TIMBER BRIDGE CONSTRUCTION IN N.S.W. II. 
trating of the loads at the apices ; thereby relieving the bottom 
chords of secondary stress. 
__ Inall the old types of trusses, the suspension rods passed through 
| ‘the floor beams, and as the braces were also butted against the 
' floor beams, the renewal of these timbers was rendered practically 
out of the question. 
In the later design, Plate 3, the floor beams 15” by 12° 
spaced 10 feet apart are placed between the suspension rods, 
‘admitting of easy renewal, and at the same time saving the 
expense of boring large holes through floor beams for the passage 
_ of suspension rods. 
- With a view to renewals, the horizontal thrust from the braces 
“is taken up by means of castings, having lugs 14” deep let into 
- the chords, and where two lugs are necessary it will be noticed 
that the deeper lug is at the back of the casting, so as to distribute 
the thrust over a larger area and reduce the risk of failure by 
= ‘shearing between the lugs. 
7 
; 
The advantage in using castings in lieu of a number of timbers 
bolted together to form butting blocks for the braces, is the doing 
Way with to a great extent of one of the most troublesome 
uestions in connection with timber bridge work, viz., the lodge- 
ment of water. No matter how carefully the timbers may be 
bolted » seed and reaiact water will, ae a aber time, find 
its way bet ffects; again, 
in the endeavour to get a a joint sine ve ee surface 
the butting surfaces will oftentimes be made slightly concave, in 
such cases when the water does penetrate—there being no escape 
the evil will be intensified. 
The batter braces, which consist of two 14” by 6}” timbers 
wed and stiffened with hardwood distance pieces have been 
tituted for principals ; thus reducing the horizontal thrust 
to such an extent as to permit of the introduction of castings 
lieu of the large timber butting blocks, with the heavy bolts, 
‘Previously necessary. 
