DIC technique for experimental validation of higher order numerical models

This paper presents an adaptation to the Digital Image Correlation (DIC) technique to aid and improve standard measurement methods in experimental mechanics. The practical application is demonstrated by the validation of the Cosserat Continuum model, using small-scale masonry specimens. Numerical models, such as the Cosserat continuum, play an important role in the identification and description of the mechanical behaviour of structures. Especially when it comes to anisotropic and quasi-brittle materials like masonry, these models are needed to evaluate significant aspects like performance, safety, or the effects of various strengthening interventions. The experimental investigation to validate a numerical model is not always straightforward and several of them remain theoretical. Addressing this, the experimentation presented in this paper evaluates the Cosserat identification in shear, where along with simple shear deformation, rigid rotations, micro rotations and micro couples are also exhibited. With such complex deformations, conventional techniques, such as strain gauges, or extensometers can no longer be adopted. The adapted DIC allows the quantification of these deformation data and validates the numerical model

Adaptation of DIC technique for simplified applications in experimental mechanics

The literature and practical application of Digital Image Correlation (DIC) present sophisticated methodologies and algorithms that through a correlation between image data, capture complex strains and deformation fields. However, its application requires extensive surface preparations, careful calibrations, high computational capabilities, and in some cases is still susceptible to errors. Through two experimental campaigns, this paper presents an adaptation of the 2D Digital Image Correlation (2D-DIC) technique, where instead of a speckle pattern to derive full-field deformation data, markers with high contrast features are adopted to extract point-wise strains. The primary goal of this adaptation is to define an approachable methodology for researchers without any background in DIC or image analysis and offer an additional tool set for experimental campaigns

Caratterizzazione della muratura periodica: metodologia per valutazione dell’influenza dell’orditura e della scala del campione.

In letteratura esistono vari modelli di identificazione per descrivere il comportamento meccanico dell’opera muraria, la cui validazione è limitata ad applicazioni numeriche. Le applicazioni pratiche di alcuni di questi modelli rappresentano spesso una sfida e sono accompagnate da consistenti approssimazioni, limitazioni geometriche, interpretazione di condizioni al bordo e complessità connesse alla relazione tra modelli analitici e risultati sperimentali. Questa ricerca trova spunto dalla differenza tra identificazioni teoriche e applicate. La caratterizzazione meccanica della muratura è stata sviluppata attraverso prove sperimentali su triplette modificate, queste sono rappresentative della tessitura muraria generica. In particolare, si sono utilizzate triplette modificate rispetto alla standard per tenere conto sia il contributo del giunto di testa sia quello di letto. Parallelamente la modalità di sperimentazione standard si è posta l'attenzione su metodi sperimentali basati sulla tecnica ‘Digital Image Correlation’ (DIC) modificata. In tal senso di e stato possibile interpretare comportamento a taglio dell’opera muraria. L’obiettivo è la validazione di modelli teorici quali continui di Cosserat o modelli micropolari.Several identification models exist in the literature to describe the mechanical behavior of masonry, yet their validation is often limited to numerical applications. Practical implementations of some models pose challenges, involving significant approximations, geometric constraints, interpretation issues with loading and boundary conditions, and further complexities in comparing the analytical models to experimental results. This research addresses this disparity between theoretical and applied characterizations of masonry. Mechanical characterization was achieved through experimental tests on modified triplets, representing generic masonry typologies on a small scale. Specifically, these modified triplets were used to account for the contribution of the masonry textures and participation of mortar joints in the overall mechanical characterization. Parallel to the experimentation, the focus was on experimental methods based on a modified Digital Image Correlation (DIC) technique. The focus is particularly on shear behavior, with the objective to evaluate and experimentally validate the Cosserat or micropolar continuum model

Panel 9. Paper 9.1: Implications of rejuvenation on tradition tank irrigation systems - A case study of Ghanapuram, a 13th century temple town in Telangana, India

Telangana state, located in the Deccan Plateau, was subjected to major droughts and floods between the years 1960-2010, which occurred due to the damage and poor management of its historic water systems. Responding to this crisis faced in the region, the Government of the newly formed state of Telangana launched the ‘Mission Kakatiya’, a scheme which aimed to restore centuries-old tank irrigation networks. The Ghanpur tank is among the major tanks that were revived as a part of this project through de-silting and strengthening of the embankment, in 2017. The Ganapuram town, tank and temple complex were established in the early 13th century by Ganapati Reddy a subordinate ruler under the Kakatiya kings, with the tank on the south, and the temple complex on the north of the settlement. The tank spreads over an area of 725 hectares, irrigating 1,200 hectares of farmland through re-laid historic water channels. Historically the tank was managed by the community as collective ownership under the temple. Over time due to change administrative systems, the community was disconnected with its resources, both historic irrigation system and the temple. Currently, each of these resources is under the ownership of various departments, who work independently, addressing parts or portions of the town in isolation, without a collective goal to form a self-sustaining system. The paper on “Implications of rejuvenation on tradition tank irrigation systems” will introduce a critical dialogue on the ways forward in carrying out rejuvenation projects within rural historic landscapes. Here participants will be encouraged to understand various aspects of traditional self-sustaining systems that work within temple towns in India. Further, they will be able to work towards demonstrating means of encouraging community ownership and involvement to facilitate sustainable reintegration, in turn reducing the need to depend on the inconsistent flow of government resources

