DISTORTIONAL EFFECTS IN LONG SPAN DOUBLE CANTILEVER BOX GIRDER BRIDGES

Abstract

The study as dotailod herein %hie diosortation has boon undertaken to know qualitatively and quantitatively though approximate to the extent of tho asoumptions in the method of analysie, the distortional effects induced under the action of 1.R.C. loadings in the two lane double canti-lever non-priocatic long opan box girder bridgos. 'Elam on <Avnt() foundation' analogy, first applied by tiright, Atdel-Samad fuld ,iobinoon to find tho diotortional effects in prismatic oingle cell and multicoll box eirder5, has been extended and a numorical procedure developed to cover non-priomatio oinglo coil or multicell box girdors with or without intermediate diaphrngmo. This bac boon achiovod by using finite difforonco numerical approach aloe, with Uewmnrk's method of discrotizing a continuous function. Based on the above, a general computer programme has been developed which can be run on a small capacity computor like ITC 1620. The method has boon used to obtain reeulte for a unit tared onal load occupying different poeitiono ammo the pan of a two lane double cantilovor non-priomatic box bridge for a number of woes c.g. box girler bridge with a hinge of the centre of each span but without the intermoliato diaphragms, with ono intermediate diaphragm centrally located, with two intermediate diaphrams oquolly opacod, with continuity at the centre in place of central htno, nd with two cell cross sectional configuration. The influence lines for the dietortional tranaverse moments and longitudinal w p g etresses for these cases are plotted and the effect due to the i.R.C. loading causing the worst effect is worked out. The envelopes of maximum distortional momenta and Toni t tunnel warping etreasse induced at various section under the unit moving torsional load are also presented. It 18 firmly established that the proposed procedure is capable of treating complex geometric configuration of a box girder bridge with ease and yielding sufficient accuracy.