Planning for Seismic
Retrofit: How Much and Where?
Upon completion, the
changes to this ca. 1932 Gothic Revival building to add base isolation at the foundation
were not visually apparent. Photo: © Jonathan Farrer |
The
integrity and significance of the historic building, paired with the cost
and benefit of seismic upgrading, need to be weighed by the owner and the
consulting team. Buildings in less active seismic areas may need little
or no further bracing or tying. Buildings in more active seismic zones,
however, may need more extensive intervention. Options for the level of
seismic retrofit generally fall into four classifications, depending on
the expected seismic activity and the desired level of performance. Realistically,
for historic buildings, only the first three categories apply.
Devising the most appropriate approach for
a particular historic building will depend on a variety of factors, including
the building’s use, whether it remains occupied during construction,
applicable codes, budgetary constraints, and projected risk of damage. From
a design perspective, the vast majority of historic buildings can tolerate
a well-planned hidden system of reinforcement. Utilitarian structures, such
as warehouses, may be able to receive fairly visible reinforcement systems
without undue damage to their historic character. Other more architecturally
detailed buildings or those with more finished interior surfaces, however,
will benefit from more hidden systems; installation of such systems may
even require the temporary removal of significant features to assure their
protection. Most buildings, particularly commercial rehabilitations, can
incorporate seismic strengthening during other construction work in a way
that ensures a high degree of retention of historic materials in place.
"The Seismic Retrofit of Historic Buildings" an Historic Preservation Brief
