144 discussion. 



Discussion. 



J. Trevor Jones — While this evening's meeting is called 

 ostensibly to discuss Prof. Warren's paper, the Professor has left 

 very little to discuss in his statements, and it seems only open to us 

 to comment upon and apply his valuable contribution. In the im- 

 mediate future it is to be hoped, a Local Government bill will be an 

 accomplished fact, and under it, it is expected, an impetus will be 

 given to municipal works all over the colony, — these works entail 

 the use of timber in large quantities, because small rivers and 

 creeks will be bridged in numbers, and for new communities 

 native timbers are found to be a very excellent substitute for stone, 

 brick, and iron, until the traffic shall justify the use of the latter 

 materials. It is a matter for congratulation that the State has 

 inaugurated a Forestry Department, and not a day too soon, as 

 the good timber was rapidly disappearing, and very little was 

 being put in to take its place. A further matter for congratula- 

 tion is that our native timbers give such excellent results under 

 tests as is shown by the Professor's former paper, and also possess 

 such exceptional durability. The results obtained by Professor 

 Warren from actual tests of ironbark timber are such as to lead 

 to the hope that the Forestry Department will devote large areas 

 to the cultivation of these valuable trees ; they require little care 

 and are found growing in the most sterile soil, yet in transverse 

 strength, in resisting crushing forces as well as shearing and 

 tensile strains, they are more like the metal from which they 

 derive their name than perhaps any other timber. "The main 

 difficulty (says the Professor) in designing timber structures is 

 due to the joints and connections, these should be so arranged 

 that they will not lose their efficiency through the shrinkage of 

 the material." These words should always be borne in mind by 

 designers of framed wood structures ; a design for a timber bridge 

 is easily conceived if one could procure timber that will not shrink. 

 The ordinary double beam timber viaducts of the Railway Depart- 

 ment give by calculation a resistance equal to that of four beams 

 laid side by side, if the cross ties would not shrink; but practically 

 they will shrink in dry weather, and cease to fill the notch in 

 which they are lodged, to an extent that almost entirely deprives 

 them of the power of giving additional resistance to bending 

 moments. In the branch of the Victorian Railways where I was 

 for many years, this shrinking of timber in trusses and in all 

 manner of framed work, entailed constant care by the maintenance 

 men in wedging up trusses, or screwing up bolts in order to make 

 the timbers take up their proper share of the stresses. The 

 Engineer for Bridges, by making some of the tension members of 

 iron, in his "type" road bridges, has afforded easy means of correct- 

 ing this defect. Colonial timber gives excellent resistance to 



