Friday, April 16, 2010

Earthquake-Resistant Construction -- Solid Business

Port-au-Prince earthquake
A severe earthquake can release 10,000 times more energy than the first atomic bomb.  On January 12, one of these subterranean explosions devastated Port-au-Prince, Haiti, killing 233,000. On February 18 a magnitude 6.5 earthquake rocked the border region between China and Russia. On February 27, an even more powerful earthquake -- with a magnitude of 8.8 -- hit Chile near its second largest city, ConcepciĆ³n, taking 700 lives. (The largest earthquake ever recorded was a 9.5 tremblor in Chile in 1960.) On April 14, six quakes hit Yushu county in China’s Qinghai province -- the largest, a 7.1 powerhouse, killed 400 people and injured 10,000.

In the first four months of 2010, 16 additional earthquakes with magnitudes ranging from 6.0 to 8.8 hammered the planet, and many more quakes of lesser force struck remote areas worldwide. We didn’t hear about those because there was little -- and in several cases zero -- loss of life.

Why did so many more people die in the Haitian quake? Haiti, a poor country, could afford to build only inelastic, frail structures, whereas structures in Chile, a more developed nation, were strong and somewhat flexible and, for the most part, withstood the 8.8 quake.

How can we prevent similar large losses of life in future seismic events? We can't control plate tectonics, but we can engineer earthquake-resistant structures.

The motions of an earthquake alone cause very little loss of life. Instead, falling objects often are the instruments of death and injury. Fires break out from broken gas or power lines. Hazardous chemicals escape when holding tanks rupture. Sewage lines break, releasing effluents that contaminate water supplies and, in turn, laying the groundwork for cholera, typhoid, dysentery and other serious diseases. Power outages, communications breakdowns and transportation interruptions after an earthquake impede rescue and recovery efforts. Records and supplies go missing, crippling businesses and government, slowing recovery even more. But amid all of that chaos, perhaps the most lethal immediate threat to human life is the collapse of buildings, bridges and other structures. Thus the old engineering adage: "Earthquakes don't kill people; buildings do."

In general, engineers erect buildings to withstand the static forces of gravity and those inherent in the structures' designs. But earthquakes generate an entirely different set of forces -- a quake's motion, particularly the side-to-side and rolling movement, subjects buildings to tremendous dynamic forces along vectors that bypass load-absorbing areas and, in the process, eliminate structural integrity and shred the structures like paper. Unless buildings are flexible enough to bend with those dynamic forces or sturdy enough to withstand them, a strong earthquake will take them down.

Knowing Where and How to Build

Image by Doug DeWitt
World Book
Mapping geographic areas that are apt suffer grievous damage during an earthquake is critical. These maps show fault zones, flood plains, areas prone to landslides and soil liquefaction, and the scarred locations of past earthquakes. Using these maps, planners restrict development and construction to zones where earthquakes are less likely to strike.

Engineers approach earthquake-resistant structures in a number of ways. For small- to medium-sized buildings, they use simple reinforcement techniques such as bolting buildings to their foundations and providing shear walls, which strengthen the structure and help resist rocking forces. Shear walls in the center of a building, often around an elevator shaft or stairwell, form a shear core. Engineers might also reinforce walls may with cross-bracing.

Researchers in the Civil and Environmental Engineering Department at the University of Michigan (U-M) simulated the effects of a large earthquake in the Structural Engineering Laboratory to test their new technique for constructing high-rise reinforced concrete buildings. Their proposed design procedure for coupling beams in a core-wall structural system passed the test, withstanding more lateral deformation than an earthquake would typically demand. The engineers used steel fiber-reinforced concrete to develop a better kind of coupling beam that requires less reinforcement and is easier to construct. Coupling beams connect the shear walls of high rises around openings such as those for doorways, windows, and elevator shafts.

