Seismic Retrofit and Earthquake Engineering

Seismic retrofitting soft-story buildings

With a better understanding of seismic retrofitting and earthquake engendered, we will talk in this article about an interdisciplinary branch of engineering and the modification of existing
structures which are to design and analyze structures, such as buildings and bridges and then make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes.

Seismic Retrofitting

Seismic retrofitting is the modification of existing structures, which aims to make them more resistant to ground motion, any seismic activity, or soil failure during earthquakes. The seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need for seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries, for example, the United States, Japan and etc, and late 1970s for many other parts of the world, such as Turkey or China, many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the following problem, many research works have been carried out. 

While the current practice of seismic retrofitting is predominantly concerned with structural improvements to lessen the seismic hazard of using the structures, it is similarly essential to reduce the hazards and losses from non-structural elements. Also it is important to keep in mind that there is no such thing as an earthquake-proof structure, even though the seismic performance can be greatly enhanced through proper initial design or subsequent modifications.

Earthquake Engineering

Earthquake engineering is one of the multiple branches of engineering that analyzes and designs structures, such as bridges and buildings, always keeping in mind the coming possible earthquakes. The overall purpose of earthquake engineering is to make such structures more resistant to earthquakes. An earthquake engineer (also a seismic engineer) aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in case of major earthquakes. Earthquake engineering is the scientific field concerned with protecting the natural environment, society, as well as the man-made environment from earthquakes by limiting the seismic risks to socio-economically accepted levels. Traditionally, it has been narrowly defined as the study of the behavior of geo-structures and structures subject to seismic loading. It is considered as a subset of structural engineering, mechanical engineering, geotechnical engineering, also applied physics and chemical engineering, and so on. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering, nuclear engineering, and from the social sciences, especially sociology, political science, economics, and finance.

seismic engineering

The main objectives of earthquake engineering are:

  • Foresee the potential consequences of strong earthquakes in urban areas and civil infrastructure.

  • Design, construct, and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.

A properly engineered structure does not necessarily have to be extremely strong or expensive. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.

The Strenght of your Building

During an earthquake, the strength of your building is put to the test. Ground forces try to tear the home apart and in many cases, cause severe damage.  It’s important that the structural frame of your home is strong enough to absorb an earthquake’s energy. The “Bolt it-Brace it-Do it” Home Retrofit Program is being offered through a partnership with the Homebuilders Association of Kitsap County, Kitsap County Emergency Management, Simpson Strong-Tie, and the Building Departments of Kitsap County. So, to understand why you should retrofit your home just ask the following 5 questions yourself.

  • Am I living in an area prone to earthquakes?

  • Was my home built prior to 1978?

  • Is my home built on a raised foundation?

  • Is my home built on a hillside?

  • Do I have a garage?

Earthquake-Prone Areas

Almost half of all Americans live in earthquake-prone areas, says the USGS, because of population growth and an increase in 'induced earthquakes' far from fault zones. The number of earthquakes shaking the US has been on the rise in recent decades, and now nearly half of all Americans now live in earthquake-prone areas, according to a recent study by the US Geological Survey (USGS) published in the journal Earthquake Spectra and the populations have grown significantly in areas prone to earthquakes, and USGS scientists have improved data and methodologies that allow for more accurate estimates of earthquake hazards and ground shaking. Also, the USGS found that approximately 57 million people live or work in areas where the kind of shaking that destroys buildings can be expected to happen at "moderately frequent intervals," or once every 475 years. This translates into a 10 percent probability of occurring within 50 years. And here you can find the list of earthquakes in the United States.

Homes Built Prior to 1978

Homes built prior to 1978 are typically more vulnerable to earthquake damage. Most homes built after 1978 were designed to conform to stricter building codes and are most likely better equipped to resist the force of an earthquake. 
Indeed, a big problem involves homes built before 1978 with a handful of steps above the ground, where there is a crawl space a few feet tall between the floor of the house and the concrete slab foundation.

Supporting Structure Under the House

If your house is not built on a concrete slab, chances are it’s built on a raised foundation - those homes typically have a crawl space. This supporting structure under the house may not have been built to resist seismic forces and can be highly susceptible to structural failure in an earthquake.

Homes built on a hillside

Homes built on a hillside typically have raised foundations and tend to have more severe failures because the structural framing supporting the house – posts and cripple walls – are built at different heights.

Garage door openings

Another reason to create vulnerable areas in a house is garage door openings. The narrow walls on either side of the garage door must be carefully designed to resist earthquake forces. This is extremely important if there is a living space above the garage because these rooms add weight that the garage framing must support.
Note: if you live in an older home with a living space above the garage or on a hillside, you’ll need to consult with a licensed structural engineer for design solutions.