historic building project photograph - an example of an earthquake strengthened historic building

FIELD & HALL LIMITED

SPECIALIST BUILDING CONTRACTORS, and specialists in Seismic Strengthening.
Since 1923
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WHAT IS EARTHQUAKE STRENGTHENING?


"Earthquake Strengthening", or "seismic strengthening", is the process of retrospectively adding strengthening elements into existing buildings in earthquake risk areas in order to make them more resistant to the stresses imposed on them during Seismic (earthquake) events. This is particularly relevant in a seismically active area such as Wellington, which experiences numerous smaller earthquakes and is at risk of a significant event, and particularly as many buildings were built before regulations required them to meet safety requirements.

During an earthquake, the surface of the ground moves both up and down and side to side. As a result of this ground shaking, the base of a structure begins to move and this movement is transferred to the top of the structure through the construction materials, and if these do not allow for either sufficient flexibility or strength to transfer this stress without failure (and therefore potential damage or catastrophic collapse), then the materials that were originally used in the construction must be strengthened (usually by incorporating structural elements that tie the various parts of the building together), as the only safe alternative would be a complete rebuild. Although significantly cheaper than ground-up construction, retrofitted seismic strengthening requires considerable design and implementation, and therefore requires specialist construction.

Any area of high seismicity in the New Zealand context, and areas therefore zoned as high risk from significant earthquake, will require older buildings to be strengthened.
Examples of the actual methods used for earthquake strengthening are the installation of structural steel beams in rigid arrangements such as "K beams" (shown in the photograph on the right), which support the existing structure but allow a certain degree of flexing and movement during earthquakes without risk of collapse. These K beams are incorporated into the existing structure, supported on new, deeper foundations and extended into the structure in order to support numerous stories above.

Structural steel beams are not the only method of Earthquake Strengthening. Sprayed concrete shear walls, carbon wrapping and micro piling are all utilised either individually or in combination to strengthen a building sufficiently to meet earthquake code requirements.

For more information on Earthquake Strengthening please email us at info@fieldandhall.co.nz
drawing of earthquake strengthening detail
earthquake strengthening K beams
earthquake strengthening shear walls
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