CIVIL ENGINEERING FORMULAS

BRIDGE AND SUSPENSION-CABLE FORMULAS 263

for flexural members with unstiffened webs with h/tw150 or for girders with
stiffened webs with a/hexceeding 3 and 67,600(h/tw)^2 :

or stiffeners are not required

For girders with transverse stiffeners and a/hless than 3 and 67,600(h/tw)^2 , the
allowable shear stress is given by

(10.56)

Stiffeners are required when the shear exceeds Fv.

MAXIMUM WIDTH/THICKNESS RATIOS
FOR COMPRESSION ELEMENTS FOR HIGHWAY BRIDGES

Table 10.6 gives a number of formulas for maximum width/thickness ratios for
compression elements for highwaybridges. These formulas are valuable for
highway bridge design.

SUSPENSION CABLES

Parabolic Cable Tension and Length

Steel cables are often used in suspension bridges to support the horizon-
tal roadway load (Fig. 10.2). With a uniformly distributed load along the

Fv

Fy

3 

C

1 C

1.15 1 (a/h)^2 

 190

B

k

Fy

 5 

5

(a/h)^2 

otherwise

k5 if

a

h

exceeds 3 or 67,600 

h

tw

2



45,000k

Fy(h/tw)^2

when

h

tw

1.25





h/tw

when 

h

tw

1.25

C1.0 when

h

tw