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T. li Piani

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Dynamic characterization of adobe in compression

The influence of fibre fraction in soil mixtures

Conference paper - T. li Piani, T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, M. Peroni, L Koene, G. Solomos, Lambertus J. Sluys

Adobe is one of the most ancient forms of masonry. Adobe bricks are sundried mixtures of clay, silt, sand and natural fibres locally available joined together using mud mortar. Adobe structures are largely spread in areas of the world prone to earthquakes or involved in military conflicts. Unfortunately, almost no literature concerns the dynamic assessment of soil-based masonry components. From earlier research, it was derived that the mechanical behaviour of adobe in statics fits in the class of quasi brittle materials. Its resemblance with cementitious materials concerns the main failure modes and the constitutive models in compression. This study deals with the experimental characterization of adobe components response in dynamics. It is aimed to study and quantify the rate sensitivity of adobe material from bricks at a wide range of strain rates, from statics up to impact conditions. In particular, the influence of fiber reinforcement in the mixture on the mechanical behaviour of the material has been addressed. Adobe bricks are commonly mixed using organic content locally available in the field, from straw to chopped wood. Fibres are added to prevent shrinkage cracks during the air drying process. In modern materials such as concrete, inclusion of artificial fibres is originally meant to enhance the mechanical performance of the material, benefiting from the selective properties of reinforcement and binder. An experimental campaign was carried out in a collaboration between Delft University of Technology, Dutch Ministry of Defence, TNO and the Joint Research Centre (JRC) of the European Commission. Two types of bricks were tested. They both had the same soil composition in terms of mineralogical family and soil elements proportions but only one was mixed using straw and wood. Cylindrical samples were subjected to compression tests at different rates of loadings in compression: low ( _ 1 = 3 104 s1), intermediate ( _ 2 = 3 s1) and high ( _ 3 = 120 s1). High strain rate tests were performed using the split Hopkinson bar of the Elsa-HopLab (JRC). For each test, high resolution videos registered the failure process and force-displacement plots were recorded. Elaboration of results revealed clear trends in the dynamic material behaviour. Adobe, as concrete, is sensitive to the loading rate. The rate effects on the main properties of the material in strength and deformation are also analytically and numerically quantified. Rate sensitivity and failure mode are significantly influenced by the inclusion of fibers in the mixture. These effects are quantified, interpreted and compared with modern SFRC. This paper presents the experimental campaign and the obtained results. Moreover, physical interpretations for the observed trends are discussed. Finally, new formulations for the assessment of the dynamic increase factor of the compressive strength of adobe are proposed.@en

Dynamic simulations of traditional masonry materials at different loading rates using an enriched damage delay

Theory and practical applications

Journal article - T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, Lambertus J. Sluys

A local damage model has been recently developed for the numerical simulation of the static behaviour of adobe bricks. Mesh insensitivity of the local model was obtained by generalizing the damage delay concept based on a Dirichlet boundary condition decomposition integrated in a ...

Ballistic model for the prediction of penetration depth and residual velocity in adobe

A new interpretation of the ballistic resistance of earthen masonry

Journal article - T. li Piani, T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, Lambertus J. Sluys

In this paper, a new one-dimensional phenomenological model is developed for the assessment of the ballistic performance of Adobe. Adobe is a masonry largely spread in areas of the world involved in military operations. Addressing fundamental ballistic parameters such as residual ...

Dynamic behaviour of adobe bricks in compression

The role of fibres and water content at various loading rates

Journal article - T. li Piani, T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, M. Peroni, L Koene, D. Krabbenborg, G. Solomos, Lambertus J. Sluys

This paper presents the results of an experimental research aimed at assessing the material performance of adobe bricks in compression for a wide range of induced strain rates, from statics to high velocity impact. Adobe connotes a traditional masonry whose bricks are made of sun ...

