CIVIL ENGINEERING FORMULAS

BUILDING AND STRUCTURES FORMULAS 239

For continuous attachment, use nequal to four times the attached length
along each faying surface.

Bolting Light-gage Members Bolting is employed as a common means of
making field connections in light-gage steel construction. The AISI Specification
for the Design of Light-gage Steel Structural Members requires that the distance
between bolt centers, in line of stress, and the distance from bolt center to edge
of sheet, in line of stress, shall not be less than 1^1 / 2 times the bolt diameter nor

(9.103)

wherePload on bolt, lb (N)
tthickness of thinnest connected sheet, in (mm)
fbbasic design stress, psi (MPa)

That specification also recommends a limit of 3.5fbfor the bearing stress, and a
maximum allowable tension stress on net section of

(9.104)

wheredbolt diameter, in (mm)
sspacing perpendicular to line of stress, in (mm)

CHOOSING THE MOST ECONOMIC STRUCTURAL STEEL*

Structural steel is available in different strengths and grades. So when choosing
steel members for a structure, the designer must compare their relative cost
based on cross-sectional areas and prices. For two tension members of the same
length but of different steel strengths, their material-cost ratio C 2 /C 1 is:

(9.105)

whereA 1 andA 2 are the cross-sectional areas and p 1 andp 2 are the material
prices per unit weight. If the members are designed to carry the same load at a
stress that is a fixed percentage of the yield point, the cross-sectional areas are
inversely proportional to the yield stresses. Therefore, their relative material
cost can be expressed as

(9.106)

whereFy 1 andFy 2 are the yield stresses of the two steels. The ratio p 2 /p 1 is the
relative price factors. Values of this factor for several steels are given in engi-
neering handbooks.*

C 2

C 1



Fy 1

Fy 2

p 2

p 1

C 2

C 1



A 2

A 1

p 2

p 1

0.1^3

d

s

fb

P

fbt

*Brockenbrough and Merritt, Structural Steel Designer’s Handbook, McGraw-Hill.