To resist a beam reaction, the minimum bearing length N in the direction of the beam span for a bearing plate is determined 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, in2(mm2), required by the bearing plate is:
where R = beam reaction, kip (kN), f 'cspecified 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 A,
Table A Allowable Bearing Stress, Fp on Concrete and Masonry
A2full cross-sectional area of concrete support, in2(mm2).
N established, usually rounded to full inches (millimeters), the minimum width of plate B, in (mm), may be calculated by dividing A1by N and then rounded off to full inches (millimeters), so that BN > or =A1. Actual bearing pressure f p, ksi (MPa), under the plate then is fp, ksi (MPa), under the plate is:
The plate thickness usually is determined with the assumption of cantilever bending of the plate:
t = minimum plate thickness, in (mm) k = distance, in (mm), from beam bottom to top of web fillet fb = allowable bending stress of plate, ksi (MPa)