RC COLUMNS Flashcards
is something which carries load from bean and slab. Defined as the members that carries load mainly in compression.
Column
In ______________, slab transfer loads directly to column and column transfer loads to footing
slab column
columns are _______members of a structural frame intended to support the __________
vertical compression members
load-carrying beams
columns support primarily ________ but usually also some bending moments
axial loads
Structural column failure is of major significance in terms of economic as
well as ___________.
human loss
What should be considered in column design to prevent failure?
Higher reserve strength than beams
Higher reserve strength than beams
Compression failure
What causes a column to fail in compression?
Axial stress exceeds its capacity
At what strain does steel start yielding?
0.002
What is the strain limit for concrete?
0.003
Concrete columns are subjected to
_____________ in addition to the
axial forces due to the _________________ generated due to the
unbalance loads.
bending moments,
eccentric moment
can be identified as
a failure of the design as we consider
the buckling effect in the design.
buckling failure
What design factor is considered for buckling failure?
What design factor is considered for buckling failure?
________loads in a structure are carried by
vertical elements such as columns and shear
walls.
lateral
are generated by winds,
earthquake loads, from retaining structures,
etc.
Lateral loads
The size of the columns is increased in the
direction of __________ to increase the _________
capacity.
shear
In structural elements such as beams and columns, higher stresses
are generated near the __________. Lack of links in these areas causes
structural failures when cyclic loadings are applied.
connections
Columns are torsionally rigid when they are
compared with the beam as they have
___________ around the section and links are
provided at _______________.
reinforcement around the section and links are
provided at closer spacings
If the _________ exceeds the limiting values, columns
could be failed in torsion.
torque
example for this failure is improperly treated
honeycomb in a column could lead
to a failure when the loads are
applied.
Failure due to Construction
Defects
also called compression member or members subjected to axial load and bending
column
columns tend to __________longitudinally and expand laterally due to ________
shortened
expand
poisson effect
lateral restraint using closely spaced ties or spirals greatly ___________ the capacity of column
increased
type of column failure when the cross section large as compared to its height. It fails due to “crushing” of column material
short column
column failure when the cross section small as compared to its height. It fails due to buckling
long/slender column
are principally of two
types, classified according to the manner in which the
longitudinal reinforcing bars are laterally supported.
Reinforced concrete columns
usually of square or rectangular shape, is
one in which the longitudinal reinforcing bars are held
in position by separate lateral ties,
tied column,
usually of circular or
square shape, is one in which the longitudinal
reinforcing bars are arranged in a circle and wrapped
by a continuous closely spaced spiral,
spirally reinforced column,
What is the strength reduction factor for spirally reinforced columns?
0.75
What is the strength reduction factor for tied columns?
0.65
What does the lower strength reduction factor for tied columns indicate?
Lower toughness compared to spirally reinforced columns
is one that uses a
structural steel shape, pipe, or tubing, with or
without additional longitudinal bars.
composite column
are the most commonly used because of lower
construction costs,
tied columns
__________or_____________ are also
used where increased ductility is needed,
spirally bound rectangular or circular columns
in a _________ the strength is governed by the strength of the materials and the geometry of the cross section
short column
assumed acting at the center of the column
axially loaded columns
will cause moment in the column
eccentrically loaded columns
load is applied at any point of the column causing moment at both x and y axes
bi-axially loaded columns
All columns are
subjected to some bending moment, which may be caused by
(1) end restraint arising from the monolithic placement of floor beams
and columns;
(2) accidental eccentricity from imperfect alignment and variable
materials;
(3) asymmetrical floor loads;
(4) eccentric loads such as crane loads in industrial buildings, and
(5) lateral loading such as from wind or induced by an earthquake.
is usually monolithic; thus reinforced concrete frames
and arches are common and advantageous.
Concrete construction
Based on the position of the _______on the cross section, columns can be classified as concentrically or
eccentrically loaded,
load
all columns have to be designed for some _______________________due to such
causes as imperfections in the vertical alignment of formwork.
unforeseen or accidental eccentricity
The _____________ used in the design of columns are the same as for any
other type of member.
load factors
The _______ factor accounts for the difference between the
compressive strength of concrete in a column and that of a concrete
cylinder.
0.85
provide lateral support so that any
tendency to buckling of individual bars would occur only between the tie
supports.
LATERAL TIES
The ____________ of the longitudinal steel, which begins to yield
or to buckle outward, causes additional load on the concrete core.
loss of stiffness
Once the
core has achieved its crushing strength, the column, unless heavily confined,
fails __________.
suddenly
All ___________________ bars for tied columns shall be enclosed by lateral
ties, at least 10 mm in size for longitudinal bars 32 mm or smaller, and
at least 12 mm in size for 36 mm or larger and bundled
longitudinal bars.
nonprestressed
The center-to-center spacing of the ties shall not exceed ____
longitudinal bar diameters, ___tie bar diameters, or the least
dimension of the column.
16
48
The clear spacing between ties
must be at least __of the maximum aggregate size.
43
________________shall be so arranged that every corner and alternate
longitudinal bar shall have lateral support provided by the corner of a
tie having an included angle of not more than ____ and no bar shall be
farther than ___. clear on either side from such a laterally
supported bar.
Rectilinear ties
135°
6 in
provides the column with the ability to absorb considerable
deformation prior to failure.
spiral
spiral does actually contribute strength to the column
through confinement but is indicated that
the spiral was ____times as effective as longitudinal reinforcement in
providing column capacity),
2.4
anchorage of spiral reinforcement shall be provided by ____ extra turns of spiral bar or wire at each end of the spiral unit
1.5
The percentage of total longitudinal reinforcement area Ast in terms of the
gross cross-sectional area Ag must be between___ and ___%
1 and 8%
_______________ may
result from end conditions, inaccuracy of manufacture, or variation in
materials even when the load is theoretically concentric.
Accidental eccentricity
represents the
dividing point between the “compression-controlled” and the “transition
zone” regions of the strength interaction diagram.
balanced strain condition, or compression control limit,
is measured from the plastic
centroid,
eccentricity eb
