Every structure has a service life -that is the expected lifetime, or the acceptable period of use in service. To ensure the smooth performance of the structure in its service life, a comprehensive maintenance plan is needed. Seismic Repair and retrofit is a core part of maintenance plan for areas with high seismic activity. In this article, we will review some aspects of seismic repair and retrofit, and how different materials can be used for this purpose. “When dealing with maintenance of any asset, the decision will come down to one of the three R’s: repair, replace, or retrofit.” (Ammad Ahmed Baig).
Inadequate and ineffective maintenance can reduce the effective service life of the structure, and make them vulnerable to major hazards, such as strong ground motions.
Seismic Repair and Retrofit
Recent advances in materials engineering has opened doors to some new retrofit and repair techniques. Retrofit and repair techniques have developed significantly over the past few years. The introduction of performance-based design has also changed the traditional design procedures, which was normally force-based criteria. For example, the concept of ductility has become an important parameter in the repair and retrofit design.
A good repair or retrofit solutions should address the main performance challenges in the structure, be performed with minimum intervention, and stay economical. In the case of existing concrete structures, the repair and retrofit should address the following main deficiencies (normally observed in older structures):
- Inadequate flexural or shear capacity
- Short lap splice lengths of the longitudinal reinforcement in potential plastic hinge regions,
- Insufficient and poorly detailed transverse reinforcement
- Inadequate shear strength required to develop hinging
Such deficiencies can reduce the capacity of the concrete elemenets, reduce their ductility, and cause pre-mature failure at critical locations (i.e. plastic hinge location, where we need high levels of ductility). In this article, we introduce two jacketing techniques.
Jacketing is a common technique in seismic retrofit of existing structures and it can improve strength, stiffness and the confinement of existing elements. Different jacketing techniques are available:
- Concrete: plain concrete, fibre-reinforced concrete or reinforced concrete, Shotcrete
- Fiber reinforced polymers (FRP) jackets
The following two documents provide a comprehensive review on two racketing techniques for the repair and retrofit of concrete structures.
CFRP has been effectively used to improve the flexural and shear response of beam and column elements. In the case of columns, FRP jacketing is a very good approach to improve the strength and ductility. However, these techniques can be used in other structural elements such as shear walls in the buildings, and concrete piers of bridges.