The right choice of steel – according to the Eurocode - Economical Bridge Solutions based on Innovative Composite Dowels and Integrated Abutments - page 29

Post weld heat treatment (PWHT)
In addition to CEN TR 10347, it should be noted that if stress relieving (PWHT) is re-
quired, which is generally uncommon in fabrication of structural steel shapes, the same
recommendations apply to structural steels, regardless of the delivery conditions AR,
N and M. The generally recommended PWHT procedures are to apply temperatures
between 530 to 580 °C and a holding time of 2 minutes per mm product thickness, but
not less than 30 minutes and not more than 90 minutes
With regard to their technological properties, the thermo-mechanically rolled steels
have therefore good cold-forming properties. Similar to conventional structural steels, they
can be flame straightened provided specific maximum temperatures are not exceeded. In
case stress relieving is considered for reducing residual stresses, the usual parameters con-
cerning temperature range and heating time according to the rules of practice must be ap-
plied. Hot-forming, which is however uncommon for the fabrication of sections, must not
be performed.
5. Example of the appliance of modern steels in high rise
buildings
The advantages of the application of HISTAR ® high strength steels can be perfectly demon-
strated on two similar buildings in the Spanish city of Barcelona (“Fig. 24”).
Both 40-storey buildings consist of the same structural concept, similar dimensions and
a comparable base grid. As a result, the values of the column loads resulting from dead load
and life loads are comparable for the same type of column of every building.
While the structural steel construction of the first erected building is fabricated based on
S 355 steel grade, the later erected second building is made of HISTAR ® 460. The result
is significant: For the highest loaded columns in the lower part of the building, the column
weight of the HISTAR ® 460 columns is reduced by 28% compared to those of S 355.
The higher yield strength of the HISTAR ® 460 steel is not the only reason for the same
column capacity of the lighter section: Because of the controlled fabrication process result-
ing in lower imperfections, EN 1993-1-1 (2005) classifies hot rolled sections in S460 /
HISTAR ® 460 in buckling curve a or a0 (Fig. 25), depending on the sections dimension. The
second effect is through reduced dimensions and plate thicknesses due to higher allowable
tresses, S 460 / HISTAR ® 460 are already in the more favourable range for the buckling
curves definition.