The major structural material employed in the towers was A36 structural steel, although higher strength steel was used in the lower elevations of the structure.

650°C.

At normal temperatures, aviation fuel gives off very little vapour. This means it doesn’t ignite easily and or form dangerous fuel-air mixtures. Once vaporised, however, jet fuel is extremely flammable and burns at a much higher temperature than other fuels.

The building’s core housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m), and contained 47 steel columns running from the bedrock to the top of the tower.

After about 9:40 a.m., no further distress calls from the restaurant were made. The last people to leave the restaurant before Flight 11 collided with the North Tower at 8:46 a.m. were Michael Nestor, Liz Thompson, Geoffrey Wharton, and Richard Tierney. They departed at 8:44 a.m. and survived the attack.

Stanley Praimnath (born 1956) is a survivor of the September 11 attacks on the World Trade Center. He worked as an executive for Fuji Bank on the 81st floor of the South Tower (WTC 2), the second tower struck that day.

1,344 people

Engineers suggested that the south tower of the World Trade Center collapsed first, even though it was hit by the second plane, because the fireball caused by the crash was larger and because the plane hit the corner of the building, rather than the center, where there is more structural support.

One World Trade Center (WTC 1) (the North Tower) was hit at 8:46 a.m. Eastern time and collapsed at 10:28 a.m. Two World Trade Center (WTC 2) (the South Tower) was hit at 9:03 a.m. and collapsed at 9:59 a.m. The resulting debris severely damaged or destroyed more than a dozen other adjacent and nearby structures.

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From Wikipedia, the free encyclopedia. A building undergoes progressive collapse when a primary structural element fails, resulting in the failure of adjoining structural elements, which in turn causes further structural failure.

Abstract. In multi-story buildings, one of the worst collapse types in terms of structural damage and loss of life is the pancake-type collapse, where some or all floors end up lying on top of each other like the layers of a pancake, with the floor contents crushed between them.

Progressive collapse is a catastrophic structural phenomenon that can occur because of human-made and natural hazards. The results show that parameters such as number of bays, height and location of eliminated elements have great influence on progressive collapse potential of buildings under seismic loading.

Minimize Risk for Progressive Collapse

1. Redundancy: The incorporation of redundant load paths in the vertical load carrying system helps to ensure that alternate load paths are available in the event of local failure of structural elements.
2. Ties:
3. Ductility:
4. Adequate shear strength:
5. Capacity for resisting load reversals:

Among the several methods, the most common is installing beams that transfer the sway, dissipation units, and incorporation of flexible material.

Abstract: Reducing failures of buildings and other structures requires compentent design; clear communication of that design to the contractor by means of engineering drawings, etc.; careful and competent construction; and effective construction supervision.

Although high temperatures and high humidity are not as damaging to the performance of masonry as are low temperatures and low humidity, periods of hot weather may adversely affect the quality of masonry construction. The primary concern during hot weather is rapid evaporation and absorption of water from the mortar.

Hydration and strength development – ‘setting’ – in mortar usually occurs at temperatures above 4oC. If mortar is used below this temperature it may not set properly and if water is retained in the joint, frost damage can result.

Mortar – Ideal temperatures for the placement and curing of masonry mortar is the range of 70°F + 10°F. In cold weather (40 degrees Fahrenheit and below) mortar materials need to be heated, otherwise the mortar is likely to exhibit slower setting times and lower early strengths.

Brick/block laying You should not lay blocks and bricks in temperatures lower than 3oC. So keep an eye on the weather forecast for your area and when you a planning work, make sure you have regard to cold conditions. If a mortar bed freezes, only a very limited bond will form.

Rendering should NOT be carried out if:

• the temperature is below or likely to fall below 2°C, or.
• backgrounds are saturated or frozen, or.
• there is a possibility that new work will be subjected to frost before it has set.

If heated concrete is not available it is advisable to delay concreting until the ambient temperature has risen above 2ºC. If young concrete is allowed to cool below freezing point it may be damaged to such an extent that it will be unfit for use.

If overnight frost is likely before the mortar within newly constructed brickwork has fully set, it should be protected with an insulating layer of hessian underneath the polythene. This would normally give some protection to the mortar joints from overnight frost.

If freshly placed concrete cools below 0ºC the water in the mix will freeze and expand. This could damage the concrete so much that it becomes useless and has to be removed. However, provided the concrete is able first to reach a strength of about 2 N/mm2, it is likely to resist this disruptive expansion.