WELCOME TO MY PRESENTATION

AHSANULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY

DEPARTMENT OF CIVIL ENGINEERING

IKHTIAR KHAN10.01.03.106

UNIAXIAL COLUMN DESIGN

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 BOTHAXES OF THE CROSS SECTION.

COLUMN LOAD TRANSFER FROM BEAMS

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.

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.

CROSS SECTION OF UNIAXIALLY LOADED COLUMN

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.

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.

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.

ACI CODE PROVISION FOR COLUMN DESIGN

TWO BASIC SAFETY CRITERIAS AREPu ≤ ØPn Mu ≤ ØMn

WHERE, Ø= 0.65 (FOR TIED COLUMNS) Ø= 0.70 (FOR SPIRALLY

REINFORCED COLUMNS)

TYPICAL EXAMPLEPROBLEM: 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.

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

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

Pg= 0.034

Kn= 0.615

Rn=0.209

THUS, REQUIRED REINFORCEMENT ISAst=Pgbh = 0.034×20×25 = 17 in²

TEN NO.12 BAR WILL BE USED AS IN FOLLOWING FIGURE.

THANK YOU FOR YOUR KIND ATTENTION