Post-tension concrete the wave of the future.Prestressed concrete prestressed concrete Concrete reinforced by either pretensioning or posttensioning, allowing it to carry a greater load or span a greater distance than ordinary reinforced concrete. In pretensioning, lengths of steel wire or cables are laid in the empty mold and stretched. application may help to expand the use of reinforced concrete reinforced concrete Concrete in which steel is embedded in such a manner that the two materials act together in resisting forces. The reinforcing steel—rods, bars, or mesh—absorbs the tensile, shear, and sometimes the compressive stresses in a concrete in structural framing of commercial buildings, say experts. The benefits of post-tensioned concrete were presented by Mike Mota, of the Portland Cement portland cement Binding agent of present-day concrete. It is a finely ground powder made by burning and grinding a limestone mixed with clay or shale. Its inventor, Joseph Aspdin (1799–1855), patented the process in 1824, naming the material for its resemblance to the Association, at a Concrete Industry Board luncheon earlier this month. Post-tensioning is a technique of reinforcing concrete, masonry, and other structural elements Structural elements are used in structural analysis to simplify the structure which is to be analysed. Structural elements can be linear, surfaces or volumes. Linear elements:
"(In normal applications) we design concrete member for a certain load. That concrete member may never see that much stress level during the life of the project," said Mota, PCA (tool, programming) PCA - A dynamic analyser from DEC giving information on run-time performance and code use. regional structural engineer--East. "With post tensioning it's different. The member is stressed to its maximum capacity right off the top." This is important to a structural designer, because post-tensioning concrete increases it tensile (bending) strength, making the concrete slab or masonry wall stiffer. "A designer can achieve longer spans with thinner concrete sections with post-tensioned concrete," said Mota. "It also gives the building owner an economical advantage in that it allows lower floor to floor height." A residential structure already under construction in New York City New York City: see New York, city. New York City City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. is The Estates at Kew Gardens in Queens. The 550,000 s/f high-rise building has a 7 1/2 inch post-tensioned reinforced concrete slab, according to Mota. The technique is also used nationwide in bridges, elevated slabs (parking garages and residential or commercial buildings), residential foundations, walls, and columns, he said. "It's widely used all over the country," Mota said. "In New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of it's catching on. It requires a little more training." The second method of prestressing is called pre-tensioning. This method consists of stressing the reinforcing inside of large steel buttresses, and then casting the concrete around the reinforcing. This method can only be done at a precast pre·cast adj. Relating to or being a structural member, especially of concrete, that has been cast into form before being transported to its site of installation. manufacturing facility and requires the completed prestressed concrete members to be trucked out to the job site and then assembled. A two-week training course is available from Local 46 Metallic Lathers Union and Reinforcing Iron Workers. For information call 212-737-0500. |
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