M. Aul
University of Hanover, W. Germany
C. J. Burgoyne
Dept of Civil Engineering, Imperial College of Science
and Technology, London, UK
The paper presents a method of
determining the variation of bending moment within a prestressed concrete beam
as it lifts off falsework; the falsework reactions can also be calculated.
The falsework is assumed to provide
an elastic restraint if the beam deflects downwards, but no restraint if the
beam lifts off.
The problem is non-linear, since it
is not known ab initio which parts of the beam go up and which down. The paper
presents a method of analysing a beam for these supports conditions, under a
generalised loading.
Results are presented for a
three-span beam as it progressively lifts off its falsework as more cables are stressed;
the effects of varying the falsework stiffness are considered.
The case of a beam being
prestressed in such a way that excessive falsework loads can be caused is also
presented.
The problems associated with a beam
resting on an elastic medium have been studied for many years, although the
primary aim has been to study the behaviour of a beam resting on soil. The
basic Winkler formulation, in which the soil is assumed to provide a reaction
in proportion to the deformation imposed on it, has been applied to many
problems (see, for example, Hetenyi’s classic book)
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