XIV. PERCY ALLAN. 
girder design, complete on bearings was £2,800 (Colonial manu- 
facture). Now, to compare the relative cost of these two bridges 
on the basis, that the planking in each bridge will require renewal 
every 12) years, the remaining timberwork every 25 years and 
that the ironwork is everlasting, it is necessary to ascertain how 
much per annum it will take to keep these bridges “ traflicable” 
for ever, in other words to ascertain how much per annum it will 
cost in each case for interest on the prime cost, tarring, painting, 
removal of old material and renewing of each portion as it wears 
out. 
Having obtained the annual charge for each bridge, the difference 
represents the saving effected. The comparison is as follows :— 
ANNUAL CHARGE FOR IRON DESIGN. 
: | a a Fund 4 zs 
3 . 
Hom. = jPriage),; Tutercet. BP ant renewal of | 84 sda 
peop timber. a 
| Rate | Amount. al Life. | Amount. a 
&., £ dj£s.d.j£ s. d. 
Planking...| 180 4°), 7 4 i £220 brig yrs. |13 18 Bshesiee 21 2-2 
Stringers --| 1380/4 5, | 5 0} £17 4D Bhi, aves 9 5 8 
Ironwork.../2490 |4 ,, [99 is ce) rit i Imai Nib Tae 99 12 0 
Painting ...|...... ‘| 60 0 260 0 2 
| eine oe 
£12800) Total annual charge ... £190 0 90 0 0 
ANNUAL CHARGE FOR TIMBER DESIGN. 
a nee Be Fund me FS 
a a Pee | Pca r | dsj eae 
: a ea | 
Rate} Amount.| & oe om a 
oe £ £8, d. £s. difadj/£ 5. a 
mking..., 180 |4°/,) 7 4 0 £220/123 yrs.|13 18 2......... 21 2 2 
Stringers, 
sses, 
floor-beams 
and re- 
mainder of 
timber ij 
superstruc- 
Ure «....... 630 |4 ,, 125 4 0) £950/25 ,, (2216 3)........48 0 3 
Ironwork...) 490 |4 ,, /19 12 0| Nil. |Infinity) Nil. |.........19 12 9 
Painting ...)::../: : WecdT vnrsan 51.5 751.5 7 
£/1300 Total annual charge ...... £140 0 0 
