CIVIL ENGINEERING FORMULAS

BUILDING AND STRUCTURES FORMULAS 217

WithNestablished, usually rounded to full inches (millimeters),the mini-
mum width of plate B, in (mm), may be calculated by dividing A 1 byNand
then rounded off to full inches (millimeters), so that BNA 1. Actual bearing
pressurefp, ksi (MPa), under the plate then is

(9.36)

The plate thickness usually is determined with the assumption of cantilever
bending of the plate:

(9.37)

where tminimum plate thickness, in (mm)
kdistance, in (mm), from beam bottom to top of web fillet
Fballowable bending stress of plate, ksi (MPa)

COLUMN BASE PLATES

The area A 1 , in^2 (mm^2 ), required for a base plate under a columnsupported by
concrete should be taken as the larger of the values calculated from the equa-
tion cited earlier, with Rtaken as the total column load, kip (kN), or

(9.38)

Unless the projections of the plate beyond the column are small, the plate may
be designed as a cantilever assumed to be fixed at the edges of a rectangle with
sides equal to 0.80band 0.95d, where bis the column flange width, in (mm), and
dis the column depth, in (mm).

A 1 

R

0.70fc

t

1

2

Bk

B

3 fp

Fb

fp

R

BN

TABLE 9.3 Allowable Bearing Stress, Fp, on Concrete and

Masonry*

Full area of concrete support

Less than full area of concrete

support

Sandstone and limestone 0.40

Brick in cement mortar 0.25

*Units in MPa6.895ksi.

0.35fc

B

A 1

A 2

0.70fc

0.35fc