Bearing Plates

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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/0.35f^‘_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 by following table

where A₂= full cross-sectional area of concrete support, in²(mm² ).

With N established, usually rounded to full inches (millimeters), the minimum width of plate B, in (mm), may be calculated by dividing A₁ by N and then rounded off to full inches (millimeters), so that BN >=A₁. Actual bearing pressure 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:

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)

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