а ти не читаш еве за зграда 7 обрни внимание
Steel loses about 50 percent of its strength at 1100°F," notes senior engineer Farid Alfawak-hiri of the American Institute of Steel Construction. "And at 1800° it is probably at less than 10 percent." NIST also believes that a great deal of the spray-on fireproofing insulation was likely knocked off the steel beams that were in the path of the crashing jets, leaving the metal more vulnerable to the heat.
FACT: Once each tower began to collapse, the weight of all the floors above the collapsed zone bore down with pulverizing force on the highest intact floor. Unable to absorb the massive energy, that floor would fail, transmitting the forces to the floor below, allowing the collapse to progress downward through the building in a chain reaction. Engineers call the process "pancaking," and it does not require an explosion to begin, according to David Biggs, a structural engineer at Ryan-Biggs Associates and a member of the American Society of Civil Engineers (ASCE) team that worked on the FEMA report. пази тука при контролирана експлозија првен подземјето експлодира па нагоре а овде читај!!!!!!! и ти кажав сеизмички бран нема од експлозив
Like all office buildings, the WTC towers contained a huge volume of air. As they pancaked, all that air — along with the concrete and other debris pulverized by the force of the collapse — was ejected with enormous energy
But jet fuel wasn't the only thing burning, notes Forman Williams, a professor of engineering at the University of California, San Diego, and one of seven structural engineers and fire experts that PM consulted. He says that while the jet fuel was the catalyst for the WTC fires, the resulting inferno was intensified by the combustible material inside the buildings, including rugs, curtains, furniture and paper. NIST reports that pockets of fire hit 1832°F.
"The jet fuel was the ignition source," Williams tells PM. "It burned for maybe 10 minutes, and [the towers] were still standing in 10 minutes. It was the rest of the stuff burning afterward that was responsible for the heat transfer that eventually brought them down."
ЕВЕ 7матаFACT: Many conspiracy theorists point to FEMA's preliminary report, which said there was relatively light damage to WTC 7 prior to its collapse. With the benefit of more time and resources, NIST researchers now support the working hypothesis that WTC 7 was far more compromised by falling debris than the FEMA report indicated. "The most important thing we found was that there was, in fact, physical damage to the south face of building 7," NIST's Sunder tells PM. "On about a third of the face to the center and to the bottom — approximately 10 stories — about 25 percent of the depth of the building was scooped out." NIST also discovered previously undocumented damage to WTC 7's upper stories and its southwest corner.
NIST investigators believe a combination of intense fire and severe structural damage contributed to the collapse, though assigning the exact proportion requires more research. But NIST's analysis suggests the fall of WTC 7 was an example of "progressive collapse," a process in which the failure of parts of a structure ultimately creates strains that cause the entire building to come down. Videos of the fall of WTC 7 show cracks, or "kinks," in the building's facade just before the two penthouses disappeared into the structure, one after the other. The entire building fell in on itself, with the slumping east side of the structure pulling down the west side in a diagonal collapse.
According to NIST, there was one primary reason for the building's failure: In an unusual design, the columns near the visible kinks were carrying exceptionally large loads, roughly 2000 sq. Ft. Of floor area for each floor. "What our preliminary analysis has shown is that if you take out just one column on one of the lower floors," Sunder notes, "it could cause a vertical progression of collapse so that the entire section comes down."
There are two other possible contributing factors still under investigation: First, trusses on the fifth and seventh floors were designed to transfer loads from one set of columns to another. With columns on the south face apparently damaged, high stresses would likely have been communicated to columns on the building's other faces, thereby exceeding their load-bearing capacities.
Second, a fifth-floor fire burned for up to 7 hours. "There was no firefighting in WTC 7," Sunder says. Investigators believe the fire was fed by tanks of diesel fuel that many tenants used to run emergency generators.
WTC 7 might have withstood the physical damage it received, or the fire that burned for hours, but those combined factors — along with the building's unusual construction — were enough to set off the chain-reaction collapse.
