JNTU
JNTU B.Tech III DESIGN OF REINFORCED CONCRETE STRUCTURES Previous Question Paper (July/August - 2023 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions. iv) Use of IS 456 and only design charts for columns from SP-16 are allowed.
Part A
Differentiate between working stress method and limit state method.
Answer
The Working Stress Method (WSM) is a deterministic approach based on the elastic theory, where structures are designed such that stresses under working loads do not exceed permissible limits, applying factors of safety to material strengths. In contrast, the Limit State Method (LSM) is a probabilistic approach based on limit state theory, which ensures the structure remains fit for use throughout its design life by considering partial safety factors for both loads and material strengths to account for uncertainties.
Give the idealized stress-strain curve for the concrete and steel.
Answer
In the limit state design of reinforced concrete structures, the stress-strain behavior is idealized to simplify analysis:
For concrete, the stress-strain curve is represented by a parabola from zero strain to a strain of 0.002, followed by a constant rectangular stress block up to the ultimate compressive strain of 0.0035. The design stress is taken as 0.67 times the characteristic cube strength (fck) divided by a partial safety factor of 1.5, resulting in a design stress of 0.446fck.
For steel, the stress-strain curve is idealized as a perfectly elasto-plastic model. It consists of a linear elastic portion up to the yield strain (fy / (1.15Es)), followed by a horizontal plateau where the stress remains constant at the design yield strength of (fy / 1.15), where fy is the characteristic yield strength and Es is the modulus of elasticity of steel (200,000 N/mm²).
When do we require splicing in steel reinforcement?
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State the spacing of shear reinforcement as per IS 456:2000.
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What is the slenderness ratio? Explain.
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What are the assumptions for limit state design of columns failing in pure compression as given in IS: 456-2000?
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Explain the minimum cover required for the footing.
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What are the situations in which combined footing are preferred to isolated footing?
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What is the Reinforcement requirement for Two-way slabs as per IS: 456?
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Write three general features of the two-way slab.
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Part B
Enumerate the five limit states commonly used in limit state design and state briefly how they are provided in the design.
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Explain the terms balanced, over-reinforced and under-reinforced section in bending. Explain which of these should be recommended in design.
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Find the moment resistance of a singly reinforced concrete beam of 200 mm width and 400 mm effective depth, reinforced with 4 bars of 16 mm dia. of Fe 415 steel. Take M20 concrete.
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Draw the singly reinforced rectangular beam cross-section and show the strain and stress diagrams.
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Design for Torsion. Determine the reinforcement required for a rectangular beam section with the following data: Width of section: 300 mm, Depth of section: 500 mm, Factored B.M: 65 kN-m, Factored torsional moment: 40 kN-m, Factored shear force: 70 kN. Use M 15 grade concrete and Fe 415 grade steel.
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A doubly reinforced beam of rectangular section 250 mm wide by 5 mm overall depth is reinforced with 4 bars of 22 mm diameter on the tension face and 2 bars of 16 mm diameter at the compression face. The effective cover is 50 mm. The beam spans over 8 m. If Fe-415 HYSD bars are used, check for the deflection control using the empirical method.
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Design a column of unsupported length 3m to carry an axial load of 2000 kN and a BM of 150kNm at service conditions. Design the column as a short column. The column is subjected to severe exposure condition and grade of steel is Fe500. Provide equal reinforcement on all the faces. Use M30 concrete. Sketch the reinforcement details.
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Write the design procedure for slender columns for both braced and unbraced column.
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Outline the procedure for design of axially loaded reinforced concrete column.
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Design a combined rectangular footing with central joining beam two columns 400 mm × 400 mm in section carry a load of 1000 kN each inclusive of the self-weight. Design a combined footing having central beam joining the columns. The c/c spacing of the columns is 4 m. The safe bearing capacity of soil is 150 kN/m2. Use M20 grade concrete and Fe 415 steel.
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What are the Indian standard code recommendations for design of footings as per IS: 456-2000?
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Design a rectangular isolated sloped footing for a column of size 250 mm × 750 mm carrying an axial load of 2600 kN. The safe bearing capacity of the soil is 300 kN/m2. Use M 30 grade concrete and Fe 500 grade steel.
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Design continuous RC slab for a 7 m wide and 14 m long classroom. The slab is supported on RCC beams spaced at 3.5 m intervals. The width of each beam is 230mm. Design the slab for a Live Load (LL) of 3KN/m2 Assume the weight of roof finishing as 1 KN/m2. Use M20 grade concrete and Fe 500 grade steel.
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Deign a dog- legged stair for a building in which the vertical distance between floors is 3.6 m. The stair hall measures 2.5 m × 5m. The live load may be taken as 2500 N/m2. Use M 20 concrete and Fe415 steel bars.
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