There are many types of buildings when it comes to commercial retrofits including:
Tilt-up construction is one of the most popular methods for building commercial buildings in the United States. Tilt-up concrete construction is becoming a more and more widely used method due to construction cost benefits, safety and speed. The buildings types vary from office to retail, manufacturing, distribution centers and many more. Early designs of these building types (mid 1990’s), only had limited or weak connections from the roof to walls and continuity ties.
With current engineering knowledge, it is well understood that these buildings need to be retrofitted to make them safer and perform better in the event of an earthquake. 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 seismic retrofit for a concrete tilt-up building is relatively inexpensive. The cost per square foot price can be quite competitive, usually around the cost of a roof replacement, depending on a building’s characteristics.
Non-Ductile Concrete is a term to describe basic 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.
Most retrofits include the addition of concrete footing, Gunite, FRP for columns and walls and drag lines to distribute the force throughout the building.
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. Structural steel framing is a durable, reliable and sustainable option to build low-rise to high-rise building projects. Typically, the building frame systems have vertical and horizontal structural elements designed by a system of structural steel beams and columns. Column spacing is typically 25 to 45 feet on center, with spacing variations lower and higher depending on architectural requirements. It is adaptable to almost any architectural layout and is used routinely on a variety of building projects.
The elements usually used to retrofit a steel building are adding or strengthening steel, brace frames, additional footings and drag line to distribute the force throughout the building.
URM (Unreinforced Masonry)
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 brick, cinderblock, tiles or other masonry material that is not braced by reinforcing materials (rebar).
Unreinforced masonry walls lack steel reinforcing bars, which add a lot of strength to the structure of a building. URM structures are vulnerable and remain at greater risk for a partial or complete collapse in an earthquake. Generally, the mortar used to hold bricks together is not strong enough to withstand much impact or ground movement without additional masonry.
Most retrofits include the addition of concrete footing, Gunite, steel reinforcement for columns, additional wall ties and drag lines to distribute the force throughout the building. Sometimes it is necessary to add plywood to the roof diaphragm due to the existing roof material being 1×6.