JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year STRUCTURAL ENGINEERING - I (RCC) Previous Question Paper (August - 2022 - R18)
Answer any five questions. All questions carry equal marks. Note: Use of only IS 456 and interaction diagram for columns from sp-16 is permitted.
Main
Explain about the balanced section as per working stress method and limit state method for design of reinforced concrete structures.
Answer
A balanced section is a design condition where the strain in concrete and the strain in steel reach their respective permissible or ultimate limits simultaneously.
- Working Stress Method (WSM): In WSM, a balanced section is one where the stress in concrete reaches its maximum permissible compressive stress (σcbc) and the stress in steel reaches its maximum permissible tensile stress (σst) at the same time. The neutral axis depth corresponds to the critical neutral axis depth (xc).
- Limit State Method (LSM): In LSM, a balanced section is defined as one where the strain in the extreme compression fiber reaches the ultimate compressive strain of 0.0035, while the strain in the extreme tension steel reaches the yield strain (0.002 + 0.87fy/Es) simultaneously. The actual neutral axis depth (xu) is equal to the limiting neutral axis depth (xu,max).
Determine the moment of resistance of a doubly reinforced concrete beam section, 300 mm wide and 400 mm effective depth, reinforced with 2 bars of 16 mm diameter in compression zone and 3 bars of 20 mm diameter in tension zone. Use M 25 grade concrete and Fe 500 steel.
Answer
Given data: b = 300 mm, d = 400 mm, d' = 40 mm (assumed cover). Steel: Ast = 3 × (π/4) × 202 = 942.48 mm2, Asc = 2 × (π/4) × 162 = 402.12 mm2. Materials: fck = 25 N/mm2, fy = 500 N/mm2.
1. Limiting Neutral Axis:
2. Actual Neutral Axis (xu): Equating C = T, 0.36fckbxu + fscAsc = 0.87fyAst. Assuming fsc ≈ 0.87fy = 435 N/mm2:
Since xu < xu,max, the section is under-reinforced.
3. Moment of Resistance (Mu):
Explain the structural behaviour of different types of RCC beams.
Answer
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An L-beam has 900 mm wide and 100 mm thick flange, 300 mm wide web and 450 mm total depth. Design the steel reinforcement to resist a factored bending moment of 450 kNm. Use M 30 grade concrete and Fe 500 steel. Sketch the reinforcement details.
Answer
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A simply supported reinforced concrete beam of effective span 5.0 m has rectangular cross-section 300 mm×500 mm (total depth). The beam is reinforced with 2 bars of 12 mm diameter in compression and 4 bars of 20 mm diameter as tension steel of which two bars are curtailed at 750 mm from the supports. Design the shear reinforcement if the beam is subjected to uniformly distributed load of 60 kN/m in addition to the self-weight. Use M 25 grade concrete and Fe 415 steel.
[15]Answer
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Design the reinforcement of a beam section, 230 mm×500 mm (effective depth), subjected to an ultimate twisting moment of 90 kNm, ultimate shear force of 120 kN and ultimate BM of 200 kNm. Use M 25 concrete and Fe 415 steel. Sketch the reinforcement details.
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Design a simply supported RCC slab for a room of clear dimensions 3.5 m×6.5 m subjected to live load of 3 kN/m² and floor finish of 1.5 kN/m². Assume the width of the supports is 230 mm. Use M 25 concrete and Fe 500 steel. Sketch the reinforcement details.
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A simply supported reinforced concrete beam of effective span 5 m has cross-section 300 mm × 450 mm (overall depth) is reinforced with 3 bars of 20 mm diameter in tension and 2 bars of 12 mm diameter in compression. The beam is subjected to super imposed working load of 40 kN/m. Determine the short term and long term deflections. Adopt M 25 grade concrete and Fe 500 steel.
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Design the reinforcement of a 450 mm×450 mm column of unsupported length 4.2 m subjected to an axial load of 1600 kN with bi-axial moments 150 kNm and 100 kNm. Use M 25 concrete and Fe 500 steel. Sketch the reinforcement details.
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Design the combined footing for two columns each of size 400 mm×400 mm and spaced at 4.2 m centre-to-centre. Each column is required to support an ultimate load of 900 kN. The safe bearing capacity of the soil is 160 kN/m². Draw the reinforcement details.
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