**Explanation:** The strength and quality of concrete are influenced by various factors. Aggregate shape, aggregate grading, and surface area of the aggregate all play crucial roles.

**Explanation:** A lower water-cement ratio in concrete leads to increased density, reduced creep and shrinkage, and enhanced bond between the components.

**Explanation:** Entrapped air in concrete enhances workability by providing better lubrication between particles.

**Explanation:** Bleeding is the property of fresh concrete where water separates from the mix during placement and compaction, rising to the surface.

**Explanation:** Segregation in concrete occurs when the ingredients separate during transportation, leading to an uneven distribution.

**Explanation:** Segregation can result in various issues such as honeycomb concrete, porous layers, and sand streaks.

**Explanation:** Ordinary cement concrete tends to shrink upon drying as it loses moisture.

**Explanation:** Increasing the amount of cement in the mix can improve the workability of concrete.

**Explanation:** Decreasing the size of the aggregate can enhance the workability of concrete by providing better particle distribution.

**Explanation:** The workability of concrete is directly related to the grading of the aggregate, as it influences the ease of placing and compacting the mix.

**Explanation:** Workability refers to the ease with which concrete can be mixed, placed, and compacted. In this context, workability decreases with an increase in the time of transit. During prolonged transportation, concrete may experience initial setting, making it less manageable upon arrival at the construction site.

**Explanation:** An air entraining agent, when introduced to concrete, improves its workability. This agent creates tiny, stable air bubbles within the concrete mix. These air bubbles act as lubricants, making the concrete more fluid and easier to work with during placement and compaction. Additionally, the entrained air enhances the durability of concrete by providing resistance to freeze-thaw cycles.

**Explanation:** The strength of concrete is directly influenced by the cement-water ratio. A higher cement-water ratio generally leads to increased strength because it contributes to better hydration of the cement particles. Adequate hydration is essential for the development of concrete strength.

**Explanation:** The strength of concrete tends to increase with an increase in the size of aggregate. Larger aggregates provide better interlocking and contribute to higher compressive strength. This effect is particularly notable in high-strength concrete mixes where the aggregate plays a crucial role in achieving the desired strength.

**Explanation:** The fineness of cement particles affects the surface area available for hydration. An increase in the fineness of cement allows for more efficient hydration, leading to a higher strength of concrete. Therefore, the correct answer is (b) increase in fineness of cement.

**Explanation:** The water-cement ratio is a critical factor in concrete strength. A lower water-cement ratio generally results in higher strength because it leads to a more complete hydration of the cement particles. Therefore, the correct answer is (b) decrease in water cement ratio.

**Explanation:** The durability of concrete is influenced by various factors, including the correct proportion of cement to aggregate. A well-balanced cement aggregate ratio contributes to the overall durability of the concrete mix. Proper proportions ensure that the mix has the necessary strength and resistance to environmental factors over time.

_{ck}=strength of concrete A,C,W are the absolute volumes of aggregate, cement, and water respectively K =constant)

_{ck}= K [C/W+C+A]

^{2}

_{ck}= K [C+A/W+C+A]

^{2}

_{ck}= K [C+W/W+C+A]

^{2}

_{ck}= K [C+W/C+W+A]

^{2}

**Explanation:** The expression represents the relationship between the strength of concrete (f_{ck}) and the absolute volumes of aggregate (A), cement (C), and water (W). The correct formula is (a), where the strength is proportional to the square of the ratio of cement volume to the sum of water and aggregate volumes.

**Explanation:** The approximate ratio of the direct tensile strength to direct compressive strength in concrete is around 0.10. This ratio provides insight into the relationship between tensile and compressive strengths, with the tensile strength generally being lower.

**Explanation:** The approximate ratio of direct tensile strength to flexural strength in concrete is around 0.5. This ratio is relevant in understanding the distribution of stresses in different loading conditions, where the flexural strength is typically higher than the direct tensile strength.

**Explanation:** The strength of concrete tends to increase with an increase in the rate of loading. This is because higher loading rates may activate additional mechanisms within the material, leading to a faster development of strength.

_{ck}

_{ck}

_{ck}

_{ck}

**Explanation:** The Young’s modulus (E) of concrete, as per IS 456-2000, is calculated using the formula 5000√f_{ck}, where f_{ck} is the characteristic compressive strength of concrete.

**Explanation:** Poisson’s ratio for concrete typically decreases with a richer mix, indicating that a higher cement content contributes to reduced lateral expansion under load.

**Explanation:** The fineness modulus of fine aggregate generally falls within the range of 2-3.5, providing an indication of the fineness or coarseness of the aggregate.

_{150}

_{200}

_{250}

_{500}

**Explanation:** According to IS 456:2000, the grade of concrete M_{500} is not recommended. This is because the code suggests a maximum permissible concrete strength of M_{60}.

**Explanation:** The durability of concrete can be affected by exposure to aggressive substances such as cider and vinegar. These substances can contribute to the deterioration of the concrete over time.

_{100}grade of concrete proportion

**Explanation:** The proportion for M_{100} grade concrete is typically 1:3:6 (cement: sand: aggregate).

_{20}grade of concrete proportion is

**Explanation:** The proportion for M_{20} grade concrete is typically 1:1.5:3 (cement: sand: aggregate).

**Explanation:** High temperatures can have a detrimental effect on the strength of concrete. Elevated temperatures can lead to thermal cracking and a reduction in the overall strength of the material.

**Explanation:** Concrete gains strength primarily through the hydration of cement, where water reacts with cement particles to form a crystalline structure. Chemical action with coarse aggregate and evaporation of water also play roles in the strength development process.

**Explanation:** Concrete placement is preferably done at a temperature of 27±2°C. This temperature range is conducive to the proper curing and setting of concrete, ensuring optimal strength development.

