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Question 1
ప్రశ్న 1
Which statement correctly describes the current general BIS framework for ordinary reinforced-concrete structural design in India?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
IS 456 provides the general code framework for plain and reinforced concrete structural use. The currently applicable published standard has to be read together with its valid amendments rather than from an unamended old textbook copy. Special structures may additionally require other specific standards used in conjunction with the general code. IS 1343 primarily deals with prestressed concrete, while IS 800 deals with steel construction. Therefore Option A is correct.
వివరణ:
Question 2
ప్రశ్న 2
What does the designation M35 principally signify for concrete under the IS 456 grade system?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The letter M in the concrete grade designation refers to the concrete mix designation. The accompanying number represents the specified characteristic compressive strength in N/mm². This strength is associated with the standard 150 mm cube tested at 28 days. It is not a cement percentage or a water-cement ratio. Therefore M35 corresponds to a characteristic cube compressive strength of 35 N/mm² and Option B is correct.
వివరణ:
Question 3
ప్రశ్న 3
The characteristic compressive strength of concrete is statistically defined as the strength value below which:
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Concrete strength naturally exhibits statistical variation even under controlled production. Characteristic strength is therefore not defined as the absolute minimum strength of every individual cube. It is the value below which not more than 5 percent of test results are expected to fall. This corresponds to a lower fractile used for structural reliability. Therefore Option B is correct.
వివరణ:
Question 4
ప్రశ్న 4
Under the amended IS 456 concrete-grade classification, which statement is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The current amended grade table differs from the earliest unamended version reproduced in some older references. Ordinary Concrete includes grades up to M20, while the Standard Concrete group extends from M25 through M60. High Strength Concrete starts at M65 in the amended classification and includes the higher listed grades through M100. This distinction is important when using updated code provisions rather than an obsolete table. Therefore Option B is correct.
వివరణ:
Question 5
ప్రశ్న 5
For reinforced concrete exposed to a mild environment, what is the minimum concrete grade specified by the general durability provisions of IS 456?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The durability requirements establish minimum concrete grades according to exposure severity. For reinforced concrete in mild exposure, the prescribed minimum grade is M20. More severe exposure conditions require progressively higher minimum grades. The grade requirement works together with limits on water-cement ratio and cementitious content. Therefore Option C is correct.
వివరణ:
Question 6
ప్రశ్న 6
For reinforced concrete with 20 mm nominal maximum aggregate under moderate exposure, which combination represents the durability requirements correctly?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Durability requirements become more stringent as environmental exposure becomes more aggressive. For moderate exposure in reinforced concrete, the minimum grade is M25. The maximum free water-cement ratio is 0.50 and the corresponding minimum cement content for the stated aggregate condition is 300 kg/m³. These requirements must be considered together rather than selecting only one of them. Therefore Option B is correct.
వివరణ:
Question 7
ప్రశ్న 7
For reinforced concrete with 20 mm nominal maximum aggregate under severe exposure, which set of durability requirements is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Severe exposure demands better protection against ingress of aggressive agents than mild or moderate exposure. The reinforced-concrete durability requirements specify a minimum grade of M30 for this exposure category. The maximum free water-cement ratio is 0.45. The corresponding minimum cement content for the stated aggregate size is 320 kg/m³. Therefore Option C is correct.
వివరణ:
Question 8
ప్రశ్న 8
For reinforced concrete with 20 mm nominal maximum aggregate under extreme exposure, which combination is specified for durability?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Extreme exposure represents the most demanding durability category in the general exposure table. Reinforced concrete in this condition requires a minimum grade of M40. The free water-cement ratio is limited to a maximum of 0.40. The corresponding minimum cement content for 20 mm nominal maximum aggregate is 360 kg/m³. Therefore Option D is correct.
వివరణ:
Question 9
ప్రశ్న 9
A designer satisfies the minimum concrete grade specified for a particular exposure but proposes a water-cement ratio higher than the maximum value permitted for that exposure. Which interpretation is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Durability cannot be judged solely from the nominal compressive-strength grade. Water-cement ratio strongly affects pore structure, permeability and the ability of aggressive substances to enter the concrete. The code requirements for minimum grade, maximum free water-cement ratio and minimum cementitious content are separately related to the exposure condition. Satisfying one requirement does not automatically cancel a violation of another. Therefore Option C is correct.
