In many areas of the United States and around the world, the prospect of an earthquake or another seismic event is a frightening reality. Building experts, architects, and engineers are hard at work on new building designs and ways for property owners to retrofit their properties to come up with earthquake building codes.
The practice of making buildings resistant to seismic activities and ground motions during an earthquake is known as seismic retrofitting. There are a variety of retrofit techniques for existing buildings. These techniques will vary based on the structural system, materials, building configuration, as well as the usage of the structure (e.g., residential, office, or hospital buildings)
Dr. Pedram Zohrevand is a scientific researcher and engineering consultant. He shares his knowledge and experience regarding two common existing building systems with seismic deficiencies and the most efficient seismic retrofit techniques for each system.
Wood Frame Structures
The wood-frame structure has always been one of the most common construction systems, especially for low-rise buildings in the US. Scientists and engineers have recorded the structural performance of wood-frame buildings during different earthquake events over the last 100 years. The building codes have been improved according to these observations and findings.
One big issue with wood-frame structures built before 1980 was their soft-/weak-story deficiencies caused by tuck-under parking and open parking areas, which was addressed in the building codes established in the late 1980s. As per recent building assessment reports, there are more than 45,000 wood frame buildings in the State of California with soft, weak, or open-front deficiencies which had been built before 1980.
Many cities in California have been recently adopted mandatory retrofit ordinances for their soft-/weak-story wood frame buildings.
The most common retrofit systems for wood-frame structures with soft-/weak story deficiencies are wood shear walls, cantilever columns, and moment frames.
Each of these retrofit systems has its pros and cons and specific requirements for their design and installation.
As per Dr. Zohrevand, it is very crucial to precisely evaluate the existing condition of a building, its layout and configuration, parking spaces, and the accessibility of open wall areas to select the most efficient retrofit system for the building.
Non-Ductile Concrete Buildings
The reinforced concrete structure has also been a common construction system for mid- and high-rise buildings over the last 80 years. Building codes have been improved for the design of such structural systems since their emergence.
During earthquake events that had happened before 1975, reinforced concrete buildings showed poor performances under lateral movements, mainly due to their common deficiencies in their steel reinforcement detailing. The lack of steel reinforcement detailing in these concrete buildings results in their non-ductile and brittle behavior, which significantly reduces their earthquake energy dissipation and consequently causing different failures and collapses in these buildings.
As such, the building codes after 1976 incorporated new provisions to address the ductility issues in concrete structures. Currently, there are several mandatory seismic retrofit programs in earthquake-prone regions, such as Californians, for their concrete buildings built before 1977.
Several retrofit techniques can be used for non-ductile concrete structures. Still, one of the most efficient retrofits approaches for these buildings is the application of fiber-reinforced polymer (FRP) materials, which have been recently introduced in the construction industry.
FRP composite materials can be applied as reinforcement on the surface of existing concrete elements with minimum destruction and interruption to the building operation, which can significantly reduce the associated retrofit construction costs, compared to other traditional retrofit techniques.
Dr. Zohrevand’s research and expertise have been focused on innovative retrofit techniques for concrete structures using advanced materials, especially fiber-reinforced polymers. He has had several workshops and speeches for engineers, contractors, and homeowners presenting the retrofit design and construction techniques using fiber-reinforced polymers.
Retrofitting Your Home or Business
Retrofitting your home or business against seismic events can be expensive and time-consuming, but it is worth looking into if you live in an area where these events are frequent.
Dr. Pedram Zohrevand underscores the importance of making your home or business safe for unexpected seismic events. If your home is retrofitted, you may be able to escape from a future earthquake without serious property damage or personal injuries.