**Explanation:** Inert material in a cement concrete mix refers to the aggregate. Aggregates, such as sand and gravel, provide bulk and stability to the concrete without actively participating in the chemical reactions.

**Explanation:** In reinforced concrete (RCC) buildings, expansion joints are typically provided if the length of the building exceeds 45 meters. These joints accommodate thermal expansion and contraction of the building components.

**Explanation:** The shear stress diagram of a homogeneous beam is parabolic. This shape reflects the distribution of shear stresses across the cross-section of the beam.

**Explanation:** The compressive strength determined from a 150mm × 150mm cylinder is generally higher than that determined from a 150mm cube due to differences in the stress distribution and size effect.

**Explanation:** Generally, as the size of the cube increases, the strength also increases, but the rate of increase decreases. Larger cubes may experience lower stress concentrations, leading to a slower rate of strength gain.

**Explanation:** Addition of sugar in concrete tends to increase the setting time. The sugar acts as a retarding agent, delaying the hydration process and extending the time it takes for the concrete to set.

**Explanation:** The relationship between the initial setting time (t) and final setting time (T) for ordinary Portland cement is approximately T = 540 + t.

**Explanation:** Unsoundness of cement due to magnesia can be determined by using Le Chatelier’s apparatus. The test involves measuring the expansion of cement paste when subjected to autoclave conditions.

**Explanation:** White cement is produced in electrical form kilns. These kilns are designed to provide the specific conditions required for the production of high-quality white cement.

**Explanation:** The modulus of rupture measures the flexural tensile strength of a material, specifically its ability to resist bending or flexural stresses.

**Explanation:** Shrinkage in concrete tends to increase its bond strength. However, it’s essential to note that excessive shrinkage can lead to cracking, affecting overall durability.

**Explanation:** The modulus of elasticity for concrete improves with age. As concrete matures, its internal structure undergoes changes, resulting in increased stiffness and modulus of elasticity.

**Explanation:** Needle vibrators, or internal vibrators, are commonly used in concrete work. They are inserted into the concrete mix to consolidate and remove air voids.

_{cr}), splitting strength (f

_{cs}), and direct tensile (f

_{ct}) strength is given by

_{cr}> f

_{cs}> f

_{ct}

_{cr}< f

_{cs}< f

_{ct}

_{cr}= f

_{cs}= f

_{ct}

**Explanation:** The relationship between modulus of rupture (f_{cr}), splitting strength (f_{cs}), and direct tensile strength (f_{ct}) is typically f_{cr} > f_{cs} > f_{ct}.

_{cr}) and cube strength of concrete (f

_{ck}) is

_{cr}= 0.35√f

_{ck}

_{cr}= 0.7√f

_{ck}

_{cr}= 0.5√f

_{ck}

_{cr}= 1.2√f

_{ck}

**Explanation:** The relationship between modulus of rupture (f_{cr}) and cube strength of concrete (f_{ck}) is generally expressed as f_{cr} = 0.7√f_{ck}.

_{ct}) and compressive strength (f

_{ck}) for cube

_{ct}= 0.35√f

_{ck}

_{ct}= 0.7√f

_{ck}

_{ct}= 0.5√f

_{ck}

_{ct}= 1.2√f

_{ck}

**Explanation:** The relationship between split tensile strength (f_{ct}) and compressive strength (f_{ck}) for a cube is generally expressed as f_{ct} = 0.35√f_{ck}.

**Explanation:** The center-to-center spacing of vertical stirrups in a rectangular beam is typically minimum near the support zones to enhance shear capacity.

^{2}) is given by

_{cbc}

_{cbc}

_{cbc}

_{cbc}

**Explanation:** The modular ratio (m) is typically given by 280/3 times the permissible compressive stress (σ_{cbc}) due to bending in concrete cubes.

**Explanation:** The presence of oils in water for concreting can reduce the strength of the concrete. Oils can act as contaminants, affecting the bonding between cement particles and overall concrete strength.

**Explanation:** In cold weather, concrete curing should be extended for at least 28 days to ensure proper hydration and development of strength.

_{20}then what would be the modular ratio

**Explanation:** The modular ratio for concrete grade M_{20} is typically 13.33, and it is calculated as the ratio of the modulus of elasticity of steel to that of concrete.

**Explanation:** Surface vibrators are most effective when the thickness of the concrete does not exceed 20 cm. They are used to consolidate the concrete surface and remove air voids.

**Explanation:** The maximum bulking factor for sand is generally considered to be 1.40. This factor represents the increase in the volume of sand due to the presence of moisture.

**Explanation:** The maximum bulking of sand typically occurs at a moisture content of around 4%. Beyond this point, the increase in volume due to moisture becomes less significant.

**Explanation:** The proportion (P) of fine to combined aggregates is given by P = (A-B/B-C)x100, where A, B, and C are the fineness moduli of coarse aggregate, combined aggregates, and fine aggregates, respectively.

**Explanation:** The size of fine aggregates typically does not exceed 4.75 mm. Fine aggregates, such as sand, are generally smaller in size compared to coarse aggregates.

**Explanation:** The factor of safety is calculated as the ratio of the ultimate load to the working load. It represents the margin of safety in a structure.

**Explanation:** The factor of safety for steel is generally higher compared to concrete. This reflects the higher tensile strength and ductility of steel, providing a greater margin of safety.
Certainly, let’s provide more detailed explanations for each answer:

**Explanation:** The factor of safety for steel is based on its yield stress, which represents the stress at which the material undergoes a permanent deformation. This choice is made to ensure that the steel remains within its elastic range, preventing plastic deformation and maintaining structural integrity. By using the yield stress in design calculations, engineers account for the point at which the material begins to experience permanent changes.

_{15}concrete is taken as

**Explanation:** The modular ratio, used in concrete design calculations, is the ratio of the modulus of elasticity of steel to that of concrete. For M_{15} concrete, the standard practice is to take the modular ratio as 18.67. This factor is crucial in determining the distribution of loads between steel and concrete in a reinforced concrete structure.

