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246449074 Difference Between Prestressed

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Difference Between Prestressed
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  ACE BOY M. SIBBALUCA BSCE 5-A Difference Between Pre-stressed Concrete & Reinforced Concrete Similarities    Reinforced concrete and pre-stressed concrete both have steel bars or wires embedded to bolster the material's weakness under tension, but the types of steel and the uses of the concrete are different. Concrete reinforcing steel is either solid bars with ribs on them, referred to as reinforcing bar or rebar, or a wire or metal mesh. Pre-stressed steel is solid bars or bundles of wire installed under tension. Reinforcing Uses    Typical uses for reinforced concrete are street and highway paving, sidewalks, foundation walls and slabs and almost any other solid concrete form where most of the pressure will be compression. The reinforcing adds tensile strength to allow a concrete slab, for instance, to flex slightly without breaking apart. The type of reinforcing will vary. Patios and sidewalks may use wire mesh; highways and other large paving projects use heavy steel bars placed in a crisscross pattern to add tensile reinforcing. Pre-stressing    Pre-stressed concrete is just that -- concrete formed under stress. Steel bars or wires are placed in a form and stretched or stressed with forces on each end pulling on them. When the tension is released, the steel will try to return to its srcinal form. When concrete is poured around the stressing bonds before pressure is released, it creates tension; when it is released the steel's tendency to try to resume its srcinal shape adds a compressive force to the concrete laterally, giving it strength to span distances. Pre-stressed Uses    Pre-stressing is used mainly to make beams and piers in such construction as highway overpasses and commercial buildings. It enables a concrete beam to support weight between piers on either side; without such reinforcing, concrete's lack of tensile strength would cause it to collapse without support in the middle. How to Reinforce    Architects, engineers, highway designers, structural builders and other professionals use precise calculations to determine the loads on concrete and the strength required.  ACE BOY M. SIBBALUCA BSCE 5-A Homeowners can seek expert advice or use Kentucky windage on small projects. If the surface to be covered in concrete is flat and level with basically even downward force throughout, it probably needs no reinforcing or simple wire mesh, much like wire fencing. If the surface is unlevel or weights will not be evenly distributed, as in a slab for a building where the outer walls will exert greater weight pressure, the concrete needs reinforcing. When in doubt, reinforce. Reinforce Two Ways    Reinforcing may be installed horizontally or vertically. Concrete walls, in a basement or a house foundation, need reinforcing bars both ways, because a house will exert uneven pressure both horizontally and vertically. Flat surfaces, like driveways and patios, generally need only one direction of reinforcing, although highways and other large surfaces require bidirectional reinforcing because weights and pressures are applied in more than one direction. Three Ways to Stress Concrete      There are roughly three ways that concrete can be stressed into having more tensile strength. First, pre-tensioned concrete refers to a procedure whereby tensile rods are put in place first and tightened, followed by concrete pouring. When the tensile rods are loosened, the static friction of the rods against the load ensures compression, increasing tensile strength. However, this method can be problematic because it requires sturdy anchoring before pouring, which sometimes is impossible. This method is common with prefabricated building elements. Secondly, compression can be applied after pouring concrete using bonds. Tendons are threaded through the material, which are tightened using hydraulic jacks once the concrete is dry. These tendons are then wedged into position. This is a common method. Finally, compression can be applied after pouring concrete, without bonds -- in other words, tensile cords can be individually placed to allow freedom of movement and are only connected to the concrete with steel anchors along the perimeter. This is another common method, although the main disadvantage is that a cable can burst out of the slab, such as during repairs, if the anchoring system fails.  ACE BOY M. SIBBALUCA BSCE 5-A Advantages of Pre-stressed Concrete    Pre-stressed concrete shows several advantages that make it a useful building material. Pre-stressed concrete cracks less frequently and can be made into thinner, stronger slabs, highly important in high-rise building floors. Thinner slabs in high-rise buildings mean additional floors for the same or lower cost. By increasing tensile strength and therefore maximum span length, pre-stressed concrete increases the amount of usable floor space in buildings. Furthermore,  joints between slabs require maintenance and are costly; by enabling longer slabs and thinner floors, joints can be used less frequently, saving on construction and maintenance costs.   Disadvantages of Pre-stressed Concrete Concrete is naturally very strong against compression but not so strong in tension. Consequently, builders and engineers often use reinforced concrete, which contains steel rods or rebar to lend it additional strength. One type of reinforced concrete is called pre-stressed concrete, because stresses induced by steel cables in the material help to counterbalance tensile stress.  Basics    Pre-stressed concrete features steel cables or tendons that have been stretched so they pull inwards on the concrete and compress it. When the concrete comes under a tensile stress like the force of gravity on a concrete beam, for example, the compression induced by the steel tendons helps hold the beam together against the tensile stress. This is much like the way you can carry a stack of books held horizontal by applying pressure to both ends. Expense    Pre-stressed concrete is more expensive than traditional building materials. It's even more costly than other kinds of reinforced concrete; not only are additional materials involved but the extra equipment needed to stretch the steel before pouring the concrete adds to the cost. Using pre-stressed concrete in a case where additional tensile strength is unnecessary -- in a concrete floor at ground level, for example -- would raise the project costs without conferring any real benefit.  ACE BOY M. SIBBALUCA BSCE 5-A Complexity    When pouring concrete, you use forms to ensure the concrete adopts the right shape as it hardens. Pre-stressed concrete requires more complex formwork, so it has less design flexibility than other kinds of reinforced concrete, which often makes design more challenging. Moreover, the margin for error in preparing pre-stressed concrete is much smaller than other more conventional materials, so more care and caution must be exercised in construction. Considerations    Lifting precast metal members into place usually requires large cranes; these also add to the cost of construction. With all of these disadvantages in mind, however, it's important also to note that pre-stressed concrete has some important benefits. Its superior strength in tension permits engineers to design longer unsupported spans. Ultimately, the choice between pre-stressed and conventional reinforced concrete should be made based on the type of project and the properties it requires. Advantages and Disadvantages in Reinforced Concrete Reinforced concrete is mixed with steel to make it stronger, more durable and less likely to fail. The material is commonly used in buildings to make the structure able to withstand high amounts of stress and weight. Construction workers use reinforced concrete in walls, beams, foundations and columns.  Strength    Compared to regular concrete, reinforced concrete has more strength and durability. Because the concrete is fabricated with steel, it's able to withstand high pressure before it becomes damaged or weakened. Much of the stress in a building is transferred to the steel, which takes the pressure off the concrete. This allows reinforced concrete to carry much more weight than regular concrete. Flexibility    In addition to having additional strength, reinforced concrete is also flexible. During the construction process, the flexibility in reinforced concrete helps the structure take shape and

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Aug 12, 2018

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