In a warehouse building that I'm working on, I noticed a few large diagonal cracks extending down at an angle from the lintels of the overhead doors. I could not see any cracks in the foundation that would indicate settlement. Also, there was no vertical displacement. In some locations, it appears that the masonry walls slid off the foundation. Does the heating and expanding of the wall cause this?
From your description, it would appear that differential movement of the clay masonry walls caused the cracking. Clay masonry walls will expand as a result of moisture expansion and thermal movement. If there isn't a sufficient number of vertical expansion joints along the length of the wall, the unrelieved horizontal movement will cause diagonal cracks to occur at openings and, in some cases, at building corners. The building can be repaired by rebuilding the masonry at the cracks and by adding vertical expansion joints at regular intervals along the wall in accordance with the recommendations of the Brick Industry Association in BIA Technical Notes on Brick Construction 18A.