వివరణ:
Question 10
ప్రశ్న 10
Why is control of the free water-cement ratio particularly important for durability of reinforced concrete?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Excess mixing water that is not chemically required can leave a more porous capillary structure after hardening. Increased permeability facilitates ingress of water, chlorides, carbon dioxide and other aggressive substances. Such ingress can accelerate deterioration of concrete and corrosion of reinforcement. A suitably controlled water-cement ratio, together with proper compaction and curing, therefore improves durability. Hence Option A is correct.
వివరణ:
Question 11
ప్రశ్న 11
Which description of nominal concrete cover is most appropriate in reinforced-concrete construction?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Concrete cover is the protective concrete layer provided between the exposed surface and the reinforcement. Nominal cover is specified to all reinforcement, including links or stirrups when they form the outermost reinforcement. It is not measured to the centre of the main longitudinal bar. Cover plays important roles in durability and fire resistance in addition to providing a suitable protective environment for steel. Therefore Option B is correct.
వివరణ:
Question 12
ప్రశ్న 12
Ignoring special permitted reductions and separate fire requirements, what nominal concrete cover is specified for durability under moderate exposure?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Nominal cover for durability increases as the environmental exposure becomes more severe. The baseline durability cover for mild exposure is 20 mm. For moderate exposure, the corresponding nominal cover is 30 mm. Higher values apply to severe, very severe and extreme environments. Therefore Option C is correct.
వివరణ:
Question 13
ప్రశ్న 13
For main reinforcement not exceeding 12 mm diameter in a member under mild exposure, the standard 20 mm durability cover may, subject to the relevant IS 456 provision, be reduced to:
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The general nominal durability cover for mild exposure is 20 mm. A specific provision permits a 5 mm reduction for main reinforcement up to and including 12 mm diameter under mild exposure. Applying that reduction gives a nominal cover of 15 mm. Other requirements such as fire resistance and member-specific detailing still have to be satisfied where applicable. Therefore Option C is correct.
వివరణ:
Question 14
ప్రశ్న 14
When both durability and fire-resistance requirements prescribe concrete cover for an RCC member, which design approach is appropriate?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Concrete cover performs more than one structural-performance function. Durability provisions protect reinforcement against environmental attack, while fire provisions limit heating of the embedded steel and concrete core. Satisfying one requirement does not automatically satisfy the other. The provided nominal cover must therefore meet all applicable governing criteria. Hence Option C is correct.
వివరణ:
Question 15
ప్రశ్న 15
Using the IS 456 expression Ec = 5000√fck N/mm², what is the estimated short-term static modulus of elasticity of M25 concrete?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
For M25 concrete, the characteristic compressive strength fck is 25 N/mm². The square root of 25 is 5. Substituting in Ec = 5000√fck gives Ec = 5000 × 5 = 25000 N/mm². The expression gives an estimated short-term static modulus because actual concrete modulus also depends on factors such as aggregate characteristics and curing. Therefore Option C is correct.
వివరణ:
Question 16
ప్రశ్న 16
Using the IS 456 expression for flexural strength, what is the estimated flexural strength of M25 concrete?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The empirical expression for flexural strength is fcr = 0.7√fck N/mm². For M25 concrete, √fck equals 5. Therefore fcr = 0.7 × 5 = 3.5 N/mm². This value is far lower than the compressive strength because concrete is relatively weak in tension. Therefore Option B is correct.
వివరణ:
Question 17
ప్రశ్న 17
What value is normally taken for the modulus of elasticity of reinforcing steel in reinforced-concrete design?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Reinforcing steel is much stiffer than normal structural concrete. The conventional modulus of elasticity used for reinforcing steel is 200000 N/mm². This is equivalent to approximately 200 GPa. The value is used for both mild and high-strength reinforcing steels for ordinary structural calculations unless a specific requirement states otherwise. Therefore Option D is correct.
వివరణ:
Question 18
ప్రశ్న 18
A reinforcing bar is designated Fe500D. What is the most accurate interpretation of this designation?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The numerical part of an Fe grade identifies the specified minimum yield stress or 0.2 percent proof stress in N/mm² as applicable. Thus Fe500 corresponds to a minimum strength level of 500 N/mm². The D suffix identifies a category having enhanced ductility-related requirements, including greater specified elongation compared with the corresponding basic grade. The suffix does not indicate bar diameter or elastic modulus. Therefore Option A is correct.
