87-492-S15+-Chapter+2-Design+of+RC+Walls

06-87- 492: Advanced Topics in Structural Engineering – Summer 2015

Column under Bi-Axial Bending

Chapter 2: Design of RC Columns and Walls

v

Concrete Design HandbookCement Association of Canada

Design of RC Columns



Example #2

The column has a cross section of 350 mm x 600 mm. Determine whether the given crosssection is adequate and confirms to CSA/A23.3-04 provisions and calculate the requiredreinforcement.

Consider the interior column shown with a clear height of 5500 mm supporting a flatslab floors. This column is part of frame structure that is fully supported against lateraldrift. The column is subjected to the given Factored axial load “including 1000 kNfactored dead load”, un-factored moments and factored shear forces.

Consider:G40 steel reinforcing bars, 30 MPa normal-density concrete, #10M ties and 2 hoursfire rating



2. Reinforced Concrete Walls



v

v

v

v

RC Walls are vertical members used to enclose or separate spaces,

Structural RC walls are designed to resist combinations of shear, moment and axialforces,

According to CSA/A23.3, Clause 2.2, Wall is a vertical element in which:

Walls can be design to resist the following loads:

Where:lw = Horizontal length of the wallhw = vertical length “height” of the walltw = Thickness of the wall.

1- Gravity loads,2- Lateral in-plane loads3- Lateral out-plane loads

ww

ww

hl

tl

2. Reinforced Concrete Walls

3/

6

≥

≥


Types of RC Walls:


1- Bearing Wall:

v

1- factored in-plane vertical loads that is ,2- weak axis moments3- the shear force necessary to equilibrate that moment.

,`10.0

1- factored in-plane vertical loads that is ,2- weak axis moments3- the shear force necessary to equilibrate that moment.

,`10.0

“about a horizontal axis in the plane of the wall”,wgc Af

“about a horizontal axis in the plane of the wall”,wgc Af

a wall that supports:

≥

≤

1.1- Non-bearing Wall:

Reinforced Concrete Walls


Types of RC Walls:


2- Shear Wall:

v

1- vertical load,2- moments about horizontal axes perpendicular to the plane of the wall “strong axis of wall”,3- shear force acting parallel to the plane of the wall,4- weak axis bending also can be present.

“when above the section of maximum moment is greater than ”

when above the section of maximum moment is less than ”

a wall or an assembly of inter-connected walls which considered part of the lateral loadresisting system of a structure. Shear walls support:

a shear wall that resist in-plane lateral loads by flexural action

2.1 Flexural-shear Wall:

hw 2lw

2.2 Squat shear wallhw 2lw

Reinforced Concrete Walls


Design of RC Bearing Walls:


CSA/A23.3-04 Empirical Method (C1.14.2.)

***** When these conditions are not met, the wall should be designed as a column*****

v

The empirical can be used when all the following conditions have been met:

1- The wall has a solid rectangular cross section that is constant along the wall height,2- The principal moments act about the weak axis,3- The eccentricity of all the axial loads is located within the middle third of the thickness,4- The wall is supported against lateral displacement along at least the bottom and top edges.

23 1

` 132

2

4.1: when walls and other bracing elements are arranged in two directions to provide lateralstability to the structure as a whole and;

4.2: Connections between the wall and its lateral supports are designed to resist a horizontalforce not less than 2% of the total factored load at the level of lateral support.

Pr c fc Ag

khu

t

Design of RC Bearing Walls


Design of RC Bearing Walls:


CSA/A23.3-04 Empirical Method (C1.14.2.)

v

Pr c fc Ag

khu

t

t*lb

=

** for concentrated loads, have to check thatthe contact stress is less than the bearingstrength

taha w

B r c fc Ab

or s++

23 1

` 132

20.8 “for full restraint against rotation topand/or bottom, or 1.0 otherwise.

