Aluminium Design and Construction John Dwight

the sign of ß x will be plus with a sagging moment and minus with
hogging.
10.5 WARPING CALCULATIONS
10.5.1 Coverage
This section gives procedures for locating the shear centre S (when its
position is not obvious), and determining the warping factor H, for
thin-walled non-hollow profiles composed of plate elements. The warping
of such sections is covered in some textbooks, but in a manner that is
inconvenient for a designer to use [29]. British Standard BS.8118 does
it in a more user-friendly form. Here we present an improved version
of the British Standard approach, extended to cover a wider range of
section shapes, including those that ‘bifurcate’.
10.5.2 Numbering the elements
The plate elements comprising the section should be numbered
consecutively (1, 2, 3, 4, etc), starting at a point O and proceeding with
a specific direction of flow around the section (Figure 10.14). We take O
at the point of symmetry when such a point is available and number
the elements on one side only of O. In such cases if O comes at the
centre of a flat web, we treat this web as two elements either side of O,
one of which is numbered. When there is no point of symmetry, we
take O at an edge of the section and number all the elements.
In a bifurcating section (Figure 10.14(c)), the two strands beyond the
point of bifurcation may be referred to as A and B, with the direction
of flow in each always away from the start point O.
Figure 10.14 Warping: numbering of the elements and ‘direction of flow’.
Copyright 1999 by Taylor & Francis Group. All Rights Reserved.