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Concrete Columns 1Lecture 26 Architectural Structures

ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN

lecture

twenty six

concrete construction:

columns & frames

Brenton Hardee

Concrete Columns 2Lecture 26

Concrete in Compression

• crushing
• vertical cracking
  • tension
• diagonal cracking
  • shear
• (^) f (^) c  http://www.bam.de

Concrete Columns 4 Lecture 26

Slenderness

• effective length in monolithic with

respect to stiffness of joint:  & k

• not slender when

r

kLu

Concrete Columns 5 Lecture 26

Effective Length (revisited)

• relative rotation

b

c

l

EI

l

EI



  

Concrete Columns 7 Lecture 26

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

Po  0. 85 fc ( Ag  Ast )  fy Ast

Concrete Columns 8Lecture 26

Columns with Bending

• eccentric loads can cause moments
• moments can change shape and induce more deflection

(P- )

P



Concrete Columns 10Lecture 26

Columns with Bending

• need to consider combined stresses
• linear strain
• steel stress at or below fy
• plot interaction diagram

Concrete Columns 11Lecture 26

Design Methods

• calculation intensive
  • handbook charts
  • computer programs