Thrust layouts in masonry gravity structures

Heyman’s ‘safe theorem’ is widely used to assess the safety of masonry gravity structures. In its original incarnation, a funicular thrust line—i.e., a hanging chain—was used to represent a possible flow of forces through a structure, though this was later found to be problematic in some cases. Following the work of Moseley, a line of resistance has also been used as a representation of a thrust line. However, although this provides a valid representation of equilibrium, it does not facilitate clear visualization of a flow of forces within a structure, making it less intuitive than a funicular thrust line. To address shortcomings associated with funicular thrust lines, the notion of a ‘thrust layout’ is also considered here. This can accurately represent a state of equilibrium while also enabling visualization of the flow of forces. Thrust layouts also allow explicit consideration of the tensile forces that can (or cannot) be reasonably sustained in a masonry construction, such as within constituent blocks but not across weak joints.