The approach proposed here is linked to Maxwell’s reciprocal representation of force and geometry for structural modelling. It is based on the approach of Fivet & Zastavni [2014] of modelling interactive constraint-based structural equilibriums in which geometrical regions are computed to assess a domain of solutions. An examination is undertaken to establish whether the integral of relevant characterising domains can represent an interactive measure of the level of robustness. The approach is applied to case studies, one of which is the Ponte della Musica in Rome, Italy (by the architect Kit Powell-Williams and engineers C. Lotti & Associati and BuroHappold). Structures are analysed in terms of their strength for withstanding different load combinations and degrees of damage. Allowable geometric areas for thrust line(s) are calculated, synthesising the strengths and dimensional constraints, as well as the redistribution of internal forces.