Abstract
M.Ing. (Civil Engineering)
Variable EI, post tensioned continuous bridge decks frequently occur in
practice. The design of such a deck is essentially a process of trial
and error. The aim of this thesis is to facilitate the design process
by eliminating the sting from the otherwise complex flexural analysis
by the development of suitable PC programs. This thesis will focus on
the following three main issues:
1 SECTION PROPERTIES
The program PROP presents a minimum input approach for the
determination of uni-axial section properties. Special enP1aSis is
placed on the section efficiency factor, being a direct quantitative
measure of a sections flexural ability, ranging from 0 to 1. The effect
of this factor on partial prestressing is also discussed.
2 THE MAGNEL DIAGRAM
The program MAGNEL presents a linear programming optimisation aid for
the design of uneracked sections (i.e. Classes 1 and 2 prestressing).
The following is catered for:
• variable prestress loss
• both sagging and hogging moments
• composite construction
• two stage stressing
• secondary moments due to prestressing
The effects of the section efficiency factor, area redistribution and
secondary moments on the Magnel diagram is also evaluated.
3 VARIABLE EI CONTINUOUS SPAN ANALYSIS
The program BEAM presents a transparent finite element approach for the
evaluation of bending moments, shears and deflections for variable EI
continuous spans. The following features are available:
• for a single span, supports may be fixed, supported or free
• up to a six span continuous structure may be analysed
• loading may consist of point loads, moments, uniformly distributed
loads, support deflection or prestressing
The direct prestressing input feature is compared against the
equivalent load method for a varying parabolIe tendon force as
developed by Catchick. The formulation of the Catchick method is also
simplified by the introduction of additional parameters.