If you own an apartment complex in the Los Angeles area, you should have been notified by now to complete a soft-story retrofitting on the property. The shaking forces of an earthquake cause buildings to rock from side-to-side. As long as the earth is moving, soft-story buildings will sway more violently and could build up enough kinetic energy to collapse. During the 1994 earthquake, many soft-story buildings did just that. The purpose of the soft-story retrofit program is prevent loss of life by making these structures more resistant to earthquakes.
How much resistance your building will need is determined by three different factors. How much does the building weigh, how close is it located to a fault line, and the highest hypothetical magnitude that fault line can experience. Three different methods are used in soft-story retrofits. Which one, or two, your building needs will help to determine the cost of the project.
Shear walls are used to strengthen the entire building and keep it from swaying during an earthquake. Adding shear walls is one of the most affordable solutions when it comes to retrofitting. During a seismic event, the walls will move laterally, and if the shaking force is strong enough, the building can separate from its foundation. The shear walls prevent this from happening so your building will be more likely to remain standing after an earthquake.
Shear walls come in two different styles; plywood and pre-fabricated steel. Simpson Strong-Tie and MiTek Industries are two companies that make shear wall panels. The pre-fabricated panels include load ratings and specifications provided by the manufacturer. Steel shear walls provide more lateral resistance than the plywood does. They are ideal for retrofitting parking areas with a low clearance and your tenants will not be impacted during the installation.
The costs of this type of retrofit is determined by which shear wall you use and how long it takes to install it. Plywood shear walls are more affordable, about $250 each and they include the necessary hardware. A pre-fabricated steel wall costs anywhere from $350 to $600 per piece. While they plywood is cheaper per panel, they typically take a two man crew two days to install. This could drive the cost up significantly. Steel shear walls only take a two man crew one day to install.
The cost of a retrofit project using plywood shearing versus a pre-manufactured steel shear wall can vary. But on a small soft-story building you can expect to pay the following prices. A 12-foot plywood shear wall can cost about $3,000 including labor and materials. Using a premanufactured shear wall like the Hardy Frame from MiTek USA can cost about $2,650 in labor and materials. We do urge you to keep in mind that a soft-story retrofit project has other costs like demolition, excavation, concrete pours, and stucco repair. Utilizing shear walls for a soft-story retrofit can cost as low as $20,000 or as high as $40,000. But keep in mind this solution is best for smaller buildings or large buildings with a small overhang. Do not expect to use this solution on a 25-unit apartment complex.
The cost of your retrofit project using steel versus plywood will vary. A small soft-story building retrofitted with a 12-foot plywood shear wall will run about $3,000, this includes labor and materials. The same building retrofitted with a pre-fabricated steel wall will cost about $2,650. Shear walls are ideal for retrofitting smaller buildings with a minimum overhang. Larger apartment complexes, such as those with 25 or more units, will require a different method. Remember that your retrofitting project as other costs too, including demolition, concrete pours, stucco repair, and excavation.
Steel Cantilever Column System
The cantilever I-beams have quickly become the most used soft-story retrofitting system. They are often more affordable than adding shear walls or special moment frames. However, they are not suitable for all buildings. Cantilever beams are ideal for retrofitting smaller buildings that have narrow spaces. If you choose this system be sure the company you hire inspects the existing wood frame. During the forces of an earthquake, the wood components will be pushed up against the steel columns which may cause them to buckle or break if they are not reinforced as well.
If the I-beam should become damaged during an earthquake, it will need to be removed and replaced, which could add more costs to your project. Typically a small apartment complex retrofitted with cantilever columns will cost around $35,000, while larger buildings with two or more stories will cost somewhere around $65,000 to $75,000.
Special Moment Frames
Special Moment Frames are the ideal solution for most soft-story retrofits. They come in a variety of sizes and can be delivered flat shipped or already assembled. One of the better frames is the bolted system by Simpson Strong-Tie. This frame comes in sections and is bolted together, making it easier to repair after an earthquake. Their frame systems are designed with a special link that absorbs the damage and shock from a seismic event and are the only ones that are reusable.
Special moment frames are used in large or heavy buildings. Depending on which manufacturer you choose, you can expect to pay around $8,500 to $10,000 per frame. A large apartment complex could cost you about $70,000 or upwards of $110,000 depending on how many frames your building needs.
The prices listed here are provided to give you an estimate of what your soft-story retrofitting project could cost. Since the goal of the job is to prevent loss of life, the cost should not be the driving factor. For a complete bid, contact one of our professional staff. RetroFitting 360 has been performing seismic retrofits throughout the greater Los Angeles area. We specialize in soft-story buildings of all sizes and our contractors have been specially trained in the field of seismic retrofits.