S2018abn
http://www.building.co.uk
Concrete Columns 1
Lecture 25
Elements of Architectural Structures
ARCH 614
ELEMENTS OF ARCHITECTURAL STRUCTURES:
FORM, BEHAVIOR, AND DESIGN
ARCH 614
DR. ANNE NICHOLS
SPRING 2018
lecture
twenty five
concrete construction:columns & frames
S2018abnConcrete Columns 2
Lecture 25
Elements of Architectural Structures
ARCH 614
Concrete in Compression
• crushing
• vertical cracking
– tension
• diagonal cracking
– shear
•cf
http://www.bam.de
S2018abnConcrete Columns 3
Lecture 25
Elements of Architectural Structures
ARCH 614
Columns Reinforcement
• columns require
– ties or spiral reinforcement
to “confine” concrete
(#3 bars minimum)
– minimum amount of longitudinal steel
(4 bars minimum)
S2018abnConcrete Columns 4
Lecture 25
Elements of Architectural Structures
ARCH 614
Slenderness
• effective length in monolithic with
respect to stiffness of joint: & k
• not slender when
22r
kLu
*not braced
S2018abnConcrete Columns 5
Lecture 25
Elements of Architectural Structures
ARCH 614
Effective Length (revisited)
• relative rotation
b
c
lEI
lEI
S2018abnConcrete Columns 6
Lecture 25
Elements of Architectural Structures
ARCH 614
Column Behavior
S2018abnConcrete Columns 7
Lecture 25
Elements of Architectural Structures
ARCH 614
Column Design
• c = 0.65 for ties, c = 0.75 for spirals
• Po – no bending
• Pu cPn
– ties: Pn = 0.8Po
– spiral: Pn = 0.85Po
• nominal axial capacity:
– presumes steel yields
– concrete at ultimate stress
stystgco AfAAfP )(85.0
S2018abnConcrete Columns 8
Lecture 25
Elements of Architectural Structures
ARCH 614
Columns with Bending
• eccentric loads can cause moments
• moments can change shape and induce
more deflection
(P-)P
S2018abnConcrete Columns 9
Lecture 25
Elements of Architectural Structures
ARCH 614
Columns with Bending
• for ultimate strength behavior, ultimate
strains can’t be exceeded
– concrete 0.003
– steel
• P reduces
with M
s
y
E
f
S2018abnConcrete Columns 10
Lecture 25
Elements of Architectural Structures
ARCH 614
Columns with Bending
• need to consider
combined
stresses
• linear strain
• steel stress at or
below fy
• plot interaction
diagram
S2018abnConcrete Columns 11
Lecture 25
Elements of Architectural Structures
ARCH 614
Design Methods
• calculation intensive
– handbook charts
– computer programs
S2018abnConcrete Columns 12
Lecture 25
Elements of Architectural Structures
ARCH 614
Design Considerations
• bending at both ends
– P- maximum
• biaxial bending
• walls
– unit wide columns
– “deep” beam shear
• detailing
– shorter development lengths
– dowels to footings
