I have heard that masonry walls can resist high wind loads by arching action. What is arching action and how does it help to strengthen masonry walls?
As the name implies, arching action works for walls much the way a jack arch works over an opening. For arching to take place, the masonry wall must be locked tightly between a rigid structural system above and below the wall. This can occur when masonry walls are infilled between floor slabs and the mortar is packed tightly between the top of the wall and the floor slab above. As the wall tries to deflect under wind loads, the ends of the wall attempt to rotate. Because the wall is locked between two structural systems, this rotation exerts tremendous compression forces in the masonry walls. Because masonry walls are strong in compression and weak in flexure, arching action can often provide more resistance to lateral loads than can flexural bond. Arching action adds significantly to the wall strength in many older masonry bearing walls. However, if the wall is locked tightly between rigid structural supports, no allowance is made for differential movement when the wall expands and the frame contracts. Such differential movement may be sufficient to crack the masonry or even dislodge it.