C. J. Burgoyne
Dept of Civil Engineering, Imperial College of Science
and Technology, London, UK
The paper presents a method by
which a designer can automatically determine a concordant cable profile that
fits within eccentricity bounds governed by the applied moment envelopes. The
method works by determining loadings which cause peak bending moments at a
particular point; these moment diagrams are scaled concordant profiles. By
using an iterative method, these loadings can be combined to give a composite
notional loading; the corresponding bending moment, when scaled by an arbitrary
factor, is the final concordant cable profile. The method also allows the shape
of the concordant profile to be varied over internal supports, so that a
smoothly curved cable can be fitted through an allowable zone which has sharp
angular changes in the limits. The engineer is thus freed from the necessity of
estimating secondary moments at the beginning of the design process. Instead, a
concordant line of thrust can be determined and linear transformations applied
to obtain the actual cable profile.
The design of continuous
prestressed concrete beams is complex and, if not approached in a logical
sequence, can lead to the designer carrying out abortive calculations which
waste time and effort.
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