Civil Engineering Reference
In-Depth Information
Table 1.4
Properties of concretes used in the examples, at age
28 days
Concrete grade
C25/30
LC25/28
Characteristic cylinder strength,
N/mm
2
f
ck
25
25
Mean cylinder strength,
N/mm
2
f
cm
33
33
Lower tensile strength,
N/mm
2
f
ct,0.05
1.80
1.60
Mean tensile strength,
N/mm
2
f
ctm
2.60
2.32
Upper tensile strength,
N/mm
2
f
ct,0.95
3.30
2.94
Mean elastic modulus,
kN/mm
2
E
cm
31.0
20.7
Weight density, reinforced concrete, kN/m
3
25.0
19.5
for both ribbed bars and welded steel fabric. The modulus of elasticity for
reinforcement,
E
s
, is normally taken as 200 kN/mm
2
; but in a compos-
ite section it may be assumed to have the value for structural steel,
E
a
=
210 kN/mm
2
, as the error is negligible.
Structural steel
Strength grades for structural steel are given in EN 10025 [21] in terms of
a nominal yield strength,
f
y
, and ultimate tensile strength,
f
u
. The grade
used in worked examples here is S355, for which
f
y
= 355 N/mm
2
,
f
u
=
510 N/mm
2
for elements of all thicknesses up to 40 mm.
The density of structural steel is assumed to be 7850 kg/m
3
. Its coefficient
of linear thermal expansion is 12
10
−6
per °C. The difference between
this value and that for normal-density concrete, 10
×
10
−6
per °C, can usually
×
be ignored.
Profiled steel sheeting
This product is available with yield strengths ranging from 235 N/mm
2
to
at least 460 N/mm
2
, in profiles with depths ranging from 45 mm to over
200 mm, and with a wide range of shapes. These include both re-entrant ribs,
and trapezoidal troughs as in Fig. 3.9. There are various methods of
achieving composite action with a concrete slab, discussed in Section 2.4.3.
Sheets are normally between 0.8 mm and 1.5 mm thick, and are protected
from corrosion by a zinc coating about 0.02 mm thick on each face.
Elastic properties of the material may be assumed to be as for structural
steel.
Shear connectors
In the early years of composite construction, many types of connector
were in use. This market is now dominated by automatically-welded headed
studs. Details of these and the measurement of their resistance to shear are
given in Chapter 2.
