Innovative Structural Enhancement Techniques for Adobe Masonry Structures

UoM administered thesis: Phd

  • Authors:
  • Kurdo Abdulla

Abstract

Earthen structures in the form of adobe masonry are found widely around the world in reflection of the associated low cost, material availability and ease of construction. However, a significant proportion of the world's adobe structures are located in regions prone to extreme naturally derived loads such as those resulting from earthquakes, floods, storm winds, etc. Due to adobe's relatively low tensile strength, heavy mass and inherent brittleness, adobe structures are vulnerable to the horizontal forces associated with these extreme events. In such circumstances, the failure and collapse of adobe structures present a real risk to occupants and is a major cause of casualties. To improve the resilience of adobe structures, it is necessary to provide a suitable means of strengthening. Given the nature of adobe material itself and the locations in which it is abundant, it is important that any strengthening system is commensurate with the cost, availability and buildability of adobe. The work presented here focuses on the use of naturally derived hemp fibre rope applied to the surface of adobe walls as a proposed strengthening method. The structural enhancement provided by the technique is investigated through a thorough study of flexural and shear behaviour of adobe masonry under static loading conditions i.e. in-plane and out-of-plane loads. The technique aims to enhance horizontal load capacity and deformation capacity while minimising the effect on wall thickness and hence usable space within a dwelling structure. To investigate the efficiency of the rope reinforcement system, a series of experimental and numerical studies was conducted. Firstly, detailed characterisation of the adobe material itself was obtained experimentally to help understand fully its mechanical properties. This data were also used to provide input for the numerical models. Additionally, experimental characterisation of the rope material was also conducted. Further experimental works were carried out to examine the effectiveness of the rope reinforcement by testing a number of unreinforced and rope reinforced adobe masonry specimens under four point bending. The results showed that the proposed reinforcement system can enhance the ultimate horizontal load carrying capacity by 2 to 3 times in comparison to the unreinforced specimens and also provides a degree of ductility and robustness. The enhancement factor provided by the reinforcement can vary depending on factors such as the boundary condition of the specimens as well as the rope diameter, rope spacing and configuration. In order to examine the effects of these factors, numerical simulations were required. For this purpose, a simplified micro-model approach utilising a combination of plasticity-based constitutive models and the extended finite element method (XFEM) was proposed. The approach was shown to be an efficient means of capturing nonlinear three-dimensional behaviour and the failure modes of masonry under vertical and horizontal loads via a series of validations against the author's experimental results and a number of other published experimental studies. Using the proposed model, comprehensive numerical investigations were conducted to address the influence of the aforementioned factors on structural performance including application to full scale structures. The results showed that the enhancement in the out-of-plane load carrying capacity provided by the various rope configurations ranged from 1.9 to 3 times the unreinforced case, while the in-plane horizontal load carrying capacity was increased by a factor of 1.4 to 1.9. The deformation capacity i.e. ductility was also increased by around 5 times more than that of the unreinforced cases. The rope reinforcement also limited the crack openings, redistributed cracks within the adobe walls and provided structural integrity. Finally, the performance of the proposed rope reinforcement was assessed numerically against other commonly available reinforcement techniques for masonry and was shown to compare favourably in terms of strengthening and deformation capacity effects.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
Award date31 Dec 2019