Operative Guidelines for Protection of Places of Worship from Terrorist Attacks

A new approach toward security design of sensitive buildings

Report - T. li Piani

The present thesis is aimed at defining operative guidelines devoted to the prevention and limitation of disastrous consequences for man's life and property in case of terrorist attacks perpetrated in places of worship. These guidelines are meant to be applied by governs of Western societies at different levels of spatial planning, with particular reference to the development of urban security plans. The guidelines are based on the study of significant patterns emerged from the statistical elaboration of a Database, collecting in parametrized form the information concerning one hundred and two terrorist attacks perpetrated against Churches or Synagogues in the world between 2001 and 2015. The list of attacks, located in African and Asian countries [1] are considered as a reliable reference in case of attacks perpetrated in all the Western countries of the world [2]. The necessity for this project is heading within the recognized vulnerability factor that the Italian religious and artistic cultural heritage would represent [3] with reference to a hypothesized escalation of the terrorist treat in Europe. In particular, among European symbols of civilization, Catholic Churches in Italy are thought to represent a particularly attractive target for Islamic terrorism, as unfortunately confirmed while this thesis was being redacted [4, 5]. In fact, with respect to the current long lasting harsh warfare [6] and despite the valuable intelligence and normative effort [7], it is not possible to totally prevent terrorist attacks from happening [8, 9]. Instead, security from terrorism risk in modern society will be based on the capability of translating the projection in the future of the current risks comprehension, in turn based on the evidence of near past or ongoing tendencies, into economically and socially sustainable protective measures [10, 11]. In this sense, the present thesis is meant to achieve the purpose through a new engineering approach applied on antiterrorism, starting from the development of a encoding paradigm of terrorist treat toward modern societies, to be declined as a safety designing tool of city's strategical buildings, within the purpose of achieving the same level of security confidence the society guarantees for dwellings subjected to dynamic loadings [12, 13]. The thesis consists of two parts. The first part is devoted at providing a quali-quantitative assessment tool of the terrorist treat towards places of worship. The second section develops operative guidelines consistently with the treat scenarios inferred in Part I. @en

Housing by people and work

Design principles for favelas residents in economies of commerce and service

Journal article - A.R. Chagas Cavalcanti, T. li Piani

This article proposes a new approach towards the design and planning of social housing destined to residents living in informal settlements of Brazil. It is aimed at restoring the proximity between the labor and domestic functions within the spatial domain of the house. This need ...

The mechanical performance of traditional adobe masonry components

An experimental-analytical characterization of soil bricks and mud mortar

Journal article - T. li Piani, T. li Piani, T. li Piani, D. Krabbenborg, J. Weerheijm, J. Weerheijm, Lambertus Koene, Lambertus J. Sluys

Adobe is an ancient building technology made of sun dried bricks joined together by mud mortar. This paper deals with the physical and mechanical characterization of three different typologies of adobe bricks and one typology of mud mortar produced in Europe. They differed in ter ...

The mechanical performance of traditional adobe masonry components

An experimental-analytical characterization of soil bricks and mud mortar

Journal article - T. li Piani, T. li Piani, T. li Piani, D. Krabbenborg, J. Weerheijm, J. Weerheijm, Lambertus Koene, Lambertus J. Sluys

The mechanical performance of traditional adobe masonry components

An experimental-analytical characterization of soil bricks and mud mortar

Journal article - T. li Piani, T. li Piani, T. li Piani, D. Krabbenborg, J. Weerheijm, J. Weerheijm, Lambertus Koene, Lambertus J. Sluys

The Adobe delta damage model

A locally regularized rate-dependent model for the static assessment of soil masonry bricks and mortar

Journal article - T. li Piani, T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, L Koene, Lambertus J. Sluys

A local damage model is proposed for the numerical assessment of the static performance of Adobe masonry components. The model was applied to simulate the experimental behaviour of sundried soil bricks and mud mortar tested in uniaxial compression and bending. Numerical simulatio ...

Dynamic simulation of masonry materials at different loading velocities using an updated damage delay algorithm of regularization

