Basic methods of reinforcing steel structures - Assessment and Refurbishment of Steel Structures - page 84

place the reinforcing (additive) material furthest from the neutral axis into the tabular
area, thereby increasing bending stiffness of the girder (Figure 4.2(a)).
Figure 4.2 Reinforcement of angled
girders
Where the effects of transverse forces are crucial, the girder wall is reinforced, leading to
a reduction of shear stresses (Figure 4.2(b)). There is often no need reinforce the girder
along its whole length at constant cross-section. It is sufficient to reinforce it in the area
of greatest internal forces. When reinforcing angled girders, the girder height is
sometimes increased, which influences the stability of the compression chord (buckling).
When choosing a method of reinforcement, it is important to establish whether it is
possible to unload the structure. Reinforcement is most effective when the structure is
disassembled, so all reinforcing elements can be fully used and all necessary works can
be performed more easily (e.g. difficult overhead welding is not necessary, but
unfortunately this is often inevitable when the upper chords of built-in girders are being
reinforced).
Schemes for the reinforcement of rolled I and U girders are shown in Figure 4.3. The
reinforcing elements can be welded (Figure 4.3A) or bolted (Figure 4.3B) to the original
cross-sections, though welding is preferable.