The CN Tower in Toronto, Ontario was the world's tallest freestanding structure on land from 1975 until the Burj Dubai surpassed it in 2007, rising 553.33 m (1,815 ft). It is currently the world's tallest completed freestanding structure on land.

The tallest standing structure is the KVLY-TV mast 30 miles (48 km) north of Fargo, North Dakota United States, at 628.8 m (2,063 ft). It is a transmission antenna, consisting of a bare metal structure supported by guy-wires.
Transmission antennas of this type are not usually included with the world's tallest buildings because they are not self-supporting. The issue is further complicated if all manmade habitable structures are considered. Under that criterion it is possible to claim 'tallest structure' records for deep mine-shafts, or the Mohole drilling rig, which can be several miles (8-10 km) in vertical length.

The CN Tower in Toronto, Ontario was the world's tallest freestanding structure on land from 1975 until the Burj Dubai surpassed it in 2007, rising 553.33 m (1,815 ft). It is currently the world's tallest completed freestanding structure on land.
The CN Tower in Toronto, Ontario, Canada, standing at 553.3 m (1,815 ft), was the world's tallest freestanding structure on land from 1976 until September 12, 2007, when it was overtaken in height by the rising Burj Dubai.[1] It has the world's highest public observation deck at 446.5 m (1,465 ft). It remains the world's tallest completed freestanding structure, pending the Burj Dubai's completion (projected for mid 2009).
The Petronius Platform stands 610 m (2,001 ft), leading some to claim it as the tallest freestanding structure in the world. However, as this oil and natural gas platform is partially supported by wires, critics argue that it is not freestanding, and the below-water height should not be counted, in the same manner as underground 'height' is not taken into account in buildings.
The Troll A platform is 472 m (1,549 ft), without any part of that height being supported by wires.
Taipei 101 in Taipei, Taiwan is currently the world's tallest inhabited building in three out the four main categories that are commonly measured: at 509.2 m (1,671 ft) as measured to its architectural height as well as roof height 449.2 m (1,474 ft) and highest occupied floor 439.2 m (1,441 ft). The Sears Tower is highest in the last category: the highest current height to the top of antenna of any building in the world at 527.3 m (1,730 ft).
The Burj Dubai, currently under construction, is already the tallest freestanding structure on land. As of 5 February 2008, the tower's developers reported its height to be 604.9 m (1,985 ft), with 159 completed floors,[2] surpassing Taipei 101 as the tallest building.[3] On its completion in 2008 or 2009 it will break the height record in all four categories for completed buildings by a wide margin. While the final height has not been released to the public, the developers state that the building will be at least 818 m (2,684 ft) including the spire. The developer, Emaar, is keeping structural details secret due to competition for the "world's tallest" with other proposed buildings, including the nearby Al Burj.[4] The CN Tower will maintain its record of the world's highest observation deck as Burj Dubai's deck will be at 442 m (1,450 ft).[5] The 'Symbol of Dubai' will have more than 160 floors, 56 elevators, apartments, shops, swimming pools, spas and corporate suites.

Tallest Building and Structure in The World 1

The under construction Burj Dubai in Dubai, United Arab Emirates is the world's current tallest freestanding structure on land, rising 604.9 m (1,985 ft). When completed, it is planned to rise over 800 m (2,625 ft).

While determining the world's tallest structure has generally been straightforward, the definition of the world's tallest building or the world's tallest tower is less clear. The disputes generally center on what should be counted as a building or a tower, and what is being measured.
In terms of absolute height, the tallest structures are currently the dozens of radio and television broadcasting towers which measure over 600 meters (about 2,000 feet) in height. There is, however, some debate about:
whether structures under construction should be included in the list
whether structures rising out of water should have their below-water height included.
For towers, there is debate over:
whether guy-wire-supported structures should be counted
For buildings, there is debate over:
whether communication towers with observation galleries should be considered habitable buildings.
whether only habitable height is considered.
whether roof-top antennas should be considered towards height of buildings; with particular interest in whether components that look like spires can be either classified as antennas or architectural detail.
These debates will likely lose some relevance in 2009, as the Burj Dubai, a building currently under construction in Dubai, United Arab Emirates, is planned to exceed all other existing above-ground structures in height, including guyed TV towers.

http://en.wikipedia.org/wiki/List_of_tallest_buildings_and_structures_in_the_world

Building Safer Structures 3

USGS scientists have installed instruments in a variety of structures across the United States to monitor their behavior during earthquakes. Examples shown include a dam, a bridge supporting a large aqueduct, a highway overpass, and a Veterans hospital.

Today there are instruments installed in hospitals, bridges, dams, aqueducts, and other structures throughout the earthquake-prone areas of the United States, including Illinois, South Carolina, New York, Tennessee, Idaho, California, Washington, Alaska, and Hawaii. Both the California Division of Mines and Geology (CDMG) and the USGS operate instruments in California. The USGS also operates instruments in the other seismically active regions of the nation.

