b/ h/ d

earthwhistleUrban and Civil

Nov 25, 2013 (3 years and 6 months ago)

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IMPORTANCE OF
DETAILING OF TRANSVERSE REINFORCEMENT FOR
BEAMS,COLUMNS AND WALLS


The detailing of reinforcement is as important as the analysis and design of any
RCC members. Specially it is true in the design of structures

against the
SEISMIC forces. The most and very important aspect of detailing is well
documented in the text book on “SEISMIC DESIGN OF REINFORCED CONCRETE
AND MASONRY BUILDINGS by T.Paulay and M.J.N.Priestley. The text extraction
is given below for the str
uctural engineers who need to know more about the
importance of the above issue.


Page: 157:

The spacing of the transverse reinforcement is as important as the quantity to be
provided. For this reason, recommended maximum spacings of sets of transverse
tie
s along a member, required for four specific purposes, are summarized here.

1.

To provide shear resistance: Except as set out in section 3.3.2(a)(vii):


In beams s≤0.5d or 600mm(24”)


In columns s
≤0.75h or 600mm(24”)


In walls s≤2.5
b
w

or 450mm(18”)

2.

To stabilize compression bars in plastic Regions: As described in section
4.5.4 for beams, but also applicable to bars with diameters db in columns
and walls[ Section
5.4(e)]:


s≤6.0
d
b,

or s≤d/4, s≤ 150mm(6”)

3.

To provide confinement of compressed concrete in potential plastic
regions: As described in sections 3.6.1(a),4.6.1(e)M AND 5.4.3(E).





s
h


b
c
/
3

, s
h



h
c
/
3

, s
h

≤6

d
b,
s
h
≤180mm(7”).

4.

At Lapped splice : As described in Section 3.6.29B),4.6.10 and 4.6.11(f)
for the end regions of columns where plastic hinges are not expected to
occur:


s≤8.0
d
b,
s
≤200mm(8”).


Page:208:

The diameter of stirrup ties should not be less than 6mm(0.25”) and the area of
one leg of stirrup tie in the direction of potential buckling of longitudinal bars
should not be less than


A
te
=∑

A
b

f
y
s



_____________(Mpa)


16 f
yt
100

For design purpose it is convenient to rearrange the above equation in the form
:
A
te
/
s
= ∑

A
b

f
y
/
1600 f
yt
(mm^2/mm)

Where

A
b
is the sum of the areas of the longitudinal bars reliant on
the tie, including the tributary area of any bars exempted from being
tied in accordance


with the proceding section.




A
te

is the area of the
stirrup tie in mm^2.




f
y

is the yield strength of longitudinal bars.


f
yt


is the yield strength of tie bars



Page 128:

Because of the re
v
ersal of shear forces

in members affected by earthquakes, the
placing of stirrups a
t an angle other than 90
Ө

to the axis of such members is
generally impractical.

The choice of the angle 45

Ө

for the plane of the diagonal tension failure in the
region of potential plastic is a compromise.

Please note that in IS 13920 it is not
recommended to use single bent up bars.


Minimum shear reinforcement:

Current codes (NewZeland) require the provision of minimum amount of shear
reinforcement in the range of 0.0015 ≤
A
v
/
b
w
s
C0.0020 in members affected by
earthquake forces.

ii) Spacing of
stirrups: To ensure that potential diagonal tension failure planes
are crossed by sufficient sets of stirrups, spacing limitations such as set out
below, have been widely used. The spacing s should not exceed:

1.

In beams:

In general :0.5d or 600mm(24”)

When
(
v
i
-
v
c
) > 0.07
f

c
: 0.25d or 300mm(12”).

2.

In columns:

When P
u
/A
g
≤0.12

f

c
; as in beams

When P
u
/A
g

> 0.12

f

c
: 0.75’ or 800mm(24”).

3.

In walls,

2.5 times the wall thickness or 450mm(18”).

Spacing limitations to satisfy requirements for the confinement of
compressed concrete and
the stabilizing of compression bars in potential plastic hinge regions are likely to be more
restrictive.


Page:233:


Design of transverse Reinforcement:

(a)

General considerations: There are four design requirements that control the amo
unt
of transverse reinforcement to be provided in COLUMNS:

1.

Shear strength;

2.

Prevention of buckling of compression bars;

3.

Confinement of compressed concrete in potential plastic hinge regions or
over the full length of column subjected to very large
compression stresses
and;

4.

The strength of lapped bar splices.