JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III REINFORCED CONCRETE STRUCTURES DESIGN AND DRAWING Previous Question Paper (March - 2021 - R15/R13)
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Main
Explain the stress block parameters of singly reinforced rectangular beam.
Answer
In the limit state method of design for a singly reinforced rectangular beam, the stress block parameters define the distribution of compressive stress in the concrete. The stress block is assumed to be rectangular up to a depth of 0.36xu (where xu is the neutral axis depth), with a uniform stress intensity of 0.446fck. The total compressive force C is calculated as 0.36fckb xu, acting at a distance of 0.42xu from the extreme compression fiber. The lever arm for the internal moment couple is defined as (d - 0.42xu), where d is the effective depth.
Determine the minimum effective depth and the corresponding area of tension reinforcement for the rectangular beam having width 230 mm to resist ultimate moment of resistance 200 kN-m using M25 grade concrete and Fe 500 HYSD bars.
Answer
For M25 concrete and Fe 500 steel, the limiting neutral axis depth ratio xu,max/d is 0.46. The limiting moment of resistance is given by Mu,lim = 0.133fckbd2.
Solving for d:
Providing an effective depth of 520 mm. To find the area of steel (Ast), use the moment equation Mu = 0.87fyAstd(1 - (Astfy)/(bd fck)):
Simplifying the quadratic equation in terms of Ast:
Solving the quadratic equation yields Ast ≈ 1045 mm2.
Explain under reinforced, balanced and over reinforced section.
Answer
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A doubly reinforced beam of rectangular section of size 250 × 600 mm overall consist of 5# of 25mm dia bars at tension zone and 3# of 25 mm dia bars on compression zone as reinforcement. If the grade of concrete is M20 and steel is Fe 415. Determine moment of resistance if the c/s is used as cantilever beam for a span 5 m. Also Calculate safe working UDL that can be applied on the beam.
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Design a slab for an hall of internal dimensions 12 × 4 m carrying a live load of 4 kN/m2. The slab is supported on the wall of thickness 230 mm. Adopt mild exposures with M20 grade concrete and Fe415 steel. Sketch the reinforcement details.
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Design a slab over a room of internal dimensions 4m × 5m supported on 230mm thick wall. All the edges of the slab are simply supported. The two adjacent corners are discontinues. Live load 2 kN/m2, floor finish 1.5 kN/m2, Adopt mild exposure with M20 grade concrete and Fe415 steel. Also sketch the reinforcement details.
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A rectangular column 300 mm wide and 600 mm deep is subjected to an axial load of 1000 kN and moments along the major and minor axis are 130 kNm and 80 kNm respectively. Assume M30 concrete and Fe 500 steel. Assume severe condition and sketch the details.
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Design a reinforced concrete footing for a rectangular column of section 300 mm by 500 mm supporting an axial factored load of 1600 kN. The SBC of the soil at site is 180 kN/m2. Adopt M20 grade concrete and Fe415 grade steel.
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Design the main stairs of a office room measuring 4 m × 6 m to carry the live load of 4 kN/m2. The vertical distance between the floors is 3.75m. Adopt mild exposure with M25 grade concrete and Fe500 steel. Sketch the details of one flight.
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A rectangular beam is to be simply supported on 230 mm thick wall, the clear span of the beam is 6m. The imposed load is 20 kN/m and the dead load on beam is 12 kN/m including self-weight. Assuming M20 concrete (Mild exposure), Fe 415 steel, design a singly reinforced beam for flexure and shear, check for deflection and sketch the reinforcement details.
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