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LECTURE5
Introductionto columns
-
‫هللا‬ ‫ذبیح‬ ‫دکتور‬ ‫پوهنمل‬
̎
‫رسولی‬
̎
INTRODUCTION
Columns are members used primarily to support
axial compressive loads and have ratio of height to
the least lateral dimension of 3 or greater.
Types of columns:
Columns may be classified based on the following
different categories.
1. Based on loading, columns may be classified as
flows:
oAxially loaded columns, where loads are assumed
acting at the center of the column section.
CONTINUED…
oEccentrically loaded columns, where loads are
acting at a distance e from the center of the column
section. The distance e could be along x or y axis.
oBiaxially loaded columns, where the load is applied
at any point on the columns section.
2. Based on length, columns may be classified as
follows:
oShort columns, where the columns failure is due to
the crushing of concrete or yielding of steel bars
under full load capacity of the column.
CONTINUED…
oLong columns, where buckling effect and
slenderness ratio must be taken into consideration
in design.
3. Based on the shape of cross section column may
be square, rectangular, round, L-shape, octagonal or
any desired shape with an adequate side width or
dimension.
4. Based on columns ties, columns may be classified
as follows:
oTied columns contain steel ties to confine the main
longitudinal bars in the columns.
CONTINUED…
oSpiral columns containing spirals to hold the main
longitudinal reinforcement and to help increase the
column ductility before failure.
5. Based on frame bracing, columns may be part of a
frame that is braced against sideway or unbraced
against sideway. Bracing may be achieved by using
shear walls or bracing in the building frame.
6. Based materials, columns may be reinforced,
prestressed, steel, composite( containing steel
section such as I-section), or a combination of steel
sections and reinforcing bars.
BEHAVIOR OF AXIALLY LOAD COLUMNS
In actual practice, there are no perfect axially
columns.
ACI CODE LIMITATION
1. For axially as well as eccentrically load column,
the ACI sets the strength reduction factor 0.65 for
tied column and 0.75 for spirally reinforced
column.
2. The minimum longitudinal steel percentage is 1% ,
and the maximum percentage is 8% of the gross
area of the section.
3. At least for bars are required for tied circular and
rectangular members and six bars are needed for
circular members enclosed by spirals.
ACI CODE LIMITATION
4. The min ratio of spiral reinforcement,𝜌𝑠, according to the ACI
code is
5. Ties column must have min diameter of 3/8 in. to enclose
longitudinal bars of no. 10 size or smaller.
6. Center to center spacing of ties shall not exceed the smallest
of 48 ties diam, 16 longitudinal diam or the least dimension.
SPIRAL REINFORCEMENT
The min spiral ratio required by the ACI Code is
meant to provide an additional compressive capacity
to compensate for the spalling of the column shell.
Where Ag is the gross concrete area and Ac is the
core area.
CONTINUED…
SPIRAL REINFORCEMENT
Spiral steel is at least twice as effective as
longitudinal bars:
CONTINUED…
The design relationship of spiral may be obtained as
follows;
DESIGN EQUATIONS
The nominal load strength of an axially loaded
columns are as follow:
DESIGN AXIALLY LOADED COLUMNS
Example 9.1
DESIGN AXIALLY LOADED COLUMNS
Example 9.2
Introduction of columns
Introduction of columns

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Introduction of columns

  • 1. LECTURE5 Introductionto columns - ‫هللا‬ ‫ذبیح‬ ‫دکتور‬ ‫پوهنمل‬ ̎ ‫رسولی‬ ̎
  • 2. INTRODUCTION Columns are members used primarily to support axial compressive loads and have ratio of height to the least lateral dimension of 3 or greater. Types of columns: Columns may be classified based on the following different categories. 1. Based on loading, columns may be classified as flows: oAxially loaded columns, where loads are assumed acting at the center of the column section.
  • 3.
  • 4. CONTINUED… oEccentrically loaded columns, where loads are acting at a distance e from the center of the column section. The distance e could be along x or y axis. oBiaxially loaded columns, where the load is applied at any point on the columns section. 2. Based on length, columns may be classified as follows: oShort columns, where the columns failure is due to the crushing of concrete or yielding of steel bars under full load capacity of the column.
  • 5. CONTINUED… oLong columns, where buckling effect and slenderness ratio must be taken into consideration in design. 3. Based on the shape of cross section column may be square, rectangular, round, L-shape, octagonal or any desired shape with an adequate side width or dimension. 4. Based on columns ties, columns may be classified as follows: oTied columns contain steel ties to confine the main longitudinal bars in the columns.
  • 6. CONTINUED… oSpiral columns containing spirals to hold the main longitudinal reinforcement and to help increase the column ductility before failure. 5. Based on frame bracing, columns may be part of a frame that is braced against sideway or unbraced against sideway. Bracing may be achieved by using shear walls or bracing in the building frame. 6. Based materials, columns may be reinforced, prestressed, steel, composite( containing steel section such as I-section), or a combination of steel sections and reinforcing bars.
  • 7. BEHAVIOR OF AXIALLY LOAD COLUMNS In actual practice, there are no perfect axially columns.
  • 8. ACI CODE LIMITATION 1. For axially as well as eccentrically load column, the ACI sets the strength reduction factor 0.65 for tied column and 0.75 for spirally reinforced column. 2. The minimum longitudinal steel percentage is 1% , and the maximum percentage is 8% of the gross area of the section. 3. At least for bars are required for tied circular and rectangular members and six bars are needed for circular members enclosed by spirals.
  • 9. ACI CODE LIMITATION 4. The min ratio of spiral reinforcement,𝜌𝑠, according to the ACI code is 5. Ties column must have min diameter of 3/8 in. to enclose longitudinal bars of no. 10 size or smaller. 6. Center to center spacing of ties shall not exceed the smallest of 48 ties diam, 16 longitudinal diam or the least dimension.
  • 10. SPIRAL REINFORCEMENT The min spiral ratio required by the ACI Code is meant to provide an additional compressive capacity to compensate for the spalling of the column shell. Where Ag is the gross concrete area and Ac is the core area.
  • 12. SPIRAL REINFORCEMENT Spiral steel is at least twice as effective as longitudinal bars:
  • 13. CONTINUED… The design relationship of spiral may be obtained as follows;
  • 14. DESIGN EQUATIONS The nominal load strength of an axially loaded columns are as follow:
  • 15. DESIGN AXIALLY LOADED COLUMNS Example 9.1
  • 16.
  • 17.
  • 18. DESIGN AXIALLY LOADED COLUMNS Example 9.2
  翻译: