Steels_ Metallurgy and Applications, Third Edition

184 Steels: Metallurgy and Applications

where Cv = Charpy V notch energy value in joules at the minimum

effective temperature

try = yield strength in N/mm 2

t = thickness in mm

It should be noted that the divisor of 355 in the above equations corresponds

to the minimum yield strength in N/mm 2 of BS 4360 Grade 50 steels.

Where severe stress concentrations occur, BS 5400 calls for more stringent tough-
ness requirements and the impact energy value is calculated from:
try
Cv > :=.[0.3t(1 + 0.67k)]
333
where k = stress concentration factor
As indicated earlier in this chapter, BS 5400 has not yet been updated to reflect the
fact that BS 4360 has now been withdrawn and superseded by European standards
for structural steels. However, it is understood that BS 5400 is currently being
revised to accommodate the changes in steel nomenclature. In the meantime, the
Department of Transport has issued document BD 13/90 Design of Steel Bridges:
Use of BS 5400: Part 3: 1990, Crown Copyright 1990, which provides guidance
on this matter.

Steel in multi-storey buildings

During the 1980s, there was a dramatic increase in the UK in the use of structural
steelwork in multi-storey buildings, primarily at the expense of in situ concrete.
The reasons cited 3~ for this situation are:

1. The reduction in the price of structural steel relative to in situ concrete.


2. The reduced costs and improved methods of fire protection for structural steel.


3. The shorter site and total construction periods achieved through the use of
   steel.

All three aspects are cost or revenue related, the last item minimizing the period
during which the capital for the investment has to be financed and decreasing the
time at which the owner of a building begins to receive a return on investment.
In order to improve its share of the construction market, British Steel first
analysed the contribution of the various items to the total cost of a steel building
frame. This analysis is shown in Figure 2.2231 and, whilst the cost of the basic
steel was very significant, items such as corrosion protection, fire protection and
fabrication also contributed very considerably to the overall cost. Each of these
items was given detailed attention and, as illustrated in Figure 2.22 the cost of
steel building frames has decreased significantly, in real value terms, over the
11-12-year period. Whereas the costs of corrosion protection and fire protection
were reduced substantially, it should be noted that the reduction in the cost of
steel played an even greater part in increasing the cost competitiveness of steel
frames.