Chapter 3 Design of concrete Walls structures.ppt

CHAPTER THREE
DESIGN OF CONCRETE WALLS
Chapter outline
3.1 Introduction
3.2 Design of plain concrete walls
3.3 Design of reinforced concrete walls
3.4 Detailing of reinforced concrete wall

3.1 INTRODUCTION
Definition
Wall- is a Member, usually vertical, used to enclose or separate
spaces
This definition fails to consider the structural actions of walls.
As per EBCS-2 Part 1Section 6.2.1(1)
A structural wall/ reinforced concrete wall is a vertical load bearing
member whose greatest lateral dimension is more than four times
its least lateral dimension, and in which reinforcement is taken
into account.
 Major factors that affect the design of structural walls are:-
1. The structural function of the wall relative to the rest of the
structure
2. The types of loads the wall resists
3. The location and amount of reinforcement

3.1 INTRODUCTION
Terminologies based on EBCS-2 Part 1 Section 6.2.1(3)
1. Short walls:-a wall may be considered short when the ratio of its
effective height to its thickness does not exceed 15.
2. Slender walls:- a wall with effective height to thickness ratio
greater than or equal to 15.
3. Braced walls:- if, at right angles to the plane of the wall, lateral
stability to the structure as a whole is provided by walls or other
suitable bracing designed to resist all lateral forces in that
direction. It shall other wise be considered as un-braced wall.

3.2 DESIGN OF REINFORCED CONCRETE WALL
(1) Walls subjected to combined flexure and axial load shall be
designed by considering vertical strips of the wall acting as columns.
(3) Effective Height: The effective height (Le) of reinforced concrete walls
in the non-sway mode shall be determined from Eq. 6.1.

 If the wall supports an approximately symmetrical arrangement of
slabs, the design axial load capacity per unit length of the wall is
given by
 If the wall supports in plane moment and a uniform axial load, a
unit length of wall can be designed as a column. The column
charts from EBCS 2 part II can be used if symmetrical
reinforcement is provided
Axial load
capacity Cube compressive
strength
Area of concrete
per unit length Area of steel
Characteristics
tensile strength of
steel

Idealization
ρ=3.5%
ρ=3.4%

Shear Resistance of Reinforced Walls (EBCS provision)
(1)Resistance of concrete for horizontal shear forces in the plane of
the wall shall be obtained by
(a) The effective depth (d) shall be taken as 0.8b as shown below
(b) Critical section for shear is at a distance smaller of b/2 or L/2
(c) When the applied shear Vsd is less than Vc the minimum shear
reinforcement is provided

3.3 Detailing provision (EBCS 2 part 1 Section 7.2.5)
Size:-
 The thickness of load bearing walls shall not be less than 1/25 of
the unsupported height or width, whichever is shorter, nor less than
150 mm, but to facilitate concreting 180mm is preferable.
7.2.5.2 Vertical Reinforcement
(1) The area of vertical reinforcement is 0.004Ac<As<0.04Ac and
should be equally divided between the two faces of the wall
(2) The diameter of vertical bars shall not be less than 8 mm.
(3)The spacing of vertical bars shall not exceed twice the wall
thickness or 300 mm

3.3 Detailing provision (EBCS 2 part 1 Section 7.2.5)
7.2.5.3 Horizontal Reinforcement
(1) The area of horizontal reinforcement shall be >=1/2*area of the
vertical reinforcement and should be provided between the vertical
reinforcement and the wall surface on both faces.
(2) The spacing of horizontal bars shall not exceed 300 mm. The
diameter of horizontal bars shall not be less than one quarter of that
of the vertical bars.
7.2.5.4 Transverse Reinforcement
(1) The mats at the two faces of a wall shall be connected to each
other by at least 4 transverse S-ties per m2
when the diameter of the
vertical reinforcement is 16 mm or greater.
(2) If the area of required reinforcement exceeds 0.02Ac, then ties
as required for columns shall be provided i.e should be provided
with links whose diameter should not be less than one-quarter the
diameter of the largest longitudinal bar nor less than 6mm

3.4 plain concrete walls
Reading assignment (for your reference)
Design of plain concrete walls for flexure and axial
loads (EBCS-2 Part 1 Section 6.2.2.1)

Example 1
Wall subjected to pure axial load
• Consider a braced wall of unsupported height 3.2m with thickness
of 220 mm and plan length of 4000 mm which is under pure design
axial load of Nsd =9800kN. Assume that the wall is restrained by
slab at top and bottom and using Concrete grade C- 30 and steel
grade S-400 class I works, design the reinforced concrete wall.
Solution

Example 2
Wall subjected to axial load and in plane bending
Consider a braced wall of unsupported height of 3m with thickness
of 250 mm and plan length of 3500 mm which is under design axial
load Nsd =11900kN, in-plane moment Msd= 4200 kNm and design
shear Vsd=1000KN. Assume that the wall is restrained by slab at the
top and bottom and using Concrete grade C- 30 and steel grade
S-460 class I works, design the reinforced concrete wall.
Solution

Example 2
Step1:- Vertical Reinforcement
 Wall is designed as a column based on steel bars on each side of the
centroidal axis lumped in to two bars each carrying half of the steel
bars as shown above.
 The wall is restrained at top and bottom edges & for walls with
two edges restrained β=1
 The clear height is 3000 mm, so the effective height is

Example 2
Horizontal Reinforcement (Design for shear)

Biaxially Loaded Walls
A wall is said to be biaxially loaded if it resist axial load plus
moment about two axes. One method of computing the strength
of such walls is the equivalent eccentricity method. In this
method, a fraction between 0.4 and 0.8 times the weak axis
moment is added to the strong axis moment. The wall is then
designed for the axial load and the combined biaxial moment
treated as a case of uniaxial bending and compression.

Chapter 3 Design of concrete Walls structures.ppt

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