Concrete Technology And Design Of Concrete Structures — Part 1 MCQs with Explanations

Workability of concrete refers to how easily fresh concrete can be mixed, placed, compacted, and finished. Compacting factor is one of the measures used to assess the workability of concrete, especially in laboratory tests. For heavily reinforced sections , concrete must be able to flow easily and fill the formwork and spaces around the reinforcement without leaving voids. When vibration is not used , the concrete must be highly workable to achieve adequate compaction under its own weight. A compacting factor of above 0.92 indicates high workability, which is suitable for such conditions. Therefore, for concreting heavily reinforced sections without vibration, the compacting factor should be above 0.92.

The Indian Standard IS 456:2000 specifies minimum reinforcement in slabs. When high-strength deformed (HYSD) bars are used, the minimum steel in either direction shall not be less than 0.12% of the gross cross-sectional area (bD) . For comparison, when plain/mild steel is used the minimum is 0.15% — the reduction to 0.12% is permitted because HYSD bars have higher yield strength and provide equivalent ductility with slightly less area of steel. This requirement (clause on minimum reinforcement for slabs) ensures adequate cracking control and ductile behaviour of slabs while taking advantage of HYSD bar properties.

Concept: When all footings are proportioned on the basis of total load (dead + full live load), the design aims to keep the same allowable soil pressure under every footing at the notional maximum loading condition. Reality of loading: In service, the live load is not fully present everywhere at the same time , and interior columns generally have larger tributary areas than exterior columns. Hence, interiors attract higher actual loads more often. Resulting behavior: Because interior footings experience higher sustained/actual pressure relative to exterior footings, they undergo greater compression of the supporting soil . Conclusion: Differential settlement occurs with the interior columns settling more than the exterior columns.

The modular ratio is defined as: m = Es / Ec Where: Es = Modulus of elasticity of steel (approximately constant) Ec = Modulus of elasticity of concrete What is Creep? Creep is the long-term deformation of concrete under a sustained load. Over time, concrete subjected to constant stress will slowly deform. This is a time-dependent increase in strain, even when the stress remains constant. How Creep Affects Modulus of Elasticity: Due to creep, the concrete shows more strain for the same level of stress. This means its effective modulus of elasticity reduces over time. In other words, Ec becomes smaller than its short-term value. Impact on Modular Ratio: Since modular ratio = Es / Ec , and Es remains constant, a reduction in Ec (due to creep) results in an increase in the modular ratio . Why Some Get Confused: In some design approaches (e.g. working stress method), to indirectly account for creep and long-term deflection, a lower modular ratio is used empirically. This is a correction based on behavior, not a direct mathematical consequence of the creep effect on elasticity. But theoretically and fundamentally, the effect of creep is to increase the modular ratio. Therefore, the correct answer is: Option B — To increase it.

To understand the correct answer, let's analyze each statement: i) Shear force at mid span is zero In a ring beam subjected to a uniformly distributed load, the ring beam is typically supported at its ends (near the supports). Due to the symmetry and equilibrium of forces, the shear force at the mid-span (middle portion between supports) is often zero. ii) Shear force at mid span is maximum This statement is generally incorrect for a ring beam under uniformly distributed load. The maximum shear force usually occurs near the supports, not at the mid-span. iii) Torsion at mid span is zero Torsion (or twisting) in a ring beam subjected to a uniformly distributed load is typically not zero at the mid-span. It can vary depending on the loading conditions and the configuration of the beam. iv) Torsion at mid span is maximum In a ring beam, the maximum torsion often occurs at the mid-span, where the beam is subjected to maximum bending moments and shear forces due to the distributed load acting over the entire span. Conclusion: Based on the typical behavior of a ring beam subjected to uniformly distributed load: Shear force at mid span is zero (i) is correct. Torsion at mid span is maximum (iv) is correct. Therefore, Option B: (i) and (iv) is the correct answer.

As per IS: 456-1978 , the minimum grade of concrete required for reinforced concrete (RC) structures is M20 . The M20 grade concrete has a characteristic compressive strength of 20 MPa after 28 days of curing. Lower grades like M15 and M10 are generally used for plain cement concrete (PCC) and are not suitable for reinforced structures. Higher grades such as M25 and above are used for structural members requiring higher strength . Hence, the correct answer is M20 (Option B).

