bearing capacities of steel angles

huangyhg

bearing capacities of steel angles?
hi.  i'll apologize in advance for the long post.....
i am an environmental engineer by trade, so i do not know a lot about this structural stuff, but here's my problem.
i have a really old house.  it's basic construction is four stone walls with a single large beam spanning from gable end to gable end to act as the main support for each floor(story).  from this main beam there are joists runing to the outer stone walls to support the floors of each storey of the building.  one of these joists (that supports a divider wall on the first floor) has cracked at the point where a smaller member is mortised into it causing the wall above to sag, throwing the doorway through the wall out of kilter.  i want to jack up the beam around the crack and install a steel angle along its length to support it.  i plan to install steel posts set on footers to support each end of the steel angle and then bolt the cracked timber to the steel.
the wood joist that cracked has dimensions of 3" x 8" x 7 feet long.  i planned to use an angle that is "l" shaped - long side 5 to 8 inches and short side 3 to 5 inches.  minimum of .25 inches thick.
problem is i do not know if any standard sized steel angles fall within this range.  nor do i know if this thickness steel angle will be as strong as the 3 x 8 timber that it's replacing/fixing.
any help is greatly appreciated, even if you can only supply me with the standard dimensions of steel angles available along with their load bearing capacities when supported by a column at each end.
i should mention that rotational forces on the steel angle should be negated by the fact that the wooden beam that it will be sistered to is mortised into the main beam and inserted into a pocket in the stone wall, both of which should hold it upright.
thanks again.
l8x6, l8x4, l7x4, l6x6, l6x4, l6x3.5, l5x5, l5x3.5, l5x3 are all standard sizes.
i am curious as to why you would choose steel angles and footings if you only have a cracked floor joist?
is it possible to jack up the cracked joist and sister some new 2x joists?  most likely 2x8 joists.
mjohan:  i don't believe that i can conventionally sister the beam for the following reasons:
in an attempt to help you understand the layout a bit better, the house is of georgian architecture. stone construction of the outer walls with timber framing to support the interior structure (walls floors and stairs)
the house has a center beam that runs the entire width of the house from gable end to gable end and is seated at each end within the stone wall of the structure.it is like this for each floor of the house.(first, second and attic)
the house is set up so that each floor has a center hall/stairwell that runs perpendicular to the main beam with one room on either side. (both the attic and basement are large undivded rooms. the stairs just enter the middle of each.)
the floor joists for the rooms are set perpendicular to the main beam.  they are attached to the beam via a mortise and tennon joint and are nestled in the stone wall at their other end.
when you are in the basement looking up at the rafters - in the area of the center hall/stairwell there are oversized joists (at least 3 x 8 inches rough cut lumber, maybe more i haven't actually taken a ruler to it yet) that frame out the area of the center hall in such a way that the dividing walls in the rooms above are situated directly above them.
the floor boards in the hallway run parallel to the gable ends of the structure (perpendicular to the main beam); therefore there are several smaller timbers joined to these oversized joists via pegged mortise and tennon joints to support the hall floor over the lengths of its floorboards.
it is at one of these joints that one of the oversized joists is cracked through.  since the dividing wall for the room upstairs rests directly on center of this joist,and there are cross   
i see your point.  i take it your beams and joists are also open.  
angles which pylco has mentioned are all angles which might interest you.  each will have a minimum standard thickness, 1/4" to 1/2".  they will all, most likely work for your purpose.  you might want to use 1/4" or bigger lag screws @ 2' on center to also attach the angle to the cracked joist.  if it is 7' long, use four lags.  only a suggestion.  good luck.
hb2u,
i wanted to let you know that a calculation assuming 500 plf on an angle 5x3x1/4" thick, assuming laterally restrained in the vertical plane, would calc. slightly overstressed according to aisc.  
it sounded like your joist is also acting as a beam.  without telling you what size, bigger is usually better.  take care.  
thanks for the information!  i spoke to the local steel place and they have  6 x 3.5 available in 3/8" thickness so i'm going to go with that.
again, thanks for all of the information.
your welcome,
one last thought... check out simpson hangers to replace that steel column you are suggesting.  it does not seem necessary to install a column and it might cause you more problems.  
i am actually going to take a column out of my basement and design a flitch plate to enable a further span of my main beam.
hb2u,
what is the span between supports of this angle beam you wish to install.
vod
voyageofdiscovery:  there will be one post at either end of the steel angle.  they will be 7 +/- feet apart.  there is a doorway centered along the seven foot span that is about 32 inches wide. loading will look like this...
    w w d d d w w
    s  t  l  a  n g  l
    p                    p
    o                   o
    s                   s
    t                   t
where "w" is the wall, "d" is the door, "stlangl"
is the steel angle.
thanks for any input that you have.
hi hb2u,
according to the march 1981 edition of civil engineering asce a single angle lintel 6 x 3.5 x 3/8 with 7ft of clear span should be good for 1314 lbs point load situated at midspan or 375 lbs/ft udl with deflection of l/921 and l/806 respectively.
your doorway may be transferring load from above, directly down to the supporting beam beneath it, so include the loads above this doorway as well when figuring your loads.
hope this helps.
vod