The adobe delta damage model

A local damage model has been developed for interpreting the dynamic performance of Adobe, a traditional form of masonry whose components are made of sun-dried and unpressed soil possibly reinforced with fibres. This paper presents a numerical model to assess the static performance of bricks and mortar of Adobe. It has been validated with reference to the results of a characterization campaign performed in 2016 on Adobe bricks and mortar produced in Germany. Although Adobe buildings are among the oldest examples of masonry constructions, spread in all continents of the world, the properties of the material and the overall mechanical performance are still poorly understood, especially with respect to the influence of the adopted mixture on the mechanical properties. As a consequence, very few numerical models are developed for Adobe. The assessment of Adobe structures is becoming a priority task because they are often spread in areas of the world prone to a wide range of dynamic hazards, whose disastrous consequences must be prevented. As for masonry, the overall performance of Adobe structures depends on the properties of bricks and mortar. Three

types of bricks and one type of mortar with different element mixture compositions were tested in compression and bending tests and their behaviour was analysed. The interpretation of experimental results classifies Adobe as a quasi brittle material, with special reference to concrete. Moreover, it was found out that for the same mineralogical family, the amount of fibres in the mixture of Adobe controls the deformation capacity of Adobe. Overall, a numerical model for Adobe was cast within a damage concept originally defined for concrete. A modified version of the last damage model by Mazars was developed. In order to avoid the typical mesh dependency that characterizes simulations of softening materials, a local regularization algorithm was implemented, starting from the damage delay model developed by Allix. Overall, only two mechanical parameters in compression and

tension are required to calibrate the loading evolution laws of the model. In fact, the initial damage strains and elastic moduli in tension and compression were derived directly from the mean values experimentally associated
to each mixture. For each type of mixture, numerical simulations on resulting bricks were performed in statics for uniaxial compression and three point bending tests using the strength and strain values experimentally derived. The mechanical parameters of the model were calibrated in order to match the experimental force displacement curves. The Adobe delta damage model proves to constitute a suitable tool to predict the material performance of Adobe. This paper resumes the experimental campaign, presents the algorithmic details of the model and the comparisons with respect to experimental data and mesh dependence.