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Concrete In Australia : June 2013
Concrete in Australia Vol 39 No 2 37 the bridge, at mid-span, to be plotted, as shown in Figure A6. ADDITIONAL COMMENTS In Figures 14, 20 and A6, X is the calculated transverse profile. Y is the average transverse profile, and Z is the transverse profile calculated using the simplifying assumptions of no torsion and infinite transverse stiffness. As expected, the calculated profile X, is between Y and Z (so far as the critical maximum deflection and hence maximum moment, is concerned) in all cases. However, the large improvement in the distribution due to the influence of torsion only as demonstrated in Figure A6, stands out. is suggests that although the more modest improvement demonstrated in Figures 14 and 20 is worthwhile, it would be enhanced by including rather than ignoring the St Venant torsional stiffness of the ribbed deck-beams. is additional benefit may be included where it becomes significant, but at the moment it is held back to build some added conservatism into the system. Also, with no St Venant torsional stiffness the resultant of the reactions supplied by beam ribs is directly below the resultant of the applied loads, at all sections along the superstructure. us, the scope for improvement over the transversely rigid approximation, which also has this feature, is limited. When St Venant torsion is significant, this feature no longer applies. While the resultant of the superstructure reactions is of course directly under the applied load resultant, the resultant of vertical reactions supplied by beam ribs is displaced by the torsional reactions, at any specific section. is is the reason for the significantly improved load distribution exhibited in Figure A6, where significant St Venant torsion occurs. e feature of interest which is demonstrated in the Appendix is that the solution is provided directly by an "exact" numerical process which must converge, since r must be < 1. e hollow plank units used as a basis for the example examined in the Appendix, are similar to precast units known as Queensland Planks, which would usually be connected by insitu concrete or mortar keys. is is a situation where the advantages of elastomeric shear keys could readily be utilised. Figure A6. Transverse deflection profile at mid-span. Figure A4. Looking at symmetrical and anti-symmetrical cases. Figure A5. Analysis of 16 m span superstructure.