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Earthquakes
What is an earthquake?
An earthquake is a sudden release of energy due to shifts in the earth’s plates that has
been stored in the rocks beneath the earth’s surface which causes a trembling or shaking of the ground. The
energy that is released from the ruptured rock travels in waves which are known as seismic
waves.
There are two types of seismic waves; body waves which travel through the interior of Earth and surface waves which travel on Earth's surface. The two body waves are primary waves (p-waves) and secondary waves
(s-waves).
Kobe Earthquake Japan 1995 Structures in Kobe built since 1981 had been designed to strict seismic codes. Most of these buildings withstood the earthquake. In particular, newly built ductile-frame
high rise buildings were generally undamaged.
http://www.vibrationdata.com/earthquakes/kobe.htm
The compressional (push-pull) wave will vibrate parallel to the direction that the wave is traveling up to speeds of 4 to 8 km per second (2.49 to 4.35 miles per second). The S-wave vibrates perpendicular to the direction of travel and can travel up to speeds of 2 to 5 km per second ( 1.24 to 3.11 miles per second).
Love waves and Raleigh waves are known as Surface waves. Surface waves are the slowest of the seismic waves, but because they travel near the surface of Earth and contain a range of oscillating frequencies they often cause the most damage
http://www.berkeley.edu/news/berkeleyan/2006/01/18_resumption.shtml
Northridge Earthquake Southern California 1994
World Earthquake Fault Lines
•www.forceborne.com/FBW/Tech/fault_line_chart.htm
Plate Tectonics A spreading boundary is where the tectonic plates are separating. These are
places where volcanic activity is at a premium because the crust is being torn open (as in splitting and cracking, like an egg breaking open). New
crust is forming when molten lava from deep down oozes out of the cracks where the plates are coming apart .
A converging boundary is when one plate (usually the lighter continental crust) rides up over the top of the other it's called a subduction zone -
because one plate margin is being subducted under the other.
What is liquefaction?
www.scieds.com
www.scieds.com
This residential and commerial building sank more than three feet into the partially liquefied soil.
Photo credit: Reinsurance Company, Munich Germany
Liquefaction is a type of ground failure in which water saturated sediment turns from a solid to a liquid as a result of shaking, often caused by an earthquake or even a volcanic eruption. In order for the liquefaction to occur the sand grains must be fine grain sand that are not closely packed together nor must it be held but some sort of cohesion. The intense shaking causes the strength of the soil to become weak and the sand and water begin to flow.
www.scieds.com
A major cause of damage was liquefaction of the recent alluvial deposits that underlaid large portions of the city. The result was excessive settlements and bearing capacity failures for countless buildings, most of which were supported on shallow foundations. This new building was not yet occupied at the time of the earthquake. Again, the bearing failure of its mat foundation was related to its relatively large height-to-width ratio.
Adapazari, Turkey, 1999 Kocaeli earthquake
www.scieds.com
What do Architects do?
Architects design buildings and structures. They advise individuals, property owners and developers, community groups, local authorities and commercial organizations on the design and construction of new buildings, the reuse of existing buildings and the spaces which surround them.
Architects work closely with other members of the construction industry including engineers, builders, surveyors, local authority planners and building control officers. Much of their time is spent visiting sites assessing the feasibility of a project, inspecting building work or managing the construction process. They will also spend time researching old records and drawings, and testing new ideas and construction techniques. Society looks to architects to define new and better ways of living and working, to develop innovative ways of using existing buildings and creating new
www.architecture.comwww.cnn.com
What do Structural Engineers do?Structural engineering's combine their knowledge of science and design making as they construct better framework for buildings and other structures to safely resist natural and made-made forces. They are involved in physical testing, mathematical modeling, computer simulation all of which support decisions that Aid in the creation and maintenance of safe and economical structures.
http://www.seaint.org / http://cee-ux49.cee.uiuc.edu/strweb/home.html
www.earthscience.org/.../geopro/seismic/seismic.html
What is Earthquake Engineering?Earthquake engineers are
concerned with creating earthquakes resistant designs and construction techniques to build of
all kinds of bridges, roads and buildings.
Earthquake engineers are faced with many uncertainties and must be
smart in their decisions in developing safe solutions to
challenging problems. They rely on state-of-the-art technology, materials science, laboratory testing and field monitoring.
www.sciencedaily.com
Earthquake-Resistant StructureBuilding designed to prevent total collapse, preserve life, and minimize damage
http://nisee.berkeley.edu/elibrary/getpkg?id=GoddenD50-69 http://www.infinityfoundation.com/mandala/t_es/t_es_agraw_quake.htm
www.transport.polymtl.ca World’s Tallest Bridge Millau, France 2004
San Francisco-Oakland Bay Bridge reconstruction, USA begun 2002
www.transportation1.org
Engineers chose a hybrid girder design that combined the rigidity, noise absorption, and low cost of concrete with the precision manufacturing offered
by steel. The system’s reinforced-concrete support piers are designed to withstand the seismic forces of earthquakes measuring up to 7.5 on the
Richter scale.
