One of the major aftermaths of the Northridge Earthquake of January 17, 1994, was the widespread connection damage that posed a major question regarding the behavior of field-welded, field-bolted moment frame connections, also known as Pre-Northridge connections.
Before the Northridge Earthquake, Steel Moment Resisting Frames (SMRFs) were believed to have ductile behavior that would achieve high-cycle fatigue. As a result, fatigue was not considered to be a failure mode for these connections during a seismic event.
After the Northridge Earthquake and the widespread connection failure in steel moment frame buildings, it was concluded that many connections failed at what appears to be relatively few cycles. Observations after the Northridge Earthquake
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These buildings were two and ten stories, respectively, and used steel moment frames as the lateral load resisting system in both directions.
Chapter two of this document describes the definition of fatigue failure and summarizes the research done in the area of fatigue behavior of steel moment connections and the concept of low-cycle fatigue.
In chapter three of the current document, the analytical case studies are explained and the investigated buildings are described. Also, the observed damage in these buildings is studied.
Chapter four contains a series of linear and non-linear time-history analyses and includes a very thorough analytical study on the stress histories at the critical locations of the buildings. Furthermore, the contribution of each mode of vibration to total stress is investigated.
Chapter five establishes a comprehensive fatigue analysis procedure, which was developed using the Palmgren-Miner method. In addition, low-cycle fatigue behavior of Pre-Northridge connections are studied in this chapter, and S-N curves established for the high-cycle fatigue range are extended to the low-cycle region using the limited test results that are available. Fatigue analyses are performed
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The FEMA 350 commentary cites low-cycle fatigue as the main cause of failure in some laboratory connection tests but does not give any information or any possible recommendations on the issue.
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Some of the SAC task groups addressed the low-cycle fatigue issue in their individual reports. For instance, the work done by Ricles et al. in 2000 [37] has a chapter on low-cycle fatigue with a proposed method for predicting crack initiation and extension over the life cycle of a connection utilizing finite element analysis [37], [38].
Barsom (2000) [6], concludes that fatigue is the failure mechanism of the connection. This report was never distributed to the practicing engineers, as only selected SAC committee members received it.
The report by Krawinkler et al. (1983) [26] cites low-cycle fatigue as the failure mechanism of the Pre-Northridge connections. The concept of “cumulative damage” is discussed in this document. The author indicates that each connection remembers the past events, and these past seismic events consume part of the predictable and quantifiable life of a
Combined with corrosion fatigue” (“Silver”).
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
Skyscrapers are amazing! Architectural defeats. Wonders of the world. How are they able to withstand even the strongest of winds and earthquakes?
...e earthquake: 1994 quake still fresh in Los Angeles minds after 20 years. Retrieved from http://www.dailynews.com/general-news/20140111/northridge-earthquake-1994-disaster-still-fresh-in-los-angeles-minds-after-20-years
There are many factors that affect the damages to a building during and after an earthquake, such as the ground beneath the building (fault line, landfills, bedrock) as well as different the types of building material (wood, steel, brick/masonry) and how it behaves during an earthquake. For example, the wood used for framing in smaller structures (i.e. houses), as well as the steel framing used in larger structures like skyscrapers.
People tremble when they hear the word: destruction, devastation, or losses while those are only the first words that come to mind when an Earthquake occurs. Earthquakes can be terrifying; the earth that had seemed so reassuringly solid and stable suddenly lurches, disrupting people’s both physical and emotional balance. Skyscrapers sway visibly, sound buildings and bridges collapse, power lines spark, gas lines rupture, and landslides scar hillsides and alter the course of the rivers. For years throughout recorded history, earthquakes have disrupted all expectations of normalcy and have imposed an adverse impact on various places around the world, killing over “3.5 million people” on average during the past two millennia (Marshak 218).
"The Great Quake: 1906-2006 / Rising from the Ashes." SFGate. N.p., n.d. Web. 10 May 2014.
Mechanical Engineering 130.2 (2008): 6 - 7. Academic Search Complete. Web. The Web. The Web.
Fatigue happens when you download the materials and discharged several times. If you download a certain threshold , and microscopic cracks will begin to focus on the level of stress, and slip bands Pollutants ( PSBs ) and total interfaces . Finally, the crack reaches critical size , the crack suddenly released , and the structure will fail .
Works Cited Journal articles: • Lane, Thomas. “Crazy Angles, Soaring Steel.” Building vol. 274 no. 8588 (28) 2009, July 17, pp. 40-46.
Review of various large span single storey steel buildings to determine the type of framing systems and sections used.
Fatigue in aviation has always been a significant issue when it comes to the safety of the crew and passengers. Fatigue in flight is not the only issue. There is also a serious safety issue in other areas of aviation such as maintenance, air traffic control (ATC), and even in areas such as baggage claim and gate security. One can find evidence of fatigue in just about every aspect of daily life. A majority of vehicle accidents can be contributed to fatigue in one way or another. One can even see it in the late night college student trying to finish a paper before its deadline. Although the last example doesn’t have any serious safety concerns it is still a very real instance of fatigue. The area of transportation has seen thousands of incidents where fatigue has
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.
According to National Geographic, “On average, a magnitude eight quake strikes somewhere every year and usually some 10,000 people die in earthquakes annually. Collapsing buildings claim by far the majority of lives”(1). Seismic retrofitting has helped protect existing infrastructure during earthquakes. Although results show that this method of earthquake proofing is successful, this solution does have negative impacts economically and culturally.
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).