Elements in Seismic Upgrading of a Building

Many buildings constructed in Canada in areas with seismic activity were constructed before there was adequate knowledge about engineering earthquake resistance. A seismic upgrade, sometimes called a "retrofit," may be necessary to keep a building in compliance with more recent building and safety codes.

Assessment

Before a seismic upgrade is performed, the particular seismic deficiency of the building is assessed. Four areas that are assessed are integrity/redundancy, which refers to how connected all the pieces of a building are to one another, adequate strength/ductility, which is how well a building absorbs or transfers cyclic load, lateral stiffness of building material, and irregularities/asymmetries in the building structure that could result in load transfer.

Objectives of Seismic Retrofit

There are several recognized objectives in seismic retrofitting. "Public safety only," is to ensure that the structure will not collapse upon its occupants and passersby. "Structure survivability" is for the structure to remain safe for exit, but with the possibility that extensive repair may be needed before it can resume its normal function. "Structure functionality" is for the primary structure to remain undamaged and able to be used in its primary function. This is the minimum level of retrofit for hospitals. "Structure unaffected" is the preferred level of retrofit for buildings and structures of high cultural importance.

Following an assessment of the building's vulnerabilities, a plan is made to upgrade the structure under the rubric of minimal structural intervention. Care is taken to determine how to make the building structurally safer without fundamentally changing the regular function, appearance, or heritage value of a building.

There are a variety of engineering interventions that can be done to strengthen existing structures, within this framework, with primary value placed on allowing for as much of the normal operation of the building to continue as possible during the retrofit.