Portal Frame Design - Considerations For Base Fixity
Portal Frame Design - Considerations For Base Fixity
Portal Frame Design - Considerations For Base Fixity
A.1
A.2
Fixed bases
Bases considered as fixed are not infinitely rigid and the rotational stiffness may
conveniently be taken as equal to the column stiffness, as in Clause 5.1.3 of
BS59501[3] and Advisory Note AD097 Nominal base stiffness[22]. This means that
the base may be modelled as a spring with rotational stiffness of 4EIcolumn/Lcolumn.
If the program cannot accept a rotational spring, the simplest solution is to add a
dummy member, continuous with the column and pinned at the far end, of stiffness
EIcolumn and of length 0,75 Lcolumn (to allow for the pinned end which reduces the
stiffness) (Figure A.1).
L Column
Column
Column
Column
Column
0.75L Column
0.75L Column
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A.3
74