To resist Hogging (Negative Bending Moment) at supports. To counter the risk of the failure of the slabs. To encounter the shear force.
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Why are bars bent?
Metal reinforcing bars, or rebar, often must be bent or cut to provide adequate support to concrete. Bar bending is the manufacture and bending of the steel reinforcing bars and beams, also known as rebar, used as reinforcement in concrete construction.
Why are steel bars bent?
Engineers design the bends of reinforcing steel in such a way that the steel sets into the concrete just where the tensile stresses occur to help the concrete resist these stresses. It is for this reason that some reinforcing rods are bent almost in a zigzag pattern.
Why extra bars are provided in slab?
Either to provide the same steel throughout the top & bottom face. Or to provide steel required for extra hogging/sagging moments at respective faces as extra.
What is alternate bent up bar in slab?
Why do we provide alternative crank bars in slab reinforcement? It is recommended that a maximum of 50% of the bars can be cranked to resist the bending moments so that steel is present in every cross-section of a slab. The alternative bent-up bars are sufficient to withstand the resulting shear force near the support.
What is crank length in slab?
Crank is a slight bending in bars at the lap so that maintains the clear cover even at the lap position. The rule that is generally practiced is that the slope of crank 1:10 & minimum length of crank 300 mm.
Why stirrups are provided?
The main purpose of stirrup is to hold the primary reinforcement bars. They also prevent columns and beams from buckling. The stirrups get placed diagonally when there is tension and compression caused by vertical and transverse tension.
How does bar bending work?
Bar bending machine is consist of electric motor, coupling, circular plate, worm gear drive, extended shaft. Electric motor transmits power to gear box where speed is decreased and torque is increased. Which is used to bend bar with the help of circular plate. Bend at any required angle for bar having dia.
What is bending bar?
Bending of bars is defined as the process of bending reinforcing steel into shapes required for reinforced concrete construction. The bar bending is completed in a particular manner, which is known as bar bending schedule. Bar bending schedule is also termed as BBS.
Why crank is given in slab?
Cranked bars / Bent up bars are provided on top of the reinforcement to resist negative bending moment/Hogging at the supports of the slab. To resist the shear force at the supports. To reduce the risk of a brittle failure of slab-column connection.
What is the maximum length of beam?
As long as you can use prestressed concrete beam there is no limit for beam length.
What is main bar in slab?
What are the main bars in a slab? The reinforcement bars that are placed in the tension zone of the slab to resist the bending moment & to transfer the superimposed loads to the supports that are provided for the slab are called main bars.
What is 0.42 D crank bar?
Here, the bent-up part of the crank bar is named “side ac”. When we add a clear span in the calculation, we already include the length of side bc and side cb in it and we have to take an extra remaining length of the side ac by deducting side bc from it. So, that is what 0.42D stands for in the cutting length formula.
What is Ld formula?
Ld is embedded length of the steel bar. σ s is permissible stress in steel. τ bd is bond stress & φ is the diameter of the bar. For any given diameter of the bar, this formula is used to calculate the required development length in mm and for limit state method as well as working stress method the same formula is used.
What is negative bar in slab?
In beam, part where moment is sagging(generally, at near mid point)reinforcement provided in lower side that is called positive reinforcement. If moment is hogging(generally, at near support), then reinforcement provided at upper side of beam, it is called as negative reinforcement. Thanks.
How is crank calculated?
= {3500mm + (2 × 40 × 12mm ) + ( 2 ×0.42D ) – [2nos. ×2 ×12mm + 4nos. × 1×12mm.]} D = 88 mm.
Why is cranking done?
1. To resist negative bending moment (hogging). 2. To resist shear force which is greater at supports.
What is the maximum spacing of stirrups?
Detailed Solution. As per IS 456:2000, the spacing between two successive stirrups in reinforced concrete beam shall not be less than 100 mm. Maximum size of the bar or whichever is greater.
What is the minimum spacing of stirrups?
The spacing of vertical stirrups should be 100 mm c/c through out the length of lapping. The minimum size of stirrups should be 8 mm diameter. »
Why is lapping used in reinforcement?
Lapping is done in reinforced concrete structures, to achieve the required design length of the reinforcement bars. Development length is necessary to ensure that the necessary bond strength between the concrete and the embedded reinforcement bar is achieved.
What machines are used for bending?
Different types of bending machines are available, namely- Metal sheet bending machine, Busbar bending-cutting-punching machine, hydraulic and mechanical Profile bending machine, Hydraulic hand, hydraulic hand/motorised pipe bending machine, sheet folding machine, sheet metal bending machine, pipe bending machine, etc.