Reinforced concrete - Wikipedia, the free encyclopedia. Reinforced concrete (RC) is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets. Reinforcing schemes are generally designed to resist tensilestresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure. Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not. Reinforced concrete may also be permanently stressed (in compression), so as to improve the behaviour of the final structure under working loads. In the United States, the most common methods of doing this are known as pre- tensioning and post- tensioning. For a strong, ductile and durable construction the reinforcement needs to have the following properties at least: High relative strength. High toleration of tensile strain.
Practical Design of RC Beam Reinforced Concrete Design Asst.Prof.Dr.Mongkol JIRAVACHARADET S U R A N A R E E UNIVERSITY OF TECHNOLOGY INSTITUTE OF ENGINEERING. 125 5.1 RCC DESIGN AND DRAWING L T P 4 1 3 RATIONALE This subject is an applied engineering subject. Diploma holders in Civil Engineering will. DESIGN OF CONCRETE BUILDINGS Worked examples Report EUR 26566 EN. European Commission Joint Research Centre. 4.2.1.1 Design of the footing. Reinforced Concrete Design Theory and Example Free Download. Reinforced Concrete Design Theory and Example Free Download. Oleh Download Center. Good bond to the concrete, irrespective of p. H, moisture, and similar factors. Thermal compatibility, not causing unacceptable stresses in response to changing temperatures. Durability in the concrete environment, irrespective of corrosion or sustained stress for example. History. Wilkinson reinforced the concrete roof and floors in the two- storey house he was constructing. His positioning of the reinforcement demonstrated that, unlike his predecessors, he had knowledge of tensile stresses. In 1. 87. 7, Monier was granted another patent for a more advanced technique of reinforcing concrete columns and girders with iron rods placed in a grid pattern. Though Monier undoubtedly knew reinforcing concrete would improve its inner cohesion, it is less known if he even knew how much reinforcing actually improved concrete's tensile strength. American New Yorker Thaddeus Hyatt published a report titled An Account of Some Experiments with Portland- Cement- Concrete Combined with Iron as a Building Material, with Reference to Economy of Metal in Construction and for Security against Fire in the Making of Roofs, Floors, and Walking Surfaces where he stated his experiments on the behavior of reinforced concrete. His work played a major role in the evolution of concrete construction as a proven and studied science. Without Hyatt's work, more dangerous trial and error methods would have largely been depended on for the advancement in the technology. Wayss was a German civil engineer and a pioneer of the iron and steel concrete construction. In 1. 87. 9 Wayss bought the German rights to Monier's patents and in 1. Wayss & Freytag. Up until the 1. 89. Wayss and his firm greatly contributed to the advancement of Monier's system of reinforcing and established it as a well- developed scientific technology. Ransome was an English- born engineer and early innovator of the reinforced concrete techniques in the end of the 1. With the knowledge of reinforced concrete developed during the previous 5. Ransome innovated nearly all styles and techniques of the previous known inventors of reinforced concrete. Ransome's key innovation was to twist the reinforcing steel bar improving bonding with the concrete. The home was designed to be fireproof for his wife. One of the first skyscrapers made with reinforced concrete was the 1. Ingalls Building in Cincinnati, constructed in 1. Small changes in the design of a floor system can have significant impact on material costs, construction schedule, ultimate strength, operating costs, occupancy levels and end use of a building. Without reinforcement, constructing modern structures with concrete material would not be possible. Behavior of reinforced concrete. When cement is mixed with a small amount of water, it hydrates to form microscopic opaque crystal lattices encapsulating and locking the aggregate into a rigid structure. The aggregates used for making concrete should be free from harmful substances like organic impurities, silt, clay, lignite etc. Typical concrete mixes have high resistance to compressivestresses (about 4,0. MPa)); however, any appreciable tension (e. For this reason, typical non- reinforced concrete must be well supported to prevent the development of tension. If a material with high strength in tension, such as steel, is placed in concrete, then the composite material, reinforced concrete, resists not only compression but also bending and other direct tensile actions. A reinforced concrete section where the concrete resists the compression and steel resists the tension can be made into almost any shape and size for the construction industry. Key characteristics. Usually steel bars are roughened or corrugated to further improve the bond or cohesion between the concrete and steel. The