huangyhg

lvl header/keybeam question
i have a 14' long header situation with bearing at 3 points (the ends and the midpoint at 7'). i am using keybeam software to size this lvl header. when i put my loading in the beam size i have selected fails, the bending moment and shear values are well within capacity, only 24%, but it fails the beam based upon "maximum reaction". i am not sure i agree with this mode of failure, curious your guys' thoughts. as long as i have proper bearing area under these bearing points shouldn't the beam be fine? i do understand that there is a horizontal shear associated with a vertical load but the software indicates i'm only at 24% of allowable shear. if i break this header up into 2, 7' headers everything is fine in the software regarding maximum reaction, but i know the builder will just put one long header in no matter what i specify. i do understand that a 14' vs. 2, 7' headers does indeed induce additional shear stress at the mid point bearing section but i'm just not convinced this beam will fail at that point. any thoughts are appreciated..
thanks,
your result may be telling that the width of the header may not be wide enough. this means that bearing pressure is too high which is causing the contact area to fail.
i agree with shin25, but as you say in your op, as long as you provide enough bearing area not to exceed the allowable you should be fine. what is the program assuming for the bearing area at the middle support? if this accurately represents your condition, then there might be a problem. if this is just a program default that doesn't represent your actual condition and you can size that support not to exceed the allowable bearing then you should be fine.
"maximum reaction" failures sounds to me like perpindicular to grain bearing failures, not shear failures. some programs will check both the beam (lvl perp. to grain values can be as high as 1000psi) and the wall top plate which may be something crappy like spf south which is around 335psi. i'm not familiar with keybeam software, though.
i think ctcray is correct. i looked more at what the program is doing and there is plenty of bearing width on the member as well on the column. i think indeed it is a perpindicular load issue. i always look at perpindicular load considerations when i have a column resting on a bottom plate, but i've never considered it for a header resting on a column. it seems the program was assuming i only had a 4x4 column for support, not the 6x6 which i actually have. thanks for the help.

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