In R.C.C. works steel
reinforcement may be used in the form of (a) plain round mild steel bars, (b)
deformed bars, (c) cold twisted bars and (d) hot drawn steel wire mostly used
in pre-stressed concrete. Square bars and flats are seldom in use. With the
introduction of deformed and twisted bars, the use of plain round bars is
rapidly decreasing.
Cold twisted deformed bars or
Tor steel
Both plain and deformed bars
may be subjected to cold twisting. The standard diameters in mm are 6, 8, 10, 12,
16, 20, 25, 28, 32, 36, 40 and 45. Minimum concrete grade for Tor steel is M
15. During this period out country adopted the use of Ribbed Tor steel Tor-40
(Fe 415) with a flexure tensile design strength of 415 N/mm2 in
tension and 330 N/mm2 in compression. Permissible stresses (IS :
456) 20 mm dia. And below is 230 N/mm2. This Tor-40 replaced
ordinary mild steel rounds with an working permissible stress 140 N/mm2
in tension for bars up to 20 mm diameter. Tor steel designed as Tor-50 (Fe 500)
with a design strength in tension 500 N/mm2 and in compression 400
N/mm2. Some types of deformed bars
as shown in fig.
Plain mild steel bars may be substituted
for tensile and compressive members without changing in concrete strength,
dimensions of section, number or bar spacing. Only diameter of bar needs to be
substituted as given below.
Substitution Table
|
Tension
Reinforcement
|
|||||||||||
|
Mild Steel dia. mm
|
8
|
10
|
12
|
16
|
20
|
22
|
25
|
28
|
32
|
36
|
40
|
|
Ribbed Torsteel dia. mm
|
6*
|
8
|
10
|
12
|
16
|
18
|
20
|
22
|
25
|
28
|
32
|
|
Compression
Reinforcement
|
|||||||||||
|
Mild Steel dia. mm
|
12*
|
16
|
20
|
22
|
25
|
28
|
32
|
36
|
40
|
|
|
|
Ribbed Torsteel dia. mm
|
10
|
14
|
2x12
|
18
|
20
|
22
|
2x18
|
2x20
|
32
|
|
|
Working stresses of M.S. bar
are considered over 20 mm dia. 130 N/mm2 in tension reinforcement,
and for compression 130 N/mm2 for all diameter. *Spacing reduced by
10%.