_{ck}

_{ck}

_{ck}

**Explanation:** The allowable stress in bending compression for Reinforced Cement Concrete (RCC) is an essential parameter in design. For practical purposes, it is often taken as 0.33 times the characteristic compressive strength of concrete (f_{ck}). This factor ensures a safe design while considering the properties of the material.

_{ck}

_{ck}

_{ck}

**Explanation:** In axial compression, the allowable stress for RCC is commonly taken as 0.25 times the characteristic compressive strength of concrete (f_{ck}). This factor ensures the safety of the structure under axial loads, considering the behavior of concrete under compression.

_{ck}

_{ck}

_{ck}

**Explanation:** The tensile strength of concrete is a critical parameter in the design of reinforced concrete (RCC) beams. For practical design purposes, the tensile strength of concrete is often considered as 0.1 times the characteristic compressive strength of concrete (f_{ck}). This value reflects the limited tensile capacity of concrete and the need for reinforcement to resist tensile forces.

_{150}is

^{2}

^{2}

^{2}

^{2}

**Explanation:** The permissible tensile strength of concrete is an important consideration in structural design. For M_{150} concrete, the permissible tensile strength is typically taken as 15 kg/cm^{2}. This value is used in design calculations to ensure the safety and integrity of the structure under tensile loading conditions.

**Explanation:** In the working stress design of RCC, the allowable bending compressive strain is a critical parameter. This strain is often taken as 0.002, reflecting the permissible amount of compression that the concrete can undergo while remaining within the elastic range. This factor is crucial in ensuring that the structure behaves within safe limits under service loads.

**Explanation:** The ultimate bending compressive strain in RCC is the maximum strain that the concrete can endure under extreme loading conditions. For practical design purposes, this value is often considered as 0.0035. This factor is essential in determining the ultimate capacity of the structure and ensuring that it can withstand high loads without failure.

**Explanation:** The ratio of the modulus of elasticity of steel to that of concrete is known as the modular ratio. This ratio plays a crucial role in the distribution of loads between steel and concrete in a reinforced concrete structure. It is a fundamental factor in design calculations, influencing the behavior of the structure under various loading conditions.

**Explanation:** Shear in a concrete beam is primarily caused by the variation of bending moment along the span. As the bending moment changes, it induces shear forces in the beam. Proper consideration of shear forces is essential in the design of reinforced concrete beams to ensure structural safety and integrity.

**Explanation:** In a concrete mix with the proportion of 1:2:4 (cement: sand: coarse aggregate), the quantity of coarse aggregate required in 100 m³ of concrete is 87 m³. This proportion ensures the desired strength and workability of the concrete mix, and accurate calculations of material quantities are crucial in achieving the specified properties of the concrete.

**Explanation:** The dimensions of a beam may need to be altered if the shear stress exceeds a certain limit to ensure the safety and integrity of the structure. In general, if the shear stress surpasses 20 kg/cm², it indicates a potential risk, and adjustments to the beam’s dimensions or reinforcement may be necessary.

_{max}) in a rectangular homogeneous beam is

**Explanation:** The maximum shear stress in a rectangular homogeneous beam occurs at the neutral axis and is typically 1.50 times the average shear stress. This relationship is essential for calculating and designing beams to ensure that the structure can withstand shear forces without failure.

**Explanation:** In the mixture 1:1.5:3 (cement: sand: aggregates), for every unit volume of the mixture, the volume of cement is 0.2 m³. This proportion is crucial for batching concrete accurately, ensuring the desired strength and properties of the concrete.

_{15}

_{20}

_{25}

**Explanation:** The ratio of C:FA:CA (1:1.5:3) corresponds to concrete grade M_{20}. This grade signifies the characteristic compressive strength of the concrete mix after 28 days of curing.

_{100}

_{150}

_{200}

_{250}

**Explanation:** The ratio 1:3:6 (cement: sand: aggregates) corresponds to concrete grade M_{100}. This grade indicates the characteristic compressive strength of the concrete mix after 28 days of curing.

**Explanation:** If the shear stress in a beam exceeds the allowable shear stress by a factor of 4 or more, it is generally necessary to redesign the beam section to ensure structural safety. This is a common practice in engineering to prevent shear failure.

**Explanation:** The advantage of reinforced concrete lies in its monolithic character, economic benefits due to lower maintenance costs, and the ability to mold it into various shapes. These factors contribute to its widespread use in construction.

**Explanation:** The weight of steel per cubic meter is approximately 7850 kg. This value is crucial in estimating the quantity of steel reinforcement required in concrete structures.

**Explanation:** The unit weight of Reinforced Cement Concrete (RCC) is commonly taken as 2.5 t/m³. This value is essential in structural analysis and design calculations.

**Explanation:** High Yield Strength Deformed (HYSD) bars exhibit higher bond strength compared to plain bars. The bond strength of HYSD bars is typically more by 60%, making them preferable in reinforced concrete structures where strong bond between steel and concrete is essential for structural performance.

**Explanation:** The strength of tor steel is generally higher than that of mild steel. Tor steel, or twisted deformed bars, is a type of high-strength reinforcement commonly used in concrete construction.

**Explanation:** A slender column is characterized by having a relatively large length compared to its cross-sectional dimensions. In structural engineering, a column is considered slender when its effective length exceeds a certain limit, making it susceptible to buckling.

**Explanation:** The load factor method considers both the contribution of concrete and steel in resisting the load on a column. The permissible load is calculated by summing the stress in concrete multiplied by the area of concrete and the stress in steel multiplied by the area of steel.

**Explanation:** The ratio of effective length of a column fixed at both ends to the distance between the supports is approximately 0.50. This ratio is a critical factor in column design and influences the critical buckling load.

