Four Steps for Earthquake Resistant Buildings – Times-Standard

The number one cause of earthquake deaths is the collapse of structures. The key to reducing earthquake casualties is making sure buildings are protected for life.

There is nothing more important to the well-being of a community than the confidence that buildings, bridges, dams, and other structures will stand while you work, sleep, eat, and play. Most of the time, we don’t think much about it. But we must ultimately support our building codes, law enforcement and modification of legacy structures that make the built environment resilient.

There are four steps to earthquake-resistant buildings: understanding forces, how structures respond to those forces, applying laws and code, and inspecting/retrofitting older buildings. I am in awe of my earthquake engineering colleagues. They need to understand all the forces acting on structures, the nature of the earth’s interior, and what happens in various earthquakes. It is not only the permanent gravitational force, but also dynamic forces such as wind and earth vibration. Even subtle things like daily and seasonal heating and cooling should be part of the mix.

There are also forces resulting from the use of the building. Vibrations from machines and even people moving in and out of places add extra loads. The people factor was something San Francisco didn’t think about in 1987 when it opened the Golden Gate Bridge to celebrate its 50th anniversary. Expecting a crowd of 50,000, the planners were stunned when they crowded 10 times onto the structure and flattened the normally arched roadbed, a load the structure was never supposed to carry.

Earthquake engineering has its roots in four different countries. It should come as no surprise that the United States (California), Italy and Japan were important players early on – all regions with relatively frequent large earthquakes. But the first quantitative studies date back to the British Isles, a region of extremely low seismicity when Robert Hooke, an English physicist, chemist, mathematician, architect, and genius, presented a series of papers in the late 18th century on earthquakes and structures. .

Over the next two centuries, earthquake engineering developed into a mature discipline. Each major earthquake provided new data and insights into how structures respond to strong vibrations. 1971 San Fernando opened its eyes to the vulnerabilities of buildings made of unreinforced brick and unstressed concrete. The 1989 Loma Prieta earthquake showed a bright spotlight on the weaknesses of ground floor garages (soft stories). The 1994 Northridge earthquake focused attention on the seams in steel-structured buildings.

The University of California at Berkeley has been one of the centers of strength in earthquake engineering. The first modern vibrating table was built around the time I started my graduate studies. Several of my professors collaborated on experiments to test how structures respond to typical seismic vibrations. There are now 12 major earthquake engineering centers in the United States and dozens worldwide. We know how to build structures that can withstand the strongest vibrations of an earthquake. Chile’s 2010 8.7 scale and 2011 Japan’s M9.1 were witnesses to how well buildings would perform in large tremors if they were designed according to modern codes.

But that’s a big deal then. It is more expensive to build structures to withstand strong side-to-side movements in earthquakes and to include redundant design elements so that if a part fails, it will not collapse. The biggest problem is what to do with legacy structures, those that were built before codes or designed to meet older code specifications.

The 2011 Christchurch earthquake provides a sobering example. New Zealand building laws are as strict as any in the United States. I visited Christchurch in 2001. It’s a wonderful city and like most American cities, it has a mix of old, middle-aged, and recently built buildings. The Christchurch earthquake was only 6.2 but had its epicenter under the city in the middle of a working day.

When the dust settled, 185 people lost their lives. It was no surprise that the unreinforced brick buildings in the Historic District sustained extensive damage, but what shocked me were the many reinforced concrete structures built in the 1960s. The collapse of two buildings – the six-storey Canterbury Television Building and the four-storey Pine Gold Guinness home – killed more than 70%. Neither of these buildings could have been built today, but, like most places in the world, the owners of the buildings were not required to bring them to the existing code.

There are thousands of buildings that are no different from Christchurch’s two buildings in California, many others in earthquake zones in the western US and we still haven’t dealt with the stock of all the other buildings with problems like unsupported construction or soft floors. West Coast states are well aware of the problem and there are a number of retrofit initiatives in the pipeline. But the cost of upgrading each old building is staggering and without massive public support to pay for retrofits, progress will still be slow.

There are two reasons structural engineering came to my mind this week. This first had nothing to do with the earthquake. The collapse of the Champlain South Towers in Surfside, Florida was a harrowing reminder of the consequences of construction failure. We won’t know the exact causes of failures for months or years, whether there was a defect in the original construction or a deterioration over time that led to the collapse, but the similarity to failures in past earthquakes is astounding (https://temblor.net/earthquake-visions/view- Florida-building-collapse-bears-similarities-to-other-tragedies-12923/).

The second was the M6.0 Antelope Valley earthquake south of Lake Tahoe on Thursday. Fortunately, it was in a remote area and other than the overturned items and a few cracks, no damages or injuries were reported. But this is the third largest or equal to the M6 ​​earthquake in California in just over two years. We were lucky because they were away from the densely populated areas of the state. In the not-too-distant future, the M6-plus will hit the San Francisco Bay Area, Southern California, or near another metropolitan area, once again testing the resilience of our engineering structures.

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