THE RESISTANCE IN THE WALL SIZING
In the wall sizing it is essential that the stresses induced by loads do not exceed the wall characteristic strength, since, otherwise, the wall will collapse to inadequacy of its strength to the load port. The wall stressed in this way tends to break for “crushing”, with disconnection and fragmentation of the elements that compose it, which, remaining in the original position in which they were manufactured, lead the wall to its ultimate ruin without movements or rotations.
SLENDERNESS IN THE SIZING OF THE WALL
Experimental researches (Tetmajer) and theoretical (Eurelo’s formulas) have allowed to establish that a prismatic solid rectilinear to them with a constant section, of any material, which is subjected to an axial load, as a wall, tends to flex for lateral instability when its slenderness (defined by the ratio of its height on the thickness) exceeds the value λ = 15 and break for buckling when the slenderness exceeds the value supplied by Eurelo’s formulas that for the rectangular section is equal to 28,7 if the wall is constrained to hinge at both ends, 57,4 if it is stuck at both ends.
For this reason Italian legislation does not allow the construction of walls with “critical” slenderness higher than λ= 20 (DM 28 November 1987) and λ= 12 in seismic areas (DM January 16, 1996) and also to the different values defined – and criticized – by last decree of the Ministry of Infrastructure of 14 January 2008.
The walls free at the top, like border fence, bounding steps, railings and similar, it is good to be completed with a bead crowning of reinforced concrete and, if done in a workmanlike manner and with cement mortar, they can have heights up to 7 times their thickness.