IV. PERCY ALLAN. 
In most of the American Howe trusses counterbraces are 
introduced, with a view of stiffening laterally the main braces, 
however the braces in the truss under consideration are compara- 
tively short, and as columns require no lateral stiffening ; counters 
in the end bays are therefore not provided. 
As all the braces in the truss are at the same angle, any 
shrinkage in the timbers can be taken up by means of the 
suspension rods ; the iron wedges in the 1886 design are therefore 
not arranged for in this later type of truss. 
The main braces are formed each of two timbers 8” by 42” 
bowed to prevent warping and twisting and connected together 
with bolts and hardwood distance pieces, all the timbers being 
connected to the cast-iron shoes at the top and botton with f° 
bolts. 
Formerly it was the practice to have the top chord in one 
piece 16” by 14” by 42’ long, which having to be bored for the 
suspension rods, rendered renewal very costly, if not impracticable. 
As one of the objects in designing a new type of truss was to 
permit of renewals, a chord, consisting of two timbers 14” by 63” 
bowed and stiffened with hardwood distance pieces was adopted, 
thus securing better timber and giving greater stiffness as @ 
column. 
The side braces adopted in previous trusses being a source of 
inconvenience when footways had to be provided, the author 
decided to design this chord as a column with a varying load, 
unsupported in a lateral direction; none of the text books however, 
consulted by the author treated of such a case. 
The stress in the top chord of a 90 feet span ranges from 69°3 
tons in the centre to 27-72 tons in the end bay. 
As the maximum stress extends only over a length of 10 feet 
of the chord, it would be obviously incorrect to take this stress 0D 
a column the total length of top chord, nor could it be assumed 
that this maximum stress was acting only on a column 10 feet 
long. ; 
