RCC: RCC stands for reinforced cement concrete, that means which type of concrete in which steel is persent.
RCC is a concrete with reinforcement embeded in it. The embedded reinforcement makes it capable of resisting tension also.
Steel bars embedded in the tension zone of concrete relives concrete of any tension and takes all tension without separating from concrete.
The bond between steel and shrounding concrete ensures strains compatibility i e, the strain at any point in the steel is equal to that in the adjoining concrete.
Reiforcing steel impacts ductility to concrete which is otherwise brittle material.Here ductility means large deflection owing to yielding of steel thereby giving ample warning of impendings collaps.
Tensile strength in concrete asise on account of deirect tension, flexural tension, diagonal tension due to temperature and shrinkage efects, restraint to deformation.Under those conditions reinforcement must be provided across potential tensile crack.
Grade of reinforcing steel:Grade of steel: The requirment of deformed steel bars or wires for used as a reinforcement in concrete is bacically categoried in following three grades.
1. Fe415
2. Fe500
3. Fe500D
4. Fe550
5. Fe600
Steel reinforcement and its requirment in concrete structure:
Steel reinforcement are used generally, in the form of bars of circular cross-sections in concrete structure. They are like a skelten in human body. Plane concrete without steel or any other reinforcement is strong in compression but weak in tension.
Steel is one of the best form of reinforcement, to take care of those stresses and strengthen concrete to bear all kinds of loads.
Bar bending schedule:
Bar bending schedule is the schedule of reinforcement bars prepared in advance before cutting and bending of rebars. This schedule contains all details of size, shape and dimentions of rebars to be cut.
Specufication of steel bar:
The reinforcement steel is generaly available in three forms.
1. Mild steel rounded bars of diffirent grades.
2. High strength deformed of diffirent grades and types.
3. Corrosion resistant steel
The structural requirment of reinforcing steel:
Reinforcing steel has to satisfy some basic requirments to efficiently perform in the concrete structure. Durability of the concrete structures will greatly depends on the basic requirments. A few of them are as given below :
Terminology used in reinforcement :
1. Bateh:
Any quantity of bars/wires of same size and grade whether in coils or bunduls presented for examination and test at one time.
2. Bundle:
Two or more coils or a numbers of lengths prolerly bound togather.
3. Elongation: The increase in the length of tensile test piece under stress. The elongation at fracture is conventionally expressed as a percentage of the original gauge length of Standard test piece.
4. Longitudinal rib: A rib of uniform cross-section parallel to the axis of bar/wire.
5. Nominal diameter or size: The diameter of a plain round bar/ wire having the same mass per meter length as the deformed bar/wire. Nominal perimeter of a deformed bar/wire 3.14 times the nominal diameter.
6. Nominal mass: The mass of the bar/wire of nominal diameter and of density 0.00785 kg/mm2 per meter run.
7. Proof stress 0.2 percent: The stress at which a non-proportional elogation equal to 0.2 percent of the original gauge length take place.
8.Tensile strength: The maximum load reached in a tensile test divided by the effective cross-sectional area of the gauge length portion of the test piece. Also termed as ultimate tensile stress.
9. Transverse rib: Any rib on the surface of bar/wire other than a longitudinal rib.
10. Yield stress: Stress at which elogation first occures in the first piece without increasing the load during tensile test. In the case of steel with no such definite yield point, proof stress shall be applicable.
Types of steel bars:
TMT Bar: Thermo Mechanically Treated Bar
TMX Bar: Thermax Power Bar
HYSD Bar: High Yield stress Deformed Bar
SD Bar: Super Ductile Bar
Chemical properties of reinforcement steel:
Physical properties of reinforcement steel:
Physical property of steel
Typical properties of rebars N/mm2 Compared to minimum reinforcement specified in the various code:
Thermo Mechanically Treated (TMT) bars produced by adopting quinching and tempering petented technology are far superior for high performance structures.
The tendency of pit propagatioa in T. M. T. 0. 42 CRS bar is comperitavely less than high strength bar produced without using alloying elements while rolling.
Pit propagatioa is also observed to be more on cold twisted deformed bars than TMT 0.42 CRS bars.
