x. PERCY ALLAN. 
The wind pressure allowed for is 56ibs. per square foot, on the 
exposed surfaces of kerbs, stringers, and ends of planking, and on 
twice the area of the handrails, ends of girders, top and bottom 
chords, braces and verticals, the whole being taken as an uniform 
moving load. : 
Whilst the author is aware that on the occasion of the 
Dandenong gale, September, 1876, the wind is recorded at the 
Sydney Observatory to have attained a velocity of 153 miles per 
hour, equal to a pressure of 115ibs per square foot, yet the author 
considers there would be no justification for assuming that such 
a phenomenal pressure would extend over such a large area as 
that occupied by such a bridge as that under consideration, and — 
in support of this opinion, points to the existing structures 
throughout the Colony, few if any of which would be now standing 
if ever subjected to anything approaching even the pressure 
allowed for in the Wagga Wagga bridge. 
The minimum factor of safety adopted for timber in the trusses 
is 7 for the stresses due to combined dead and live loads. 
Although this factor may appear to be somewhat liberal, yet it 
must be borne in mind that the ultimate strength of ironbark has 
been taken from tests made on small specimens of picked timber, 
and that a reduction in strength is only to be anticipated in 
large scantlings, again the flitches being sawn, the grain will run 
more or less across the line of the sticks, and as defects in timber 
are so liable to escape even the most severe inspection, it is 
necessary, in the opinion of the author to make a liberal allowance 
to cover such contingencies. 
The floor system adopted in this bridge presents some novel 
features, which, so far as the author is aware, have not previously 
been adopted in any structure in any part of the world. (8 
Plate 7). The main points kept in view were :— 
Ist. The necessity of having a camber in deck to permit of the 
quick escape of water. ‘ 
2nd. The desirability of having a lower lateral system Of 
windbracing, so arranged that the triangulation lines of the 