**Explanation:** The ratio of the effective length of a cantilever column to its height is approximately 2.0. This ratio is significant in analyzing the stability and behavior of cantilevered columns.

**Explanation:** The minimum cover to the ties or spiral in a reinforced concrete column should not be less than 25 mm. This cover is essential to protect the reinforcement from environmental conditions and ensure adequate durability.

**Explanation:** The minimum cover provided at the end of reinforcement in a column is 25 mm or 2 θ of the bar, whichever is greater. This cover is crucial for maintaining the integrity and corrosion resistance of the reinforcement.

**Explanation:** The permissible limits for the percentage of longitudinal reinforcement in a column are typically in the range of 0.8% to 6%. Adhering to these limits ensures the structural stability and performance of the column.

**Explanation:** In practical design considerations, the maximum permissible reinforcement in a column is often limited to 4%. Exceeding this limit may lead to construction difficulties and affect the overall behavior of the column.

**Explanation:** The minimum amount of steel required in an RCC column with dimensions 230×350 mm is 600 mm². This minimum steel reinforcement is essential to ensure the strength and ductility of the column under various loading conditions.

**Explanation:** The minimum number of main bars in a circular column is typically 6. This provides adequate reinforcement to resist the various loads and ensure the stability of the column.

**Explanation:** The minimum number of main bars in an octagonal column is generally 8. This arrangement of bars helps distribute the load effectively and enhances the structural performance of the column.

**Explanation:** According to IS 456:2000, the minimum diameter of reinforcement in a column should not be less than 12 mm. This specification ensures that the reinforcement provides sufficient strength and ductility.

**Explanation:** The diameter of bars typically used in a column falls within the range of 12-25 mm. This range is common in practice and provides the necessary strength for column reinforcement.

**Explanation:** The slenderness ratio (l/r) of an RCC column is calculated as the effective length (l) divided by the radius of gyration (r). It is a critical parameter in determining the column’s behavior, especially in terms of buckling.

**Explanation:** A column is considered as a long column if its slenderness ratio (l/r) exceeds a certain limit, often considered as 40. Long columns are more prone to buckling failure.

**Explanation:** According to IS: 456, a column is considered a short column if its slenderness ratio (l/r) is less than or equal to 10. Short columns are less susceptible to buckling.

**Explanation:** The slenderness ratio is calculated as the effective length divided by the radius of gyration. In this case, the slenderness ratio is 55.

**Explanation:** Long columns take a lesser load compared to short columns due to their higher susceptibility to buckling failure.

**Explanation:** A column that fails by buckling is referred to as a long column, while a column that fails by crushing is called a short column. The distinction is based on the dominant mode of failure.

**Explanation:** Buckling can occur in columns, especially in long columns, due to the lateral instability. It is not limited to columns that are either “great” or “too great” in a specific sense.

**Explanation:** The maximum spacing between longitudinal bars in a column is typically limited to ensure proper distribution of reinforcement and to enhance the column’s load-carrying capacity.

**Explanation:** The pitch of the ties in a column is determined by the least of the provided options, which includes the least lateral dimension of the column, 16 times the diameter of the smallest longitudinal bar, or 48 times the diameter of the transverse reinforcement.

**Explanation:** Helically reinforced columns generally have a higher load-carrying capacity compared to tied columns, and the difference can be around 5% more.

**Explanation:** According to standards like IS 456:2000, the minimum cover for a longitudinal reinforcing bar in a column should not be less than the diameter of the bar or 25 mm, whichever is greater.

**Explanation:** The spacing of longitudinal bars measured along the periphery of the column is subject to limits defined by standards such as IS 456:2000. In this case, the spacing should not exceed 30 cm.

**Explanation:** In a singly reinforced beam, plane sections transverse to the center line of the beam before bending remain plane sections after bending. This is a fundamental assumption in the theory of flexural (bending) behavior.

**Explanation:** The effective depth in a singly reinforced beam is measured from its compression edge to the center of the tensile reinforcement.

**Explanation:** Over-reinforcing a beam can increase its moment of resistance, but there are limits to this increase. Generally, increasing the reinforcement beyond a certain point does not lead to a proportional increase in the moment of resistance.

**Explanation:** In the steel beam theory of doubly reinforced beams, tension is resisted by tension steel, compression is resisted by compression steel, and the stress in tension steel equals the stress in compression steel. This reflects the balance of forces in a doubly reinforced beam.

**Explanation:** The distribution of shear intensity over a rectangular section of a beam follows a parabolic curve. This is a characteristic pattern that represents the variation of shear stress across the depth of the beam.

**Explanation:** The spacing of transverse reinforcement in a column is decided by considering the least lateral dimension of the column, sixteen times the diameter of the smallest longitudinal reinforcing rod, and forty-eight times the diameter of transverse reinforcement. All of these factors play a role in determining the appropriate spacing.

**Explanation:** The minimum embedment of reinforcement in a concrete flexural member is typically specified as a certain multiple (such as 30 times) of the diameter of the reinforcement.

**Explanation:** Main reinforcement in an RCC beam is primarily used for resisting bending moments. It helps to withstand tensile stresses induced by bending.

**Explanation:** Shear reinforcement in an RCC beam is provided to resist shear forces and prevent shear failure. It helps in enhancing the shear capacity of the beam.

**Explanation:** Bottom reinforcement in a beam is subjected to tension. It helps to resist the tensile forces induced by bending.

**Explanation:** Increased depth of a beam leads to increased stiffness of the section. This can contribute to the overall strength and performance of the beam.

**Explanation:** In a rectangular R.C.C beam, the ratio of the maximum shear stress to average shear stress is typically around 1.33.

**Explanation:** Side face reinforcement is provided in a beam when the depth of the web exceeds a certain threshold, often around 750 mm. This helps in preventing shear failure.

