete or steel jacketing of columns — cheap, well understood, but intrusive and wet.
- Steel bracing frames — fast, reversible, visible; often best for industrial and car-park structures.
- Shear wall infill — very effective for a soft storey, but it changes the load path and usually the foundations.
- Base isolation — expensive, exceptional performance, viable when the building must stay functional immediately after an event.
- Supplemental damping — good where occupancy cannot be interrupted and drift, not strength, is the deficiency.
The part clients underestimate
Retrofit is a construction-sequencing problem more than a design problem. A strengthening scheme that is correct in its final state can leave the building weaker than it started during week six. Every one of our retrofit packages includes stability checks for the intermediate conditions, and a phasing plan the contractor is contractually bound to.
Questions