Non-Ductile Concrete Structures

What is a non-ductile reinforced concrete building?

Non-ductile reinforced concrete buildings are structures with highly brittle connections and columns. In short, these buildings were constructed with a limited amount of reinforcing steel in the columns and walls, thus making them susceptible to movement and failure during strong seismic events.  

Is my concrete building non-ductile?

Most concrete buildings designed and built prior to the implementation of the 1976 building code fall under this category. However, a structural evaluation performed by a licensed civil engineer, structural engineer, or architect is necessary to determine whether a structure meets the specifications for a non-ductile reinforced concrete building.

Why must they be retrofitted?

Multiple events—including the Mexico City earthquake (1985), Northridge earthquake (1994), Great Hanshin earthquake (1995), Christchurch earthquake (2011), and Kumamoto earthquakes (2016)—drew attention to the hazards of concrete buildings constructed under outdated building codes.  Structures of this type exhibited poor performance due to the lack of adequate lateral (side-to-side) confinement of the concrete core within the beams, columns, and joints. When subjected to lateral movements during an earthquake, which cause inadequately confined concrete cores to break up, these structures are often unable to sustain gravity loads, making them vulnerable to collapse. Retrofitting non-ductile concrete buildings is necessary to correct these inadequacies and improve anticipated performance of the building in future seismic events.

What action is necessary?

Buildings categorized as non-ductile reinforced concrete construction must undergo a structural analysis by a qualified individual. If the building does not meet the minimum earthquake standards specified by the ordinance, it must be either retrofitted to improve the lateral-force restraining system, or demolished. As required by the ordinance, both tenants and occupants of any non-ductile concrete building must be notified of the structure’s status. Refer to your municipality’s ordinance for more information. 

How can non-ductile reinforced concrete buildings be retrofitted?

Possible retrofitting techniques include the addition of appropriate shear walls, addition of steel moment-resisting frames, and several other types of structural intervention. It is recommended to seek expert advice in order to select the most practical and economical solution for each unique structure.  

What is the compliance timeline?

Each municipality listed to the left has a unique timeline that specifies deadlines for assessment, tenant notification, and retrofit. See the links for more detail on the timeline for your municipality.

 

The information provided on SeismicOrdinances.com is general in nature and should not be relied upon as fact. Persons requiring specific information on seismic ordinances should contact their local municipality or e-mail seismicordinances@wje.com.