alkaline chemical environment provided by the alkali reserve (KOH, Na. OH) and the portlandite (calcium hydroxide) contained in the hardened cement paste causes a passivating film to form on the surface of the steel, making it much more resistant to corrosion than it would be in neutral or acidic conditions. When the cement paste is exposed to the air and meteoric water reacts with the atmospheric CO2, portlandite and the Calcium Silicate Hydrate (CSH) of the hardened cement paste become progressively carbonated and the high p. H gradually decreases from 1. Carbonatation of concrete along with chloride ingress are amongst the chief reasons for the failure of reinforcement bars in concrete. Reinforcing bars are normally round in cross- section and vary in diameter. Reinforced concrete structures sometimes have provisions such as ventilated hollow cores to control their moisture & humidity. Distribution of concrete (in spite of reinforcement) strength characteristics along the cross- section of vertical reinforced concrete elements is inhomogeneous. Maintaining composite action requires transfer of load between the concrete and steel. The direct stress is transferred from the concrete to the bar interface so as to change the tensile stress in the reinforcing bar along its length, this load transfer is achieved by means of bond (anchorage) and is idealized as a continuous stress field that develops in the vicinity of the steel- concrete interface. Anchorage (bond) in concrete: Codes of specifications. The main requirement for safety against bond failure is to provide a sufficient extension of the length of the bar beyond the point where the steel is required to develop its yield stress and this length must be at least equal to its development length. However, if the actual available length is inadequate for full development, special anchorages must be provided, such as cogs or hooks or mechanical end plates. The same concept applies to lap splice length mentioned in the codes where splices (overlapping) provided between two adjacent bars in order to maintain the required continuity of stress in the splice zone. Anti- corrosion measures. Good design and a well- chosen concrete mix will provide additional protection for many applications. Uncoated, low carbon/chromium rebar looks similar to standard carbon steel rebar due to its lack of a coating; its highly corrosion- resistant features are inherent in the steel microstructure. It can be identified by the unique ASTM specified mill marking on its smooth, dark charcoal finish. Epoxy coated rebar can easily be identified by the light green colour of its epoxy coating. Hot dip galvanized rebar may be bright or dull grey depending on length of exposure, and stainless rebar exhibits a typical white metallic sheen that is readily distinguishable from carbon steel reinforcing bar. Reference ASTM standard specifications A1. A1. 03. 5M Standard Specification for Deformed and Plain Low- carbon, Chromium, Steel Bars for Concrete Reinforcement, A7. Standard Specification for Hot Dip Galvanised Reinforcing Bars, A7. Standard Specification for Epoxy Coated Steel Reinforcing Bars and A9. Standard Specification for Deformed and Plain Stainless Bars for Concrete Reinforcement. Another, cheaper way of protecting rebars is coating them with zinc phosphate. Sealants include paint, plastic foams, films and aluminum foil, felts or fabric mats sealed with tar, and layers of bentonite clay, sometimes used to seal roadbeds. Corrosion inhibitors, such as calciumnitrite . The nitrite anion is a mild oxidizer that oxidizes the soluble and mobile ferrous ions (Fe. Fe(OH)3). This causes the passivation of steel at the anodic oxidation sites. Nitrite is a much more active corrosion inhibitor than nitrate, which is a less powerful oxidizer of the divalent iron. Reinforcement and terminology of beams. At the outer face (tensile face) of the curvature the concrete experiences tensile stress, while at the inner face (compressive face) it experiences compressive stress. A singly reinforced beam is one in which the concrete element is only reinforced near the tensile face and the reinforcement, called tension steel, is designed to resist the tension. A doubly reinforced beam is one in which besides the tensile reinforcement the concrete element is also reinforced near the compressive face to help the concrete resist compression. The latter reinforcement is called compression steel. When the compression zone of a concrete is inadequate to resist the compressive moment (positive moment), extra reinforcement has to be provided if the architect limits the dimensions of the section. An under- reinforced beam is one in which the tension capacity of the tensile reinforcement is smaller than the combined compression capacity of the concrete and the compression steel (under- reinforced at tensile face). When the reinforced concrete element is subject to increasing bending moment, the tension steel yields while the concrete does not reach its ultimate failure condition.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2016
Categories |