148 





DISCUSSION. 







Member. 



Stress as given. 



Stress 



as proposed 



17 1 • 



43-88 





31-5 



F 10 . 



24-52 



• • • 



3-0 



y, 



35-53 



• • • 



13-0 



Y, 



21-19 





Nil 



James Vicars, b.c.e. — In discussing the valuable paper read 

 before this Society by Professor Warren I am the more interested 

 in the subject, as for several years past I have given close 

 attention and research into the various applications of timber 

 for constructive purposes, and especially into its use in bridge 

 building. My remarks will be chiefly directed to the Cowra 

 bridge section of the paper, especially so from the criticisms and 

 deductions brought out in Mr. Haycroft's remarks. The design 

 of the Cowra bridge as illustrated in Plate 8 will be found to 

 contain details of a novel and well thought-out character, forming 

 perhaps the most important feature in the design ; and when the 

 stresses on the various members of the structure are being 

 determined, these important details must be taken into account. 

 The wedges at the feet of the diagonal braces, for instance, are 

 so arranged as to enable any shrinkage in the latter to be taken 

 up in the line of direct stress, thus maintaining the points of 

 intersection, and by them also is counteracted any tendency to 

 produce tension in the diagonals. Under these conditions the 

 stresses determined graphically in Plate 9, and checked by 

 Kankine's method of sections, are correct. When computing 

 the stress on any particular diagonal, all loads, whether dead or 

 alive, which would tend to produce tension in that brace, must 

 be ignored for reasons already given. For example, take load (1) 

 nearest the left support, part of it is transmitted to the right 

 support through the system of diagonals running from left 

 downwards to right, i.e., through Z 2 , Y 3 , F 4} Y 5 , Y 6 and the 

 end inclined post, but no other diagonals can be affected by this 

 load as they are not connected up ; part of load (2) is trans- 

 mitted to the right support through the same system omitting, of 

 course, Y 2 ; also part of load (3) goes to the right support 

 through the same system, omitting Y 2 and F 3 , the remainder of 

 load (3) gets to the left support through diagonal Y x x and the 

 end inclined post, but does not affect diagonals Y 2 or Y s . By 

 similar reasoning no other loads than (1) and (2) can affect 

 diagonal Y Si which must therefore always be in compression. 

 The stress in diagonal jT 4 is obtained by considering only loads 

 (1), (2) and (3) as acting and loads (4), (5), (6) and (7), which 

 can have no affect on this brace, as non-existent ; and the stresses 

 in the other braces are similarly obtained. I cannot, therefore, 

 agree with that portion of Mr. Haycroft's remarks wherein the 

 stresses as tabulated in the "Summary" and the methods of 