U-M New Building Design Withstands Earthquake Simulation




Engineering earthquake-resistant skyscrapers is much more problematic than building small- to medium sized buildings, and engineers approach them with a couple of techniques. One practice is to tie the foundation to the superstructure -- the upper part of the building -- as solidly as possible to the foundation so that, when the ground shakes, the building and the foundation move as a unit, which helps prevent the collapse of upper floors. Another method, seemingly at complete odds with the first line of thought,  is to design the superstructure to move on the foundation. Base isolators between the building and its foundation act like shock absorbers, damping some of the lateral motion that would otherwise cause damage. This configuration helps the building stay in one place while the foundation shakes beneath it. Base isolators are effective but, unfortunately, prohibitively expensive for construction in poor countries such as Haiti.

Using yet another approach, engineers erect a building to be as stiff and strong as possible in the hope that it'll retain its integrity and stay intact through a quake. Once again, there's a second method that's completely unlike the first. In this second approach, engineers design segments of the frame to move so that, during a quake, the entire frame deforms slightly and absorbs the quakes energy, dissipating it throughout the entire structure and in that way maintaining the structure's integrity.

The approached might be different but the objective is the same: Improve the construction of  buildings to withstand one of Earth's awesome forces and subsequently save lives.

Wired Science 8: High Tech Quake Survival

Earthquake-Resistant Construction -- Solid Business

Port-au-Prince earthquake
A severe earthquake can release 10,000 times more energy than the first atomic bomb.  On January 12, one of these subterranean explosions devastated Port-au-Prince, Haiti, killing 233,000. On February 18 a magnitude 6.5 earthquake rocked the border region between China and Russia. On February 27, an even more powerful earthquake -- with a magnitude of 8.8 -- hit Chile near its second largest city, ConcepciĆ³n, taking 700 lives. (The largest earthquake ever recorded was a 9.5 tremblor in Chile in 1960.) On April 14, six quakes hit Yushu county in China’s Qinghai province -- the largest, a 7.1 powerhouse, killed 400 people and injured 10,000.

In the first four months of 2010, 16 additional earthquakes with magnitudes ranging from 6.0 to 8.8 hammered the planet, and many more quakes of lesser force struck remote areas worldwide. We didn’t hear about those because there was little -- and in several cases zero -- loss of life.

Why did so many more people die in the Haitian quake? Haiti, a poor country, could afford to build only inelastic, frail structures, whereas structures in Chile, a more developed nation, were strong and somewhat flexible and, for the most part, withstood the 8.8 quake.

How can we prevent similar large losses of life in future seismic events? We can't control plate tectonics, but we can engineer earthquake-resistant structures.

The motions of an earthquake alone cause very little loss of life. Instead, falling objects often are the instruments of death and injury. Fires break out from broken gas or power lines. Hazardous chemicals escape when holding tanks rupture. Sewage lines break, releasing effluents that contaminate water supplies and, in turn, laying the groundwork for cholera, typhoid, dysentery and other serious diseases. Power outages, communications breakdowns and transportation interruptions after an earthquake impede rescue and recovery efforts. Records and supplies go missing, crippling businesses and government, slowing recovery even more. But amid all of that chaos, perhaps the most lethal immediate threat to human life is the collapse of buildings, bridges and other structures. Thus the old engineering adage: "Earthquakes don't kill people; buildings do."

In general, engineers erect buildings to withstand the static forces of gravity and those inherent in the structures' designs. But earthquakes generate an entirely different set of forces -- a quake's motion, particularly the side-to-side and rolling movement, subjects buildings to tremendous dynamic forces along vectors that bypass load-absorbing areas and, in the process, eliminate structural integrity and shred the structures like paper. Unless buildings are flexible enough to bend with those dynamic forces or sturdy enough to withstand them, a strong earthquake will take them down.

