Buildings change over time. Materials weather, water reaches places it should not, repairs go undocumented and the use of a space shifts, sometimes from residential to commercial or from a few occupants to many. Many older buildings were also designed before current earthquake provisions existed.
Retrofitting is the engineering response: bringing an existing structure to a performance level it was never designed for. It only works when the starting point is understood.
Why older buildings come up for retrofit
Each trigger asks a different question, and the investigation should be matched to it. A planned change of use calls for different checks than a local repair or a concern about movement.
- Deterioration such as corrosion of reinforcement, leakage and weathering.
- Change of use, or added floors, equipment or loads.
- Seismic upgrading of buildings designed to earlier codes.
- Damage after settlement, fire, flooding or an earthquake.
Evidence before intervention
Visible cracking, moisture and corrosion are observations that need interpretation in context. They are not automatic proof of a particular failure mechanism, and a repair that treats only the visible symptom may leave the cause untouched.
Options include local repair, strengthening a member or joint, changing the load path and foundation work. Temporary support, access, sequencing and inspection of concealed work are part of the solution and should be settled before work begins.
- Collect drawings, repair history and alteration records.
- Map defects together with the conditions around them.
- State what was inspected and what could not be verified.
- Use an approved, project-specific repair method.