Seismic Retrofitting is the method of strengthening of the already built damaged/undamaged old/new structures those are found to be weak in earthquake loadings that may occur in future. Generally, structures vulnerable to earthquakes are retrofitted by means of Steel jacketing, Concrete jacketing, Galvanized steel mesh reinforcement, Inclusion of new Supporting walls / Concrete shear walls, Steel bracings, Fiber Reinforced Polymer (FRP) sheets.
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with the recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Earthquake engineering is applied for the seismic retrofit of structures that involves alteration of existing structures to obtain resistance to seismic activity or soil failure due to earthquakes. Retrofit is now widely performed, especially in the active seismic zones.
Seismic retrofitting may be executed on concrete masonry, unreinforced masonry, soft story and concrete tilt-up construction. Soft story building is a multi-story building with abundant open space and in concrete tilt-up construction. Concrete is filled in the panels that form the walls of the structure. Since the concrete tilt-up walls are normally heavy, seismic retrofitting may be necessary. The motive for the concrete tilt-up retrofit is to prevent the separation of the roof from the building walls.
Most houses need to be seismically retrofitted in three ways:
1. The cripple walls of the house need to be braced with plywood.
2. The house needs to be bolted to the foundation.
3. The floor of the house needs to be attached to the braced cripple walls.
There are several categories of seismic retrofitting and their nature depends upon the purpose for which the retrofit is executed. The main form is the public safety retrofit involving structural reinforcement to save human life though some degree of injury is acceptable. Such retrofit is performed on structures that are not extremely expensive and for which a complete rebuild is not desired. A lower level retrofit may be selected to ensure earthquake endurance of the structure with some repairs needed after the earthquake. Extensive retrofit may be essential for buildings that are important due to cultural, historical or other reasons. Mostly, retrofit is performed on buildings that are extensively high, with an unsafe earthquake vibration frequency. Roads also have a priority in retrofit because their service is essential during an earthquake to ensure the function of emergency services.
There are numerous techniques that are used for the seismic retrofitting of structures. Their selection is based on the objective of retrofit, type of structure, soil conditions and the expenditures involved. Seismic retrofitting of buildings may reduce the earthquake damage by suitable structural modifications, but no technique will completely eliminate the risk of seismic waves. Reinforcement of the buildings by the use of girders and trusses are normally implemented to make the buildings safe.
Proper study of the existing structure using various analytical tools need to be carried out to identify the weak zones within the structure prior to carrying out retrofitting works. It also helps in the selection of proper retrofitting measure that should be adopted in terms of economic and safety aspects.
To get started today or for more information, contact us today to schedule a FREE on-site inspection by our team of soft-story experts or call us now at (818)287-8002.
Posted on Monday, April 15th, 2019.