How many buildings damaged on 911

In many cases, the record of what items companies and institutions had in their collections and files was lost along with the items themselves. The Sphere for Plaza Fountain, a large rotating metal sculpture by German artist Fritz Koenig that was one of the most recognizable works of public art at the World Trade Center, was the only public art work there to survive. The damaged piece was moved to Battery Park and displayed in its dented state as part of a memorial to the victims of the attacks.

We take a look at some of the items lost in the rubble of the World Trade Center and damaged Pentagon. Infrastructure Damage Yet even that staggering total understated the overall damage to the city's physical infrastructure. The attack had destroyed or seriously damaged several major switching hubs for telephone and cellular lines, along with the giant antenna atop the north tower, leaving much of the city without phone service, broadcast television or radio.

The collapse of 7 World Trade Center had destroyed a major electrical substation located beneath it, as well as the multi-million-dollar Emergency Command Center on its 23rd floor.

Rapid Rebuilding Within weeks, work began on the replacement or restoration of many of these essential systems. Within a year, the subway tunnel had been rebuilt, and service restored, while planning had begun on the reconstruction of the PATH line, not only to restore the original service, but also to provide a genuine improvement — a new connection to the city's subway system.

It was the start of what planners intended to be a new downtown "Grand Central," a transportation hub that would not only link several existing subway lines and the PATH train but, it was hoped, new high-speed lines to Kennedy Airport and the Long Island Rail Road. This new center would fulfill a goal that had been talked about for decades but never acted upon — to provide lower Manhattan with the kind of regional transportation hub that midtown Manhattan had enjoyed since the start of the 20th century.

An Eternal Memorial It was in that same spirit that planners began exploring the future of the World Trade Center itself, hoping to find new possibilities for the future of the city in the tragedy. Everyone recognized that a significant part of the site would need to be set aside as a memorial to the thousands who had been lost there. Indeed, as proposals for an international competition took shape, planners anticipated that the memorial would become one of the most heavily visited places in the world.

Respect for the City Grid Much of the site was to be rebuilt as urban fabric, not only to replace the revenues generated by the trade center, but as a way of making Lower Manhattan whole again. By the start of , officials had begun to put in place a process for re-envisioning the future of the acre site. From the earliest proposals, it was obvious that the World Trade Center's s "superblock" plan, which effectively turned its back on the rest of the city, would be superseded by an approach that, in concordance with the ideas of urban activist Jane Jacobs, respected the traditional grid of streets and blocks.

Liberty Tower In the months to come, a convoluted planning process — by turns inspiring and frustrating — would proceed as state and city officials, civic groups, and private developers attempted to determine not only what should be built, but how to go about making the decision.

The release of six massing studies for the site, developed by local planning consultants, provoked so vocal an outcry — especially from 5, New Yorkers gathered at an extraordinary daylong public forum at the Jacob Javits Center — that the project sponsors, rapidly changing gears, chose to cast their net more widely, inviting noted architects from around the world to submit proposals.

That approach yielded nine initial designs, then two developed schemes, then a single striking proposal by the Polish-born architect Daniel Libeskind, featuring a 1, foot-tall "Liberty Tower" along with several other office buildings , a series of lower-rise cultural institutions, and a large memorial located in the sunken pit defined by the original concrete "bathtub" which surrounded the towers' foundations.

Though there were sure to be many changes in the months and years to come, the Libeskind scheme, officials hoped, would provide a basis for moving forward. Discover the fascinating story of Elizebeth Smith Friedman, the groundbreaking cryptanalyst who helped bring down gangsters and break up a Nazi spy ring in South America. An oxyacetylene torch or a Bunsen burner is a pre-mixed flame.

A fireplace flame is a diffuse flame burning in air, as was the WTC fire. Diffuse flames generate the lowest heat intensities of the three flame types. If the fuel and the oxidant start at ambient temperature, a maximum flame temperature can be defined. This maximum flame temperature is reduced by two-thirds if air is used rather than pure oxygen. The reason is that every molecule of oxygen releases the heat of formation of a molecule of carbon monoxide and a molecule of water.

If pure oxygen is used, this heat only needs to heat two molecules carbon monoxide and water , while with air, these two molecules must be heated plus four molecules of nitrogen. Thus, burning hydrocarbons in air produces only one-third the temperature increase as burning in pure oxygen because three times as many molecules must be heated when air is used.

But it is very difficult to reach this maximum temperature with a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse flame are mixed in the best ratio. Typically, diffuse flames are fuel rich, meaning that the excess fuel molecules, which are unburned, must also be heated.

This fuel-rich diffuse flame can drop the temperature by up to a factor of two again. Some reports suggest that the aluminum from the aircraft ignited, creating very high temperatures. While it is possible to ignite aluminum under special conditions, such conditions are not commonly attained in a hydrocarbon-based diffuse flame.

In addition, the flame would be white hot, like a giant sparkler. There was no evidence of such aluminum ignition, which would have been visible even through the dense soot. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. The additional problem was distortion of the steel in the fire.

The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform.

This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire. Nearly every large building has a redundant design that allows for loss of one primary structural member, such as a column.

However, when multiple members fail, the shifting loads eventually overstress the adjacent members and the collapse occurs like a row of dominoes falling down. The perimeter tube design of the WTC was highly redundant. It survived the loss of several exterior columns due to aircraft impact, but the ensuing fire led to other steel failures. With a Pa floor design allowable, each floor should have been able to support approximately 1, t beyond its own weight.

The total weight of each tower was about , t. As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below with its 1, t design capacity could not support the roughly 45, t of ten floors or more above crashing down on these angle clips.

This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of km per hour. There are several points that should be made. First, the building is not solid; it is 95 percent air and, hence, can implode onto itself. Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure.

Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity. To summarize all of these points, a , t structure has too much inertia to fall in any direction other than nearly straight down. The World Trade Center was not defectively designed. No designer of the WTC anticipated, nor should have anticipated, a 90, L Molotov cocktail on one of the building floors.

Skyscrapers are designed to support themselves for three hours in a fire even if the sprinkler system fails to operate. This time should be long enough to evacuate the occupants. No normal office fires would fill 4, square meters of floor space in the seconds in which the WTC fire developed.