huangyhg

bearing plate
i have a bearing plate design example that i follow. i often come up with plate thicknesses exceeding 1", as a result of both the load and the beam shape "k1" value.
if the flange width of the beam exceeds the maximum possible plate width, i see no reason to have the plate thickness exceed 3/8" or just enough to have threaded anchors shop welded to the top, since there will be no cantilever bending.
what are your thoughts?
thank you!
don't forget about osha requirements for base plates.
mbones
you do not know there will be no cantilever until it occurs, which is why most designs allow extra material strength, it is also a little difficult to test all plate materials to standard so assumptions have to be made that some might contain slight shear and crystal problems.
mikehydrophys
mdshydroplane
i'm not sure what you mean by the beam flange exceeding the maximum possible plate width, your plate size should be determined by the allowable bearing stress and the beam reaction.
i assume you are referring to a beam bearing on cmu but i suppose concrete would not be any different. a 1" thick bearing plate may seem thick but if you have a beam with a large reaction bearing on cmu it is not uncommon to have a plate 1" thick, or more.
when you say there is no cantilever i assume you mean there is no cantilever if the bearing plate does not extend past the beam flange, that is only true if you consider the beam flange as distributing the load to the cmu. if you did that you would have to check bending in the beam flange from "k1" to the edge of the flange. i believe this is allowed but in most cases i doubt the flange would be thick enough to resist the bending moment.
its easy to get caught up in the "technical" issues of design sometimes and miss accomodating the real problem.....i would recommend making the bearing plate of ample width, wider than the beam flange, to allow the beam to be installed on the plate properly. contractors find it difficult to set a bearing plate in a grout filled cmu wall or cast-in-place concrete wall in exactly the right spot to allow the beam to rest upon it.
i size my bearing plates with at least 2" extra width on each side of the beam flange so that if there is a slight problem with getting the bearing plate in the right position, the beam will still land on the plate. for example, if i have a beam with a 6" flange, i would design a 10" wide bearing plate to accomodate the beam....that way i've accomodated slight errors and misalignments.
i agree with kvillebasser, you gotta over size the bearing plate. typically they want (need?) to tack weld the beam to the bearing plate to at the least keep it stable but also to stablize the wall for lateral forces as well as possible transfer diaphramatic shear loads too. if the plate is smaller than the beam that is really tough to do and you need to detail it to achieve positive connection someway.
i have a 16.125" wide flange, bearing on a 1.5" thick, 16" wide bearing plate, bearing on a 12" deep (parallel to beam), 16" wide, reinforced concrete core, wrapped inside 8" split-faced, hollow-core, concrete masonry.
the allowable bearing stress exceeds the applied. and the beam is fastened with 0.75" diameter threaded rod anchors shop welded to the top of the bearing plate.
this current situation is taken care of.
for future reference, if my bearing plate is cast into reinforced, poured concrete or reinforced concrete masonry, if the vertical steel reinforcing proves to support the axial load, would the vertical steel reinforcing supersede the need to consider allowable stress on the cemetitious material, thus allow to neglect or ignore any "required" thickness of the plate?
thank you!

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