వివరణ:
Question 19
ప్రశ్న 19
What is a principal structural advantage of deformations or ribs on high-strength reinforcing bars?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
For reinforced concrete to act compositely, forces must be transferred effectively between steel and concrete. Surface ribs and deformations provide mechanical interlock in addition to adhesion and friction. This generally gives deformed reinforcement better bond behaviour than comparable smooth bars. Deformations do not eliminate the need for proper development length and anchorage. Therefore Option B is correct.
వివరణ:
Question 20
ప్రశ్న 20
Why are chemical composition and carbon-equivalent limits relevant to reinforcing steel?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The metallurgy of reinforcing steel influences both strength and fabrication characteristics. Carbon content and carbon equivalent are particularly relevant to weldability. Excessively unfavorable chemistry can increase the risk of brittle behaviour or require special welding precautions. Compliance with a reinforcing-steel grade therefore involves more than simply achieving a specified yield strength. Hence Option A is correct.
వివరణ:
Question 21
ప్రశ్న 21
Which pairing of currently applicable material standards is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Material specifications must be distinguished from structural design codes and mix-proportioning guidelines. IS 383 deals with coarse and fine aggregates intended for concrete. IS 1786 is the published specification covering high-strength deformed steel bars and wires for concrete reinforcement and is used with its applicable amendments. IS 456 provides the general structural concrete code rather than serving as the manufacturing specification for reinforcement. Therefore Option A is correct.
వివరణ:
Question 22
ప్రశ్న 22
Which statement about the use of sea water in ordinary structural concrete is consistent with the current IS 456 requirements?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Water used in concrete can introduce dissolved substances that affect durability and reinforcement corrosion. Sea water contains salts, particularly chlorides, that are undesirable for structural concrete. Current IS 456 wording does not permit sea water for mixing or curing concrete. Increasing the concrete grade does not cancel this material restriction. Therefore Option C is correct.
వివరణ:
Question 23
ప్రశ్న 23
According to the amended durability provisions, why should cement content excluding mineral admixtures not simply be increased without limit beyond about 450 kg/m³?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
More cement is not automatically equivalent to more durable concrete. High cement content can increase heat generation and contribute to early thermal cracking, particularly where temperature rise is significant. It can also increase drying-shrinkage concerns in susceptible sections. Current amended provisions therefore require special consideration before using cement contents excluding relevant mineral admixtures above the stated level. Hence Option B is correct.
వివరణ:
Question 24
ప్రశ్న 24
A composite cement is proposed for reinforced-concrete construction under the amended IS 456 material provisions. Which combination correctly states the specific conditions associated with its permitted use?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The current amended material provisions expressly recognize composite cement for reinforced-concrete construction subject to stated conditions. The cement is required to conform to the relevant composite-cement specification. The declared clinker content is required to be at least 45 percent and fly ash content is limited to not more than 25 percent for this provision. A minimum 28-day compressive strength of 43 MPa is also specified. Therefore Option A is correct.
వివరణ:
Question 25
ప్రశ్న 25
Consider the following statements about RCC materials and durability:
1. Characteristic concrete strength is based on a 5 percent lower fractile concept.
2. In the amended IS 456 grade classification, M60 belongs to Standard Concrete.
3. The D suffix in Fe500D indicates enhanced ductility-related requirements compared with the corresponding Fe500 category.
4. Providing higher-strength reinforcement automatically permits the nominal concrete cover required for environmental exposure to be ignored.
Which statements are correct?
1. Characteristic concrete strength is based on a 5 percent lower fractile concept.
2. In the amended IS 456 grade classification, M60 belongs to Standard Concrete.
3. The D suffix in Fe500D indicates enhanced ductility-related requirements compared with the corresponding Fe500 category.
4. Providing higher-strength reinforcement automatically permits the nominal concrete cover required for environmental exposure to be ignored.
Which statements are correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Statement 1 is correct because characteristic strength is defined so that not more than 5 percent of results are expected to fall below it. Statement 2 is correct under the amended concrete-grade classification, in which Standard Concrete extends through M60. Statement 3 is correct because the D designation signifies enhanced ductility-related characteristics for the reinforcement category. Statement 4 is incorrect because required concrete cover is governed by durability, fire and detailing provisions rather than being cancelled merely by increasing steel strength. Therefore Statements 1, 2 and 3 are correct and Option B is the unique answer.
