61. For limit state of collapse, the partial safety factors recommended by IS 456: 2000 for estimating the design strength of concrete and reinforcing steel are respectively

1. 1. 1.15 and 1.5

   
   
   

   2. 1.0 and 1.0

   
   
   

   3. 1.5 and 1.15

   
   
   

   4. 1.5 and 1.0

   
   
   

---

1. View Hint View Answer Discuss in Forum

   1.5 and 1.15

   Correct Option: C

   1.5 and 1.15

---

62. In a random sampling procedure for cube strength of concrete, on sample consists of X number of specimens. These specimens are tested at 28 days and average strength of these X specimens is considered as test result of the sample, provided the individual variation in the strength of specimens is not more than ± Y percent of the average strenght. the value of X and Y as per IS: 456-2000 are

1. 1. 4 and 10 respectively

   
   
   

   2. 3 and 10 respectively

   
   
   

   3. 4 and 15 respectively

   
   
   

   4. 3 and 15 respectively

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Number of specimen = 3
   Individual variation in strength = 15%. 42.

   Correct Option: D

   Number of specimen = 3
   Individual variation in strength = 15%. 42.

---

---

63. A rectangular column section of 250 mm × 400 mm is reinforced with five steel bars of grade Fe 500, each of 20 mm diameter. Concrete mix is M 30. Axial load on the column section with minimum eccentricity as per IS: 456-2000 using limit state method can be applied up to

1. 1. 1707.37

   
   
   

   2. 1805.30

   
   
   

   3. 1806.40

   
   
   

   4. 1903.7

   
   
   

---

1. View Hint View Answer Discuss in Forum

   P_u + 0.4 × f_ck × A_c + 0.67 f_y × A_SC
   

   Correct Option: A

   P_u + 0.4 × f_ck × A_c + 0.67 f_y × A_SC
   

---

64. If the characterisitc strength of concrete f_ck is defined as the strength below which not more than 50% of the test results are expected to fall the expression for f_ck in terms of mean strength f_m and standard deviation S would be

1. 1. f_m – 0.1645S

   
   
   

   2. f_m – 1.645S

   
   
   

   3. f_m

   
   
   

   4. f_m + 1.645S

   
   
   

---

1. View Hint View Answer Discuss in Forum

   f_m + 1.645S

   Correct Option: D

   f_m + 1.645S

---

---

65. The percentage loss of prestress due to anchorage slip of 3 mm in a concrete beam of length 30 m which is post-tensioned by a tendon with an initial stress of 1200 N/mm² and modulus of elasticity equal to 2.1 × 10⁵ N/mm² is

1. 1. 0.0175

   
   
   

   2. 0.175

   
   
   

   3. 1.75

   
   
   

   4. 17.5

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Strain =	S	=	3	1 × 10-4
   	l		30 × 103

   
   Strain loss = strain × Ec
   = 1 × 10^-4 × 2.1 × 10⁵ =
   21 N/mm²
   

   % loss =	21	× 100= 1.75%
   	1200

   Correct Option: C

   Strain =	S	=	3	1 × 10-4
   	l		30 × 103

   
   Strain loss = strain × Ec
   = 1 × 10^-4 × 2.1 × 10⁵ =
   21 N/mm²
   

   % loss =	21	× 100= 1.75%
   	1200

---