The given slab dimensions are 3m x 3.5m. Since (3.5/3) < 2 , it is classified as a two-dimensional slab . Deflection criteria as per IS 456:2000: - For a simply supported slab , the span/depth ratio = 35 - For a continuous slab , the span/depth ratio = 40 Since we always design the slab for the shorter span (3m): Effective depth (d) = 3000 mm / 40 = 75 mm Thus, the minimum overall depth of the slab should be 75 mm to satisfy vertical deflection limits .

In a simply supported beam, the primary purpose of providing reinforcement bars at the support is to resist tensile stress. At the supports, the top fibers of the beam experience compression, while the bottom fibers experience tension. To resist this tension, reinforcing bars (tensile reinforcement) are provided at the bottom near the supports. This reinforcement ensures that the beam can safely handle the tensile forces, preventing cracking or failure in that zone.

Tensile and compressive is the correct answer to “In symmetrically reinforced sections, shrinkage stresses in concrete and steel are respectively”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

At a distance of $$\frac{{\text{d}}}{2}$$ from periphery of column/capital/drop panel is the correct answer to “Critical section for shear in case of flat slabs is (adopting standard notations)”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

depends on as, only is the correct answer to “If the depth of neutral axis for a singly reinforced rectangular section is represented by kd in working stress design, then the value of k for balanced section”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

More than 5 mm and also more than one-fourth of diameter of main bar is the correct answer to “The diameter of ties in a column should be”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

4% is the correct answer to “Bulking of sand is maximum if moisture content is about”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Using thinner bars but more in number is the correct answer to “If a beam fails in bond, then its bond strength can be increased most economically by”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Decreases with increase in diameter of bar is the correct answer to “Ultimate strength of cold drawn high steel wires”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

40% is the correct answer to “In working stress design, permissible bond stress in the case of deformed bars is more than that in plain bars by”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

40% is the correct answer to “The percentage of voids in cement is approximately”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

0.3% is the correct answer to “According to Whitney’s theory, ultimate strain of concrete is assumed to be”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Increasing the depth is the correct answer to “When shear stress exceeds the permissible limit in a slab, then it is reduced by”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

More than 1 m is the correct answer to “For a simply supported beam of span 15m, the minimum effective depth to satisfy the vertical deflection limits should be”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Tensile everywhere is the correct answer to “In a spherical dome the hoop stress due to a concentrated load at crown is”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

3.0 m and 3.0 m is the correct answer to “If the size of panel in a flat slab is 6m x 6m, then as per Indian Standard Code, the widths of column strip and middle strip are”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

150 mm is the correct answer to “In reinforced concrete footing on soil, the minimum thickness at edge should not be less than”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

25 mm is the correct answer to “The minimum cover to the ties or spirals should not be less than”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

42 MPa and 35 MPa is the correct answer to “Cube strength of controlled concrete to be used for pretensioned and post-tensioned work respectively should not be less than”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

±15% of average is the correct answer to “The individual variation between test strength of sample should not be more than”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Time of transit is the correct answer to “Workability of concrete is inversely proportional to”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Is always less than 1 is the correct answer to “For a slab supported on its four edges with corners held down and loaded uniformly, the Marcus correction factor to the moments obtained by Grashoff Rankine’s theory”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

150 x 150 x 700 mm is the correct answer to “To determine the modulus of rupture, the size of test specimen used is”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Increase in tensile strength but decrease in ductility is the correct answer to “High carbon content in the steel causes”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Greater than 2 is the correct answer to “The slab is designed as one way if the ratio of long span to short span is”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

2.5 is the correct answer to “A continuous beam is deemed to be a deep beam when the ratio of effective span to overall depth (1/D) is less than”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Less than 12 is the correct answer to “According to IS : 456-1978, minimum slenderness ratio for a short column is”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

4 is the correct answer to “Maximum percentage reinforcement in case of slabs is limited to”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Bleeding is the correct answer to “The property of fresh concrete, in which the water in the mix tends to rise to the surface while placing and compacting, is called”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Three cantilevers is the correct answer to “A T-shaped retaining wall mainly conssits of”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Front face only is the correct answer to “In a counterfort retaining wall, the main reinforcement in the stem at mid span is provided on”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Increased by 25% for bars in compression is the correct answer to “The average permissible stress in bond for plain bars in tension is”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

Increases with richer mixes is the correct answer to “Poisson’s ratio for concrete”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.

15 mm is the correct answer to “The minimum cover in a slab should neither be less than the diameter of bar nor less than”. This question is standard in competitive examination syllabi for Concrete Technology And Design Of Concrete Structures.