High-Speed Magnetic Levitation Rail Line Shanghai, China 2004
www.pubs.asce.org
Nepal Develops Earthquake Resistant Architecture A plan for safer houses in rural areas
Nepal has a history of being devastated by major earthquakes every 75 to 100 years, with the first
recorded as early as 1255 AD. In 1934 Nepal experienced a deadly earthquake that resulted in the death of 8,500 people and destruction of 20 percent
of valley structures, at a time when the population was far less than at present. Seismologists are
predicting the occurrence of a large earthquake of this kind in the near future, which is likely to be most
intense in the urban core. http://www.archidev.org/rubrique.php3?id_rubrique=273
Ninety percent of Nepalese houses are made of stone and unfired bricks. The Structural Engineers in Nepal are retrofitting current structures for about $25/home. By creating a one-meter square grid of punched holes in the stone wall covered with a 10 cm mesh of bamboo on the inside and outside the homes become earthquake resistant. This net is Secured to the wall by means of 12-gauge Gabion wire, (a form of riprap contained in a wire cage that is very useful in erosion control.), which is inserted through the holes and fastened strongly. It is covered with a stucco of mud, which is used in rural areas in order to ensure
The Lefkas (Greece) earthquake resistant technique Two-story houses are built with a ground
floor of rough boulder masonry and three lines of wooden posts (one along each long wall, and one in the middle of
the room) support the first floor. This one is erected in wood-frame construction (Dajji).
Foundations are laid on a three-layer round-poles mat, which could behave as a spring if a gap was left around. The main benefit is outspread of the foundation surface.
"Dajji" is traditional in Cashmere (India). It is very efficient and affordable. A wooden frame is built without bracing. The empty rectangular or
square "panels" are filled with a mesh of wood and stone cemented with mud. These panels work as
bracing, but allow slight movement, and give elasticity to the whole structure. Thus, the house is
able to move and to absorb the earthquake’s movement.
Another advantage of this technique is to be (comparatively) lightweight, and thus being less
stressed by earthquakes.
http://www.archidev.org/article.php3?id_article=1027
Kobe Earthquake Japan 1995
6.9 Magnitude
Homes and building construction was older built with heavy tile roofs that collapsed
http://www.seismo.unr.edu/ftp/pub/louie/class/100/effects-kobe.html
Another anomaly was the large number of about 20-year-old high rise buildings that collapsed at the fifth floor. The older version of the code they were built
under allowed a weaker superstructure beginning at the fifth floor.
http://www.seismo.unr.edu/ftp/pub/louie/class/100/effects-kobe.html
Behind this completely collapsed wood-frame house is a house of reinforced concrete that suffered no structural damage. The number of wood versus masonry buildings that
collapsed in Kobe astonished most observers, as wood-frame structures are usually thought to be much better at resisting shear forces. Possibly the concrete house was
http://www.seismo.unr.edu/ftp/pub/louie/class/100/effects-kobe.html
http://www.niksula.hut.fi/~haa/kobe.html
http://www.niksula.hut.fi/~haa/kobe.html
http://www.city.kobe.jp/cityoffice/15/020/quake/disaster/d-index_e.html
Mexico City Earthquake, 19858.1 Magnitude
Poorly constructed buildings caused thousands of deaths
http://www.johnmartin.com/earthquakes/eqshow/647003_06.htm
Damage to the Intercontinental Hotel during Mexico City's 1985 earthquake was severe even though the building was relatively new
http://www.calstatela.edu/dept/geology/G351.htm
Building Design After the earthquake in Mexico City, Mexican officials adopted a new design that can protect the buildings from earthquakes. This design was developed by some engineers at the University of California at Berkeley.Looking at the diagram below you can see that the braces form an X which are anchored in concrete blocks at the base and on the roof of the building.
In diagram A we have conventional steel bracing. Under the stress of the earthquake one of the braces collapses under the stress. If all the braces begging to snap then the structural integrity of the building fails. Now in diagram B, the engineers at Berkely used a hydraulic jack to pull or stretch the rods. Once the rods are prestressed they can now be anchored to the base and to the roof of the building. The braces now have some room to contract thereby strengthening the structural integrity of the building.
Northridge Earthquake, 1994 Southern California, USA
6.7 Magnitude
most houses were wooden and did not collapsewww.survival1.com/
Problems for Building Structures when Seismic Waves pass For tall buildings the top may sway in the opposite direction as the base
Buildings in close proximity with one another may collide do to differing phase motions.