వివరణ:
Answer Key సమాధానాల పట్టిక
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Question 1 ప్రశ్న 1Answer: A. IS 456:2000, read with its applicable amendments, remains the general code of practice for plain and reinforced concrete. సమాధానం: A.
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Question 2 ప్రశ్న 2Answer: B. A characteristic compressive strength of 35 N/mm² for a 150 mm cube at 28 days సమాధానం: B.
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Question 3 ప్రశ్న 3Answer: B. Not more than 5 percent of test results are expected to fall. సమాధానం: B.
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Question 4 ప్రశ్న 4Answer: B. M60 is Standard Concrete, while M65 and higher listed grades up to M100 are classified as High Strength Concrete. సమాధానం: B.
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Question 5 ప్రశ్న 5Answer: C. M20 సమాధానం: C.
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Question 6 ప్రశ్న 6Answer: B. Minimum grade M25, maximum free water-cement ratio 0.50, minimum cement content 300 kg/m³ సమాధానం: B.
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Question 7 ప్రశ్న 7Answer: C. M30, maximum water-cement ratio 0.45 and minimum cement content 320 kg/m³ సమాధానం: C.
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Question 8 ప్రశ్న 8Answer: D. Minimum grade M40, maximum free water-cement ratio 0.40, minimum cement content 360 kg/m³ సమాధానం: D.
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Question 9 ప్రశ్న 9Answer: C. The proposal does not satisfy the durability provisions because minimum grade, water-cement ratio and cementitious requirements are individually related to exposure. సమాధానం: C.
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Question 10 ప్రశ్న 10Answer: A. A lower appropriate water-cement ratio generally reduces capillary porosity and permeability of adequately compacted concrete. సమాధానం: A.
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Question 11 ప్రశ్న 11Answer: B. The design depth of concrete cover to the reinforcement, including links or stirrups where they are the outermost steel సమాధానం: B.
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Question 12 ప్రశ్న 12Answer: C. 30 mm సమాధానం: C.
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Question 13 ప్రశ్న 13Answer: C. 15 mm సమాధానం: C.
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Question 14 ప్రశ్న 14Answer: C. Provide cover adequate to satisfy all applicable requirements, which generally means the governing larger requirement. సమాధానం: C.
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Question 15 ప్రశ్న 15Answer: C. 25,000 N/mm² సమాధానం: C.
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Question 16 ప్రశ్న 16Answer: B. 3.5 N/mm² సమాధానం: B.
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Question 17 ప్రశ్న 17Answer: D. 200,000 N/mm² సమాధానం: D.
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Question 18 ప్రశ్న 18Answer: A. It has a specified minimum yield or 0.2 percent proof stress of 500 N/mm², and the D category has enhanced specified ductility or elongation requirements. సమాధానం: A.
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Question 19 ప్రశ్న 19Answer: B. They improve mechanical interlock and bond between reinforcement and surrounding concrete. సమాధానం: B.
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Question 20 ప్రశ్న 20Answer: A. They influence characteristics such as weldability and the risk of brittle behaviour. సమాధానం: A.
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Question 21 ప్రశ్న 21Answer: A. IS 383:2016 – coarse and fine aggregates for concrete; IS 1786:2008 with applicable amendments – high-strength deformed steel bars and wires for concrete reinforcement సమాధానం: A.
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Question 22 ప్రశ్న 22Answer: C. Sea water should not be used for mixing or curing concrete because of the presence of harmful salts. సమాధానం: C.
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Question 23 ప్రశ్న 23Answer: B. Excessive cement content can increase risks such as drying-shrinkage cracking, early thermal cracking and damage associated with alkali-silica reaction, so special consideration is required. సమాధానం: B.
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Question 24 ప్రశ్న 24Answer: A. It should conform to IS 16415, have declared clinker content not less than 45 percent, fly ash content not more than 25 percent, and minimum 28-day compressive strength of 43 MPa. సమాధానం: A.
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Question 25 ప్రశ్న 25Answer: B. 1, 2 and 3 only సమాధానం: B.