How are earthquake-proof buildings designed

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Of all the possible natural disasters that threaten Switzerland, an earthquake could cause the greatest damage. However, most of the buildings in the country are not earthquake-proof.

This content was published on May 22, 2012 - 11:00 am
Rachel Marusak Hermann, swissinfo.ch

The earthquake in northern Italy on May 20th destroyed numerous buildings, historical and newer ones. It also reminded people of the need for earthquake-proof construction.

In Switzerland, around 90% of buildings still do not comply with earthquake-proof standards. The country still needs a lot of improvement before its structures can withstand a major quake. Retrofitting a building can be quite expensive.

"The only action that can be actively taken to reduce earthquake damage and save lives is to make buildings earthquake-resistant," explains Hugo Bachmann from the Institute for Structural Analysis (IBK) at ETH Zurich to swissinfo.ch.

Bachmann had been a professor at the IBK since 1969. He is one of the pioneers in earthquake engineering in Switzerland. Although progress has been made in the country's building structure, Switzerland still has a long way to go before it is prepared for severe earthquakes in this area, says Bachmann.

Highest damage potential

"We have initiated the process, but Switzerland is not yet prepared. It will take many decades to reach this point," explains Bachmann.

According to the Federal Office for the Environment, around 90% of the structures in Switzerland were built without adhering to the earthquake building standards. It is not known how susceptible these structures are to earthquake damage, but the standard could be quite high.

In Switzerland, earthquakes are considered to be the natural disasters with the highest damage potential. Although they happen less frequently than floods, they can have far greater consequences in terms of the extent of damage and devastation.

Rigorous earthquake construction standards

The first earthquake building standards were introduced in Switzerland in 1970. Since then, the requirements have been tightened with revisions in 1989 and 2003. According to today's standards, the extent to which a building should be earthquake-proof depends on a number of factors. Important criteria are the earthquake zone, the type of subsoil, the importance of a structure and the construction method and materials.

The importance of a structure (the so-called structure class) depends, among other things, on criteria such as the average occupancy, the damage potential and the usefulness of a structure immediately after an earthquake. For example, a fire station would be classified as more important than a single-family house.

Thomas Wenk, President of the Swiss Society for Earthquake Engineering and Building Dynamics, was involved in developing the specifications for the SIA earthquake building standards. He explains that ideally all structures should be built according to earthquake standards.

"It's not expensive for new buildings - it costs practically nothing. Because it is much easier to design something correctly from the ground up," Wenk told swissinfo.ch.

Mixed compliance

Since the year 2000, the federal authorities have increasingly focused their attention on earthquake prevention and damage prevention and have taken a number of measures to better prepare the country for a major earthquake.

As part of the federal government's program of measures to reduce the earthquake risk, all new federal buildings will be built in accordance with earthquake building standards.

The state government is also actively upgrading existing structures for which it is responsible. "The state government is way ahead. It systematically checks its structures, including highways and bridges," says Wenk.

However, according to the Federal Office for the Environment, private buildings make up around 95% of the building fabric in the state. Wenk explains that improving earthquake security is not just a matter for the federal government.

"Each canton has its own building and planning law. In addition to the cantons, the legal responsibility for the building industry also lies in part with the municipalities. We are of the opinion that the enforcement of earthquake building standards is insufficient in certain cantons," says Wenk.

At the moment, only five cantons - Aargau, Basel Stadt, Jura, Nidwalden and Valais - stipulate that before a building permit is granted, it is checked whether the construction plans comply with earthquake standards. Therefore, there are no statistics on how many new buildings in Switzerland are being built in accordance with the earthquake building standards. Many experts estimate that a significant proportion do not meet these standards.

Retrofitting costs

The most expensive way of increasing the earthquake resistance of buildings in Switzerland is to retrofit existing buildings. According to the Federal Office for the Environment (FOEN), retrofitting can be quite expensive, up to 20% of the building's value - on average it is between 5 and 10%.

The main building of the professional fire brigade was retrofitted on the basis of a risk analysis in the canton of Basel Stadt. The building was constructed from reinforced concrete in 1942, and the analysis concluded that the pillars on the ground floor would not even withstand a relatively weak quake.

In this case, the retrofitting was considered necessary because the building is located in a high-risk area and because in the event of an earthquake it is an essential building for emergency care.

Basel turned to Bachmann for expertise and the best strategy for making the building more earthquake-proof. He recommended making it "softer" so that the building can react more flexibly to seismic activity. The upper floors were separated from the basement with a horizontal cut and placed on earthquake bearings.

The retrofitting of the building, which could now withstand an earthquake measuring 6.5 to 7 on the Richter scale, was completed in 2008. The costs amounted to 3 million Swiss francs. That is around 23% of the building's value.

insurance

In Switzerland, the earthquake risk is not insured under the mandatory building insurance for fire and natural hazards.

In 1978, 18 cantonal building insurance companies joined together to form a pool that voluntarily provides benefits in the event of an earthquake.

The pool has around CHF 2 billion a year to cover damage - significantly less than the estimated amount of damage in the event of a major earthquake.

According to the Federal Office for Civil Protection, the damage caused by an earthquake measuring 6.5 to 7 on the Richter scale would amount to CHF 50 to 100 billion.

The building insurance of the canton of Zurich has its own fund for earthquake damage. The coverage is one billion francs.

In order to fill the previous loophole, various federal authorities are in favor of compulsory earthquake insurance. Parliament sees it similarly. In March 2012, it passed a motion calling on the government to ensure that compulsory earthquake insurance with uniform premiums is offered in the future.

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