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Earthquake engineering
When earthquakes occur, they devastate populations killing many and destroying property. Earthquake engineering provides a strategy to reduce some of the earthquake or seismic risk to structures when correctly used. In the event an earthquake occurs, buildings suffer damage and sometimes collapse damaging much property, interrupting lives including business, and causing many casualties. The design of building codes help to minimize some of the impact, by ensuring minimal damage and little collapse. Using earthquake engineering contributes toward being earthquake resistance thus limiting the levels of damages to buildings, reducing property loss, and minimizing incidents of collapse; however, failure to be earthquake resistant may lead to additional damage as exemplified in the Haiti earthquake and China.
Earthquake engineering refers to the application of technical and non-technical efforts available in subject areas such as geophysics, geology, seismology, vibration theory, structural dynamics, structural engineering, and construction to build structures safe from seismic risks (Bozorgnia & Bertero, 2004, p. 1.10). The building designs moreover ensure that when an earthquake occurs, the damage is at an acceptable socio-economic level. Notably, earthquake engineering does not focus solely on reducing the impact of earthquakes on buildings but on reducing the effect of seismic risks to other factors within the social and economic arenas. Furthermore, the discipline incorporates attributes from a diverse range of disciplines in science and engineering.
To understand the basics of earthquake engineering, it is paramount to consider the nature of earthquakes and the associated problems that necessitate earthquake engineering. According to Scawthorn (2006, p. 1), earthquakes refer to a broad spectrum of vibratory ground motions induced from either tectonic ground motions, volcanic action, landslides, rock bursts, and man made explosions. Most result from naturally occurring tectonic ground movements caused by shifting in rock along the faults within the earth’s crust.
Seismic hazards or risks signify the effect of the earthquake. The seismic hazards or risks facilitate the damage an earthquake can cause to the built environment. The risks include fault damage, ground shaking or vibration, inundation such as tsunamis, fire, ground permanent ground failure, and release of hazardous materials (Scawthorn, 2006, p. 1). The earthquake-related hazards usually differ between earthquakes, with one form being more dominant in one earthquake compared to another. For example, one area can experience massive damage through ground motion causing collapse of buildings, whereas another can experience considerable inundation causing damaging tsunamis.
To reduce the presented damage, it is advisable for countries to execute various earthquake preventative measures for protection from earthquakes. This is especially important considering the high loss of life, injuries, and socio-economic losses attributed to earthquakes (Bozorgnia & Bertero, 2004, p. 1.11). Earthquake engineering provides a useful way to control the built environment thus reducing the seismic risks resulting from an earthquake.
The basics of earthquake engineering start from understanding its use, which is to limit the amount of losses that result from an earthquake event to acceptable levels (Bozorgnia & Bertero, 2004, p. 1.11). Notably, every earthquake results in some form of damage; however, these can either be massive or minor depending on the magnitude of the quake and the possibility of structural stability. Earthquake engineering makes newly built or modified structures more resistant to seismic activity, cushions them against soil failure in cases of earthquake, and reduces the impact of ground motion (BluEnt, 2010). Earthquake engineering process promotes structural stability thus reducing the impact on structures; hence, minimizing potential damage to buildings, bridges, roads, port facilities, and public utilities as well as reducing risk of loss of life that would result from the earthquake.
The process in earthquake engineering involves initially seismic hazard identification. This requires the concerned team to determine the anticipated earthquake and the possible seismic hazards such as determining the possibility of liquefaction at the site (Day, 2002, p. 1). The earthquake engineer may consider whether the upcoming or planned structure will be able to withstand an earthquake considering the presented factors such as soil structure and strength, which may play a significant part in reducing the impact. Other consideration may include presented slope movement, and presence of excessive settlement that can affect the forces attributed to an earthquake.
Earthquake engineering also involves structural analysis, and design, to prevent structural collapse and reduce damages to property. When determining structural attributes, the earthquake engineer may consider the type of foundation they require for the structure considering anticipated earthquake (Day, 2002, p. 1). The structural foundation may be shallow or deep, with the decision based on the foundation likely to present the best resistance to the effects of the anticipated earthquake and seismic risks.
