RCC

Question 1

minimum R/F in slab

Answer 1

0. 15 % for mild steel

0. 12% for HYSD

Question 2

deep beam length to depth ratio?

and effective length?

Answer 2

2.0 for SS
2.5 for continious
Leff = minimum of
1.15*Lclear
or C-C distance

Question 3

location of splicing of bars in rcc beam

Answer 3

moment < Mmax/2

SF should also not be max

Question 4

anchorage of bends and hooks equivalent to

Answer 4

4d for 45 degree bend

Question 5

location of critical sections for footing design

flexure, one way shear, punching shear

Answer 5

flexure - on face of column
one way - d from column
punching - d/2 from column

Question 6

minimum r/f in pedestal

Answer 6

0.15%

Question 7

types of post tensioning system

Answer 7

Freyssinet system -conical concrete wedges , 8~24 wires
Magnel Blaton system- flat steel wedges, 2 wires
Gifford-Udall system - split conical wedges, 1 wire
Lee-McCall system - high strength nuts, thick bar 8~22mm

https://theconstructor.org/concrete/prestressing-system-types-anchorages/3300/

Question 8

limiting principle tensile stress in uncracked prestressed concrete

Answer 8

0.24*sqrt(Fck)

Question 9

max tension to be allowed during prestress tensioning

Answer 9

0.80* ultimate tensile strength

Question 10

minimum spacing between group or duct of prestressing cables

Answer 10

post tensioning max of 
- 40 mm
- max size CA +5mm
pre tensioning max of
- 3 dia of cable
- max size CA +5mm

Question 11

brick masonary is devided in 5 catagories

on basis of earthquake resistance feature

Answer 11

1. reinforced
2. Unreinforced
3. without fill
4. with heavy fill
5. abode construction

Question 12

slenderness ratio of brick wall

Answer 12

higher of

• l/t
• h/t

Question 13

load dispersion angle of brick masonry

Answer 13

45 degree for good masonry
60 degree for poor masonry
height of wall > 1.25 * height of triangle

Question 14

effective thickness of a wall after eccentric load

Answer 14

b = 3*[ t/2 -e]

Question 15

standard deviations table in strength of concrete

Answer 15

grade - std
10-15 MPa - 3.5
20-25 MPa - 4
30-50 MPa - 5

Question 16

effective flange thicknesss of T beam if 3/7Xu < Df

Answer 16

Yf = 0.15Xu + 0.65Df

Question 17

max permissible crack width in different exposure condition

Answer 17

mild - 0.3mm
moderate and severe - 0.2mm
v.severe and Extreme- 0.1mm

Question 18

design of footing

Answer 18

• find area by using 1.1 times P
• find exerted factored load from bottom
• find design depth as per one way shear
  Γc = w.B.[Ox-d] / [B.d]
  Γc = 0.28 for p=.15%
• find design depth as per B.M
• check punching shear value
  Γ = 0.25.sqrt(Fck)
• Find Ast = max{Ast.min, Ast.req}
• find spacing and bars
• check development length requirements

Question 19

design helical reinforcement

Answer 19

• find ratio of Vspiral/Vcore
• equate to 0.36fck/fy *[ (Ag/Ac) -1 ]
• check S < [ 75, Dc/6]
• S > [ 25, 3.h]

Question 20

Provisions for curtailment of tension reinforcement in flexural members :

Answer 20

Provisions for curtailment of tension reinforcement in flexural members :
1. For curtailment, reinforcement shall extend beyond the point at which it is no longer required to resist flexure for a distance = max[effective depth(d), 12φ] , except at simple support or end of cantilever.

2. Flexural reinforcement shall not be terminated in a tension zone unless any one of the following conditions is satisfied:
   (i) The shear(V) at the cut-off point does not exceed 2/3 that permitted, including the shear strength of web reinforcement provided.
   (ii) Stirrup area in excess of that required for shear and torsion is provided along each terminated bar over a distance from the cut-off point equal to 3/4th d.
   The excess stirrup area >= 0.4 b.s/fy , where b is the breadth of beam, s is the spacing.
   The resulting spacing shall not exceed d/8 *βb, where βb is the ratio of the area of bars cut-off to the total area of bars at the section, and d is the effective depth.
   (iii) For 36 mm and smaller diameter bars, the continuing bars provide double the area required for flexure at the cut-off point and the shear does not exceed 3/4th that permitted.
3. Positive moment reinforcement
   (i) At least (M/3) positive moment reinforcement in simple members and (M/4) reinforcement in continuous members shall extend along the same face of the member into the support, to a length equal to d/3.
   (ii) When a flexural member is part of the primary lateral load resisting system, the positive reinforcement required to be extended into the support as described in (a) shall be anchored to develop its design stress in tension at the face of the support.
   (iii) At simple supports at points of inflection, positive moment tension reinforcement shall be limited to a diameter such that Ld < M1/V + L
   where,
   L0 = Sum of the anchorage beyond the center of the
   support and the equivalent anchorage value of any
   hook or mechanical anchorage at simple support;
   and at a point of inflection, L0 is limited to the
   effective depth of the members or 12φ, whichever is
   greater;
   Ld < 1.3*M1/V + L when the ends of the reinforcement are confined by a compressive reaction.
4. Negative moment reinforcement
   At 1/3 of the total reinforcement provided for negative moment at the support shall extend beyond the point of inflection for a distance >= effective depth of the member of 12φ or 1/16th of the clear span
   whichever is greater.

Question 21

Provision of ductile detailing of column given by IS code

Answer 21

General Design Considerations : Columns considered for ductile detailing are those subjected to ultimate axial stress greater than 0.1 fck under the effect of seismic forces.
Also the minimum dimension of column section shall not be less than 0.4.
However, in frames having beams of centre to centre span greater than 5.0 m or columns with unsupported length greater than 4.0 m, the smaller dimension of column section shall >= 300 mm.

Longitudinal Steel in Column : Lap splices are not provided near the ends of column where spalling of concrete shell is likely to occur.
It is provided in the central half of column and designed as tension splices.
Hoops are provided over the entire length of a splice at spacing not more than 150 mm. Not more than fifty percent of the bars shall be spliced at any section.

Special Confining Reinforcement : It is provided in the form of hoops at small intervals to provide greater ductility and allowing the section to undergo large deformation in certain length of beam. It is provided over a length L0 at each joint, where flexural yielding may occur under seismic forces.
The length L0 >= max[larger lateral dimension of column, 1/6 of the clear height, 450 mm].
The spacing of the hoops used as special confining reinforcement <= [1/4 of minimum dimension(B), 100mm ] but >=75 mm.

Question 22

table 19 of IS 456 Γc

Answer 22

p% – M20 – M25

0. 15 – 0.28 – 0.29
1. 25– 0.36 – 0.37
2. 50 – 0.48 – 0.49
3. 75 – 0.56 – 0.57
4. 00 – 0.62 – 0.64
5. 25 – 0.67 – 0.70
6. 50 – 0.72 – 0.74
7. 75 – 0.75 – 0.78

Question 23

Design bond stress in limit state method for plain bars table

Answer 23

26.2.1.1 Design bond stress in limit state method for plain bars in tension shall be as below:
Grade -M20 M25 M30 M35 M40
Tau.bd 1.2 1.4 1.5 1.7 1.9