DRCS - Quick Reference (Unit 1 & 2)

Unit I:

Grade of Concrete:
Grade of Concrete is a measure of its strength and is designated by writing the value of the 28days cube strength in KN/Sqm after an alphabet 'M'

Various Grades:
M15, M20, M25, M30, M35,....

As per IS:256-2000, minimum grade of M20 should be used for design

Grades of Steel:
Fe250 - Mild Steel - will have characterestic strength of 250N/Sqm
Fe415 & Fe500 - High Yield Strength Deformed (HYSD) bars

Most commonly used grade is Fe415

Unit II

Flexural Members or Beams:
1. Singly Reinforced Beams - simply supported / fixed/ cantilever beams where depth is not a constraint.
2. Doubly Reinforced Beams - designed when depth of beam is limited. Usually at the supports of beam.
3. T Beams & L Beams- beams can be designed as T-beam or L-beam by taking the advantage of compressible strength of slab. Usually at the mid span of simply supported/fixed beams

Methods of Design:
1. Working Stress Method
2. Limit State Design Method

In Limit State Design Method:

Based on depth of NA, beams are

1. Balanced beams (if Xu = Xumax)

 MR = C x Z or T x Z

2. Under Reinforced Beams (if Xu< Xumax)

MR = T x Z

3. Over Reinforced Beams (if Xu > Xumax)

MR = C x Z

Where

C = 0.36 fck b Xu
T = 0.87 fy Ast
Z = d-0.42Xu

Xumax Equation: Xumax / 0.0035 = d-xumax / (0.87fy/Es + 0.002)

Fe250 -  0.53d
Fe415 -  0.48d
Fe500 -  0.46d

d = effective depth = Overall depth of beam - Clear Cover - Half of Dia. of Steel bar

Clear Cover = 25mm for beams

Xu:

Find Xu by Equating C = T

Singly Reinforced Beams:

Type of Problems:

1. Find Ultimate Moment of Resistance of a given Beam

Procedure:

1. Write Given Data
2. Find Xu by equating C=T
3. Find Xumax for given grade of Steel
4. Find section of beam (balanced / under reinforced / over reinforced)
5. Find MR based on section
6. Draw Cross Section of beam and show steel reinforcement details

2. Design Beam for a given Bending Moment

Procedure

1. Write Given Data
2. Find Load, Factored Load, and Factored BM
3. Find Xumax for a given grade of steel (assume balanced section)
4. Find 'd' by equating BM =C x Z
5. Find Overall depth of beam
6. Find Steel Reinforcement by equating BM = T x Z
7. Find No. of bars. (Assume 12mm/16mm/20mm/25mm dia based on Ast required)
8. Draw Cross Section of beam and show steel reinforcement details

Check: D is in between 1/10 to 1/15 of the span

Doubly Reinforced Beams:

Type of Problems:

1. Find Ultimate Moment of Resistance of a given Beam

Procedure:

1. Write Given Data
2. Find Mu = Mu limited + Mu2
3. Find Mu Limited = C1 x Z1 or T1 x Z1 (assume balanced section like singly reinforced beam)
4. Find Mu2 = C2 x Z2 or T2 x Z2
5. Find C1 = 0.36fck b Xu
6. Find Z1 = d-0.42Xu
7. Find T1 = 0.87fy Ast
8. Find C2 = fsc Asc - fcc Ac
9. Find T2 = d-d'
10. Find d' = d - top clear cover - half of dia of top steel bar
11. Draw Cross Section of beam and show steel reinforcement details

2. Design Beam for a given Bending Moment

Procedure

1. Write Given Data
2. Find Load, Factored Load, and Factored BM
3. Find Mu limited = C x Z
4. If Mu > Mu limited, then design as Doubly reinforced beam
5. Mu = Mu limited + Mu2
6. Find Mu2 = Mu - Mu limited
7. Find Ast1 by equating Mu limited = T1 x Z1
8. Find Ast2 by equating Mu2 = T1 x Z2
9. Total Ast = Ast1 + Ast2
10. Find Asc by equating Mu2 = T2 x Z2
11. Draw Cross Section of beam and show steel reinforcement details

T - Beams & L - Beams:

Type of Problems:

1. Find Ultimate Moment of Resistance of given T-beam or L-Beam

Procedure:

1. Write Given Data
2. Assume Xu lies in Slab and find Xu by Equating C = T
3. Find C = 0.36 fck bf
4. Find T = 0.87 fy Ast
5. bf for T - beam = L/6 + bw + 6 Df (for multiple spans)
6. bf for L - beam = L/12 + bw + 3 Df  (for multiple spans)
7. Find MR based on Xu lies in 1) xu < Df    2)  3/7 Xu > Df or Df/d < 02  3) 3/7 Xu< Df or Df/d > 0.2
8. Draw Cross Section of beam and show steel reinforcement details

2. Design T - Beam or L - Beam:

Procedure:

1. Write Given Data
2. Find Load, Factored Load, and Factored BM
3. Assume Xu lies in Slab
4. Assume Depth of Beam (1/2 to 1/15 of span)
5. Find Steel Reinforcement by equating BM = T x Z
6. Find No. of bars. (Assume 12mm/16mm/20mm/25mm dia based on Ast required)
7. Draw Cross Section of beam and show steel reinforcement details

Note: bf for Isolated T-beam and L-beam can be found from IS Code

Tips to get Maximum Marks:

1. Given Data
2. Assumptions
3. Design Procedure
4. Write references taken from IS Code book
5. Formula or Equation with terminology Ex. MR = Momnet of Resistance, d = effective depth
6. Draw Cross Sections of structures with Steel Reinforcement Details
7. Units