Specimen size sensitivity on diagonal compression tests for masonry

Experimental testing on masonry specimens is an important field of study for obtaining actual information on material properties, which becomes input information to effectively carry out structural analysis and to design potential strengthening interventions. In both cases, the definition of an accurate numerical model of a masonry structure is fundamental, hence material properties should be determined precisely. When historical masonry specimens are tested (in-situ, taken from site to laboratory, or constructed in laboratory by simulating historical material properties), the quasi-brittle material behaviour given by the poor mechanical properties/ performance of the masonry constituents, pose several challenges. Several authors have already recognized these issues and suggested modifications to the testing rules [1], by modifying specimen and load orientation [2], or by proposing specimens with a reduced scale [3]. The latter approach can be considered successful, as it proposes a valid possibility to perform larger number of tests, allowing for a better reproducibility and reliability. This work focuses on the evaluation of the size sensitivity of the masonry specimen on the results of diagonal compression tests and their interpretation in terms of masonry shear behaviour. Two different specimen sizes are assumed and tested, first square wallets with width and height equal to 0,5 m, and modified masonry triplets, composed of three brick courses. In both the cases Italian ‘standard’ clay bricks are adopted (0,25 x 0,12 x 0,05 m3), with mortar joints of 1 cm thickness and the ‘running bond’ masonry texture is considered. The test results are investigated by focusing on masonry shear stiffness and strength. The deformations are captured by adopting a simple and effective non-contact measurement technique based on Digital Image Correlation (DIC)

Experimental evaluation of elastic shear components for masonry in a Cosserat Continuum

The current research proposes an experimental methodology to evaluate masonry pure shear components, with a particular focus on the validation of the Cosserat or micropolar model by adopting small-scale specimens. The Cosserat continuum model’s ability to represent rich media or textures is well-defined in the literature and ideal for characterizing anisotropic materials such as masonry. The experimental validation is proposed using specimens derived from the REV (Representative Elementary Volume) at the micro-scale. This is realized by introducing mortar head joints to the standard triplet specimen, where two periodic masonry textures, the running and the stack bond (limit cases defining perfect and no overlap), are defined. These specimens are tested in two configurations, first simulating shear along the bed joints and second along the head joints, illustrating orthotropic shear configurations of a Cosserat model

Shear characterization of periodic masonry through numerical and experimental validations at the elementary scale

The literature on periodic masonry provides us with various identification models, with promising numerical validations. However, experimental investigations essential for the practical application of these models are limited. They pose challenges in terms of geometries, unmanageable specimen scales, and even complex boundary conditions, that are nearly impossible to be replicated numerically without the aid of large approximations. Especially, when it comes to experimental validation of strengthened masonry, the number of specimens that are needed for a holistic mechanical characterization is not practically feasible. The current research aims at addressing this limitation, by adopting a masonry specimen at the scale closest to the elementary characteristic cell - the Triplet. Being the smallest scale at which the texture and defining characteristics of a periodic masonry can be sufficiently represented, two masonry configurations, the running bond triplet and the stack bond triplet were realized by intro- ducing vertical mortar joints (head joints) to the standard triplet. The research also adopts a cosserat continuum identification model, which when compared to the classical model gives an opportunity to take into consideration smaller specimen-unit ratios, the micro-deformations, and micro-rotations. In addition to this, FEM models were built and analyzed.The experimental campaign conducted has its focus on shear characterization, where the triplets were tested in a pure shear setup. In addition to the new configurations, the standard triplet was also subjected to these shear stresses, which formed a benchmark for comparisons. The outcome of the experiments allowed the validation of the analytical and numerical models

Panel 9 The Importance of Irrigation Systems in the Rural Landscape

Water has become a vital element in studying heritages, since researchers has realized that heritages are not only about sites per se, but also include multiple elements that reflect human social and cultural development along historical evolution, and water is one of the most important sector to study. To study authenticity of water, it is necessary to take interactions between human and water into consideration, and notice different interactions would result in different discussion on further water management and preservation, for water systems have been changed and reformed by human to adapt to environment and sustain future generations. In this case, the author would like to discuss further water management and preservation based on different interactions between human, water and sites. The examples of heritages along Silk Roads would be provided to illustrate the author\u27s point that further practical approaches on water management and preservation should base on the relationship among human, water and sites

A geometric approach to evaluate the safety of masonry constructions: the case study of St. Scolastica Abbey in Subiaco

The paper presents the structural assessment of the neoclassical Church at the Abbey of St. Scholastica in Subiaco, located close to Rome, Italy. Here the Renaissance and gothic layers, along with the neoclassical reconstructions from 1769, are uncovered to study their role in the overall stability of the structure. With the aid of historic references, on-site visual inspection and a laser-scanning survey conducted, an understanding of the geometrical and structural configuration that defines this historic construction was established. Adopting an assessment methodology based on limit analysis and graphic statics, the structural evaluation was conducted for each of the individual structural elements i.e., by isolating the arches, vaults, buttresses, and for the integrated system as a whole. Through this analysis, the Geometric Factor of Safety (GFS) related to the global equilibrium of the church's section was calculated. Without any claim of comprehensiveness in the case study, this work stands as a paradigmatic example for people intending to check the stability of historical buildings. In fact, the purpose of the research is to present, through a case study and with the aid of limit analysis approach, how the use of GFS can characterise the degree of safety in a simple and straightforward manner