The majority of deaths and injuries from earthquakes are caused by the damage or collapse of buildings and other structures. These losses can be reduced through documenting and understanding how structures respond to earthquakes. Gaining such knowledge requires a long-term commitment because large devastating earthquakes occur at irregular and often long intervals. Recording instruments must be in place and waiting, ready to capture the response to the next temblor whenever it occurs. The new information acquired by these instruments can then be used to better design earthquake-resistant structures. In this way, earth scientists and engineers help reduce loss of life and property in future earthquakes.

Mehmet Celebi, Robert A. Page, and Linda Seekins
COOPERATING AGENCIES, COMPANIES, AND INSTITUTIONSCalifornia Department of TransportationCalifornia Division of Mines and GeologyCity of Los AngelesGeneral Services AdministrationMetropolitan Water District of Southern CaliforniaOregon Department of HighwaysU.S. Army Corps of EngineersU.S. Department of EnergyU.S. Department of Veterans AffairsWashington Department of HighwaysWashington Department of Natural ResourcesPrivate building owners
For more information contact:Earthquake Information Hotline (415) 329-4085U.S. Geological Survey, MS 977345 Middlefield Road, Menlo Park, CA 94025USGS Menlo Park Earthquakes Home Page
U.S. Geological Survey Fact Sheet-167-95 1995

Building Safer Structures 2

On October 17, 1989, the magnitude 7.1 Loma Prieta earthquake struck the Santa Cruz Mountains in central California. Sixty miles away, in downtown San Francisco, the occupants of the Transamerica Pyramid were unnerved as the 49-story office building shook for more than a minute. U.S. Geological Survey (USGS) instruments, installed years earlier, showed that the top floor swayed more than 1 foot from side to side. However, no one was seriously injured, and the Transamerica Pyramid was not damaged. This famous San Francisco landmark had been designed to withstand even greater earthquake stresses, and that design worked as planned during the earthquake.

Earthquakes are a widespread hazard in the United States. Colors show magnitudes of historical earthquakes: red, 7 or greater; orange, 5.5 to 7; yellow, 4.5 to 5.5. The U.S. Geological Survey operates instruments in many structures in the seismically active areas shown. These instruments measure how structures respond to earthquake shaking.

Designing and building large structures is always a challenge, and that challenge is compounded when they are built in earthquake-prone areas. More than 60 deaths and about $ 6 billion in property damage resulted from the Loma Prieta earthquake. As earth scientists learn more about ground motion during earthquakes and structural engineers use this information to design stronger buildings, such loss of life and property can be reduced.
To design structures that can withstand earthquakes, engineers must understand the stresses caused by shaking. To this end, scientists and engineers place instruments in structures and nearby on the ground to measure how the structures respond during an earthquake to the motion of the ground beneath. Every time a strong earthquake occurs, the new information gathered enables engineers to refine and improve structural designs and building codes. In 1984 the magnitude 6.2 Morgan Hill, California, earthquake shook the West Valley College campus, 20 miles away. Instruments in the college gymnasium showed that its roof was so flexible that in a stronger or closer earthquake the building might be severely damaged, threatening the safety of occupants. At that time, these flexible roof designs were permitted by the Uniform Building Code (a set of standards used in many states). Many industrial facilities nationwide were built with such roofs.

Seismic records (upper right) obtained during the 1984 Morgan Hill, California, earthquake led to an improvement in the Uniform Building Code (a set of standards used in many states). The center of the gym roof shook sideways three to four times as much as the edges. The Code has since been revised to reduce the flexibility of such large-span roof systems and thereby improve their seismic resistance.

Building codes provide the first line of defense against future earthquake damage and help to ensure public safety. Records of building response to earthquakes, especially those from structures that failed or were damaged, have led to many revisions and improvements in building codes. In 1991, as a direct result of what was learned about the West Valley College gymnasium roof, the Uniform Building Code was revised. It now recommends that such roofs be made less flexible and therefore better able to withstand large nearby earthquakes.
Earth scientists began recording earthquakes about 1880, but it was not until the 1940's that instruments were installed in buildings to measure their response to earthquakes. The number of instruments installed in strucures increased in the 1950's and 1960's. The first abundant data on the response of structures came from the devastating 1971 San Fernando, California, earthquake, which yielded several dozen records. These records were primitive by today's standards. The first records from instruments sophisticated enough to measure twisting of a building were obtained during the 1979 Imperial Valley, California, earthquake.

Building Safer Structures 1

The Transamerica Pyramid in San Francisco, built to withstand earthquakes, swayed more than 1 foot but was not damaged in the 1989 Loma Prieta, California, earthquake

In this century, major earthquakes in the United States have damaged or destroyed numerous buildings, bridges, and other structures. By monitoring how structures respond to earthquakes and applying the knowledge gained, scientists and engineers are improving the ability of structures to survive major earthquakes. Many lives and millions of dollars have already been saved by this ongoing research.

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