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IITK-BMTPC Earthquake Tip 19

How do Columns in RC Buildings resist Earthquakes? page 2
(b) Over the distance specified in item (a) above and
below a beam-column junction, the vertical spacing
of ties in columns should not exceed D/4 for where Spacing of ties
D is the smallest dimension of the column (e.g., in a not more than D/4, but need
not be less than 75mm nor
At least larger of

rectangular column, D is the length of the small D, h c/6 and 450 mm more than 100 mm
side). This spacing need not be less than 75mm nor
more than 100mm. At other locations, ties are
spaced as per calculations but not more than D/2. Beam
(c) The length of tie beyond the 135° bends must be at
Ties required
least 10 times diameter of steel bar used to make h c/4 in joint region also
the closed tie; this extension beyond the bend See Earthquake Tip 20
should not be less than 75mm. Spacing of ties
Construction drawings with clear details of closed not more than D/2

ties are helpful in the effective implementation at h c
construction site. In columns where the spacing
between the corner bars exceeds 300mm, the Indian Lapping of Spacing of ties in lap length
not more than smaller of
vertical bars

Standard prescribes additional links with 180° hook in middle-half D/2 and 150 mm
ends for ties to be effective in holding the concrete in of column
its place and to prevent the buckling of vertical bars.
These links need to go around both vertical bars and Spacing of ties
horizontal closed ties (Figure 3); special care is not more than D/2
required to implement this properly at site. Ties required
Extra Links h c/4 in joint region also
See Earthquake Tip 20

Beam

At least larger of
D, h c/6 and 450 mm Spacing of ties
not more than D/4, but need
not be less than 75mm nor
more than 100 mm

D
180° links around
BOTH vertical bars Figure 4: Placing vertical bars and closed ties in
and 135° ties columns – column ends and lap lengths are to
be protected with closely spaced ties.

Column

Earthquake Tip
Figure 3: Extra links are required to keep the Related -

concrete in place – 180° links are necessary to Tip17: How do Earthquakes Affect Reinforced Concrete Buildings?

Tip18: How do Beams in RC Buildings Resist Earthquakes?
prevent the 135° tie from bulging outwards.
Reading Material
Lapping Vertical Bars IS 13920, (1993), “Indian Standard Code of Practice for Ductile Detailing
In the construction of RC buildings, due to the of Reinforced Concrete Structures Subjected to Seismic Forces,” Bureau
of Indian Standards, New Delhi
limitations in available length of bars and due to Paulay,T., and Priestley,M.J.N., (1992), “Seismic Design of Masonry
constraints in construction, there are numerous and Reinforced Concrete Buildings,” John Wiley & Sons, USA

occasions when column bars have to be joined. A
simple way of achieving this is by overlapping the two Authored by:
bars over at least a minimum specified length, called C.V.R.Murty
lap length. The lap length depends on types of Indian Institute of Technology Kanpur
reinforcement and concrete. For ordinary situations, it Kanpur, India
is about 50 times bar diameter. Further, IS:13920-1993 Sponsored by:
prescribes that the lap length be provided ONLY in the Building Materials and Technology Promotion
middle half of column and not near its top or bottom Council, New Delhi, India
ends (Figure 4). Also, only half the vertical bars in the
column are to be lapped at a time in any storey. This release is a property of IIT Kanpur and BMTPC New
Further, when laps are provided, ties must be Delhi. It may be reproduced without changing its contents
and with due acknowledgement. Suggestions/comments
provided along the length of the lap at a spacing not may be sent to: nicee@iitk.ac.in Visit www.nicee.org or
more than 150mm. www.bmtpc.org, to see previous IITK-BMTPC Earthquake Tips.

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