Further, earthquake engineering involves retrofitting, where if the determined structural attributes differ from those in the original planning, the engineers may refit the plan to accommodate the need for earthquake protection. According to Day, engineers may access the effects of ground movement in relation to seismic forces on the structure and accommodate the results on the anticipated displacement (Day, 2002, p. 1). Retrofitting ensures that the structural design fits with the area as per anticipated earthquake, for both structures under renovation and new structures.
The earthquake engineering involves building earthquake resistant structures. This denotes construction of structures that respond to safety and durability. Structures that benefit from this form of architecture include bridges, dams, road viaducts, and towers, while others use it through retrofit such as un-reinforced masonry, and insufficiently enforced concrete structures (BluEnt, 2010). Earthquake resistant architecture should follow the right procedure in carrying out mitigation measures. The procedure involves estimating the risks, examining mitigation alternatives, and choosing the most appropriate alternative.
When constructing earthquake resistant structures or modifying existing structures to adhere to requirements, possible investigations should follow to determine suitability (Godden, 1997). Such investigations contribute to determining the structures have followed seismic building codes and guarantee safety in terms of collapse and damage.
The architecture differs between high-rise and low-rise buildings (BluEnt, 2010). The construction of low-rise buildings such as those up to 10 stories is relatively stiff and light to ensure they have a higher resonant frequency. High-rise buildings on the other hand incorporate ductile steel frames that respond to their lower natural frequencies because of their height.
Failure of buildings during earthquakes relate to incompetent workmanship and haphazard selection of structural materials for construction (Godden, 1997). Proper inspection during the construction process ensures these problems are avoidable problems. During construction, it is important to choose materials with the specified qualities and to carry out every procedure as stipulated in construction planning to avoid unnecessary failures in buildings.
When designing earthquake resistant architecture, it is significant to choose a layout and substructure system with various elements that contribute toward a structurally sound build. This protects buildings, which are at sites characterized by loose, poor, and saturated granular soils (Godden, 1997). Where the soils are soft and subject to liquefaction, it is advisable to use piles. They are effective in this scenario if designed appropriately to work as a unit and if designed to withstand both axial and shear and bend forces.
An analysis of the recent Haiti and China earthquakes provide cases for demonstrating how earthquake engineering diminishes the impact of earthquake. The most recent earthquake in China occurred on May 14, 2010 with a magnitude of 6.9 (Woodrow, 2010). Initial reports on possible effect of the earthquake showed that about 400 people had died and 8000 more had suffered injury. Additionally, the earthquake reduced to rubble some buildings and roads found in line of the seismic hazard.
The massive destruction related to the earthquake occurred within a country that had embraced earthquake engineering a few decades before, giving evidence to poor execution in some areas in the country. The development of earthquake engineering development in China followed in three phases starting with the period between 1950s and 1960s when earthquake engineering became a branch of science and technology (Yuxian, 2002, p. 1). This period marks the first zonotion map and seismic design code prepared and used as part of engineering design. Other factors incorporated during this period included the effects of sites on design and site selection.
In the second phase of execution, China experienced strong earthquakes that contributed to some of the most valuable lessons learned in the country in relation to earthquake engineering (Yuxian, 2002, p. 1). The engineers incorporate the lessons toward making appropriate design codes and implementing them as part of the construction process.
The third phase involved mostly disaster management efforts with the government engaging in a series of documentations marked by significant legislation on mitigation of earthquake disaster (Yuxian, 2002, p. 1). The Standing Committee of the National People’s Congress of the People’s Republic of China adopted the first such legislation in 1997 specific to the protection and mitigation of earthquake disaster. Following this decision were provincial and municipal laws enacted in support of the national law. They were to enable the implementation of the law on a smaller scale or on a localized scale.
