3.When the system is subjected to a uniformly distributed vertical load, in the effective interaction zone most of the loading will be transferred to the edges of the plate or support regions owing to the arching action. The distribution of vertical stress sz in the wall will then become non-uniform. The intensity of the arching effect may be described by a stress non-uniformity ratio, ksz =sz(avg)/sz(max), while beyond the interactive zone the vertical stress distributes uniformly, and theintensity of the stress is the same as that of the applied load, i.e. szt/w = 1.