Earthquake Loads & Earthquake Resistant Design of Buildings
1. 1
2. Summary 2
3. Earthquake Design - A Conceptual Review 2
4. Earthquake Resisting Performance Expectations 3
5. Key Material Parameters for Effective Earthquake Resistant Design 3
6. Earthquake Design Level Ground Motion 4
6.1. Elastic Response Spectra 4
6.2. Relative Seismicity 5
6.3. Soil amplification 6
7. Derivation of Ductile Design Response Spectra 7
8. Analysis and Earthquake Resistant Design Principles 8
8.1. The Basic Principles of Earthquake Resistant Design 8
8.2. Controls of the Analysis Procedure 8
8.3. The ‘Conventional’ Earthquake Design Procedure 11
9. The Capacity Design Philosophy for Earthquake Resistance 11
9.1. General Approach 11
9.2. The Implications of Capacity Design 12
10. Earthquake Resistant Structural Systems 12
10.1. Moment Resisting Frames: 12
10.2. Shear Walls 13
10.3. Braced Frames 13
11. The Importance & Implications of Structural Regularity 13
11.1. General 13
11.2. Vertical Regularity 14
11.3. Horizontal Regularity. 14
11.4. Floor Diaphragms 14
12. Methods of Analysis 15
12.1. Integrated Time History Analysis 15
12.2. Multi-modal Analysis 15
12.3. Equivalent Static Analysis 15
13. Trends and Future Directions 16
14. Conclusions 16
15. References 17
1.
Summary
The primary objective of earthquake resistant design is to prevent building collapse during earthquakes thus minimising the risk of death or injury to people in or around those buildings. Because damaging earthquakes are rare, economics dictate that damage to buildings is expected and acceptable provided collapse is avoided.
Earthquake forces are generated by the inertia of buildings as they dynamically respond to ground motion. The dynamic nature of the response makes earthquake loadings markedly different from other building loads. Designer temptation to consider earthquakes as ‘a very strong wind’ is a trap that must be avoided since the dynamic characteristics of the building are fundamental to the structural response and thus the earthquake induced actions are able to be mitigated by design.
The concept of dynamic considerations of buildings is one which sometimes generates unease and uncertainty within the designer. Although this is understandable, and a common characteristic of any new challenge, it is usually misplaced. Effective earthquake design methodologies can be, and usually are, easily simplified without detracting from the effectiveness of the design. Indeed the high level of uncertainty relating to the ground motion generated by earthquakes seldom justifies the often used complex analysis techniques nor the high level of design sophistication often employed. A good earthquake engineering design is one where the designer takes control of the building by dictating how the building is to respond. This can be achieved by selection of the preferred response mode, selecting zones where inelastic deformations are acceptable and suppressing the development of undesirable response modes which could lead to building collapse.
2. Earthquake Design - A Conceptual Review
Modern earthquake design has its genesis in the 1920’s and 1930’s. At that time earthquake design typically involved the application of 10% of the building weight as a lateral force on the structure, applied uniformly up the height of the building.
Heller, Arnie. "The 1906 San Francisco Earthquake." Science & Technology (2006): 4-12. Web. 8 May 2014.
The science of the natural disaster has baffled many, but from studying the San Francisco earthquake, scientists have made a number of important discoveries and they have a better understanding of earthquakes. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared at an incredible twenty-one feet along the San Andreas fault, surpassing the annual average of two inches (“San Francisco Earthquake of 1906”)(“The Great 1906 Earthquake and Fires”). The shearing caused a loud rumble in the Californian city of San Francisco. A few seconds later, the destructive earthquake occurred. The ground shifted at almost five feet per second, and the shaking could be felt all the way from southern Oregon to southern Los Angeles to central Nevada (“Quick”)(“The Great 1906 San Francisco Earthquake”). Moreover, the earthquake could be recorded on a seismograph in Capetown, South Africa, an astounding 10,236 miles away from San Francisco (“San Francisco ea...
From studying the science behind the San Francisco earthquake, scientists have made a number of important discoveries involving how earthquakes function. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared each other at an incredible twenty-one feet along the San Andreas fault, surpassing the annual average of two inches (“San Francisco Earthquake of 1906”) (“The Great 1906 Earthquake and Fires”). A few seconds later, the destructive earthquake occurred. The ground shifted at almost five feet per second, and the shaking could be felt all the way from southern Oregon to southern Los Angeles to central Nevada (“Quick”) (“The Great 1906 San Francisco Earthquake”). In fact, the earthquake could be registered in a seismograph on Capetown, South Africa, an astounding 10,236 miles away...
Healy, J. H., Rubey, W. W., Griggs, D. T., & Raleigh, C. B. (1968, September). The Denver Earthquakes. Science, 161(3848), 1301-1310. Retrieved from JSTOR database.
