Repair and reconstruction of civil structures - Assessment and Refurbishment of Steel Structures - page 159

In the plane of the upper chords of tie beams, a new load-bearing system of longitudinal
and transverse girders (Figure 5.29) was proposed, which would redistribute short-term
accidental loads from the roof deck. It also forms a supporting system that would prevent
porous concrete panels from falling out by providing an underlayer and filler.
The original vertical reinforcement between the roof trusses was dismantled and
replaced by strut reinforcers. The reinforcing system was completed by transverse and
longitudinal chords of reinforcement (Figure 5.30) located under the plane of the roof
deck. Some of the material from the dismantled vertical reinforcement could be used
here.
Figure 5.30 The new window system
under the roof deck
All of the new structure was designed bearing in mind the possibility that the roof deck
might later be replaced by a new, lighter one.
The reconstruction was completed within five months under full production operations
in the hall. In the original steel structure, 47 tonnes of reinforcement was dismantled, and
of that material 35 tonnes were used in the newly designed reinforcing system. In the roof
structure, 130 tonnes of new rolled steel and gusset plates were fitted.
5.1.7 Reconstruction of a metal foundry
This metal foundry was built at the end of the nineteenth century. The original roof
structure was wooden, bedded on external brick masonry. Nailed tie beams with span of
25 m were spaces 5 m apart, and a skylight of width 5 m and height 2.2 m was located in
the longitudinal axis of roofing. On the basis of a detailed examination of the roof
structure and static calculations for the wooden tie beams, and the bracing in the roof
structure, it was found that part of the original structure was in emergency condition due
to overloading by fly-ash to depths ranging from 100 to 150 mm that had not been
removed regularly, and by increasing number of layers of cardboard roofing used during
maintenance of the roof deck. It was also found that the original roof structure did not