beam to masonry wall

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beam to masonry wall
i have a w section which is tying in to a parallel 8" masonry block wall. the wall is existing. i am planning to place reinforced cmu below the seating of the beam. i would like to have a 4" bearing surface but it's not clear how many blocks i should replace with the cmu to provide a sufficient bearing surface. the reaction at beam end is about 10kips. any help would be great. thanks.
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i recently reviewed a failure where the beam sat on a plate anchored correctly into a masonry block with three courses filled below. the location was at a t wall insection. the beam held about a 40'x 30' corner of roof. under heavy snow load the rotation at the end of the beam actually popped the block out just under the concrete filled third course down and dropped the roof about 3 inches. the fix was to remove the block, dowel into the foundation, reinforce and fill two cells for the complete height to the beam seat. good luck.
thanks. as far as anchoring goes. how should be beam be anchored to the wall and/or plate?
what do you mean when you say replace block with cmu?  block is cmu where i'm from.
you may detail a steel bearing plate or a steel plate embedded in the end of the wall.  the beam would frame into this and have a single shear plate connection.  the bearing plate will keep you from inducing addional moment in the wall due to an eccentric connection.  the shear plate would probably allow for more beam end rotation through bolt slip.  either way, use a bolted connection with slotted holes to allow for expansion of the steel beam.  make sure the bolts do not get overtightened, and you may even use a teflon washer between the nut and the flange if you use the bearing condition.  no matter what you do i would make sure you have a good two or three filled and reinforced cells at the connection.
if this is a roof beam, you may also have uplift. is this the case? it may affect how you choose to anchor the beam to the wall.
it is a beam supporting roof joists.
what is the uplift load?
the uplift load is large due to a flat roof.
you want to make sure your uplift doesn't pull off several courses of block so i would suggest that your beam be welded to the bearing plate and the bearing plate have a couple of deformed bar anchors lapped with vertical rebar in grouted masonry cores. extend the vertical rebar sufficiently to engage enough block to resist the uplift. don't forget that you can only use 0.6 x d to resist the uplift and provide enough safety factor (1/0.6 = 1.67).  
if you weld the beam to the bearing plate, when the beam contracts or expands it will pull part of your wall with, cracking it pretty good.
a common detail adopted in the uk would be for the beam to bear onto either a concrete padstone, or a padstone of engineering brickwork.
uplift resistance may be achieved by vertical restraint strapping, which should be sufficiently long to mobilise the dead weight of a section of the masonry panel sufficient to resist the uplift.