= the vertical unsupported length of the wallbetween the horizontal supports

= wall thickness= the gross concrete cross-section area of

the wall=

1.0 m for uniform distributed load

= for concentrated loads, the smallest of. 18,

0.85 `

k =

hu

tAg

lb

Br



RC Walls Minimum Requirements:


v

ü

ü

ü

ü

ü

ü

Walls should be reinforced with distributed vertical and horizontal reinforcement bars arranged inone or two layers,

At least one reinforcement layer “curtain or mesh” is mandatory for walls of thickness less than210 mm “usually basement and retaining walls”. For wall thickness greater than 210 mm, twocurtains of reinforcement where each curtain should be placed not greater than t/3 from the wallsurface.

Minimum required area of distributed vertical reinforcement is

Minimum required area of distributed horizontal reinforcement is

Maximum nominal bar diameter for the distributed reinforcement is

Maximum allowable bar spacing for distributed vertical and horizontal reinforcement

,min. 0.0015

,min. 0.002

,max /10

max 3

max 500

Av Ag

Ah Ag

db t

S t

s m



RC Walls Minimum Requirements:


vü

ü

ü

ü

ü

In addition to the distributed reinforcement, a minimum of 2-15M (1 bar/layer) bars concentratedvertical reinforcement should be used at each wall end,

In addition to the distributed horizontal and vertical reinforcement, a minimum of 2-15M (1bar/layer)should be provided around all openings in wall “doors or windows” to resist diagonalcracks

Walls may contain extra concentrated vertical reinforcement “zone reinforcement” and extrahorizontal reinforcement to resist seismic forces,

Minimum concrete cover is 20 mm for interior walls, 40 mm for exterior walls exposed toweather and 75 mm for walls cast against and permanently exposed to earth

Minimum wall thickness

150

25/

25/

min,

min,

min,

100

30/

30/

min,

min,

min,

“for exterior face”

where l and h are the unsupportedlength and height

mmt

ht

lt

w

w

w

mmt

ht

lt

w

w

w

≥

≥

≥

≥

≥

≥


for Non-load Bearing walls


Typical minimum RC Walls Requirements:


v

Brzev and Pao




Example 3



Design of RC Bearing Walls Example


Shear Walls:


ü

v

The term shear wall is used to describe a wall that resists lateral wind or earthquake loadsacting parallel to the plane of the wall in addition to the gravity loads from the floors and roofadjacent to the wall.

Bearing/Shear walls Core wallsShear walls/Frame system

Brzev and Pao

RC Shear Walls



Loads on Shear walls

i. Vertical axial force due to gravity loads;ii. Moment about the major axis, horizontal axis perpendicular to the plane of the wall,iii. And shear forces due to lateral loads acting in the plane of the wall

RC Shear Walls


Shear Walls:


Flexural Shear Wall:

Squat Shear Wall:

ü

v

ü

hw/lw>2

hw/lw<2,

,

Tall, slender walls mainly influenced by the flexural moment.Behaves like a vertical cantilever beam.

Short and sturdy walls found in low tomedium-rise buildings.The behaviour is mainly shear-controlled.

Macgregor and Weight

RC Shear Walls



Design of Shear Wall having Uniform Distributed Verticals:ü

Mr s fyAvtlw

Pf

s fyAvt

clw

= Distributed vertical reinforcement

c

lw

TC

s fy Avt

c fc lwt

Pf

c fc lwt

cf cf≥−= ≥−=

0.5 1 1

2 1 1` `

67.00025.097.0 `1 67.00015.085.0 `

1b a

Avt

1. Moment Resistance

Design of RC Shear Walls


V


Design of Shear Wall having Uniform Distributed Verticals:

Check the shear capacity in a manner similar to beams. Horizontal reinforcement inwalls acts like stirrups in beams. General and simplified methods can be used.

cot

2. Shear Resistance

bw = tw & dv = 0.8 lw

r > Vf

VssAhdv

s= Minimum horizontal reinforcement of 0.02 Agw.

Design of RC Shear Walls

ü



The exterior RC wall shown is part of a five-storyreinforced concrete building. The wall resists theshown loads at each floor level.

It is required to design the wallaccording to CSA/A23.3-04 provisions

Example 4

Use: 30 MPa concrete and G/40 reinforcing bars

87-492-S15+-Chapter+2-Design+of+RC+Walls

Documents

design of rc columns

structural rc walls

flexuralshear wall

walls2 shear wall

wall strong axis of

design of rc bearing

types of rc walls

advanced topics