SPECIFIC ATIOKS FOR STEEL HIGHWAY BRIDGES. 35 
of pin plates shall be provided to give each jaw the full 
strength of the compression member. At least one pair 
of these plates shall extend to the far edge of the tie- 
plates, and the others not less than 6 inches beyond the 
near edge of the tie-plates. 
Pins shall be proportioned for the maximum shears and pi^fnut^ ^^^ 
bending moments produced by the stresses in the mem- 
bers connected, if there are eyebars among the parts 
connected, the diameter of the pin shall be not less than 
two-thirds of the width of the ^adest bar attached. 
Pins shall be of sufficient length to secure a full bearing 
of all parts connected upon the turned body of the pin. 
They shall be secured in position by hexagonal cham- 
bered nuts or by hexagonal solid nuts with washers. 
Where the pins are bored, through rods with cap washers 
may be used. In general, malleable castings conforming 
to the requirements of Section 7, Division I, shall be used 
for pin nuts. Pin nuts shall be secured by cotters in the 
screw ends. 
Unless specifically authorized, bolted connections will 39. Bolts. 
not be permitted. Bolts, when used, shall be unfinished 
or turned as specified and shall meet the requirements of 
Article 19, Section 1, Division II. 
Bolts in tension shall have double nuts. 
Bars and rods wdth screw ends shall be upset to provide 40. xjpset ends. 
a cross-sectional area at the root of the thread which shall 
exceed the net section of the body of the member by at 
least 15 per cent. 
Sleeve nuts shall not be used. 41. sieevenuts. 
Provision for expansion and contraction to the extent 42. Expansion. 
of 3^ inch for each 10 feet of span shall be made for all 
bridges. Expansion ends shaU be firmly secured against 
Hf ting or lateral movement. 
Spans of less than 70 feet may be arranged to shde 43. Expansion 
upon metal plates with smooth surfaces. Spans of 70^^^^°^^- 
feet and over shaU be provided mth rollers or rockers, or 
with the special shding bearings described below. Neither 
rollers nor rockers shall be used for expansion bearings 
at the top of trestle posts. 
Fixed bearings shall be firmly anchored. 44. f i x e d 
Spans of 70 feet and over shall have hinged or pin ^^4''5"'g -pged or 
bearings at both ends. The pedestals or shoes shaU be p^° hearings. 
so designed that all loads will act through the end pins, 
which will be located directly over the geometrical center 
of the bearing. 
Expansion rollers shall be not less than 4 inches in 46. RoUers. 
diameter for span lengths of 100 feet or less, and this 
minimum shall be increased not less than 1 inch for each 
additional 100 feet of span and proportionately for inter- 
mediate lengths. They shall be connected by substan- 
tial side bars and shall be effectually guided so as to 
prevent lateral movement, skewing, or creeping. The roll- 
ers and bearing plates shall be protected from dirt and 
water as far as possible, and the construction shall be such 
