Gothic Barrel Vaults under Differential Settlement: The Effects of Boundary Conditions and FRP on Structural Behaviour

Abstract

Vaults are fundamentally strong structures, however, they are particularly susceptible to forced deformation. The 15th century Gothic quire at Bothwell Parish Church is an example of the type of imposed deformations a barrel vault might experience. The vault and its supporting walls exhibit extensive deformation due to ground movement. Failure patterns give insight into the stress distribution and redundancies of a structural system. This information can be used to help diagnose specific problems in structures or predict locations where intervention techniques will be necessary. By isolating a barrel vault’s response to a particular type of deformation, the resulting failure pattern can be defined. This study was undertaken to further the current understanding of the effects of differential settlement on the structural response of a pointed barrel vault. This research explores the pathology and collapse modes of pointed barrel vaults under asymmetric linear vertical displacement through experimental investigation, and assesses the suitability of fibre reinforced polymers (FRP) as a strengthening method for improving the stability of a pointed barrel vault like that at Bothwell.

Historic Barrel Vaults Undergoing Differential Settlements

“…This experimental test has been found to be appealing as it dealt with the simple geometry of barrel vaults, avoiding the complex conditions along intersections at groin vaults or the oversimplification of an arch. Moreover, the test interpreted reasonably well the real deformation of an existing vault (Bothwell) under differential settlement [27]. This made easier the evaluation of the potential of a block-based modelling approach in vaults.…”

“…2) can be noted. For example, on the left of the apex, where the experimental test shows a fast-developing detachment [27] while in the numerical model this failure is smoother and results suggest the generation of a hinge (Fig. 5).…”

“…1c), as the foundations had slipped outwards and the clay under the south-east corner had settled significantly, and had to undergo repair and bracing (2014-16). The horizontal spread component of this vault was examined first [30] in an experimental and analytical programme of a homogeneous model and then the vertical settlement only in a masonry-replica model [27], showing the vulnerability of the scheme to such instability. The two damage patterns were quite similar as well, which makes repair to a certain extent easier to plan.…”

“…Then, PVA glue and water were added. This mixture was used in previous experiments involving cross vaults [31] and it has been found to be convenient for construction reasons [27].…”

“…However, since in this case the experimental set-up was made by timber blocks, for simplicity the blocks have been described by means of an isotropic linear elastic material law, adopting the values 520 kg/m 3 , 9 GPa and 0.25 for density, Young's modulus and Poisson's coefficient, respectively. Since the experimental campaign [27] did not investigate the mechanical response of mortar joints, the mechanical characterization of the contact behaviour has been primarily carried out using the parameters calibrated in [25,26] from small-scale tests. In particular, three different settings (S1, S2 and S3) of the main mechanical parameters, i.e.…”