Civil Engineering Reference
In-Depth Information
3.14.5 Failure Modes
The main modes of failure in HCS are:
fl
exural shear and web shear tension.
Flexural shear occurs when a
exural crack develops into a shear crack and leads to
a relatively ductile failure. Web shear tension is brittle failure and may not be
preceded by any warning of impending failure [
104
,
111
].
Precast HCSs do not have web widths exactly equal, therefore, once a shear
failure occurs in the critical web, it propagates rapidly throughout the unit of
HCS [
110
].
fl
3.14.6 Design of HCS
3.14.6.1 BS 8110 Modi
ed Method
To determine the
ber contribution to shear, Paine [
101
] used the Narayanan and
Darwish
s equation [
112
].
To account for FRC beams failing in web shear tension, Narayanan and Darwish
altered the equation of BS 8110 [
98
] to:
'
q
f
fct
;
sp
þ
0
V
Rd
¼
0
:
67bh
:
8
r
cp
f
fct
;
sp
ð
3
:
36
Þ
where the tensile split cylinder strength, f
fct,sp
, is found empirically from cube
compression tests:
p
F
f
fc
;
cub
20
p
þ
0
f
fct
;
sp
¼
:
7
þ
ð
3
:
37
Þ
and:
F
¼ g
b
V
f
k
f
ð
3
:
38
Þ
where
V
f
is the
ber volume fraction,
ʻ
f
is the
ber aspect ratio and
ʷ
b
is a bond
ef
ber types.
The use of the split cylinder strength in plain HCS design has been shown to
produce exaggeratingly high results [
109
]. Equations for shear strength of
prestressed FRC, with the tensile strength derived indirectly from
ciency factor to account for different
fl
exural strength
or toughness may be more acceptable.
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