**Explanation:** The maximum spacing of side-face reinforcement in a beam is typically specified to ensure effective distribution and anchorage, and it is commonly around 300 mm.

^{2})

^{2}d)

**Explanation:** The maximum shear stress (τ_max) in a singly reinforced beam subjected to shear force (F), with depth (d) and width (b), is given by the formula τ_max = F/(b * d).

**Explanation:** In a singly reinforced beam, the effective cover is measured from the centroid of the steel reinforcement to the outer face of the outermost layer of concrete.

**Explanation:** If the concrete in a singly reinforced beam reaches its allowable stress before the steel, the section is considered over-reinforced.

**Explanation:** An under-reinforced section means that the amount of steel provided is insufficient, and it will lead to premature failure of the steel before the concrete reaches its full capacity.

**Explanation:** In a balanced failure, the stress in concrete and steel reaches their permissible values simultaneously, and the neutral axis location matches with the critical neutral axis.

**Explanation:** If the amount of steel in an RCC beam increases, the depth of the neutral axis (N.A.) increases as well.

**Explanation:** The minimum length of the bar that must be embedded in concrete beyond any section to develop bond is known as the development length.

**Explanation:** The lap length of a direct tension reinforcement bar should be more than twice the development length or 30 times the diameter of the bar, whichever is greater.

**Explanation:** The minimum straight lap length in tension bars with hooks is typically specified as 15 times the diameter of the bar or 200mm, whichever is greater.

**Explanation:** The minimum lap length at the splice of compression reinforcement is generally specified as 24 times the diameter of the bar or lap length, whichever is greater.

**Explanation:** The minimum vertical spacing of the main bars in an RCC beam is generally specified as the maximum size of the bar or 2/3 of the maximum size of the aggregate.

_{25}under bending compression

^{2}

^{2}

^{2}

^{2}

**Explanation:** not available

**Explanation:** Cover blocks are used to maintain the specified cover on the sides and below the reinforcement in concrete.

**Explanation:** The minimum cover to the main bars in an RCC beam is typically specified as 25mm or the diameter of the bar, whichever is greater.

**Explanation:** The minimum thickness of the cover at the end of a reinforcing bar is generally specified as twice the diameter of the bar or a minimum of 25mm.

**Explanation:** Number-supported beams are provided to resist bond stress and ensure proper development of bond between concrete and reinforcement.

**Explanation:** The decision between singly reinforced and doubly reinforced beams is primarily based on the bending moment requirements.

**Explanation:** Doubly reinforced beams are often used when there are restrictions on the depth and width of the beam, and additional strength is required.

**Explanation:** In the analysis of a doubly reinforced beam, the assumption is made that the deformations in concrete and steel on both sides remain proportional to their distance from the neutral axis.

**Explanation:** A doubly reinforced beam is economical because it allows compressive steel to be under-stressed, leading to efficient use of materials.

**Explanation:** In a doubly reinforced beam, the maximum shear stress occurs on planes between the neutral axis and the compressive reinforcement.

**Explanation:** Steel beam theory is often used for the analysis of doubly reinforced beams, especially when compressive stress in concrete is ignored.

^{2}and concrete used is M

_{15}, then the depth of the neutral axis for a singly reinforced balanced beam will be

**Explanation:** The depth of the neutral axis for a singly reinforced balanced beam is typically around 0.40 times the effective depth (d).

**Explanation:** The maximum span to satisfy vertical deflection limits for a cantilever beam with an effective depth of 50cm is 3.5m.

_{s}/ rbd

_{s}/ 4rbd

_{s}/ 3rbd

_{s}/ 3rbd

**Explanation:** The development length of bars in tension is given by the formula θσ_{s} / 4rbd as per I.S: 456.

**Explanation:** The maximum diameter of bars in a beam is generally limited to one-eighth of the least dimension of the beams.

**Explanation:** Transverse shear reinforcement in RCC beams can be provided as open or closed loops, in addition to other forms like ties or helical loops.

**Explanation:** The spacing of shear reinforcement is typically kept maximum at the center as compared to the end of a beam.

**Explanation:** A simply supported beam is deemed to be a deep beam if the ratio of effective span to overall depth is 2 or less.

**Explanation:** A continuous beam is deemed to be a deep beam if the ratio of effective span to overall depth is 2.5 or less.

**Explanation:** A beam curved in plan is designed for bending moment, shear, and torsion, as it experiences these forces due to its curvature.

^{4}/ 384El

^{3}/ 64El

^{2}/ 384El

**Explanation:** The formula for the deflection of a simply supported beam with a uniformly distributed load is 5wL^{4} / 384El.

**Explanation:** Due to shrinkage stress, a simply supported beam with reinforcement only at the bottom may tend to deflect upward or downward.

**Explanation:** Shear reinforcement in an RCC beam is provided to resist diagonal tension, which is a common mode of shear failure.

**Explanation:** A diagonal crack is introduced in a beam primarily due to shear force (SF).

**Explanation:** In the case of a cantilever beam, main reinforcement is typically provided on the top face of the beam.

**Explanation:** Shear stress is primarily resisted by inclined or diagonal reinforcement, and vertical steel is not as effective in resisting shear.

**Explanation:** Tension reinforcement in R.C.C. beams can be cut off when it is no longer needed if the shear at the cut-off point does not exceed two-thirds of the permissible value at that section.

**Explanation:** The radius of the bend to form a hook should not be less than twice the diameter of the bar.

**Explanation:** The length of the straight portion of a bar beyond the end of the hook should be at least four times the diameter of the bar.

**Explanation:** The anchorage value of a standard hook is significant in ensuring the proper development length of reinforcing bars in concrete. When the hook is formed at a 180° angle, it provides optimal anchorage, and its value is considered as 16 times the diameter of the reinforcing bar. This means that the length of the bar, as far as anchorage is concerned, is effectively extended by 16 times its diameter, ensuring adequate bond strength between the steel and the surrounding concrete.

