For greater fire safety, many structures are now reinforced with concrete, which is not as robust as structural steel, such as the Empire State Building. However, by utilizing appropriate form work processes, we can accomplish 4 days per story for concrete high-rise structures; however, this does not include time for the envelope (windows) and fit-out, which takes time. For example, one major project in Chicago used hand-made wood forms that took about 10 weeks to complete. The walls were then pumped out with hydraulic pumps and allowed to cure for 1 year before the interior finish materials were put into place.
The typical concrete structure is at least 30 feet tall and usually weighs between 20,000 and 50,000 pounds. It should be poured within a week of receiving the final design drawings or you will have to wait another month before the material can be placed into shape. The first step is to pour a small sample area of about 200 square inches. This should take about an hour and provide enough information for the contractor to decide how to proceed with the rest of the building.
A reinforced concrete building starts with the same basic steps as any other building type: site survey, plan review, goal analysis, market analysis, design/bid process, selection of construction methods, procurement of materials, scheduling, budgeting, labor planning, execution of project tasks, monitoring and close-out.
Reinforced concrete buildings require special attention to detail during the design phase to ensure adequate strength and durability of the finished product.
The majority of work is still done manually and on-site, which is costly and time-consuming. A skyscraper, for example, might now take five years or more to finish. It only took around 13 months to build the Empire State Building. 1st of May, 2014.
However, new technologies are being developed to make construction processes faster and less expensive. For example, robots are being used in building sites to do dangerous tasks such as stacking bricks or drilling holes for windows. These robots can be controlled from a distance by workers who then have time to do other things instead. Robots will be able to do almost any job that is not too difficult or dangerous to perform automatically.
Some buildings are finished in just a few days. For example, the Burj Khalifa in Dubai was completed in under four months. It is the tallest building in the world!
Modern skyscrapers use large numbers of components made using industrial manufacturing processes. Each component has specific skills to speed up construction time. For example, one component is the elevator, which takes people between floors. It must be strong enough to carry heavy people but also bulky to save space.
Buildings have become much taller over time. The Eiffel Tower, for example, is 109 meters high and takes about six months to complete. It is mostly built of iron and wood, which are both heavy materials.
Concrete will attain a reasonable strength in three to seven days and will continue to strengthen over time. The concrete's curing process also affects the length of time that it can be exposed to outdoor elements. Curing times for common concrete mixes are as follows: Rapid-set Concrete - 3 hours; Standard-set Concrete - 4 hours; Slurry-set Concrete - 12 hours.
The exposure time depends on the temperature and humidity outside and how often you need to check on the foundation. If you detect any signs of movement such as cracks or bowing, you should investigate what caused this phenomenon first before assuming the concrete is failing.
In general, if there's no moisture on the surface and no signs of deterioration such as browning of the soil beneath the foundation, then the foundation should last at least 20 years unless you see cracks or other damage which would allow water in. You should call a professional when repairing concrete foundations because some problems may not be apparent until after they're fixed.
Skyscrapers are buildings with very high floors, usually used for office space. They are so called because they "scratch" the sky when viewed from the ground.
In fact, the word "skyscraper" comes from the name of the construction material used in these buildings: steel. The first known use of this term is in an article that appeared in the New York Times on May 28, 1881. However, the building itself wasn't completed until about four years later.
The tallest building in the world is currently the Burj Khalifa in Dubai. At 2,723 feet (837 m), it is not only the highest, but also the most expensive skyscraper in the world. The cost was $1 billion and takes about six months to complete one floor.
There are many other factors that determine how long it takes to build a skyscraper. For example, if it uses any kind of prefabrication technique, then that can save time.
Concrete normally cures in 24–48 hours, at which point it is safe for normal foot activity. After one week, concrete is usually sufficiently hardened to withstand ongoing building, including heavy machinery. Concrete is considered to have attained maximum strength 28 days after it is placed. At this time, it is necessary to allow the concrete to cure further before removing the tool used to stir it.
Maximum strength will vary depending on the type of concrete and the method used to make it. For example, ordinary home-made concrete used in walkways and driveways can be expected to reach maximum strength about a month after it is made. Concrete made with aggregate larger than 2mm in diameter will never fully harden. Instead, it will keep hardening as long as there are more molecules to join together.
The strength of concrete varies by its purpose. The strength of concrete used in buildings must be sufficient to support itself under its own weight, but not so strong that it cannot be worked when needed. Concrete used in parking lots should be able to support vehicles weighing up to 10,000 pounds, while that used to build bridges should be able to support objects weighing many times that amount.
As mentioned, the strength of concrete varies depending on how it is made. Home-made concrete has a lower water/cement ratio than commercial concrete, which leaves it with less ability to resist heat and pressure.
The 7-day compressive strength of cement concrete is roughly 0.65 times that of cement concrete's 28-day compressive strength. Concrete cube strength is normally evaluated after 28 days since concrete increases strength with time after casting. The minimum requirement for concrete in most countries is a 28-day compression strength of at least 45 MPa (6000 psi). Higher strengths are available but only for special applications.
Cement concretes typically have compression strengths that range from 20 to 100 MPa (280 to 1400 psi) after 3 months age and 30 to 120 MPa (420 to 1800 psi) after 6 months age. Cements that yield higher early strength have less plasticity and thus cannot be used as construction materials for large structures such as bridges or buildings. Some cements can reach peak strength within one week of pouring but they are usually used in mixes that include additional ingredients such as plasticizers to reduce the hardening speed and improve workability.
Strength decreases gradually until it reaches its ultimate value at which point no more strength can be developed regardless of the duration of loading. Concrete strength declines due to hydration, crystallization, and loss of surface area due to spalling.
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