Raft Foundation Design Tutorial Using Orion Pdf
Gifford Brickley
The raft foundation is a very commonly used type of foundation system. Raft foundation is also known as Mat foundation. Definition of raft foundation along with working principle, when to choose raft, types of raft foundation, materials of raft foundation, raft construction steps etc are discussed below.
Raft foundation is actually a thick concrete slab resting on a large area of soil reinforced with steel, supporting columns or walls and transfer loads from the structure to the soil. Usually, mat foundation is spread over the entire area of the structure it is supporting.
Raft foundation transmits the total load from the building to the entire ground floor area. Stress distribution mechanism of raft foundation is very simple. Total weight of the structure and self-weight of the mat is calculated and is divided by the total area of the foundation it is covering to calculate the stress on the soil.
As in case of raft foundation the contact area of the foundation with soil is much more than any other type of foundation, so the load is distributed over a larger area and thus the stress on soil is lesser and the possibility of shear failure of soil is also reduced.
Several types of Raft foundation may be used depending on the condition of soil and the load imposed on the foundation.
Followings are the different types of raft foundation used in construction:
This is the simplest form of raft foundation. This type of mat is used when the columns and walls are uniformly spaced at small intervals and the subjected loads are relatively small. Reinforcement is placed in both directions and more reinforcement is required at the column locations and load-bearing walls. The thickness of this types of raft foundation is generally restricted within 300mm for economic reason. A thicker slab would not be economical.
When the columns and load bearing walls are subjected to heavier loads, the slab is thickened under the columns and walls and extra reinforcement is provided to resist against diagonal shear and negative reinforcement.
In this type of raft, beams are cast monolithically with the raft slab connecting the columns and walls. This type of raft is suitable when the columns are placed at a larger distance and the loads on the columns are variable.
This type of raft foundation is supported on piles. A piled raft is used when the soil at a shallow depth is highly compressible and the water table is high. Piles under raft help in reducing settlement and provides resistance against buoyancy.
In this type of raft, the foundation walls act as a deep beam. Rigid frame mat is referred when columns carry extremely heavy loads and the connecting beams exceeds 90cm depth. Here two concrete slabs are placed, one on top of another and connected with foundation walls in both directions and thus forms a cellular raft foundation. This type of raft is very rigid and is economical when the required slab thickness is very high.
To conclude, mat is one of the most common and popular type of foundation system due to its simple construction process and its effectiveness where soil condition is poor at a shallow depth. One must investigate the soil condition and analyze the loading condition of the building for an optimum use of the foundation and necessary precautions should be taken for a safe construction.
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And not just clothing. As scientists have established, a host of remarkable things occurred to our species at about that time. It marked a dividing line in our history, one that made us who we are, and pointed us, for better and worse, toward the world we now have created for ourselves.
For now, the answers are the subject of careful back-and-forth in refereed journals and heated argument in faculty lounges. All that is clear is that about the time of Toba, new, behaviorally modern people charged so fast into the tephra that human footprints appeared in Australia within as few as 10,000 years, perhaps within 4,000 or 5,000. Stay-at-home Homo sapiens 1.0, a wallflower that would never have interested Lynn Margulis, had been replaced by aggressively expansive Homo sapiens 2.0. Something happened, for better and worse, and we were born.
Today The Struggle for Existence is recognized as a scientific landmark, one of the first successful marriages of theory and experiment in ecology. But the book was not enough to get Gause a fellowship; the Rockefeller Foundation turned down the twenty-four-year-old Soviet student as insufficiently eminent. Gause could not visit the United States for another twenty years, by which time he had indeed become eminent, but as an antibiotics researcher.
Lynn Margulis, it seems safe to say, would have scoffed at these assessments of human domination over the natural world, which, in every case I know of, do not take into account the enormous impact of the microworld. But she would not have disputed the central idea: Homo sapiens has become a successful species, and is growing accordingly.
Other creatures are much less flexible. Like apartment-dwelling cats that compulsively hide in the closet when visitors arrive, they have limited capacity to welcome new phenomena and change in response. Human beings, by contrast, are so exceptionally plastic that vast swaths of neuroscience are devoted to trying to explain how this could come about. (Nobody knows for certain, but some researchers now think that particular genes give their possessors a heightened, inborn awareness of their environment, which can lead both to useless, neurotic sensitivity and greater ability to detect and adapt to new situations.)
Human societies are far more varied than their insect cousins, of course. But the true difference is their plasticity. It is why humankind, a species of Canbys, has been able to move into every corner of the earth, and to control what we find there. Our ability to change ourselves to extract resources from our surroundings with ever-increasing efficiency is what has made Homo sapiens a successful species. It is our greatest blessing.
Historians have provided many reasons for this extraordinary transition. But one of the most important is that abolitionists had convinced huge numbers of ordinary people around the world that slavery was a moral disaster. An institution fundamental to human society for millennia was swiftly dismantled by ideas and a call to action, loudly repeated.
Less well known, but equally profound: the decline in violence. Foraging societies waged war less brutally than industrial societies, but more frequently. Typically, archaeologists believe, about a quarter of all hunters and gatherers were killed by their fellows. Violence declined somewhat as humans gathered themselves into states and empires, but was still a constant presence. When Athens was at its height in the fourth and fifth centuries BC, it was ever at war: against Sparta (First and Second Peloponnesian Wars, Corinthian War); against Persia (Greco-Persian Wars, Wars of the Delian League); against Aegina (Aeginetan War); against Macedon (Olynthian War); against Samos (Samian War); against Chios, Rhodes, and Cos (Social War).
As a relatively young species, we have an adolescent propensity to make a mess: we pollute the air we breathe and the water we drink, and appear stalled in an age of carbon dumping and nuclear experimentation that is putting countless species at risk including our own. But we are making undeniable progress nonetheless. No European in 1800 could have imagined that in 2000 Europe would have no legal slavery, women would be able to vote, and gay people would be able to marry. No one could have guessed a continent that had been tearing itself apart for centuries would be free of armed conflict, even amid terrible economic times. Given this record, even Lynn Margulis might pause (maybe).
Evolutionarily speaking, a species-wide adoption of hara hachi bu would be unprecedented. Thinking about it, I can picture Lynn Margulis rolling her eyes. But is it so unlikely that our species, Canbys one and all, would be able to do exactly that before we round that fateful curve of the second inflection point and nature does it for us?
A three-time National Magazine Award finalist, Mann has received writing awards from the American Bar Association, the American Institute of Physics, the Alfred P. Sloan Foundation, the Margaret Sanger Foundation, and the Lannan Foundation.
Also, his liberal championing of Progress is somewhat nauseating. The figures on declining violence are dubious at best, relying on relative rather than absolute statistics (Does Mann not count human lives as having equal worth? Lets not forget how bloody the 20th century was), and completely externalising violence on the natural world.
The only other option is to go back to hunter-gatherer lifestyle, where you spend all your day searching for food, then starve during the winter. Remember, just a few short centuries ago most people worked all day long, every day. That was to get hardly enough food and a roof over your head.
Now westerners work a third of the day, five seventh of the week with a few weeks off plus holidays. The average westerner today lives better then royalty or nobles did 200 years ago. We live three times longer and have access to every type of food from around the world. We can jump on a plane and see Australia, or take a train across the continent. You can spend your evenings watching movies, or bad TV, or go out drinking, watch football in person, play rugby, or do one of thousands of hobbies.
On the weekends you can go boating, or fly your own microplane. You can talk to almost anyone in the world from your living room. You can walk around the city with a computer that talks to you and responds to your voice, science fiction just 30 years ago.
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