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What You Need to Know: Earthquake Resistant Buildings

Earthquake resistant buildings save lives. They limit property damage and comply with the latest seismic building codes.

If you do business in high earthquake hazard areas, here’s what you need to know about seismic building codes.

1. Seismic Building Codes are Getting Tougher

In 2015, Los Angeles overhauled their seismic regulations. 15,000 buildings needed retrofitting to better withstand the effects of earthquakes.

For decades, safety advocates worked to pass ordinances strengthening two types of structures. First were the brittle concrete buildings on L.A.’s major boulevards. Second, the boxy wood-frame apartment buildings built on top of carports. Over 65 people died when these types of buildings collapsed during earthquakes in 1971 and 1994.

2. Designing Earthquake Resistant Buildings is a Regional Endeavor

Building codes are based on the base shear formula. This formula measures how much earthquake-generated shear force will try to push the house off the foundation base. The simple formula multiplies the expected ground acceleration by the building’s weight.

But there’s no set amount for anticipated ground acceleration. For example, Los Angeles anticipates a different base shear than the California Building Code does.  The International Existing Code’s ground acceleration is different still. Keeping this in mind, it’s always best to use a base shear that’s tailored to your geographic region.

3. It’s Not Just the Building, It’s The Ground Underneath

Earthquake resistant buildings are great. But let’s say a building’s foundation sits on soft soil. Despite the advanced engineering techniques used, it could still collapse in an earthquake.

But, if the soil beneath a structure is solid, engineers can improve how the entire building foundation system responds to seismic activity.

One example is base isolation. In this method, a building is floated above the foundation on bearings, springs or padded cylinders. A solid lead core is used for vertical strength with rubber and steel bands for horizontal flexibility. This allows the foundation to move without moving the structure above.

4. Seismic Engineering has a Bright Future

All around the world are examples of newer structures withstanding earthquakes. One example is the Transamerica Pyramid in San Francisco.

During the Loma Prieta quake, the building shook for more than a minute and the top floor swayed a foot side to side. A deep concrete and steel foundation and a buttressed exterior allowed the building to escape structural damage.

Sensor readings were taken from the building’s frame and processed by the U.S. Geological Survey. The results showed the building could withstand an even larger seismic event.

The future of seismic engineering doesn’t just look forward. Retrofitting older buildings is as important as new construction. One bright spot is engineers are effectively and economically adding base-isolation systems to existing structures.

After the 1989 Loma Prieta quake, engineers retrofitted the city halls of San Francisco, Oakland, and Los Angeles. These earthquake-resistant structures will be tested. When and how remains to be seen.

The Final Analysis

More jurisdictions are mandating seismic building code compliance. That’s where DHG comes in. Our experience with earthquake resistant design ensures your clients’ buildings will comply with the latest codes.

To see our seismic engineering services up close, contact us for a consultation.

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