CE 14
Principles of
Reinforced/Prestressed Concrete
(Computation)
Design of Column
FELISA E GOMBA
Professor
What is a column?
Column is a vertical compression member whose
unsupported length Lu shall not exceed sixty times of b
(least lateral dimension), if restrained at the two ends.
Further, its unsupported length of a cantilever column shall
not exceed 100b2/D, where D is the larger lateral
dimension which is also restricted up to four times of b.
What is a column?
1) Lu shall be taken as the clear distance between
floor slabs, beams or other members capable of
providing lateral supports in the direction being
considered.
2. Lu shall be measured where column capitals or
haunches are present to the lower extremity of
the capital or haunch in the plane considered.
What is a column?
Classification of columns
1. Based on Column Ties(Reinforcement )
2. Based on Length
3. Based on Loading
4. Based on Frame Bracing
Based on Column Ties(Reinforcement )
Based on Column Ties(Reinforcement )
Based on Length
Based on Length
Based on Length
Based on Length
Based on Length
Based on Length
Based on Loading
Based on Loading
Based on Loading
Analysis
Analysis
Based on Frame Bracing
1. Columns in a frame that is braced against
sidesway. The effects of the slenderness may
be neglected when
Klu/r < 34 – 12M1/M2 < 40
where M1/M2 is positive if the column is
bent in a single curvature and negative if the
member is bent double curvature.
Based on Frame Bracing
2. Columns in a frame that is not braced against sidesway.
The effect of the slenderness may be neglected when
Klu/r < 22
a) r=0.30 times the overall dimension in the direction
stability for rectangular compression members(tied
column)
b) r = 0.25 times the diameter of circular compression
members(spiral column)
Sample of column structures
Analysis and Design of short column subject to axial and bending
Column Load transfer from beams and slabs
1) Tributary Area Method
Load on column = area x floor load
Analysis and Design of short column subject to axial and bending
Column Load transfer from beams and slabs
2) Beams reaction method
Analysis and Design of short column subject to axial and bending
Analysis and Design of short column subject to axial and bending
Analysis and Design of short column subject to axial and bending
Analysis and Design of short column subject to axial and bending
Analysis and Design of short column subject to axial and bending
Analysis and Design of short column subject to axial and bending
Analysis and Design of short column subject to axial and bending
e = eccentricity of a column
load is the distance from the
load to the plastic centroid.
PLASTIC CENTROID
represents the locations
of the resultant force by
the steel and concrete.
Analysis and Design of short column subject to axial and bending
Location of PLASTIC CENTROID
All concrete is assumed to be stressed in compression 0.85f’c and all
steel to fy is compression.
For symmetrical sections
For non-symmetrical sections –
– the plastic centroid coincides
with centroid of the column
cross-section
it can be located by taking
moments.
Assignment :
1. Read Chapters 9 and 10 on Column of the
McCormac and Brown (2014) Reinforced
Concrete Design
2. Read Sections on Column NSCP 2015