Repair and reconstruction of civil structures - Assessment and Refurbishment of Steel Structures - page 178

The structure of the roof is designed using steel lattice tie beams 2.0 m high with 19.9
m span, anchored on steel columns (Figure 5.55). Steel web trusses of I 160 profile are
fixed to the lattice tie beams at a distance of 2.0 m by gusset plates. Plate of RANNILA
RAN 35-0.75 mm is fitted to the trusses. The vertical load-bearing structure uses the
original reinforced concrete columns in the existing skeleton of the building, and
reinforcement of the atrium structure acts in the plane of roof, secured by diagonal roof
stiffeners.
The roof structure was built in 2001. Such structures present a number of unusual
problems. All modifications, repairs, realignment, reinforcement and refurbishment of the
steel structures must be done in ways that will secure the stability and safety of the
structure.
5.2 Refurbishment of steel structures after fire damage
Fire resistance of steel structures must meet the valid standards. Structures can be
protected against fire hazard by proper constructional design and surface protection. In
high temperatures fire (see Chapter 2 Section 2.4.3) the limit states in capacity and
serviceability may be exceeded. What follows is an example of a light hall structure
without fire hazard protection, whose capacity limits were suddenly exhausted by a fire.
It collapsed and was irreparably damaged (Figure 5.56).
Figure 5.56 The steel structure of a
light hall damaged by fire
In this case it was found that the effect of the temperature of the fire on structure
depended mostly on the amount, properties and arrangement of the combustible material,
and on the oxygen access and spatial arrangement of the building. The hall was originally
built to store canned fruit. Because of poor crops, at the time of fire other combustible