An example of a code operational in China is the GB 500011 comparable to the ISO 3010. The two codes provide a guide for earthquake return period, conceptual design, site classification, and structural strength and ductility requirements as well as deformation limits (Yayong, 2004). Further, the codes provide attributes related to seismic levels, earthquake loading mode dumping factors, and structural control. This exemplifies some of the useful country codes useful in reinforcing structural architectural in China.
However, as indicated by the occurrence of devastation following earthquake events, China is yet to adopt a universal implementation of the earthquake engineering related laws. One of the most recent major earthquakes critically highlighting this is the May 12 2008 earthquake that hit Sichuan Province. Strong ground motions attributed to its shallow focal point characterized the earthquake. The impact of the earthquake was widespread heavily destroying buildings in Beijing, which are 930 miles away as well as those in Shanghai, Taipei and Hong Kong. Eighty percent of the buildings in the area around Sichuan province collapsed, and cut telephone and power lines.
Additionally, a school collapses killing, and trapping close to 900 students, while five other schools also suffered damaging. Two chemical plants also collapsed with more than 80 tons of ammonia leaking, and contributed to death rates estimated at 75000 deaths, 500000 destroyed properties, and 5 million homeless people. Remarkably, strong establishment of the buildings according to the earthquake engineering standards then the magnitude of destruction that destroyed schools, homes, and roads would have been less.
Another case is that of Haiti struck by a 7.0 magnitude earthquake on January 12, 2010. Haiti is one of the poorest countries in the western hemisphere, which makes the devastation of the earthquake was more meaningful. The earthquake resulted in about 230000 people loosing their lives, injured 300000 people, and 1.2 million people lost their residence and needed emergency shelter after the occurrence (Disasters emergency committee, 2008). Essential services such as health facilities also suffered in the earthquake, with the approximate figure of schools destroyed by the quake being between 2500-4600. Other destructions experienced were for government buildings, transport, and communication infrastructure.
Notably, Haiti’s buildings could not withstand the earthquake because of poor adoption of earthquake engineering in the country. According to Joyce (2010), Haiti has only one earthquake engineer, which raises questions on the implementation of earthquake engineering in the country as well as use of guidelines to ensure buildings are able to withstand earthquakes. Furthermore, this poor implementation also reflected on the presidential palace believed to be the strongest and most stable building but was could not withstand the earthquake. Increasing the concern in Haiti is that the country also lacks a national building code a factor that allows poor construction (Joyce, 2010). This contributed to the massive collapse of schools, hospitals and residential structures after the earthquake hit the country.
Haiti can learn from countries that have adopted and benefited from implementation of earthquake resistant laws related to earthquake engineering such as the United States. In the United States, most earthquakes occur in the pacific coast with 80% of these occurring in Alaska and California. In California there are several bills put in place to guard against earthquake damage. Examples are senate bills 1953 and 1661 and California Earthquake Hazards Reduction Act Sections 8871-8871.5.
Senate bill 1953 makes it mandatory for hospitals to retrofit buildings that have a high probability of suffering in the event of an earthquake to facilitate better seismic safety standards by the Year 2013 (Bozorgnia & Bertero, 2004). Prior to commencement of the project, the implementers need the approval of appropriate authorities. The bill became operational by 1998, amending a 1983 bill that dealt with the challenge of retrofitting. The implementation of the senate bill 1661 was to facilitate the compliance of the hospitals to the bill 1953. These two bills attest to the notion that in the State of California the government cared for the safety of its people and provided legislative guidance to that effect. Another example of legislation in the United States is the California Earthquake Hazards Reduction Act Sections 8871-8871.5. These laws were put in place with the aim of reducing earthquake hazards, improving earthquake disaster response and guiding reconstruction and recovery efforts.
California presented the first local building codes considering earthquake resistance after the Santa Barbara earthquake in 1925 (Bozorgnia & Bertero, 2004, p. 3.2). The codes adoption accelerates in the state after another earthquake that occurred in 1933 in Long Beach. After Long Beach, the public wanted action relating to structural safety leading to the adoption of Field and Riley Acts that recognized the role of structural engineers.
