ledger board construction concern

huangyhg

ledger board construction concern
i just bought a house and have some concerns, or perhaps i'm a bit paranoid, about the weight i'm placing on the 1st floor.
the idea of ledger board construction was new to me, and i really never considered it until after buying the house.  the whole concept is distressing.  how do i know when i am placing to much weight on the floor?  i have the rooms packed with chairs, tables, and couches. i also have several thousand books in cases made for me.  in a month i will have 50 people over for an event.  how do i make sure the floor is safe?  should i just get some lolly (spelling?) columns and a 4x4 to reinforce the pressure put on the main beam and the small strip of wood that was run along the main beam 90 years ago to sit the joists on?
thanks in advance,
jeff
i'm not familiar with ledger board construction, but, if it the the manner of securing a horizontal member to a stud wall and bearing the ends of the joists on this   
ledger construction
the usual ledger construction is a 2x2 or 2x3 nailed to the side of beam with notched joists bearing on the ledger. in this case the joist load is limited to that which will have a joist reaction that will not exceed the cross grain allowable bearing on the joist end or the the ledger. the usual case 1 1/2 x 1 1/2 inch area times allowable bearing stress for the wood species and grade (in the neighborhood of 400 psi)is approximately 900 pounds. the lateral load capacity of the ledger nailing must also be adequate to safely sustain the load. the nail spacing should be such that the joist reaction (live + dead loads) does not cause nail loads that the exceed the allowable. see the nds manual for fastener loads on wood of a given density. hire a structutal engineer.
jmcnpe:
thanks for the enlight; i hadn't encountered "ledger board" construction as a common method, before.
jmcnpe's advice about having a structural engineer come look at the framing is good.  but if the structure has been standing for 90 years, it has probably been fairly well load tested unless the occupancy has changed or there is evidence of deterioration.
i have run into ledger boards in old houses....and many times they aren't 2x material, but 1x, barely 7/8 of an inch across! fortunately, code loading is quite conservative, and there's a very large safety factor in allowablew nail strength. also, the wood used a hundred years ago is considerably stronger than currently harvested material.
if it were my house, i would replace the ledger with joist hangers.make sure that any hangers you get are wide enough for the joists, because the old sawn lumber standard was somewhat wider than current 2x material.
with the reference to 'old' framing.  is the manner of construction similar to what we refer to as 'balloon framing'?
i only use ledger strips for a construction guide till the joist hangers can be installed.
what about installing a few columns with the metal plates at the top?  if the plate covers the strip of wood that the joist hangs on, it should in theory take load off the ledger board, at least i think?  since i only use the basement for storage, the columns seem like an easy, quick, and cheap solution to my fears.  does this make sense?
thanks again in advance.
consider installing a beam (column supported) under the joists.
ledger construction for floor joists in quite common in my area.  typically the code covers the method by which the ledger must be installed.  granted your house pre-dates most building codes.  the strength is provided as the others have indicated, through shear and compression.  where i see most of them fail is through rotation and subsequent deflection as the support.  calling an engineer is a good idea, but perform a common-sense double check first, does ledger look like it is sagging or rotated under the current 'furniture' load. if there are hardwoods above, does the flooring have significant gaps or undulations?  if you do have a problem and the ledger is in good shape, you may be able to simply screw it back to resist rotation and nail it under the joists to provide shear.