SPECIFICATIONS FOE STEEL HIGHWAY BRIDGES. 25 
In all statically determinate structures provision shallj^^'^^sr^^ai 
be made for expansion due to an extreme variation of 
160° F. with a normal temperature of 60° and a range 
from —40° to +120°. In all statically indeterminate 
structures the temperature stresses resulting from the 
foregoing variation shaU be provided for in the design. 
SECTION 3. UNIT STRESSES. 
Unless otherwise provided the several parts of a i- General, 
structure shall be so proportioned that the unit stresses 
will not exceed the following, except as provided for 
Structural Steel Design under Combined Stresses, 
Secondary Stresses and Allowance for Overload. Un- ^ 
less otherwise noted, all unit stresses are given in pounds 
per square inch. 
STEEL STRUCTURES. 
Tension. ^ 2. Structural 
Axial tension, structural members, net section 16, 000 grade and rivet 
Rivets in tension, where permitted, 50 per cent ^*'®^^- 
of single shear values. 
Bolts, area at root of thread 10, 000 
Axicd compression. 
Axial compression, gross section 15000-50L/r 
but not to exceed 13500 
L=length of member, in inches, 
r= least radius of gyration, in inches. 
Bending on extreme fiber. % 
Rolled shapes, built sections and girders, net section- _ 16, 000 
Pins .._ _ 24, 000 
Shear. 
Girder webs, gross section 10, 000 
Pins and shop-driven rivets 12, 000 
Power-driven field rivets and turned bolts 10, 000 
Hand-driven rivets and unfinished bolts 7, 500 
Bearing. 
Pins, steel parts in contact and shop-driven rivets 24, 000 
Powder-driven field rivets and turned bolts 20, 000 
Hand-driven rivets and unfinished bolts 15, 000 
Expansion roUers, pounds per linear inch where 
d=diameter of roller in inches 600d 
Countersunk rivets. 
^ In metal ^ inch thick and over, half the depth of counter- 
sink shall be omitted in calculating bearing area. 
In metal less than ^ inch thick, countersunk rivets shall 
not be assumed to carry stress. 
Diagonal tension. 
In webs of girders and rolled beams, at sections where 
maximum shear and bending occur simultaneously- _ 16, 000 
Axial tension. o o^hpr m^N 
Wrought iron 12, 000 als. '' '' 
Bending on extreme fiber. 
Cast steel 12, 000 
Cast iron 3, 000 
Shear. 
Cast steel 10, 000 
Cast iron 3, 000 
Bearing. 
Cast steel 14, 000 
Cast iron 10, 000 
Bronze sliding expansion bearings 3, 000 
Bearing on concrete masonry, limestone masonry, * 4. Bearing on 
and better ^ !_ 500 bridge seats. 
