AS1- COLUMNS

COLUMN

A member of a structural system designed to carry compressive loads.

Axial Loads (compressive), Bending Moments, lateral forces (Earthquake and Wind)

In reality columns are not limited to that of carrying compressive loads. Actual conditions subject columns to both ______________ and ____________ brought about by ____________________

Bi-Axial Bending

Bending Moments applied to the column normally ACT in BOTH AXES of the cross section. Some cases simultaneously.

PEDESTALS, SHORT COLUMN, LONG SLENDER COLUMN

Concrete columns can be roughly divided into

height < 3(b), b= width of column

FOR PEDESTALS OR SHORT COMPRESSION COLUMNS/ BLOCKS WHAT IS ITS HEIGHT

short

A column is said to be _________if its height is such that lateral buckling need not be considered.

Ht/r < 45

for short columns what is the height

material failure

what causes short columns to fail

Ht/r > 45

for short columns what is the height

increases, decreases, slenderness effects

It is recognized that as the height of the column ____________, the load carrying capacity of the section ____________ because of the ___________________

significantly less

true or false: The capacity of long columns is the same of a short column given the same cross section

P-Δ Effect

When a column is subject to primary moments, the axis of the member will deflect laterally, with the result of that additional moments equal to the column load times the lateral deflection will be applied to the column.

secondary moments or P-Δ Moments

When a column is subject to primary moments, the axis of the member will deflect laterally, with the result of that additional moments equal to the column load times the lateral deflection will be applied to the column. These latter moments are called

tied, spiral, composite

Reinforced concrete columns are referred depending on the method used for laterally bracing or holding the bars in place:

closed ties

A column is said to be tied if it has a series of

ductility

Properly detailed ties confine the concrete core, providing increased

shear reinforcement

Tie serve as

spiral column

Uses a continuous helical spiral that is wrapped around the vertical bars

composite column

RC Columns that are reinforced by steel sections instead of reinforcing bars

buckle

what happens to unsupported bars

the creep

the larger the percentage of dead loads and the longer they are applied, the greater __________ in the concrete

concrete creep

Deformation of structure under sustained load.

direction the force is being applied

where does deformation usually occur in concrete creep

equal

Because the steel and concrete are bonded together, the strains in the concrete and steel are

longitudinal strains εdevelop uniformly across the section

When a symmetrical column is subjected to axial load P,

Pno reaches a maximum

Failure occurs when

little effect

The proportions of live and dead loads, the length of loading, and other such factors have __________ on the ultimate strength

Interaction diagrams

are useful for studying the strengths of columns with varying proportions of loads and moments.

Any combination of loading that falls inside the curve is satisfactory, whereas any combination falling outside the curve represents failure.

crushing column

Failure is due to crushing of concrete or yielding of rebars (short column)

buckling failure

The capacity is reduced by slenderness effects (long column)

false, sudden

true or false: in short columns, failure is gradual and slow

buckling

resulting from structural instability due to compressive action on the member

shear failure

commonly manifests as diagonal cracks along the height of the column

plastic hinging

caused by the combined action of the Axial force and a large amount of bending moment.

false, it affects

true or false: Proper Column placement does not affect the cost of the structure

sporadic pattern

Avoid placing columns in a

true

true or false: Placing columns in a grid-like pattern will not only economize your structure it will also improve its structural response to external loads

40mm

concrete cover of columns

50mm

Column widths and depths are generally varied in increments of

300mm

the shortest cross sectional dimension measured on a straight line passing through the geometric centroid shall be at least

0.4

the ratio of the shortest cross sectional dimension to the perpendicular dimension shall be at least

3

minimum number of vertical bars for triangular ties

4

minimum number of vertical bars for rectangular or circular ties

6

minimum number of vertical bars for column enclosed by spirals or for columns of special moment frames enclosed by circular hoops

less than 1%

The percentage of longitudinal reinforcement (vertical bars) may not be_____________of the gross cross sectional area of the column.

greater than 8%

The maximum percentage of steel may not be ____________ of the gross sectional area of the column.

limited to 6%

for ductility requirements in regions of high seismic activity, this value is ______________of the gross cross sectional area.

4%

Usually the percentage of reinforcement should not exceed ________ when the bars are to be lap spliced

1-2%

the most economical tied column section generally involves percentage steel of

bundled

If the percentage of steel is very high, the bars may be

40mm

minimum clear spacing of longitudinal reinforcements

(4/3) dagg

minimum clear spacing of ties

10mm

what is the diameter of a tie bar for 32mm diameter or smaller longitudinal bars

12mm

what is the diameter of a tie bar for 36mm diameter or larger longitudinal bars

150mm

What is the maximum distance an unsupported bar can be from a supported bar?

135deg

What is the maximum allowed angle for the corner of a tie?

150mm

ends of circular ties should overlap by at least

10mm

spirals should not be less than

25mm , 75mm

Spiral spacing shall not be less than _________on center or be greater than_________.o.c.

48db or 300mm

Should splices be necessary for spirals, they are to be provided by welding or by lapping _____________ whichever is greater.

0.65

rho used for tied columns

0.75

rho used for spiral columns

radius of gyration

the radius of a cylindrical surface coaxial with the axis of rotation of a body such that if the entire mass of the body were concentrated in that surface the moment of inertia and energy of rotation would be unchanged

concrete and steel part

For Concrete Columns, one must consider the effect of both materials acting against the load.