Knowing Where and How to Build

Image by Doug DeWitt
World Book
Mapping geographic areas that are apt suffer grievous damage during an earthquake is critical. These maps show fault zones, flood plains, areas prone to landslides and soil liquefaction, and the scarred locations of past earthquakes. Using these maps, planners restrict development and construction to zones where earthquakes are less likely to strike.

Engineers approach earthquake-resistant structures in a number of ways. For small- to medium-sized buildings, they use simple reinforcement techniques such as bolting buildings to their foundations and providing shear walls, which strengthen the structure and help resist rocking forces. Shear walls in the center of a building, often around an elevator shaft or stairwell, form a shear core. Engineers might also reinforce walls may with cross-bracing.

Researchers in the Civil and Environmental Engineering Department at the University of Michigan (U-M) simulated the effects of a large earthquake in the Structural Engineering Laboratory to test their new technique for constructing high-rise reinforced concrete buildings. Their proposed design procedure for coupling beams in a core-wall structural system passed the test, withstanding more lateral deformation than an earthquake would typically demand. The engineers used steel fiber-reinforced concrete to develop a better kind of coupling beam that requires less reinforcement and is easier to construct. Coupling beams connect the shear walls of high rises around openings such as those for doorways, windows, and elevator shafts.

U-M New Building Design Withstands Earthquake Simulation




Engineering earthquake-resistant skyscrapers is much more problematic than building small- to medium sized buildings, and engineers approach them with a couple of techniques. One practice is to tie the foundation to the superstructure -- the upper part of the building -- as solidly as possible to the foundation so that, when the ground shakes, the building and the foundation move as a unit, which helps prevent the collapse of upper floors. Another method, seemingly at complete odds with the first line of thought,  is to design the superstructure to move on the foundation. Base isolators between the building and its foundation act like shock absorbers, damping some of the lateral motion that would otherwise cause damage. This configuration helps the building stay in one place while the foundation shakes beneath it. Base isolators are effective but, unfortunately, prohibitively expensive for construction in poor countries such as Haiti.

Using yet another approach, engineers erect a building to be as stiff and strong as possible in the hope that it'll retain its integrity and stay intact through a quake. Once again, there's a second method that's completely unlike the first. In this second approach, engineers design segments of the frame to move so that, during a quake, the entire frame deforms slightly and absorbs the quakes energy, dissipating it throughout the entire structure and in that way maintaining the structure's integrity.

The approached might be different but the objective is the same: Improve the construction of  buildings to withstand one of Earth's awesome forces and subsequently save lives.

Wired Science 8: High Tech Quake Survival

Tuesday, April 13, 2010

Nanosats -- Specks in Space

Sputnik I
iPSTAR-1
In 1957, Russia launched Sputnik I, a beachball-sized device that weighed in at 183.9 pounds and struggled to carry a thermometer and two radio transmitters that functioned for just 21 days. Times passed. Boosters built enough muscle by 2005 to put iPSTAR-1 into orbit -- a 14,341-pound monster that will provide Internet access and broadband services to businesses and consumers around the world for an indefinite period of time. But the next chapter in the satellite story will be  about nanosats, devices with a mass between 2.2 and 22 pounds and vast potential in communications and recon applications -- from humanitarian to military. (There are even picosatellites in the offing, weighing as little as 0.22 pounds.)

Cubesat

Nanosats like the SMDC-ONE weigh less than 10 pounds and are about 4x4x13 inches in size. Developed by the U.S. Army Space and Missile Defense Command and the Army Forces Strategic Command, SMDC nanosats are inexpensive by satellite standards, costing about $1 million each, and expected to be much less as manufacturing processes are refined. The first SMDC nanosat went into orbit in 2009.

Engineers foresee nanosats functioning in swarms -- clouds of devices that will work together in varieties of configurations to accomplish ever-changing missions. Some swarms will answer to a larger mother satellite to communicate with each other and with ground controllers.

