Every building is different, and the approaches to safeguarding a structure against earthquake damage are incredibly diverse.
Naturally, every building owner has specific questions about his or her project: What will you need to do to my building? How long will it take? How much will it cost?
It’s impossible to answer without seeing the property, measuring it and calculating the work to be done based on seismic engineering.
What is a Soft-Story Structure?
Even though every project is different, there are some similarities in virtually every soft-story retrofit project.
Let’s start by going over some of the characteristics of a soft-story structure—a type of architecture commonly used for apartment buildings, with parking situated on the ground floor and dwelling units built above.
Soft-story structures are common among apartment buildings, characterized by open parking on the ground floor and dwelling units built above. Those constructed prior to 1978 are considered extremely vulnerable to collapse in a major earthquake and a growing number of cities have passed laws requiring them to be retrofitted.
For most soft-story structures, the installation of a steel moment frame or frames helps to prevent the excessive swaying that can lead to building collapse.
Where to place the frame and how many of them to use are subject to the unique distinctions of each individual building.
The frames are installed not for weight-bearing support, but to stabilize the building during an earthquake. It’s important that the frames themselves be somewhat flexible. Strategic location of frames can enhance their ability to absorb some of the shock of the earthquake and minimize the building sway that can lead to collapse.
The University of California at San Diego, home to the world’s largest outdoor shake table, has done repeated tests replicating the effects of a quake on a variety of structures. They recently conducted experiments on the performance of soft-story structures and determined that collapse can happen when a building sways excessively—causing the building to collapse.
The steel frames must be secured by foundations, which means they must be firmly connected and rooted into the ground beneath the structure.
This should be done by trenching the area where steel frames are to be installed, then fortifying the area with concrete and rebar. Existing concrete is bonded to the new material with rods that are inserted into a series of holes drilled into the existing foundation and secured with epoxy. The rebar is then placed inside the trench and all points are firmly secured. Finally, the new concrete is poured into the trench to hold it all together.
The dragline is the term used to describe the means of delivery of earthquake loads to steel frame. It’s important to make sure that the dragline is properly secured to the structure itself to provide additional support and stability.
We often go in and do a comprehensive securing of the dragline to the structure, which also provides added strength and support.
Educate Yourself about the Law and Your Building
The Apartment Association, California Southern Cities is hosting a series of educational seminars to help inform members about the laws, applications and other important information regarding seismic retrofits.
The next seminar will be: Wednesday, Oct. 11, 6 p.m. to 7:45 p.m. Downey City Library Cormack Room 11121 Brookshire Ave. Downey, CA 90241
Feel free to stop by with any questions you may have. Remember: Performing your due diligence is an important part of the process.