Civil Engineering Reference
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Brace prevents
lateral deflection
and twist rotation
b
f
= 146.4 mm
t
f
= 10.9 mm
254 ×146 UB 37
h
=
256 mm
12 kN/m at top flange
t
w
=
6.3 mm
70kN
r
=
7.6 mm
483 cm
3
3
W
pl,y
=
1
2
571 cm
4
I
z
=
457 ×191 UB 82
= 15.3 cm
4
I
t
8.0 m
4.5m
4.5m
70
kNm
= 0.0857 dm
6
I
w
(c) Example 3
(b) Properties of
(a) Example 2
254 ×146 UB 37
Figure 6.31
Examples 2 and 3.
6.15.2 Example 2 - checking a braced beam
Problem
. The 9 m long 254
×
146 UB 37 braced beam of S275 steel shown
in Figure 6.31a and b has a central concentrated design load of 70kN (which
includesanallowanceforself-weight)andadesignendmomentof70kNm.Lateral
deflections
v
and twist rotations
φ
are effectively prevented at both ends and by a
brace at mid-span. Check the adequacy of the braced beam.
Design bending moment.
R
3
={
(
70
×
4.5
)
−
70
}
/
9
=
27.22kN,
M
Ed
,2
=
27.22
×
4.5
=
122.5kNm.
Section resistance.
t
f
=
10.9 mm,
f
y
=
275 N/mm
2
EN10025-2
ε
=
√
(
235
/
275
)
=
0.924
T5.2
c
f
/(
t
f
ε)
=
(
146.4
/
2
−
6.3
/
2
−
7.6
)/(
10.9
×
0.924
)
T5.2
=
6.20
<
9 and the flange is Class 1.
T5.2
c
w
/(
t
w
ε)
=
(
256
−
2
×
10.9
−
2
×
7.6
)/(
6.3
×
0.924
)
T5.2
=
37.6
<
72 and the web is Class 1.
T5.2
M
c
,
Rd
=
275
×
483
×
10
3
Nmm
6.2.5
=
132.8kNm
>
122.5kNm
=
M
Ed
and the section resistance is adequate.
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