To resist a beam reaction, the minimum bearing length N in the direction of the beam span for a bearing plate is deter- mined by equations for prevention of local web yielding and web crippling. A larger N is generally desirable but is limited by the available wall thickness.
When the plate covers the full area of a concrete support, the area, in 2 (mm 2 ), required by the bearing plate is
A 1 = R / 0.35 f ‘ c
Where R = beam reaction, kip (kN), f ‘ c = specified compressive strength of the concrete, ksi (MPa). When the plate covers less than the full area of the concrete support, then, as determined from Table
Full area of concrete support 0.30 f 'c
Sandstone and limestone 0.40
Brick in cement mortar 0.25
♣
Units in MPa = 6.895 X ksi
where A 2 = full cross-sectional area of concrete support, in 2 (mm 2 ).
With N established, usually rounded to full inches (millimeters), the minimum width of plate B, in (mm), may be calculated by dividing A 1 by N and then rounded off to full inches (millimeters), so that BN ³ A 1 . Actual bearing pres- sure f p , ksi (MPa), under the plate then is
F p = R / BN
The plate thickness usually is determined with the assumption of cantilever bending of the plate:
t = ( ( 1 / 2) B – k ) ( 3 f p / F b ) ½
where t = minimum plate thickness, in (mm)
k = distance, in (mm), from beam bottom to top of web fillet
F b = allowable bending stress of plate, ksi (MPa)
