The document discusses columns, which are structural members that primarily carry axial compressive loads. It defines short columns that do not require consideration of lateral buckling and slender columns that do. It describes uniaxially loaded columns that experience either axial load alone or combined axial and bending load about one axis. It provides examples of column cross-sections and outlines the process for designing uniaxial reinforced concrete columns according to ACI code provisions. This includes calculating load and moment capacities, determining reinforcement ratios from design charts, and checking capacities against demands with safety factors.

2. DEPARTMENT OF CIVIL ENGINEERING
IKHTIAR KHAN
10.01.03.106

4. WHAT IS COLUMN?
 COLUMNS ARE DEFINED AS MEMBERS THAT
CARRY LOADS CHIEFLY IN COMPRESSION.
 SIMULTANEOUSLY BENDING MOMENTS ARE
ALWAYS PRESENT AS WELL ABOUT ONE OR BOTH
AXES OF THE CROSS SECTION.

5. COLUMN LOAD TRANSFER FROM
BEAMS

6. TYPES OF COLUMN
SHORT COLUMN,
FOR WHICH LATERAL
BUCKLING NEED NOT
BE CONSIDERED.
SLENDER COLUMN, FOR
WHICH THE STRENGTH
MAY BE SIGNIFICANTLY
REDUCED BY LATERAL
DEFLECTION, SO
LATERAL BUCKLING
NEED TO BE
CONSIDERED.
USUALLY MOST COLUMNS IN PRESENT DAY
PRACTICE ARE CONSIDERED AS SHORT
COLUMN.

7. WHAT IS UNIAXIALLY LOADED
COLUMN?
WHEN A COLUMN IS SUBJECTED
TO EITHER COMBINED AXIAL
COMPRESSION (P) AND
MOMENT (M) AS IN FIG-1 OR
ONLY AXIAL LOAD (P) APPLIED
AT AN ECENTRICITY e=(M/P) AS
IN FIG-2 SO THAT THE COLUMN
IS TRYING TO BEND ABOUT
ONLY ONE AXES OF THE
COLUMN CROSS SECTION IS
KNOWN AS UNIAXIALLY
LOADED COLUMN.

8. CROSS SECTION OF UNIAXIALLY
LOADED COLUMN

9. IN THIS CASE,COLUMNS
ARE SUBJECT TO
TENSION OVER A PART
OF THE SECTION AND
IF OVERLOADED MAY
FAIL DUE TO TENSILE
YIELDING OF THE
STEEL ON THE SIDE
FARTHEST FROM THE
LOAD.

10. PROCESS TO BE FOLLOWED FOR
UNIAXIAL COLUMN DESIGN
 SELECT TRIAL CROSS
SECTION DEIMENSION
b AND h.
 CALCULATE THE RATIO
γ BASED ON REQUIRED
COVER DISTANCE TO
THE BAR CENTROIDS
AND SELECT THE
COLUMN DESIGN
CHART.

11.  CALCULATE COLUMN PARAMETERS
Kn= Pu/Øf´Ag
Rn=Mu/Øf´Agh
WHERE Ag=bh
Ø = Ast/Ag
USING THOSE VALUES AND FROM THE
GRAPH REQUIRED REINFORCEMENT RATIO,
Pg CAN BE FOUND.
CALCULATE THE TOTAL STEEL AREA,
Ast=Pgbh.

12. ACI CODE PROVISION FOR
COLUMN DESIGN
 TWO BASIC SAFETY CRITERIAS ARE
Pu ≤ ØPn
Mu ≤ ØMn
WHERE,
Ø= 0.65 (FOR TIED COLUMNS)
Ø= 0.70 (FOR SPIRALLY REINFORCED
COLUMNS)

13. TYPICAL EXAMPLE
 PROBLEM: IN A THREE-STOREY STRUCTURE, AN
EXTERIOR COLUMN IS TO BE DESIGNED FOR A SEVICE
DEAD LOAD OF 222 kips, MAXIMUM LIVE LOAD OF 333
kips, DEAD LOAD MOMENT OF 162 ft-kips AND LIVE
LOAD MOMENT OF 232 ft-kips. ARCHITECTURAL
CONSIDERATION REQUIRE THAT A RECTANGULAR
COLUMN BE USED, WITH DIMENSIONS b=20" AND
h=25". FIND THE REQUIREED COLUMN
REINFORCEMENT FOR THE CONDITION THAT FULL
LIVE LOAD ACTS.
 GIVEN THAT, f´c= 4000 psi AND fy= 60,000 psi.

14. SOLUTION:
ACCORDING TO ACI CODE PROVISIONS,
ULTIMATE LOAD, Pu=1.2×222+1.6×333
=799 kips
ULTIMATE MOMENT, Mu=1.2×162+1.6×232
=566 kip-ft

15. ASSUMING BAR COVER 2.5“ WE
GET,
γ = (25-5)/25
= 0.8
Kn = Pu/Øf´Ag
= 799/(0.65×4×500)
= 0615
Rn =Mu/Øf´Agh
= 566×12/0.65×4×500×25
= 0.209

16. Pg= 0.034
Kn=
0.615
Rn=0.209

17. THUS, REQUIRED REINFORCEMENT IS
Ast=Pgbh
= 0.034×20×25
= 17 in²
TEN NO.12 BAR WILL BE USED AS IN FOLLOWING
FIGURE.