A Combined Empirical and Computational Approach to Creep in Replicas of Historic Mortar

Open Access
Author:
Gimbert, Sally Jean
Graduate Program:
Architectural Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 08, 2008
Committee Members:
  • Thomas E Boothby, Thesis Advisor
  • Charles E Bakis, Thesis Advisor
  • Dr Daniel Linzell, Thesis Advisor
  • Dr Andres Lepage, Thesis Advisor
Keywords:
  • finite element
  • shrinkage
  • modulus of elasticity
  • sand-lime
  • lime-based
  • pozzolanic
  • numerical
  • computational
  • compression
  • creep
  • masonry
  • pozzolan
  • admixtures
  • eggs
  • middle ages
  • beeswax
  • beer
  • mortar
  • historic
  • viscoelastic
  • time-dependent
  • homogenized
  • holistic building
  • FEA modelling
Abstract:
Experimental, analytical and computational methods of analysis are applied to the nonlinear problem of creep in historic masonry. Twelve (12) historically replicated mortars are studied in two (2) sets of six (6) stacked masonry prisms. In addition to the use of a ‘crushed brick’ pozzolan, three (3) popular Middle Ages additives, eggs, beeswax and beer, are also studied across the masonry sets. The mortars are placed under a compressive configuration at a constant stress of 309psi (2.13MPa) for 120 days. Elastic and creep strains are monitored; shrinkage is also noted as a competing variable to the magnitude of creep. Average strains generate a homogenized performance trend; a viscoelastic analytical model is matched to this trend as a predictive mathematical description. The experimental data is found to closely match a modified Burger’s body. Further, a set of material properties are furnished from the derivation of the model including Young’s modulus of Elasticity, Eh; the Bulk modulus, Kh; the Elastic Shear modulus, G2, and other suitable variables to describe the viscosity; G1, η1, and η2. The analytical results are implemented as a constitutive material property law in the commercial program ANSYS by using implicit creep numerical integration schemes. Following, the nonlinear material formulation of the mortar is employed in five (5) preliminary time-dependent models of various solid-unit volume fractions. The numerical results are translated into an overall effective Modulus of Elasticity. These stiffness values are to be implemented as viable numerical modeling references in holistic deformability models of historical masonry structures.