It is observed that TMT 0.42 CRS bars have a competitive edge over other rebars where crossion resistance is concerned.
Procedure of reinforcement
1. Material received at site should be IS certification mark or the supplier should be pre appoval from QA department after verification of physical and chemical properties as specified in IS 1786. Bars should be marked to identify categories.
2. For diameter up to 12 mm, one sample per diameter per supplier/manufacturer for every 60 ton must be tested in an independent/external laboratory. For diameter above 12 mm, one sample per diameter per supplier/manufacturer for every 100 ton must be tested in an independent/external laboratory.
3. Proper equipment/ jig should be available straighteng the coil steel and mandrel for bending and cutting machine for cutting steel bar.
4. Use of letest revisons of drawings and bar bending schedule should be done.
5. Bent bar of identical size, shape and type must be bundled togather and labeled correctly before placing.
6. Steel surface should be free from grease, oil, mud, mould oil, loose mill scales, excessive rust scales and loose concrete.
7. Bending wires must be bent inwards or loose ends cut so that they do not come in cover zone and/ protrude out of concrete.
8. Beam -column junctions reinforcement steel bars should bunched or spaced prolerly to avoid congestion.
9. Enough spaced between bars should be available to place and compact concrete.
10. Radius of bend given to dowel construction joints must be as per drawing or as specified by structural consultant.
11. For long duration of storage, steel bar must be protected by corrosion resistant passivator/coverter coat.
12. Bars of diffirent types and diameter must be stored separetly and clear identify between tested and untested steel should be marked at site.
13. Reinforcement bars received at site should be stored at hard concreted plateform and clear above the ground with the use of timber sleeper, concrete sleeper or any other means. Reinforcement should be kept covered by tarpaulin or plastic sheet to avoid excessive corrosion and other contamination.
14. Cover blocks should be of non. Corrosive material such as plastic or concrete /mortar but not wooden or broken tile, broken brick or stone. Especially PVC made cover spacer should be used in the works.
15. Binding wire should be 16 or 18 gauge conforming to IS 280. It should be free from rust, oil, paint, grease or any deleterious material.
16. Splices should be provided as for as possible away from sections of maximum stress and must be staggerd.
17. Where more than one half of the bars spliced at a section or where splices are made at a point of maximum stress, speacial precaution should be taken, such as increasing the length of lap and/or using spirals or closely spaced stirrup around the length of splice. Staggerd lap or sugested by structural consultant.
18. ( I) A horizontal distance between two parallel main reinforcing bars shall usually not less than gretest of following :The diameter of bar if the diameters are equal. The diameter of large bar if the diameters are unequal.5 mm more than the nominal maximum size of coarse aggregate.
19. Greater horizontal distance than the maximum specified in
(I) wherever possible. However the niddle vibrators are used, the horizontal distance between bars of a group may be reduced the two-third the nominal maximum size of a coarse aggregate, provided that sufficient space is left between groups of bars to enable vibrator to be immesred
20. Where there are two or more rows of bars, the bars shall be vertically in line and the minimum vertical distance between the bars shall be 15mm, two-third the maximum nominal size of aggregate, or the maximum size of of bars whichever is greater.
Details of spacing for cover blocks:
Details of chair spacing for slab/raft reinforcement:
Test required for reinforcement steel:
1. Physical test:
I. Rolling margin.
II. Tensile test - 0.2% proof stress, yielding stress, elogation etc.
III. Bend and rebend test.
2. Chemical test:
I. Carbon
II. Sulphur
III. Phosphorous
IV. Sulphur +Phosphorous
V. Cilicon
VI. Manganese
VII. Corrosion resistant elements.
Following cheque point should be chqued after placing of steel:
1. The cutting and bending are in order.
2. Spacing of bars as per drawing.
3. The effective depth, top and bottom cover in slab as per drawing.
4. Position of top steel bars in case of cantilever slab.
5. Corrosion inhibiting layer applied over the steel bars if specified.
6. The lap length and hoock length/angle of bars as per drawing.
7. The welding of bars as per drawing or as per standard details.
8. Deviation due to any reason is verified by design office.
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