Abuh001:
You know what you are looking at, but we can’t see it from here. A simple, well proportioned sketch, with a plan, elevation and section, some dimensions, loads, etc. would truly be worth a thousand words. And, you might get some meaningful, helpful, answers to your problem. I just don’t know what “the bearing length at 0.4 x the height of the wall under the pad-stone consists of 1.5m of brickwork of strength 1 N/mm2 and 1m of brickwork of strength 3.5 N/mm2" really means. Are these two wythes of brick making up the total wall thickness, or are these stacked atop each other making up a 2.5m high wall of one wythe, or are these one wythe of brick stacked end to end making up a 2.5m length of wall, with the beam atop them in some way? The “the bearing length at 0.4 x the height of the wall under the pad-stone,” is a real mystery. Your first, however many words, just don’t explain the problem. Your problem really depends upon how the beam and its bearing plate (pad-stone?) loads the brick below. The stronger/stiffer brick will likely take the majority of the load as a function of the relative stiffness of the two types of brick, and this might lead to differential movement (deflection, compression, shortening) of the two types bricks. If the two types of bricks are stacked atop each other, the beam reaction is distributed over a longer wall length as you move further below the beam bearing, so a higher bearing stress immediately below the beam, in the stronger brick, might be o.k. by the time you get down to the weaker brick below. Maybe the beam baring plate can be designed to accommodate/tolerate this brick strength difference. But, finally the brick strength/stiffness isn’t the only issue, you should test a panel of each brick and use the strength of the brick/mortar combination for your design values.
