Civil Engineering Reference
In-Depth Information
in detail, as the load-slip relationship is influenced by many variables,
including:
(1)
number of connectors in the test specimen,
(2)
mean longitudinal stress in the concrete slab surrounding the
connectors,
(3)
size, arrangement and strength of slab reinforcement in the vicinity
of the connectors,
(4)
thickness of concrete surrounding the connectors,
(5)
freedom of the base of each slab to move laterally, and so to impose
uplift forces on the connectors,
(6)
bond at the steel-concrete interface,
(7)
strength of the concrete slab, and
(8)
degree of compaction of the concrete surrounding the base of each
connector.
The details shown in Fig. 2.9 include requirements relevant to items
1 to 6. The amount of reinforcement specified and the size of the slabs are
greater than for the British standard test, which has barely changed since
it was introduced in 1965. The Eurocode test gives results that are less
influenced by splitting of the slabs, and so give better predictions of the
behaviour of connectors in beams [17].
Tests have to be done for a range of concrete strengths, because the
strength of the concrete influences the mode of failure, as well as the
failure load. Studs may reach their maximum load when the concrete
surrounding them fails, but in stronger concrete, they shear off. This is
why the design shear resistance of studs with
h
/
d
≥
4 is given in Eurocode
4 as the lesser of two values:
08
.
f d
(
π
/ )
4
2
u
P
=
(2.14)
Rd
γ
V
and
02
.9
2
dfE
(
)
/
12
ck
cm
P
=
(2.15)
Rd
γ
V
where
f
u
is the ultimate tensile strength of the steel (
500 N/mm
2
), and
f
ck
and
E
cm
are the cylinder strength and mean secant (elastic) modulus
of the concrete, respectively. Dimensions
h
and
d
are shown in Fig. 2.6.
The value recommended for the partial safety factor
≤
γ
V
is 1.25, based
on statistical calibration studies. When
f
u
=
450 N/mm
2
, Equation 2.14
governs when
f
ck
exceeds about 30 N/mm
2
.
