F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

BS 81IO design procedure 265
Table 7.2-1 Values of /I(= leflo) for braced columns (BS 8110: Clause 3.8.1.6)
End condition at bottoma
End condition at top 8
(1)
'Fixed'
(2)
Partially
restrained
(3)
'Pinned'
(1) 'Fixed'
(2) Partially restrained
(3) 'Pinned'
0.75
0.80
0.90
0.80
0.85
0.95
0.90
0.95
1.00
• End conditions (1), (2) and (3) are defined as follows:
( l) The column is connected monolithically to beams on each side which are at least as deep
as the overall depth of the column in the plane considered. If the column is connected to
a foundation structure, this must be designed to carry moment.
(2) The column is connected to beams or slabs on each side which are shallower than the
overall depth of the column in the plane considered. (The I.Struct.E. Manual (5) is more
specific; it states that such beams and slabs should not be less than half the column
depth, in order to satisfy this condition.) .
(3) The column is connected to members which provide only nominal restraint against
rotation.
7.3 Eccentrically loaded short columns (BS 8110)
7 .3(a) BS 8110 design procedure
BS 8110: Clause 3.8.1.3 defines a braced short column as a braced column
for which both the ratios lexlh and Le/b are less than 15, where Lex is the
effective height in respect of the major axis (Table 7.2-1); ley is the effective
height in respect of the minor axis (Table 7.2-1); h is the depth in
respect of the major axis; and b is the width of the column.
The design of axially loaded short columns was explained in Section 3.4.
For eccentrically loaded short columns, the strength may be assessed by
the following equations:
N = 0.405/cubx + /~tAst + /s2As2 (7.3-1)
M = 0.203fcubx(h - 0.9x) + /~tA~t(~- d') - /s2As2(~- d2)
(7.3-2)
where N = the design ultimate axial load;
M =the design maximum moment under ultimate condition; M
should not be taken as less than Nemin where emin is the design
minimum eccentricity; BS 8110: Clause 3.8.2.4 stipulates that
the design minimum eccentricity emin should be taken as 0.05h
or 20 mm whichever is less (see Example 7.1-4(b));
A~ 1 = the area of compression reinforcement in the more highly
compressed face (see Fig. 7.1-6);
As2 = the area of reinforcement in the other face (see Fig. 7.1-6)