Types of Buildings & Seismic Retrofits – Which Buildings Are High Risk for Seismic Activity?
Below is a description of each type of building and which ones are the most vulnerable of concrete tilt-up, URM (unreinforced masonry), non-ductile, steel frame and soft-story.
Concrete Tilt- up buildings have limited or weak connections from the roof to walls and weak connections connecting the walls together (continuity ties). Because of the heavy concrete walls, in the event of an earthquake, these walls want to pull apart from the roof, creating a collapse hazard. Evidence from previous earthquakes suggests that these buildings can be quite dangerous during a seismic event and suffer extensive damage.
A URM (Un-Reinforced Masonry building) is a type of building where load bearing walls, non-load bearing walls or other structures are made of red brick. Other types of weak wall materials that could be unreinforced are cinderblock, tiles or other material that does not have by reinforcing materials (rebar). Unreinforced masonry walls lack steel reinforcing bars, which add strength to the structure of a building.
Non-Ductile concrete is a term to describe a building made with concrete floors and walls. The characteristics of these types of buildings – they are very strong but, brittle. “Non-ductile” means inflexible therefore, non-ductile concrete buildings are more likely to crumble or collapse in an earthquake, posing greater financial and life-safety risk.
Steel frame is a building design usually with a “skeleton frame” of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all attached to the frame. Steel frame buildings are durable, reliable, ductile and a sustainable option to build low-rise to high-rise building projects.
Soft-story is a multi-story structure built with a first floor that is open in nature, much less rigid (soft) than the floors above. There are many examples of buildings with soft-story conditions including multi-family apartment buildings with tuck-under parking or subterranean parking as well as retail centers with open storefronts and minimal reinforcement on at least one elevation.
Which buildings are most at risk?
Concrete Tilt-Up – Buildings built before 1986.
URM (Unreinforced Masonry) – Buildings built without reinforcing. Almost all of them.
Non-Ductile – Buildings built before 1977.
Steel Frame – Buildings built before 1996.
Soft-Story – Buildings built before 1977.
Saunders Construction has over four decades of experience performing seismic retrofits. We have completed thousands of projects on every type of building and work closely with structural engineers to ensure the safety and strengthening capabilities of your real estate assets. If you are interested in protecting your assets, contact us https://saundersseismic.com/contact/.
Sources: FEMA * Seismicordinances.com * LADBG.org