Soft story buildings get their names for having the first stories less rigid, when compared to the above stories. These buildings are vulnerable to earthquakes because of the large unreinforced opening on their ground floors, and their typical wood frame based construction.
The unreinforced openings usually accommodate large windows, doors, or parking spaces and expansive lobbies in retail and residential buildings. Usually, when the first floor folds during a quake, the upper floors crush everything below it. So without inadequate design considerations, these buildings won’t stand a chance against the lateral forces generated by earthquakes.
Soft Story Retrofitting
The first step of any soft story seismic retrofitting is to analyze the structure well, and then determining the best way to strengthen the property. Contractors and structural engineers consider several factors while determining the best method for soft story retrofit of a building, and ensure that their work meets the structural standards required by the seismic retrofit Los Angeles ordinance.
To strengthen the existing walls, finishes like stucco or drywall should be replaced with sturdy plywood. Walls are anchored to the foundation as part of this process. Adding shear walls is very effective for providing lateral stability to the structure, but you will need to make sure that the extra wall would not interfere with the structure function. If they do, using steel frame will be the best option.
The cost for soft story retrofit works differs greatly, and mostly varies according to the type of building and the method used. Retrofitting large buildings could cost above $100,000, where a small structure won’t need even half of that amount.
Clearly, it is evident that soft-story seismic retrofitting isn’t cheap, but it is worth spending money for. A survey by Caltech found that there is a benefit to cost ratio of 7:1 for the money spent on shear walls and in case of steel frame retrofits with a 4:1 ratio for money spent.
Still, most building owners prefer not to take the matters into their hand because of the expense, so the city officials are adopting varies approaches to encourage owners or in some cases requires them to retrofit their buildings. Remember that retrofitting the building will make it earthquake safe and its sole purpose is to make the building stand during and after an earthquake.
Posted on Wednesday, January 24th, 2018.