Theory and practical applications

Abstract - T. li Piani, J. Weerheijm, J. Weerheijm, Lambertus J. Sluys

Buildings and structures in many cities have recently been exposed to an increased number of highly dynamic hazards. These include not only floods and earthquakes but also man made threats such as ballistic impacts and blasts. Thus, the assessment of the dynamic performance of structures made of quasi-brittle materials must account also for high strain rate loadings. In engineering software, numerical simulations of dynamic failure processes are often carried out in a framework of damage mechanics, in which failure is interpreted as a degradation of the elastic material capacity. However, for many damage models, the link between the implemented numerical functions representing the corresponding physical mechanisms aimed is still a controversial issue. This is also the case because damage models suffer from a numerical pathology which prevents the objective evaluation of failure for different spatial discretization. To solve this issue, non local regularization algorithms are often used to solve mesh dependence, often at the expenses of complex identification procedures and non- trivial code implementation. Instead, a locally regularized rate dependent model has been developed by the authors for the static assessment of unbaked masonry materials made of clay sand and silt [1]. It adapts damage delay functions originally proposed in [2] in a local damage model developed for cementitious materials [3] based on the decomposition of the Dirichlet boundary conditions solved with an implicit solver. The regularization properties of the model were shown in [1] in statics. The regularization properties of the algorithm are analysed in this contribution for the dynamic problem of a bar uniaxially compressed at high velocity deformation rates. Furthermore, the physical background of the delay formulation is interpreted in light of the main failure processes commonly depicted for quasi-brittle materials in dynamic tests. In particular, the material parameters of the delay function in [1] are linked in this study to the bridging processes of micro-cracks starting from initial flaws inside the material and the resulting macro-crack development up to failure. Considering the physics shown in literature for quasi-brittle materials under multi-strain rate tests, the constant parameters in [1] are made functions of internal and environmental factors, namely material mineralogical properties and applied loading rates in this study. The resulting delay formulation produces an improvement in the capability of the model both to address the complete stress-strain curve of the response of traditional masonry materials subjected to a dynamic load and the rate of enhancement of the main mechanical parameters typical for these rate sensitive materials when subjected to multi-strain rates tests. This is shown in this paper by means of theoretical tests and practical applications with regards to the results of an experimental campaign performed by the authors on adobe specimens subjected to dynamic tests at three different strain rates, ranging from statics to Split Hopkinson bar tests.@en

Experimental-numerical material characterization of adobe masonry

Tests and simulations on various types of earthen bricks and mortar in statics and dynamics

Doctoral thesis - T. li Piani

Research in this thesis is aimed at comprehensively characterizing the mechanical performance of adobe components. Adobe is a traditional masonry made of sundried bricks and mortar. Bricks are made of soil mixed with fibres and joined together by mud mortar. Adobe is largely spread in areas of the world prone to seismic risk or involved in military conflicts. Its low environmental impact attracts scientific attention also for sustainable applications in current building industry. Unfortunately, the material and structural properties of adobe are still hardly assessed, as a result of centuries of progressive abandonment of this building technology in western countries after introduction of modern building materials in the market. In this doctoral research, a combined experimental and numerical approach was followed. It has been aimed at fulfilling experimental data and knowledge gaps in the study of the main properties of this material. Experimental tests have been performed on bricks and mortar characterized by different mineralogical compositions, fibre percentages and moisture content. Mechanical tests consisted of bending and compression tests. Tests in compression have been performed at different rates of deformation from statics to high velocity impact. Data derived from tests have constituted a solid dataset aimed at interpreting and modelling the mechanical performance of adobe. Experimental trends resulted in physical theories concerning the main features of the quasi brittle response of adobe. In particular, the role of fibres and water content in the mixture on the mechanical response of adobe bricks and mortar has been addressed in this study in the static and dynamic regimes of the spectrum of strain rate induced loadings. The main mechanical parameters in compression and tension for adobe have been statistically determined from the static and dynamic tests. Mechanical properties and physical theories have been framed in several models that interpret the response of adobe for different applications. Constitutive models have been derived to address the uniaxial response in compression at different strain rates of adobes of different mineralogical composition and water contents. A finite element damage model has been developed to simulate the main failure modes specifically observed in earthen bricks at different loading conditions and rates, including high velocity impacts. The numerical study has been devoted at ensuring objectivity of analysis to the results of simulations performed using different mesh refinements of the geometrical model of the tested brick. Furthermore, engineering ballistic models that address the response of adobe walls to small caliber penetrations have been developed in this doctoral research. This thesis contains the description of the performed experiments, the analysis of data, the theoretical interpretations and the models developed for the material characterization of adobe masonry. @en

The Ballistic Resistance of Adobe Masonry

An analytical model for impacts on mud bricks and mortar

Conference paper - T. li Piani, J. Weerheijm, J. Weerheijm, L Koene, Lambertus J. Sluys

A significant number of published papers in the field of penetration mechanics devotes attention to the study of targets made of metal and ceramic materials for protective equipment. In recent times, the progression in harshness of urban warfare is leading western governments to ...

