The Structural Engineer > Archive > Volume 15 (1937) > Issues > Issue 1 > Correspondence. Bridge Design
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Correspondence. Bridge Design

Sir,-It is noted that the author of the article on “Recent Progress in Bridge Design in Tanganyika Territory" admits the accuracy of the deductions concerning the stresses in the structure referred to in my letter published in the September issue of your Journal. I have read again with care the original article, and can see no reference whatsoever to the decking slab being cast some considerable time after the webs of the beams. If this procedure to be followed it is hard to understand the reference to a factor of the safety in the Rolled Steel Joists of 3 due to dead load, if the bridge is to be constructed in such a fashion that this loading cannot come on the naked steel joists. Whether the design is such that the slab may be considered adequately bonded to the web of the tee beam is open to serious question, and most designers in structures of this type place the top flange of the R.S.J. just under the top surface of the slab. (Water & Water Engineering, Midsummer, 1932, page 260, etc.) The use of comparatively heavy and unwieldy R.S.J.'S under the conditions visualised in the paper would hardly appear to be justified as a normally designed reinforced concrete beam would contain much less steel and would only necessitate vertical strutting. Such reinforced concrete beam bridges for similar spans have been constructed in numerous cases during the past 20 years by the South African P.W.D. utilising native labour.