**Explanation:** In reinforced concrete structures, bars in tension need to be properly anchored to resist forces. The anchorage value of a standard hook for bars in tension is considered equivalent to a straight length of 16 times the diameter of the reinforcing bar. This ensures that the tension forces can be adequately transferred from the concrete to the reinforcing steel without slippage or failure.

**Explanation:** Similar to hooks, bends in reinforcing bars also contribute to anchorage. The anchorage value of a standard bend, formed at a 90° angle, is considered as 8 times the diameter of the reinforcing bar. This means that the effective anchorage length is increased by 8 times the diameter, providing sufficient bond strength between the steel and the surrounding concrete in tension zones.

**Explanation:** In the construction of reinforced concrete beams, it is common practice to bend the reinforcement bars at a 90° angle at the ends of the beam. This 90° bend helps in proper anchoring of the bars, ensuring that they can effectively resist tension forces. The perpendicular orientation of the bars at the ends facilitates a smooth transfer of forces between the concrete and the reinforcing steel.

**Explanation:** In the context of reinforced concrete beams, N.A stands for the neutral axis. The neutral axis is a crucial concept in structural engineering, representing the plane within a beam where the bending stress is zero. Understanding the location of the neutral axis is essential for designing beams that can effectively resist bending moments and distribute loads.

**Explanation:** The depth of the neutral axis in a reinforced concrete beam is influenced by the distribution of steel reinforcement. As the area of steel increases, the neutral axis tends to move towards the tensile face of the beam, resulting in an increase in the overall depth of the neutral axis. This is because the additional steel provides more resistance to tension forces, causing the neutral axis to shift and the beam’s section to effectively become more ductile.

**Explanation:** The neutral axis of a T-beam, which has a flange and a web, can exist in various locations. It may be within the flange, at the bottom edge of the slab, or below the slab, depending on the specific geometry and loading conditions. The neutral axis is a critical parameter in the analysis and design of T-beams, as it influences the distribution of stresses and the overall behavior of the structure.

**Explanation:** The behavior of a T-beam is influenced by the location of its neutral axis. When the neutral axis remains within the flange, the T-beam behaves structurally like a rectangular beam with a width equal to its flange. This simplification is often used in the analysis and design of T-beams, allowing engineers to apply principles similar to those used for rectangular beams.

**Explanation:** In the case of T-beams subjected to heavy loads, the overall depth of the rib (or the depth of the web) is typically considered to be 1/12 of the span. This design consideration helps ensure that the T-beam can effectively support and distribute the applied loads while maintaining structural stability.

**Explanation:** In the design of simply supported slabs, where bars are provided for reinforcement, alternate bars are often curtailed at approximately 1/7th of the span. Curtailing refers to the intentional shortening or terminating of reinforcement bars in a structural element. This practice is commonly employed to optimize the distribution of reinforcement while considering factors such as construction constraints and material efficiency.

**Explanation:** For a slab that is simply supported and spans in one direction, the maximum recommended ratio of span to depth is typically 30. This ratio is an important design consideration to ensure that the slab performs well under the applied loads while maintaining structural integrity.

**Explanation:** In the case of a slab that is simply supported and spans in two directions, the maximum recommended ratio of span to depth is generally 35. This ratio takes into account the additional considerations for slabs spanning in two directions, providing guidelines for effective load distribution and structural performance.

**Explanation:** To ensure effective load distribution and proper structural behavior in a slab, the pitch of the main reinforcement (spacing between the bars) should not exceed three times the effective depth of the slab. This design criterion helps maintain the integrity of the slab under various loading conditions.

**Explanation:** In a two-way slab, which spans in both directions, the main reinforcement bars are typically designed and placed along the short span. This comprehensive placement of main bars helps in distributing the loads effectively and provides balanced reinforcement throughout the slab.

**Explanation:** The pitch of the distribution reinforcement in a slab (spacing between bars) should not exceed five times the effective depth. This guideline is essential for preventing cracks and ensuring that the distribution reinforcement effectively controls shrinkage and temperature-related stresses in the slab.

**Explanation:** Distribution reinforcement in a simply supported slab serves multiple purposes. It helps distribute loads, controls temperature-induced stresses, and addresses shrinkage stresses. By providing reinforcement to address these factors, the slab’s overall performance and durability are enhanced.

**Explanation:** The amount of reinforcement for main bars in a slab is primarily based on the maximum bending moment that the slab is expected to experience. This ensures that the slab can effectively resist bending stresses and provides the required structural strength.

**Explanation:** The minimum cover in a slab should be neither less than the diameter of the bar nor less than 15 mm. This minimum cover requirement is crucial for protecting the reinforcement from corrosion and ensuring the durability of the structure.

**Explanation:** The minimum spacing between horizontal parallel reinforcements of the same size in a slab should not be less than one diameter. This specification is important to maintain proper spacing between bars and to facilitate effective concrete placement.

**Explanation:** When dealing with horizontal parallel reinforcements of different sizes in a slab, the minimum spacing should not be less than one times the diameter of the thicker bar. This ensures adequate spacing between different-sized bars and facilitates proper concrete consolidation during construction.

**Explanation:** The minimum overall depth of a continuous slab to satisfy vertical deflection limits depends on various factors, including the span, loading conditions, and material properties. For the given size of the slab (3m x 3.5m), a minimum overall depth of 7.5cm may be required to meet deflection criteria while considering structural stability and performance.

**Explanation:** The ratio of the diameter of reinforcing bars to the slab thickness is an important consideration in the design of reinforced concrete slabs. A common guideline is to maintain a ratio of 1/8, meaning the diameter of the bars should be no more than 1/8th of the slab thickness. This ratio helps ensure proper concrete cover and adequate reinforcement.