Stringent seismic criteria related to construction in the San Diego area made it difficult for Kahn's structural engineer to convince local building officials, who wanted him to use steel frame, that concrete, Vierendeel truss system would have the required flexibility. They agreed only after a 400 page report of undoubtedly integrated deflection computations that shows how post-tensioned columns would provide the main resistance to lateral seismic forces. These columns absorb both dead and live load compression plus vertical post-tensioning forces. They were also designed to maintain zero tension if subjected to lateral movements by earthquake. The trusses are 9 ft deep, spaced 20 ft on center and have a clear span of 65 ft (diagram 2). He made use of the 9 ft high resultant space as service area, allowing pipe chases to be dropped to the 65x 245 ft floor below with more latitude than before.
benchmark for the future, and integrated investigation into the effects of earthquakes in the U.S.
Skyscrapers are amazing! Architectural defeats. Wonders of the world. How are they able to withstand even the strongest of winds and earthquakes?
In 1910 a series of fifty-two earthquakes struck Arizona between September 10th-23rd and it caused much of the Flagstaff residents to flee the area as even strong households cracked and chimneys crumbled. The fifty-two earthquakes were all light-shock earthquakes with magnitudes between 4.0-4.2 that came right after another. If only one earthquake occurred in that timespan then it is likely that only objects would be knocked from shelves but no damage would be done to infrastructure, but the earthquakes happened right after another causing significant slight
The New Madrid Earthquake is referred to the area that exposed to the robust earthquakes in the United States of America. The area is located in Southeastern Missouri, Northeastern Arkansas, Western Tennessee, Western Kentucky and Southern Illinois, which is the most active seismic in the USA east of the Rocky Mountains. Historically, in 1811-1812, the New Madrid seismic zone suffered a sequence of earthquakes that included three very large earthquakes estimated to be between magnitude 7 and 8, which led to destroy most of the buildings. Therefore, the man-mad infrastructures were a main cause of injuries and deaths among population (United States Geological Survey, 2016).
An earthquake is one of nature’s most frightening as well as most destructive circumstances on the planet earth. The earthquakes are also most frightening when it first begins. This is due to the fact of the unknown. You have no idea how long the earthquake will occur or how violent it will be.
The failure of beam-to-column connections in steel Special Moment Resisting Frames had the most to do with most of the damage in these buildings. In response to the pattern of buildings including SMRF's, there have been studies to improve the design and construction practices to allow for better and more improved buildings. The higher building codes wanted engineers to find new ways to allow homes, apartments or skyscrapers the ability to sustain a powerful earthquake. These engineers borrowed the model from New Zealand engineer Bill Robinson. His method was to use lead-rubber bearings, which minimize the vibrations caused by the earthquake, improving its performance during seismic activity. Many of the old buildings that took damage during the earthquake had to be retrofitted. This was done by either infilling the walls, adding braces, adding buttresses, adding new frames, exterior or interior, completely rebuilding or isolating the building. All of these techniques of retrofitting a building all add extra support to the remainder of the building. Most of the residential structures that took damage and were deemed uninhabitable were the apartments or condominiums that were made of light, wood frames. Also, many houses made using stucco took extensive damages. This was due to the fact that the stucco was not properly installed in the first place,
According to recent David Fisher’s Dynamic Tower, as it appears for many years all the buildings were stable, but nowadays for example, David Fisher’s Dynamic Tower is a new thinking for future architecture. The rotating tower shows three main futuristic patterns or revolutions. The first revolutionary is about it’s shape, which changes it’s look continuously, and with this each floor rotates distinctly. The second revolution that the Dynamic Tower brings is the system of construction, beside the concrete use, the tower is made of prefabricated unites ,including flooring water piping air conditioning , this units made of steel, aluminum, carbon fiber also other modern materials. The third revolution is came with joining technology with environment (The Dynamic Team, 2014). “Time is the most powerful dimension of our lives. All our life depends on time," states Fisher. "Today's life is dynamic, so the space we are living in should be dynamic as well, adjustable to our needs that change continuously, to our concept of design and to our mood," he states, in a media publication. Buck...
Taher, R. (2011). General recommendations for improved building practices in earthquake and hurricane prone areas. San Francisco, CA: Architecture for Humanity Retrieved from
Some other things that have become evident are that geometric simplicity and symmetry are key to constructing an earthquake resistant building. Simplicity often leads to symmetry, and in turn symmetry tends to decrease the likelihood of a concentration of mass. This idea of lighter buildings being safer can be explained mathematically using the formula F=MA. To understand how this formula works it is pertinent to recognize that earthquakes alone do not cause damage because all they provide is an acceleration.
Earthquakes belong to the class of most disastrous natural hazards. They result in unexpected and tremendous earth movements. These movements results from dissemination of an enormous amount of intense energy in form of seismic waves which are detected by use of seismograms. The impact of earthquakes leaves behind several landmarks including: destruction of property, extensive disruption of services like sewer and water lines, loss of life, and causes instability in both economic and social components of the affected nation (Webcache 2).