Repair and reconstruction of civil structures - Assessment and Refurbishment of Steel Structures - page 141

Figure 5.2 Stiffener for fixing the
response of the two-hinged frames
It was assumed that the original frame structure would be retained and used during
reconstruction. According to the proposal by Stavoprojekt Bratislava, both transverse and
longitudinal maintenance footbridges were to be suspended by inclined draw bars from
the original frame structure below the level of the brackets of the reinforced concrete
decking. However, the flat steel two-hinged frames proved not to have a sufficient
reserve for the additional loading and so this solution would have reduced the height of
the lighting of the hall.
The actual reconstruction was done according to Figure 5.3. The static system was
changed with, the two-hinged frame being replaced by a lattice tie beam. The original
frame (welded I cross-section) forms the upper chord and the horizontal stiffening
members at both ends of the frame form part of the lower chord of new planar tie beams.
The theoretical heights of the middle tie beams is 6.44 m and that of the outer tie beams
in ties 1 and 6 is 5.54 m.
The internal forces of the cross bonds were determined in two stages. In the first stage,
the cross bond acted as the original frame structure (the inclined suspensions were
temporarily retained, so that the stiffeners taking over the horizontal reactions of the two-
hinged frame could be suspended from them), which was loaded by the weight of the
original structure after removal of the roofing material, the weight of its supporting base,
and at the weight of the skylight structure. After these parts had been removed, a new
lower chord, together with the skeleton of the transverse footbridge, were suspended by
means of diagonals. Then the connected, so that the original two-hinged frame structure
was thereby changed into additional lower chord with the draw bar of horizontal
stiffeners was a lattice girder with a 52.28 m span.