Concrete beams in which the reinforcing steel bars are placed near the bottom of the beam where they are most effective in resisting tensile stresses. In such a way the concrete on top would be able to resist the compression force, however being weak in tension it would be compensated by steel bars resisting it.
Singly reinforced beams have steel reinforcement in tension zone but in doubly reinforced beam steel reinforcement is provided in the tension zone as well as in compression zone
if reinforcement is provided in tension zone in a beam, then that beam is called singly reinforced beam.if the reinforcement is provided in top & bottom of the beam i.e., at tension zone as well as compression zone also then that beam is called doubly reinforced beam.
A singly reinforced beam only has steel reinforcement on the tension side (along the bottom of the cross section) where as a doubly reinforced beam has steel reinforcement on both the tension and compression sides, ie. the top and bottom of the cross section.
singly reinforcement beam have steel provided only one side tension an another side compression. tension takes steel load or tensile load and compression takes concrete or compressive load.
The singly reinforcement beam has steel reinforcement on the tension side. The double reinforcement beam has steel reinforcement on both sides.
Center of beam
The neutral axis of a reinforced concrete beam is the area where the beam is neither in a state of tension or a state of compression. This is determined by having the length and breadth of the beam available.
It proves shear reinforcement in the beam.
when our demand is more than capacity then designer prefers to choose doubly reinforced beam .for example your maximum moment is greater than nominal momentthen doubly reinforced beam is used.
to resist shear force
Reinforced concrete is made by placing steel bars in the tension zone of the beam x-section.
Total Depth - cover
25 mm cover should be given
because of the cement that can hold them tightly
Under reinforced is that in which provided steel ratio is less than balanced steel ratio. Concrete beams are designed as under reinforced beams. The reason is that the failure start by yielding of steel instead of crushing of concrete. Mian Yaqoob
A beam bridge is originally made of wood logs to connect two ends over a river. Modern bridges are constructed out of reinforced concrete or steel.
Singly reinforced beams have reinforcing only on the tension face. Doubly reinforced beams have reinforcing on the tension and compression face. Doubly reinforced beams can increase section capacity, but are primarily used to increase the ductility of the concrete beam. In certain codes, if the concrete section is controlled by the concrete failing in compression before the tension steel rebar yields (called a compression-controlled or brittle section), the calculated section capacity must be reduced to account for the brittle and sudden/unpredictable nature of a compression controlled (also called a brittle) failure. In order to make the section controlled by the yielding of the tension reinforcement (called a tension-controlled or ductile section), the ductility must be increased. This can be accomplished by adding steel in the compression zone, which gives strength to the compression area, thereby delaying the failure of the concrete. Enough compression steel can cause the section to switch from a brittle mode-of-failure to a ductile mode-of-failure, thereby permitting the designer to not decrease the section capacity from its calculated value. When identifying a doubly- reinforced beam, be sure that the steel in the compression area is meant to be for strength. Oftentimes, all faces of a beam will have some reinforcing for temperature/shrinkage protection and to tie the stirrups to. Steel that is only there for temp/shrinkage or to facilitate tying the rebar will usually be small and not much of it. In buildings, they will be often #3 bars @ 12" centers. In bridges, they may be #4 bars. These small bars should not be counted as compression-zone reinforcing. Look for bars in the compression zone that are of similar size to the main tension reinforcing.
A doubly reinforced beam is provided reinforcement in compression side also as to take care of extra load due to big section and to take care of tension in compression side ie compressive stresses so the section is safe.
When the maximum stresses in steel and concrete simultaniously reaches allowable value the section is called balanced section when the %of steel in a section is less than that required for a balanced section it is under reinforced section when the %of steel in a section is more than that required for a balanced section it is over reinforced sectionover reinforcement is as per section design I.e Ast1+Ast2>Ast Ast1+Ast2An 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. As the tension steel yields and stretches, an "under-reinforced" concrete also yields in a ductile manner, exhibiting a large deformation and warning before its ultimate failure. In this case the yield stress of the steel governs the design.An over-reinforced beam is one in which the tension capacity of the tension steel is greater than the combined compression capacity of the concrete and the compression steel (over-reinforced at tensile face). So the "over-reinforced concrete" beam fails by crushing of the compressive-zone concrete and before the tension zone steel yields, which does not provide any warning before failure as the failure is instantaneous.
The resisting bending moment is the product of the yield strength (of the beam material) and the section modulus of the beam. The RBM thus combines the material attributes as well as the geometric attributes of the beam and gives a useful metric to compare different beams irrespective of material or sectional geometry.
RCC stands for reinforced concrete cement. it is a building structure made by combining the steel rod with cement concrete mixture. like beam ,pillers etc.
The "W" in steel I-beam designations refers to wide-flanged beams. Most wide-flanged beams are symmetric about both the vertical and horizontal axes.
Generally with steel reinforcing bars (sometimes fondly known as rebars). Steel rebars are provided in tension zone of the beam x-section as concrete in very weak in tension.