Assessment

As mentioned previously, assessment is the first step in the process of retrofitting. The seismic vulnerability of a building must first be ascertained before deciding whether or not to retrofit. Building assessment usually consists of two stages. An initial or preliminary assessment begins the process. Some countries have developed assessment procedures based upon extensive knowledge of their local building types, construction methods and materials and history of seismic code devel-opments.7, 8 After a brief visual inspection to identify any serious structural weaknesses, such as critical configuration problems, structural engineers 'score' a building, expressing its strength as a percentage

Section Undamaged column

135° hook

135° hook

Section Undamaged column

Section Damaged column

Hook still effective

Section Damaged column

▲ 12.5 Incorrectly bent column (and beam) ties are dangerous. During an earthquake their hooks open out and the ties lose all their effectiveness.

of current seismic code requirements. Depending on the result, a decision is made either not to retrofit or to proceed to a second level of assessment which involves a far more thorough procedure. An on-site inspection, possibly involving some minor demolition to determine welding or reinforcing steel details, is followed by extensive structural engineering analysis. Only then is a final decision made on whether or not to retrofit.

Poor structural configuration, such as short-columns or a soft-storey, often necessitates retrofit. Inadequate detailing can be another reason. Poor details, like incorrectly bent column ties in a reinforced concrete frame building, effectively rob their columns of most of their shear strength and confinement during a designlevel earthquake. Such a small detail - 90 verses 1 35 degree tie hooks - has such severe consequences for a building's seismic safety (Fig. 12.5). Inferior construction materials, such as under-strength concrete or reinforcing steel that is too weak or brittle, can also be an issue. The quality of the construction might be poor. Column or beam ties might be missing, reinforcing bars not lapped properly or placed incorrectly - the list of potential problems is lengthy. Some problems on their own may not be too serious. However, others definitely require remedying.

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