An experimental and theoretical investigation of the structural behaviour of cross-bracing in transmission line steel towers
Date
2016-07-15
Authors
Behncke, Roberto Hector
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Abstract
This thesis presents the results of theoretical and experimental
investigations into the behaviour and ultimate load capacity of
latticed lower panels with cross-bracing diagonals made of
equal-leg, hot-rolled steel angles under the effects of in-plane
loads.
Loading tests to collapse are carried out on cross-bracings in
reduced-scale two-dimensional frames of various arrangements.
The Southwell-plot of deflection measurements immediately prior
to first yield of the diagonals is used to define equivalent end
eccentricities and effective length factors, which therefore
account for geometric and material imperfections of the test
specimens.
A proposal for new design formulae for calculating the
resistance of struts is presented. The new design equations are
based on the secant formula and are calibrs"ed against the
experimental results.
A computer model is developed based on flexibility equations
which do not require an narative analysis procedure. The
non-linear effects are given through the inclusion of Berry
stability functions. The effects of eccentric forces and nodal
restraints are simulated at all joints in which diagonals and
main chords are connected . An additional model is formulated
using a mainframe finite-element cod, demonstrating that it is
now possible to perform non-linear analyses of complex frames
including asymmetric members.
Experimental results from this and other investigations are
compared with ultimate load predictions based on the new design
equations and the computer models and also usual buckling
curves for design of steel transmission towers. In all cases the
proposed models give acceptable predictions ot the behaviour and
ultimate capacity of the bracings.
In particular, failure loads calculated with the new design
equations show improvements with respect to predictions based on
current design buckling curves. These equations, therefore, can
be used for design of steel latticed tower structures with angle
members.
Description
A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 1992.