James Cutler, an assistant professor in the Department of Aerospace Engineering at the University of Michigan, is working with SRI International, one of the world's largest contract research institutes, to develop nanosatellites such as the Radio Aurora Explorer (RAX), a craft funded by the National Science Foundation to study space weather. RAX, a Cubesat device weighing 6.6 pounds, is scheduled for a launch in May 2010.

A team of engineering students working under Cutler is designing a deployable high-gain UHF antenna for nanosatellites. They’ll  integrate the antenna into an eXtendable Solar Array System (XSAS) that’s currently in development. Typical nanosatellite antennas have low-gain (2-5dBi) as a consequence of size constraints. In order to use a nanosaatellite for tracking or remote data collection applications, such as tracking animal migration, pipeline sensor data collection and emergency beacon communication, the nanosat requires a higher gain antenna. The student team’s goal is to design an antenna with 11dBi gain that will be deployed with the XSAS system. They explain their project in the following video.

Nanosatellites will also be a tool to help keep space clean. Fifty years of abandoning spacecraft in orbit has left about 5,500 tons of debris cluttering space around the planet and posing a substantial threat to hugely expensive unmanned and manned spacecraft. If current practices prevail, engineers expect that number to grow at a rate of five percent a year. Although nanosats won't cut the amount of debris already whizzing overhead, they will help stop future missions from adding to the problem.

Nanosats -- Specks in Space

Sputnik I
iPSTAR-1
In 1957, Russia launched Sputnik I, a beachball-sized device that weighed in at 183.9 pounds and struggled to carry a thermometer and two radio transmitters that functioned for just 21 days. Times passed. Boosters built enough muscle by 2005 to put iPSTAR-1 into orbit -- a 14,341-pound monster that will provide Internet access and broadband services to businesses and consumers around the world for an indefinite period of time. But the next chapter in the satellite story will be  about nanosats, devices with a mass between 2.2 and 22 pounds and vast potential in communications and recon applications -- from humanitarian to military. (There are even picosatellites in the offing, weighing as little as 0.22 pounds.)

Cubesat

Nanosats like the SMDC-ONE weigh less than 10 pounds and are about 4x4x13 inches in size. Developed by the U.S. Army Space and Missile Defense Command and the Army Forces Strategic Command, SMDC nanosats are inexpensive by satellite standards, costing about $1 million each, and expected to be much less as manufacturing processes are refined. The first SMDC nanosat went into orbit in 2009.

Engineers foresee nanosats functioning in swarms -- clouds of devices that will work together in varieties of configurations to accomplish ever-changing missions. Some swarms will answer to a larger mother satellite to communicate with each other and with ground controllers.

James Cutler, an assistant professor in the Department of Aerospace Engineering at the University of Michigan, is working with SRI International, one of the world's largest contract research institutes, to develop nanosatellites such as the Radio Aurora Explorer (RAX), a craft funded by the National Science Foundation to study space weather. RAX, a Cubesat device weighing 6.6 pounds, is scheduled for a launch in May 2010.

A team of engineering students working under Cutler is designing a deployable high-gain UHF antenna for nanosatellites. They’ll  integrate the antenna into an eXtendable Solar Array System (XSAS) that’s currently in development. Typical nanosatellite antennas have low-gain (2-5dBi) as a consequence of size constraints. In order to use a nanosaatellite for tracking or remote data collection applications, such as tracking animal migration, pipeline sensor data collection and emergency beacon communication, the nanosat requires a higher gain antenna. The student team’s goal is to design an antenna with 11dBi gain that will be deployed with the XSAS system. They explain their project in the following video.

Nanosatellites will also be a tool to help keep space clean. Fifty years of abandoning spacecraft in orbit has left about 5,500 tons of debris cluttering space around the planet and posing a substantial threat to hugely expensive unmanned and manned spacecraft. If current practices prevail, engineers expect that number to grow at a rate of five percent a year. Although nanosats won't cut the amount of debris already whizzing overhead, they will help stop future missions from adding to the problem.