**Explanation:** In the given scenario, where the slab thickness is 100 mm, the maximum diameter of the reinforcing bar placed in the slab is often recommended to be 12 mm. This choice of bar diameter ensures proper structural performance and adherence to design standards.

**Explanation:** An RCC roof slab is designed as a two-way slab when the ratio of spans in both directions is less than two. This design approach is suitable for distributing loads effectively in both directions and ensuring stability under various loading conditions.

**Explanation:** If the corners of a two-way slab are held down firmly, it can lead to stress concentrations, resulting in cracks near the corners. This phenomenon occurs due to restraint, and the development of cracks is a common issue in such situations.

**Explanation:** A slab that is built integrally with the supporting columns without any beams is referred to as a flat slab. In flat slab construction, the slab directly rests on the columns, and there are no beams providing additional support.

**Explanation:** The enlarged head of a supporting column in a flat slab is technically known as a capital. The capital serves to distribute loads effectively from the slab to the column and enhances the overall structural performance.

**Explanation:** The thickened part of a flat slab over its supporting column is technically known as a drop panel. This drop panel provides additional strength and stiffness to the slab-column connection, improving load distribution and structural performance.

**Explanation:** In a two-way slab, the main reinforcement is typically provided along the breadth of the slab. This arrangement helps in effectively resisting bending moments in both directions and ensures structural integrity.

**Explanation:** In the case of a cantilever slab, the main reason for placing the main reinforcement bars at the top is to resist tension forces. The tension at the top face of the cantilever slab is critical for preventing cracking and ensuring the structural stability of the slab under loading conditions.

**Explanation:** The lifting of corners in a two-way slab occurs due to torsional moments. Torsional moments create twisting effects in the slab, leading to the upward movement of corners. This phenomenon is more prominent in slabs with irregular or unbalanced loading conditions.

^{th}of the short span

^{th}of the short span

^{th}of the long span

^{th}of the long span

**Explanation:** The length of mesh of torsional reinforcement in a slab is typically taken as 1/5th of the short span. This provision helps in effectively resisting torsional forces and enhancing the overall structural stability of the slab.

**Explanation:** Torsion steel in a two-way slab is provided both at the top and bottom of the slab. This dual reinforcement is intended to effectively counteract torsional moments and ensure the slab’s resistance to twisting forces.

**Explanation:** The minimum diameter of bars for a slab is generally considered to be 8 mm. This minimum diameter is specified to ensure adequate strength and durability of the reinforcement in the slab.

**Explanation:** A circular slab, when subjected to external loading, deforms to assume a shape of a paraboloid. The deformation is influenced by the distribution of loads and structural behavior, resulting in a curved shape resembling a paraboloid.

**Explanation:** A rib slab can be provided for various purposes, including plain ceiling, acoustic insulation, and heat insulation. The ribs in the slab add architectural features, and the voids between ribs can be utilized for insulation or other functional purposes.

_{s}/ 3π

_{bd}

_{s}/ 4π

_{bd}

_{s}/ 5π

_{bd}

_{s}/ 6π

_{bd}

**Explanation:** The development length of bars in compression as per IS 456:2000 is given by the formula Φσ_{s} / 5π_{bd}, where Φ is the diameter of the bar, σ_{s} is the permissible stress in compression, b is the breadth of the member, and d is the effective depth.

^{6}N/cm²

**Explanation:** The modulus of elasticity for steel as per IS 456-2000 is 200 KN/mm². This value represents the stiffness of steel and is an important parameter in structural analysis and design.

_{15}

_{20}

_{10}

_{25}

**Explanation:** The minimum grade of concrete to be used in reinforced concrete as per IS 456-2000 is M_{20}. This specifies the characteristic compressive strength of the concrete mix.

**Explanation:** The minimum cover at the end of reinforcement should be the maximum of either 20 times the diameter of the bar (20 Φ) or 25 mm. This ensures adequate protection of the reinforcement from environmental factors and corrosion.

**Explanation:** For a cantilever beam, the span to effective depth ratio is generally restricted to a value of 7. This limitation helps maintain the stability and strength of the cantilevered structure.

**Explanation:** In a Reinforced Brick (R.B.) slab, the permissible compressive stress in bricks is generally taken as 10 kg/cm². This value ensures the safe and efficient performance of the brick material in the slab structure.

**Explanation:** The slope of weep holes is generally provided at a ratio of 1 in 8. Weep holes with appropriate spacing and slope are used in retaining walls to facilitate drainage and prevent water buildup behind the wall.

**Explanation:** Weep holes are provided in retaining and breast walls to facilitate drainage and prevent water accumulation behind the walls. They allow water to escape, reducing the risk of hydrostatic pressure and potential damage to the structure.

**Explanation:** In the case of the foundation of a rigid base, the distribution pressure on the soil is generally uniform. This uniform distribution helps in preventing excessive settlement and ensures stability.

**Explanation:** The minimum overall depth kept at the edge of Reinforced Concrete (R.C.) footings is typically 15 cm. This depth provides adequate strength and support for the footing structure.

**Explanation:** If a beam fails in bond, one approach to address the issue is to use thicker but fewer numbers of bars. This helps enhance the bond strength between the concrete and the reinforcement.

**Explanation:** The resistance offered to slipping of steel bars in concrete is primarily due to frictional resistance between the steel and the surrounding concrete. Adhesion and mechanical resistance also play a role in preventing slippage.

**Explanation:** When a material is loaded with tensile force at both ends, the test is known as a tensile test. This test is conducted to measure the material’s response to tensile stress and deformation.

**Explanation:** The safe bond stress between concrete and steel is determined by the pull-out test. This test assesses the bond strength between the concrete and the embedded steel reinforcement by applying a tensile force to the bar and measuring its resistance to pull-out.

_{eft}/ b of the column is considered as a long column if its value is

**Explanation:** The ratio l_{eft} / b of a column is considered as a long column if its value is greater than 12 to 15. This indicates that the effective length of the column in relation to its least lateral dimension is significant, leading to a long-column behavior.

