On the loads driving tile detachments

Abstract

Tile detachment from building façades is mainly due to debonding mechanisms triggered by hygrothermal effects. Yet, the hygrothermal loading modes that drive these mechanisms have not been clearly identified, and hygrothermal loads are commonly described directly by heat and moisture fluctuations, which obscures their structural-mechanics implications. This paper addresses both gaps. First, we propose the differential free strain at the interfaces — the vector of differences between the free strains of adjacent layers — as the structural language for hygrothermal loads: a dimensionless measure that maps many hygrothermal states onto one structural response and removes the ambiguity of heating and cooling. Second, we use it to order the hygrothermal loading space into six basic modes: uniform expansion or contraction of the substrate, the adhesive, or the tile. Third, we show, by a kinematic argument at the tile corners and a nonlinear cohesive finite-element model, that only two of them drive debonding — tile shrinkage and substrate expansion, the two modes whose DFSI has a single positive entry — whereas their reverses stop it and the adhesive modes are essentially neutral. Fourth, we show that this selection holds across a 384-case factorial of layer moduli, thicknesses, tile size, and aspect ratio, for tiles bonded to substrates much stiffer in bending than the tile, such as concrete and masonry walls: in every case, the sign of the governing corner peeling traction is preserved. The two drivers coincide with those identified independently in field surveys of detached tiles.