Effect of Rotational Base Stiffness on the Behaviour of Loadbearing Masonry Walls

• Author / Creator

  Pettit, Clayton Edward James

• Slender, loadbearing masonry walls are typically used in low-rise commercial and industrial settings, as they are an efficient system to resist out-of-plane (OOP) and gravity loads. Masonry walls are usually built upon concrete footings, with their first course mortared upon the concrete surface, and their reinforcement is spliced to dowels cast into the foundation. Despite the inherent rotational stiffness of this type of connection, when the walls are slender (height-to-thickness ratio > 30) North American codes instruct the designer to assume a pinned condition at the base, neglecting any rotational stiffness provided by the foundation. This results in an underestimation of the capacity of the wall. The goal of this research is to (1) quantify the reactive rotational stiffness at the support for typical foundations used in masonry construction, (2) assess the increase in loadbearing capacity provided by the foundation stiffness, and (3) determine the effect of the foundation stiffness on critical aspects of the structural response of the walls, such as stiffness, ultimate capacity, and failure modes. Overall, it is expected that this research will lead to a better understanding of the OOP behaviour of slender masonry walls accounting for the presence of the foundation in a rational manner.
  To achieve these goals, the research was divided into two steps. The first step comprised a full-scale experimental program in which a total of four identical wall specimens were tested under a combination of OOP and gravity loads. Each specimen featured a unique rotational support stiffness, determined through the evaluation of common foundation geometries and soil properties. Data acquired from the experimental program was then used to evaluate the effect of rotational support stiffness on the flexural stiffness, the failure modes, and the ultimate load capacity of the walls.
  The second step of the research consisted of the numerical modelling of all four wall specimens and of experimental results obtained from similar studies. An analysis model based on the differential equation that governs the displacement of elastic beam-columns subjected to axial and distributed lateral loads was used to investigate the response of the walls including the presence of the foundation. The model accounts for material and geometric nonlinearities through a fibre-section approach. Specimens from multiple experimental programs were simulated using the model with the predicted results showing a good agreement with experimental findings in terms of load-displacement response, failure modes and load capacity. Applications of the model are presented, and the limitations discussed.

• Subjects / Keywords

  • cyclic
  • loadbearing
  • masonry
  • base stiffness
  • flexure

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-0h0h-3z52

• License

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