**Explanation:** The cover provided in the column with a size less than 200 mm x 200 mm is typically 25 mm. Cover is the protective layer of concrete that separates the reinforcement from the external environment, providing durability and corrosion resistance.

**Explanation:** The types of failure occurring in a beam due to shear force are termed as diagonal tension failure. This failure mode involves the development of diagonal cracks in the tension zone of the beam.

_{415}is taken as

**Explanation:** The tensile strength of Fe_{415} steel is taken as 415 N/mm². This represents the maximum tensile stress that the steel can withstand.

**Explanation:** The gross sectional area of the RCC element is 1 m and 0.5 m, m = 0.5 , m². The minimum reinforcement is 1% of this area, which is 0.01 times 0.5 , m² = 0.005 , m² = 5000 , mm².

**Explanation:** In a singly reinforced beam, as the load increases, the concrete resists tension until it reaches its tensile strength. After that, the steel reinforcement takes over to resist tension.

**Explanation:** The laps in bars, which refer to the overlapping of two reinforcing bars, are generally in the range of 1.5 to twice the bond length. This ensures proper transfer of stresses and maintains the integrity of the reinforcement.

**Explanation:** The amount of reinforcement for main bars in a slab is based upon the maximum bending moment. This is because the main bars are primarily designed to resist bending stresses in the slab.

**Explanation:** A column is considered as a long column if its slenderness ratio (\(l / r\)) is more than 12. The slenderness ratio is the ratio of the effective length of the column to its least radius of gyration.

**Explanation:** The states of concrete include the plastic state (during mixing, placing, and compaction) and the hardened state (after curing and gaining strength). The plastic state refers to the moldable, fresh concrete, while the hardened state is the final, cured and set concrete.

**Explanation:** In a balanced design of a beam, the maximum stresses occurring, whether in concrete or steel, are equal to the permissible stress. This means that both materials reach their maximum capacity simultaneously, resulting in a balanced condition.

**Explanation:** The ultimate tensile strength of structural mild steel is approximately 420 N/mm². This represents the maximum tensile stress that the steel can withstand before failure.

**Explanation:** A reinforced concrete beam will crack if the tensile stress developed in the concrete below the neutral axis exceeds the permissible stress for concrete. Cracking occurs when the tensile stress reaches a critical value.

**Explanation:** The moment of resistance of an under-reinforced section is primarily computed based on the tensile force developed in the steel reinforcement. The contribution of concrete in compression is also considered, but the tensile force in steel is a critical factor.

**Explanation:** Such a section is known as a balanced section, a critical section, or an economical section. In this condition, both concrete and steel reach their permissible stresses simultaneously, leading to a balanced and efficient design.

**Explanation:** A rigid frame is a structure where the members are connected by rigid joints, allowing minimal rotation at the connections. This characteristic helps distribute moments and provides stability to the frame.

**Explanation:** All the mentioned factors—compaction during placement, proper curing after placement, and an appropriate water-cement ratio—influence the strength and durability of concrete. These factors play crucial roles in achieving the desired concrete properties.

**Explanation:** Lime concrete in foundations should be kept wet for a minimum period of 7 days without the construction of masonry over it. This ensures proper curing and development of strength in lime concrete.

**Explanation:** Placing two layers of tensile reinforcement bars in a flexural member in such a way that they are close to the tension face minimizes the effective depth. This arrangement helps in optimizing the use of reinforcement and improving the performance of the member.

**Explanation:** In a reinforced concrete section, the shear stress diagram is typically parabolic above the neutral axis and rectangular below the neutral axis. This distribution of shear stress helps in understanding and designing for the shear forces in the structure.

**Explanation:** A one-way slab is designed to bend primarily in one direction, and its reinforcement is provided to resist the bending stresses in that direction.

**Explanation:** In an over-reinforced section, where the amount of steel is more than needed for balanced design, failure typically initiates in the compression zone.

**Explanation:** The maximum strain in the tension reinforcement at failure is determined by the material properties of the steel and is often specified to ensure ductility and proper performance.

**Explanation:** In a flat slab system, the slab is directly supported by columns that are monolithically connected with the slab, eliminating the need for beams.

**Explanation:** In a simply supported beam loaded transversely, the maximum compressive stress develops at the top fiber of the beam.

**Explanation:** The ratio of ultimate strength to working stress is commonly known as the safety factor, representing the factor by which the design strength is reduced to ensure the safety and reliability of the structure.

_{lim}of singly reinforced section

_{lim}of singly reinforced section

_{lim}of single reinforced section

**Explanation:** In a doubly reinforced section, extra compressive reinforcement is provided to handle bending moments beyond the limit of a singly reinforced section.

_{20}for the limit state method of design should be (for plain bars)

**Explanation:** The maximum value of bond stress is often limited to ensure the integrity of the bond between the concrete and the reinforcing bars.

**Explanation:** The size of the aggregate is limited to avoid issues such as honeycombing and to ensure workability. In no case should the size be greater than 1/4 of the minimum thickness of the member.

**Explanation:** The effective span of a simply supported slab is the clear span plus the effective depth of the slab, taking into account the supporting conditions.

**Explanation:** The slenderness ratio is a measure of how slender or stocky a column is. If the slenderness ratio is high, the column is considered long.

**Explanation:** Bond stress is the force exerted between the reinforcing bar and the surrounding concrete per unit area of the bar’s surface.

**Explanation:** The spacing of stirrups in a rectangular beam is often increased towards the center to provide adequate shear reinforcement where the shear forces are higher.

**Explanation:** The amount of reinforcement for main bars in a slab is based on the maximum bending moment to ensure that the slab can resist the applied loads.

**Explanation:** The effective width of a column strip in a flat slab is typically taken as half the width of the panel, considering the distribution of loads and moments.