The purpose of retrofitting is to reduce the vulnerability of a building's inhabitants and the building itself - its structure, non-structural elements and possibly its contents to earthquake damage. To retrofit a building is to improve its seismic performance. Alternative terms for retrofit, such as ' rehabilitation','upgrading',' i improvement' , and perhaps ' strengthening', essentially convey the same meaning, but since ' retrofit' is well established, especially in the USA, it is used in this book. If the context of the term is unclear it can be preceded by ' seismic' to convey unambiguously one's involvement in one or more existing buildings possibly deficient from the perspective of seismic performance. The hesitation regarding the use of ' strengthening' is that sometimes it may be more appropriate to retrofit a building by merely increasing its ductility or even weakening selected structural members than by strengthening, but more on that later.
Retrofitting can be appropriate for any scale of building of any material. Wooden and stone houses are retrofitted, as are huge monumental concrete buildings. But, whereas wood-framed domestic construction, for example, can in many cases be retrofitted by their owners, larger projects are technically very challenging and require high levels of skill and experience in both the design and construction teams.
Although the retrofit or repair of earthquake-damaged buildings has been undertaken for centuries, the practice of retrofitting yet undamaged buildings in order to prepare them for a future damaging quake is far more recent. Thousands of buildings have already been retrofitted in California and New Zealand, as well as in other seismically active countries. Most retrofitting has yet to be put to the test by a large earthquake but evidence from at least one earthquake-damaged region confirms its value. ' Risk reduction efforts by the City of Los Angeles and neighboring communities greatly reduced the economic losses and threats to life in URM [unreinforced masonry buildings] during
the 1994 Northridge earthquake. In stark contrast, communities like Fillmore, which do not require URM risk reduction, suffered greater losses'.1
In contrast to the construction of a new building, retrofit begins with a process of assessment. Often undertaken in two stages, a preliminary assessment against pre-determined criteria is the basis for deciding whether any seismic deficiencies in a building warrant a more thorough investigation prior to recommending that retrofitting should or should not be undertaken. The subsequent steps of design and construction are also different from those of new construction due to their complexity. Designers and contractors usually find retrofit projects far more demanding than new construction. An existing building constrains their options and approaches. A successful retrofit scheme usually not only improves seismic performance but enhances functional and aesthetic building qualities.
Unfortunately much retrofit activity, at least in commercial and retail buildings, has failed to address aesthetic issues adequately. Look, Wong and Augustus, although writing in the context of retrofitting historic buildings summarize the situation:
'Although historic and other older buildings can be retrofitted to survive earthquakes, many retrofit practices damage or destroy the very features that make such buildings significant. Life-safety issues are foremost and, fortunately, there are various approaches which can save historic buildings both from the devastation caused by earthquakes and from the damage inflicted by well-intentioned but insensitive retrofit procedures. Building owners, managers, consultants, and communities need to be actively involved in preparing documents and readying irreplaceable historic resources from these damages ' .2
Retrofits of all but historic buildings are usually driven by structural engineering and economic concerns rather than by architectural considerations. A cursory examination of retrofit schemes in downtown San Francisco reveals retrofit structure clashing with, and demeaning much of, the existing architecture (Fig. 12.1). Similar criticism, which can also be levelled at other cities, has initiated thinking that challenges the current approach often devoid of architectural merit.3 Research-by-design retrofit proposals for a 1960s concrete frame office building and an early 1900s brick revivalist building give glimpses of alternative approaches indicative of a more architectural response (Figs 12.2 and I2.3).4 While reading the following sections, which discuss retrofit issues pertaining to architects, keep in mind the desirability of retrofit solutions possessing architectural integrity.
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