Strengthen or Demolish and Rebuild? The Decision Criteria

Before deciding whether to strengthen or to demolish and rebuild, the seismic performance of the existing building and the interventions through which it could reach the target level must be established. The layout of the structural system, the properties of the concrete and reinforcement, existing damage, and foundation and soil conditions are all important in this assessment. In some buildings an appropriate strengthening solution can be achieved with limited intervention, while others may require extensive structural and foundation work. Deciding on the basis of the building's age or a single test result is therefore not sufficient. The technical feasibility and approximate cost of the strengthening option must be set out.

In the next stage, the strengthening and rebuilding options are compared in terms of cost, time and conditions of use. In addition to construction costs, evacuation, relocation, rent or loss of operation, and any necessary architectural renewal are taken into account. In rebuilding, zoning conditions and possible loss of floor area can matter; in strengthening, the effect of the interventions on current use can. In some cases, even where rebuilding appears more favourable, strengthening may be preferred because of loss of area or other constraints. The decision should be taken once the technical assessment and the costs are clear, considering the owners' needs and the conditions particular to the structure together.