Considerably, California represents some of the most advanced laws related to earthquake protection in the United States and possibly in the world (Bozorgnia & Bertero, 2004, p. 3.2). However, some states in the United States have failed to follow this lead such as failing to evaluate building site safety. For example, though Oregon incorporated California’s standards in upgrading its building codes, its land use laws relating to geological hazards continue essentially unchanged.
A classical example of an area with earthquake sensitive laws in the United States is Los Angeles. Prior to the discussed case of Los Angeles in 1952, the United States was lacking in the development of building codes accompanied by ordinances maintaining safety of building sites (Bozorgnia & Bertero, 2004, p. 3.2). In 1952, the City of Los Angeles adopted the first grading ordinance and set up a grading section in the Department of Building and Safety. Precipitating this move was an ongoing series of landslides affecting the increasing population at Los Angeles that was moving into the surrounding hills. In 1963, the city made another monumental decision relating to the support of development projects, where geotechnical engineering and engineering geology reports would support them. Further, soils engineer and engineering geologists started supervising grading operations. The result of this decision was the establishment of geological consulting firms and employment of geologists into engineering firms.
Alaska and many other states affected by earthquakes also have legislation that cushions citizens against hazards that would occur because of earthquakes. The United States is advanced in practicing earthquake engineering and this could explain why earthquakes do not have such an overwhelming effect on the country though they occur. Other countries such as Haiti can learn from the case of California, an earthquake prone territory and use their codes as possible guidelines toward making codes for earthquake resistance structures. This would help safe property and life lost or damaged in an earthquake event.
In conclusion, earthquake engineering offers countries with the opportunity to build structures that can withstand earthquakes and related tremors. When earthquakes occur, they result in high damage; however, when well executed, earthquake engineering can ensure that structures do not suffer the maximum damage that occurs in structures that have not followed building codes. Notably, unsound structures increase the possibility of collapse or damage causing deaths and casualties’ otherwise preventable using earthquake engineering. Exemplifying the cost of structurally unsound buildings when an earthquake occurs are the 2010 earthquake occurrences in Haiti and China that left thousands dead, millions displaced, and millions worth of property destroyed. However, if the countries utilized earthquake engineering they could minimize on the effect of the earthquakes. Laws exist guiding the implementation of earthquake engineering such as building codes executed in the United States that have been contributory to earthquake resistant architecture. Notably, earthquake engineering is useful in construction of ensuring structures such as bridges, and houses are earthquake resistant, which helps limit possible damages in relation to fatalities, and destruction of property.
Reference List:
Bertero, V., & Bozorgnia, Y. (Eds). (2004). Earthquake Engineering: from Engineering Seismology to Performance-based Engineering. Boca Raton, FL: CRC Press.
BluEnt. (2010). Building Earthquake Resistant Architect. Retrieved May 31, 2010 from http://www.bluentcad.com/architecture/earthquake-engineering.shtml
Day, R. W. (2002). Geotechnical Earthquake Engineering Handbook. New York, NY: McGraw-Hill Companies, Inc.
Disasters Emergency Committee. (2008). Haiti Earthquake-Facts and Figures. Retrieved May 31, 2010 from http://www.dec.org.uk/item/425
Godden, W. G. (Ed). (1997). Structural Engineering Slide Library. The Regents of the University of California.
Joyce, C. (2010). Haiti’s Buildings Weren’t fit to Withstand Earthquakes: NPR.
Scawthorn, C. (2006). Fundamentals of Earthquake Engineering. In Wai-Fah Chen and E. M. Lui (Eds), Earthquake Engineering for Structural Design. Boca Raton, FL: CRC Press.
Woodrow, C. (2010). China hit by 6.9 Earthquake: Hundreds Dead, Minimal Rescue Resources. Gather News.
Yayong, W. (2004). Comparisons of seismic actions and structural designs requirements in Chinese code GB50011 and international standard ISO3010. Journal of Earthquake Engineering and Engineering Vibration. 3(1)
Yuxian, H. (2002). Earthquake Engineering in China. Journal of Earthquake Engineering and Engineering Vibration, 1(1)
