Every building is different, and the approaches to safeguarding a structure against earthquake damage are incredibly diverse.
Yet in spite of these differences, there are some similarities in retrofit approaches based on building type – one of the most common being wood-framed, soft-story structures.
These apartment buildings, characterized by open parking on the ground floor and dwelling units above, are considered extremely vulnerable to collapse in a major earthquake. Many cities now require those built before the mid-1970s to be retrofitted for seismic safety.
Steel Frame Installation
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.
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 earthquakes on a variety of structures. Recent experiments on the performance of soft-story structures showed that collapse can happen when a building sways excessively – causing the building to collapse. To see a video of their testing, visit http://jacobsschoolofengineering.blogspot.com/2013/08/shaking-house-down.html.
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, new concrete is poured into the trench to hold it all together.
Drag Line Installation
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 your building risks
Many Californians live in earthquake denial. But this is an issue that should be in the forefront of everyone’s minds.
The California Earthquake Authority recently reported there is a greater than 99% chance of a magnitude 6.7 or larger earthquake, and a 93% chance of a magnitude 7.0 or greater occurring in California in the next 30 years.
San Diego is much more seriously at risk of earthquake devastation than previously thought.
A study released this year at the National Earthquake Conference by the Engineering and Environmental Research Institute projects extensive damage for the San Diego area should the Rose Canyon fault release a devastating 6.9-magnitude earthquake:
- $38 billion in building and infrastructure damage (roughly 10% of the total value of buildings and infrastructure in the region)
- 120,000 buildings sustaining moderate to complete damage
- 8,000 buildings damaged beyond repair
- 36,000 households displaced
Have we taken the measures we can to safeguard our homes, our places of business, our hospitals, schools and community? How many building owners will face lost income for prolonged periods? Are our buildings resilient enough to withstand the looming earthquake threats?
Is your building at risk? Contact Optimum Seismic today to arrange for a free assessment of your property today or call (833) 978-7664. Use the knowledge you gain to help safeguard your future.