that greater risks had to be taken in wartime”.
In 1939, a recommendation was made that for government buildings,
design should be based on the “more exact design methods” proposed by the
Committee, but Baker notes “there is no evidence that this last wise
recommendation has ever been acted upon”.
Holding nothing back!
In 1943, BS 449 was revised, still not embracing the more exact methods. One
senses a degree of disappointment when Baker notes “the third revision….
owes nothing to the tests of existing buildings and the other resources…
except that it has achieved almost all the economy possible in beams without
bothering to define the vital end-connections to be used”. He suggests it
perpetuates “a design method which neglects almost every effect but axial
load and can only be defended on the score of expediency”. He does not
spare his criticism – the method which was originally adopted as “an empirical
method well proved by years of use to be safe… has been changed in a
haphazard way unjustified by practical experience or the results of scientific
investigation”. The method which so frustrates Baker is the assumption of
nominal moments due to beam end reactions 100 mm from the face of a
column – a method still loved in the UK found in clause 4.7.7 of BS 5950 and
available to Eurocode designers via NCCI.
Baker concludes that further economy was certainly possible and that too
much attention should not be paid to the complexity of the proposed design
method “for it does less than justice to the abilities of steelwork designers”.
Some 70 years later, perhaps we are on the advent of embracing semicontinuous
design, being armed with numerical methods and software that
will determine the stiffness of connections and software which can include
connection stiffness in the frame analysis.
Lessons from the war
Appendix B of Volume 1 reports on multi-storey steel frames subject to air
attack. The appendix notes that it also shows what happens when these
structures are subject to conditions of overload.
Of interest is the comment that “the floor (construction) which can best tie
the members of the main frame together is to be preferred”. Today, we would
discuss the subject under “the avoidance of disproportionate collapse”. Baker
notes that “hardly ever does progressive collapse take place”, unless “the
explosion caused failure of certain beam-to stanchion connections” (on the
façade) “and allowed the external wall framework to move outwards, when a
certain amount of collapse ensued”. Today, we would recognise the need for
connections to not only carry the vertical shear, but also the tying forces to
avoid exactly this problem. The appendix also makes recommendations about
the layout of beams, which we would recognise as the arrangement of
horizontal ties. Despite these clear recommendations, the disproportionate
collapse at Ronan Point in 1968 (Figure 3) is usually noted as the catalyst for
the modern tying rules, perhaps because the risk of blast from high explosive
ended in 1945.
Many of the features of our modern
codes have their roots in work
completed many years ago – some
expressions are precisely those
proposed over 50 years ago. That
original work was hugely significant,
influencing much of what we do today,
from loading to resistance calculations.
Perhaps the tools that structural
engineers now have available will
finally facilitate progress from the
empirical methods which Professor
Baker described as “almost entirely
irrational and therefore incapable of
To appreciate something of the
background and reasons for certain
requirements must always be helpful.
As Professor Baker notes: “it is important
that the steelwork designer should not
become a technician blindly applying
irrational rules. He can only escape from
this role if he has the information on
which he can base better rules”
Figure 3: Ronan Point
1 Horne, M. R. and Ajmani, J. L.
Design of columns restrained by side rails
The Structural Engineer, August 1971
2 Horne, M. R. and Ajmani, J. L.
Failure of columns laterally supported on one flange
The Structural Engineer, September 1972
3 Failure of columns laterally supported on one flange; Discussion
The Structural Engineer, July 1973
4 Horne, M. R and Morris, L. J.
Plastic design of low-rise frames
5 Horne, M. R. Shakir-Khalil, H. and Akhtar, S.
The stability of tapered and haunched beams
Proceedings, Institution of Civil Engineers, Part 2, September 1979
6 Baker, J. F.
The steel skeleton, Volume 1, Elastic behaviour and design
Cambridge University Press, 1954
7 Baker, J. F; Horne, M, R; Heyman, J.
The steel skeleton, Volume 2, Plastic behaviour and design
Cambridge University Press, 1956