Frames - The Behaviour and Design of Steel Structures to EC3 - page 387

100 100 100

4 5 6

(a) Truss and loads
(m, kN)

8.0

2

1 3

8.0 8.0 8.0 8.0

(cm 4 ) A (cm 2 ) y (N/mm 2 )

Member Section I f

z

14, 36 305 305 UC 97 ×

×
×
×

7308 123 275

(b) Member
properties

45, 65 305 05UC 8

305 305 UC 97
305 305 UC 97

12569 201 265

12, 32
42, 62

7308 123 275

7308 123 275

Member M (kNm)
L

M (kNm)
R

N(kN)

14 16.8 -68.8 -217.4

(c) Elastic
actions

45
56
12

-150.2
249.8
-16.8

249.8 -172.7
-150.2 -172.7
8.9

159.1

42 81.5 -40.6 8.5

Figure 8.15 Example 14.

properties and the results of a first-order elastic analysis of the truss under the
design loads are shown in Figure 8.15b and c.
Determine:

(a) the effective length factors k cr of the compression members and the frame
elastic buckling load factor α cr ,
(b) theamplifiedfirst-orderdesignmoments M Ed forthecompressionmembers,
(c) the adequacy of the members for the actions determined by elastic analysis,
(d) the plastic collapse load factor α p , and
(e) the adequacy of the truss for plastic design.

8.6.2 Example 15- unbraced frame design

The members of the unbraced rigid-jointed two-storey frame shown in
Figure 8.16a are all of S275 steel. The member properties and the results of
a first-order elastic analysis of the frame under its design loads are shown in
Figure 8.16b and c.
Determine:

(a) the column effective length factors k cr , the storey buckling load factors α cr , s ,
and the frame buckling load factor α cr ,
(b) the amplified first-order design moments M Ed for the columns,
(c) the adequacy of the members for the actions determined by elastic analysis,