TIMBER BRIDGE CONSTRUCTION IN N.5.W. VII. 
___ As the two flitches in the bottom chord are independent of one 
another, the whole stress in each flitch has to be taken by the 
two 12” by 3%” wrought-iron plates placed on either side of the 
beam ; on each of these plates four wrought-iron strips 12” deep 
_ by 13” wide by 1” deep are rivetted ; these strips are let tightly 
into the timber and are designed’to take up the whole of the 
_ stress, and as the stress in each flitch is 31°18 tons and there are 
four strips giving a total bearing area of 48 square inches, the 
crushing strain is only -65 tons per square inch, thus giving a 
4 factor of safety of 7} against crushing, whilst for shearing along 
_ the grain a minimum factor of 15 is provided. 
Following American practice, the bolts passing through cover 
: plates are not in any way relied upon, being simply provided to 
j keep the plates up to their work, however as the bolts had to be 
_ provided the author determined to obtain the benefit of them, and 
"arranged for the bolts to be turned and passed through drilled 
_ holes in the plates. | te 
The above joint has also met with the approval of the Engineer- 
— in-Chief for Railways and has been adopted for some of the 
Proposed bridges on the Narrabri-Moree line, whilst in some of 
the later American railway bridges it has proved successful, 
’ despite the fact of it being necessary in some of these pine 
: bridges to arrange for fitting in, eight strips in each plate, 
instead of four as shown in Plate 5. 
_ With this joint, requiring as it does only a straight cut, no 
difficulty is found in obtaining an almost perfect bearing with 
ironbark timber, and so far in the 146 joints in the bridges 
Already erected in this Colony, no trouble has been found in 
effectively making this connection. 
_ The suspension rods, which in the author’s design of truss have 
4 minimum diameter of 2” and 1}” respectively, are placed on 
- tither side of floor beams, and pass through the space between the 
: chords, thus saving the boring of holes through chords and floor 