НАЈУВАЖНО ПАЗИ ЕВЕ ГИ СЕИЗМИЧКИТЕ ПОДАТОЦИ
On that graph, the 8- and 10-second collapses appear — misleadingly — as a pair of sudden spikes. Lamont-Doherty's 40-second plot of the same data (Graph 2) gives a much more detailed picture: The seismic waves — blue for the South Tower, red for the North Tower — start small and then escalate as the buildings rumble to the ground. Translation: NO BOMBS.
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The September 11 attacks inflicted casualties and material damages on a far greater scale than any other terrorist aggression in recent history. Lower Manhattan lost approximately 30 percent of its office space and a number of businesses ceased to exist. Close to 200,000 jobs were destroyed or relocated out of New York City, at least temporarily. The destruction of physical assets was estimated in the national accounts to amount to $14 billion for private businesses, $1.5 billion for state and local government enterprises and $0.7 billion for federal enterprises. Rescue, cleanup and related costs have been estimated to amount to at least $11 billion for a total direct cost of $27.2 billion.
Immediate and Short Term Indirect Impacts
Immediately after the attacks, leading forecast services sharply revised downward their projections of economic activity. The consensus forecast for U.S. Real GDP growth was instantly downgraded by 0.5 percentage points for 2001 and 1.2 percentage points for 2002. The implied projected cumulative loss in national income through the end of 2003 amounted to 5 percentage points of annual GDP, or half a trillion dollars.(ГЛЕДАЈ ЗАГУБА ПОЛА ТРИЛИОН ЛОГИЧНО ТИ Е СЕГА!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!)
With production disrupted in some areas (airlines) and consumers increasingly cautious, real GDP shrank in the third quarter of 2001. But in the fourth quarter, demand held up better than initially feared, and GDP increased. However, private sector fixed investment registered a steep decline, and inventories were slashed. Offsetting these forces, however, were household consumption, helped by falling energy prices, and government spending. Defense spending in particular grew by about 9.25% in real terms in the fourth quarter, at a seasonally adjusted annual rate.
Some sectors or firms actually witnessed an increase in demand, notably in the area of security and information technology. Still, while overall demand proved fairly resilient, a number of sectors were hit hard, with declining output and profits continuing into the mid-term.
Overall however the short-term adverse economic impact of the attacks was far less than feared initially, thanks in large part to good economic crisis management. The Federal Reserve, the Administration and Congress acted quickly to restore confidence, inject liquidity and provide resources to deal with the consequences of the attacks. The Federal Reserve by lowering the price of credit and temporarily providing vast amounts of liquidity helped safeguard the integrity of the financial system and saved many firms from bankruptcy.(банкарите ги намалија каматите за да спречат банкрот)
Medium Term Impacts
Looking beyond the short term, the fact that the attack was premeditated and therefore could be repeated has had a significant impact on five main areas: (1) insurance; (2) airlines; (3) tourism and other industries associated with travel; (4) shipping; and (5) increased defense/security expenditures. In turn, developments in these areas have had a broader effect on wide areas of economic activity.
Insurance. The losses from the terrorist attacks for the insurance industry (including reinsurance) are estimated at between $30 and $58 billion with the main uncertainty concerning liability insurance. By comparison the losses associated with Hurricane Andrew's 1992 damage in Florida came to around $21 billion. Even if the final cost is close to the lower estimate, insured losses in 2001 are likely to have been the highest ever.
Following the attacks, most primary insurers have increased their premiums and curtailed or dropped altogether coverage for terrorism-related risk. The increases in insurance premiums have adversely affected several key industries. The strongest impact has been on aviation, but other sectors, including transportation, construction, and tourism and energy generation have also been affected. Overall it is estimated that commercial property and liability insurance rates have been raised by 30 percent on average.
Airlines. The United States' airline industry was already in a weak financial position before the attacks with rising debt ratios and falling returns on investment. Even with cutbacks in service of the order of 20 percent and significant government support, airline passenger traffic has apparently remained below normal, 100,000 layoffs have been announced and employment in October and November fell by 81,000 (almost 8 percent). Equity valuations compared to the overall market illustrate these difficulties. The U.S. Airline sector has lost around 20 percent of its relative value since September 10.
Tourism and Other Service Industries. Other industries have also been badly affected, such as hotels, tourism, automobile rentals, travel agents, and civilian aircraft manufactures.
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