Changing types of wave motion cause damage.
Buildings with different resonant frequencies will be affected differently by passing
seismic waves depending on the wave frequency.
http://www.mines.utah.edu/~schuster/gg103/res/resonance.html
http://www.scarborough.k12.me.us/wis/teachers/dtewhey/webquest/nature/earthquake_images.htm
Loma Prieta Earthquake, 1989San Francisco Bay, California
7.1 magnitude
• Many homes were damaged because of old construction- unreinforced bricks and mortar
• Many building and homes were built on were unconsolidated flood plain sedimentary land (In contrast, nearby sections of the city experienced only minor damage. These areas contain sturdy wood frame houses built on relatively stable marine terraces.)
As the second story of this building collapsed, its facade fell into the street, knocking down the tree which in turn damaged the car. This building in downtown was one of the heavily damaged buildings situated on the unconsolidated flood plain sediments of the
San Lorenzo River.
•http://www.es.ucsc.edu/~es10/fieldtripEarthQ/Damage2.html
An automobile lies crushed under the third story of this apartment building in the Marina District. The ground levels are no longer visible because of
structural failure and sinking due to liquefaction
•http://pubs.usgs.gov/dds/dds-29/
Collapsed brickwork from a corner apartment building, Marina District.
•http://pubs.usgs.gov/dds/dds-29/
Structural Design ProjectYou and your partner have been hired as the structural engineers in charge of designing a new 2-story art building for Cal State Hayward. There are many building codes you must follow. Each floor of the building must support at least 250 grams of weight. Also, the building will be located near the Hayward Fault; therefore your building must be able to withstand both small and large earthquakes. Since the building will be used for art classes, you may be as creative as you like with the shape and design of the building (it does not need to be box shaped).
Supplies
• You are limited to the following materials:
• 1 cardboard base (approximately 25 cm by 25 cm)
• 30 straws • 100 paper clips (one box) • 20 pins • 2 meters of string
45
REQUIREMENTS • Your building must meet the following requirements: •The building must fit on the base. Attach your building to
the base using pins, paper clips, or string. •Your building must be at least 36 cm tall. •Your building has 2 stories that are each at least 18 cm tall (approximately the height of 1 straw). •Each story must support the weight of at least 1 sand bag (250 grams) without collapsing. •A construction drawing with measurements and analysis must be submitted before earthquake testing. •To survive an earthquake test, the building must not collapse for 10 seconds after the earthquake begins. The weights must stay on the building. You have 1 minute to repair any damage to your building before the next earthquake test. 46
HINTS AND TIPS • Hints and tips: •PLAN CAREFULLY! Additional supplies will not be
provided. •Remember these words of wisdom: “Measure twice. Cut once.” •Use the concepts of tension and compression. If an element is in tension and not compression, you can use string instead of straws. •Try building without pins first, then add pins where connections need reinforcement. •Make sure that your foundation is very strong. •Remember to design a way to secure the weights so that they don’t fall off AND so you can add additional weights to the top story.
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GRADING • Grading:
25 points Building stands by itself, fits on the base, is secured to the base, is at least 36 cm tall, and has 2 stories that are each at least 18 cm tall.
10 points Building supports 1 sand bag on the first story. 10 points Building supports 1 sand bag on the top story. 10 points A clear, detailed construction sketch was completed. Straws and string should be easily distinguished.
All important design features and all critical measurements should be labeled on the sketch. 20 points A structural analysis of your building was completed. The following questions should be answered
clearly and completely: • During construction, how did you test the strength and stability of your structure? • During construction, what strategies did you use to strengthen the weaker areas? Why? • What are the strongest parts of your building? Why? • What are the weakest parts of your building? Why? • Where did you use string in your structure? Why? • Where did you use pins in your structure? Why? • If you had 5 more straws, where would you add them? Why?
5 points Building remains standing with 1 sand bag on the top story after a mild earthquake. 5 points Building remains standing with 1 sand bag on the top story after a major earthquake. 5 points Building remains standing with 1 sand bag on the top story and 1 sand bag on the first story after a
major earthquake. 5 points Building remains standing with 2 sand bags on the top story and 1 sand bag on the first story after a
major earthquake. 5 points Building remains standing with 2 sand bags on the top story and 2 sand bags on the first story after a
major earthquake. 54
• Bonus: The building in each class that can hold the most weight and remain standing after a major earthquake will be awarded 20 bonus points.
Deadline:
** The last day for earthquake testing is ______________________. **
If you test your building before the final deadline, you may start over from scratch with new materials to try to win the bonus points. However, you will not be able to make up points that you lost with your first building. Therefore, do your best with your first building, but if you earthquake test your building before the deadline, then you will have a second chance to win the bonus points. 55
