huangyhg

allowable maximum span for three side-by-side 2x12s - reside
structural loading of wood members is not my forte, but in an attempt to assist my son who is enclosing space in a dry basement, and needs to move a lolly column (if possible) to improve usable space in the new basement room, i pose the following question.
ranch house, one story construction, wood frame, poured concrete basement. usable residential space footprint ~47' x 27' rectangle. three side-by-side 2x12s centered in the building, that support one end of the transverse floor joists, run the length of the building supported on 9' centers by four steel lolly columns. there are no end joints in the runs under discussion, which joints appear first in one 2x12 at the #2 column. the lumber appears to be #1, generally free of knots.
he would like to move the #1 lolly column a distance of 5'-6" so that the resulting first span would become 14'-6" with a consequential shortening of the #2 span. that #1 span currently carries part of the load of the kitchen with normal equipment on one side of the main, three member wood beam, and part of the adjacent living room load on the other side with no unusually heavy furniture. if the column were moved, the new #1 span would carry all of the load of each room.
the load of the hearth of the fireplace of the living room would be better picked up by the proposed new location of the #1 column as it would be almost exactly on the same line. the refrigerator is located at almost the exact proposed location of the #1 column. the stove lies above either the old or new span #1. the floors are wood. the water heater is in the basement.
is moving this #1 column to the new proposed loaction safe to consider? would a shorter new span, approximately 14' or even 13'-6" (but no less), be acceptable?
thanks.
gbcurtis,
of course you know the 'correct' answer - talk to a friendly local structural engineer. he/she will know that timber comes in varying strengths and species, and that no-one can give you a properly considered solution without seeing the beams for themselves.
however, even without doing any calculations at all, it is clearly very ambitious to try to increase the beam span by 50% or more. that could increase the maximum stress by more than 100%.
if we assume that the beam was properly designed in the first place (which could be a rash assumption?), then it is reasonable to conclude that there is not that much reserve capacity in it. after all, why use three 2*12 if two would have done the job?. i would be astonished if you could increase the span as you suggest without strengthening the beam considerably.
don't be too surprised if your structural engineer tells you to add at least another two 2*12, or stiffen the beam locally by bolting on steel channels, or replace the entire beam with a steel section.
also to be considered:
-what will be the floor loadings if you have a big party in the house?
-what are the floor loadings required by your local design codes?
-what will your insurance company say if you change the safety factors in the house and a collapse occurs?
-will you carry any responsibility to any third party who visits the house or purchses the property at a later date?
i agree with austim; employ a structural engineer and sleep well at night.
to austim and jeg:
thank you for a reasoned response.
too much wishful thinking on my part without professional input.

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