Seismic Strengthening
Approaches
Limited intervention should correct obvious structural deficiencies, such as tying
vulnerable elements together and repointing masonry. Upon replastering and
painting these reinforcements will not be visible. Photo: Courtesy, Historic Preservation Partners for Earthquake Response. |
Seismic strength within buildings is achieved
through the reinforcement of structural elements. Such reinforcement can
include anchored ties, reinforced mortar joints, braced frames, bond beams,
moment-resisting frames, shear walls, and horizontal diaphragms. Most historic
buildings can use these standard, traditional methods of strengthening successfully,
if properly designed to conform to the historic character of the building.
In addition, there are new technologies and better designs for traditional
connection devices as well as a greater acceptance of alternative approaches
to meeting seismic requirements. While some technologies may still be new
for retrofit, the key preservation principles previously outlined should be applied,
to ensure that historic buildings will not be damaged by them.
There are varying levels of intervention for
seismically retrofitting historic buildings based on the owner’s program,
the recommendations of the team, applicable codes, and the availability
of funds.
Maintenance/Preparedness
Adequate maintenance ensures that existing
historic materials remain in good condition and are not weakened by rot,
rust, decay or other moisture problems. Without exception, historic buildings
should be well maintained and an evacuation plan developed. Expectation
that an earthquake will occur sometime in the future should prepare the
owner to have emergency information and supplies on hand.
Check roofs, gutters, and foundations for
moisture problems, and for corrosion of metal ties for parapets and chimneys.
Make repairs and keep metal painted and in good condition.
Inspect and keep termite and wood boring
insects away from wooden structural members. Check exit steps and porches
to ensure that they are tightly connected and will not collapse during
an emergency exit.
Check masonry for deteriorating mortar, and
never defer repairs. Repoint, matching the historic mortar in composition
and detailing.
Contact utility companies for information
on flexible connectors for gas and water lines, and earthquake activated
gas shut-off valves. Strap oil tanks down and anchor water heaters to wall
framing.
Collect local emergency material for reference
and implement simple household or office mitigation measures, such as installing
latches to keep cabinets from flying open or braces to attach tall bookcases
to walls. Keep drinking water, tarpaulins, and other emergency supplies
on hand.
"The Seismic Retrofit of Historic Buildings" an Historic Preservation Brief