Modelling the mechanical response of adobe components under uniaxial loadings

Abstract - T. li Piani, T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, L Koene, Lambertus J. Sluys

This paper presents a constitutive relationship to describe the uniaxial response in statics of brick and mortar samples of Adobe. This defines a traditional masonry whose components are made of soil mixture reinforced with fibres. Only recently Adobe has started attracting scientific attention, primarily as a consequence of the dramatic failures these structures have suffered in regions prone to earthquakes due to dynamic loadings. Furthermore, it possesses eco-friendly material properties which are attractive features for western countries forced to reduce the environmental impact of modern building industry. Nevertheless, the mechanical properties of Adobe are still largely neglected, especially with regards to the influence of soil mixture components. The study of the structural performance of masonry starts from the assessment of the material performance of its components. Thus, an extensive characterization campaign was organized and performed by Delft University of Technology and the Military Engineering Laboratory of the Netherlands, in order to characterize the material properties of Adobe components. Three types of bricks and one type of mortar, made with different mixture components proportions, were subjected to granulometry, moisture content, density tests and uniaxial compressive and three point bending tests. Predictive formulations for compressive and tensile strength and deformation values have been proposed by the authors [1]. These relations include the dependency of mixture components and moisture contents. In this paper, constitutive laws are developed for Adobe in pure compression and tension according to the experimental results. In compression, the force-displacement curves were interpolated according to several existing constitutive laws and the model originally developed by Priestley for concrete masonry elements was finally selected as best fitting. Despite the differences in terms of mechanical parameters, the analytical assessment revealed that the experimental force-displacement graphs of all the different types of bricks could be interpolated using the same model with the same calibrating values. Furthermore, the uniaxial response in tension was derived according to an inverse approach. A numerical model recently developed and calibrated with respect to the compressive and bending tests was used to simulate uniaxial tensile tests [2]. Also in this case, a common trend among types was observed. The results of the constitutive modelling frames components of Adobe within the class of quasi brittle (geo)materials, with particular reference to concrete-like materials. This paper presents the experimental results of the tested samples and the related analytical and numerical modelling. @en

Progettazione Struttural e Funzione Sociale dello Spazio quale vulnerabilita e soluzione al terrorismo urbano

Journal article - T. li Piani

This article presents the knowledge gaps and the methodological steps inherent the process of standardization of the terrorist threat in urban environments for the structural design and rehabilitation of buildings for civilian use. The necessity for a revision of the current technical codes for building constructions which shall include also the terrorist threat, appears as cogent in light of the progression in number and harshness, of the terrorist attacks recently involving soft targets inserted in highly urbanized environments of European cities, with the aim of provoking the highest number of civilian victims within their everyday life. The normative integration of the terrorist threat in the design process of civil constructions implies performing a number of delicate methodological steps. In fact, the physical-mechanical nature of impact waves referred to explosions or hyper-velocity impacts is different from the ones associated to dynamic loadings already known and properly treated within design codes for civilian buildings, such as earthquakes (or wind). The peculiarity of the threat is reflected in the different behavior which the different types of dynamic loadings provoke on the same structure, requiring an update not simply to the validations currently employed within the structural design, but also including the approach itself inherent the anti-seismic philosophy of design when dealing with terrorism. The unique phenomenology of the terrorist threat with reference to the involved target, primarily lies on the social function of the spatial distributions and relative interactions of the urban fabric of the city in which the target is inserted, that the terrorist attack is primarily aimed to disaggregate. This unique feature requires also the comprehension and subsequent quali-quantitative assessment of the social function of the target and of the social dimension of the attacker (the carrier of the terrorist threat), within the standardization process of the terrorist input. However, this source of vulnerability to man-made threat, intrinsic to most of the buildings and constructions in Europe, potentially rises as promoter of the recovery of an urban harmony often neglected within the Architecture of the contemporary city, toward a philosophy of design of the single building which includes the humanistic function of the architectural and urbanistic elements in which it is inserted. http://www.sicurezzaterrorismosocieta.it/fascicolo-8-2018/@en

Critical review on the material characterization of adobe elements

Journal article - T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, Lambertus J. Sluys

Adobe is a traditional masonry made of sundried earthen bricks and mud mortar. Despite a millennial history of buildings of architectural value, adobe still connotes a so called ‘not engineered’ construction type. Namely, the material and structural properties of adobe are still ...

Development of a dataset on the in-plane experimental response of URM piers with bricks and blocks

Journal article - Paolo Morandi, Paolo Morandi, Luca Albanesi, F. Graziotti, F. Graziotti, T. li Piani, Andrea Penna, Andrea Penna, G. Magenes, G. Magenes

In this paper, a dataset collecting the results of in-plane cyclic tests on unreinforced masonry piers, carried out within different research projects, is presented. The dataset includes brick and block walls with different materials, bed-and head-joint typologies, dimensions, bo ...

Lateral strength Of urm piers: comparison between codified criteria and in-plane test results

Conference paper - Luca Albanesi, Paolo Morandi, F. Graziotti, T. li Piani, Andrea Penna, Guido Magenes

The lateral resistance represents one of the most significant wall parameters to be used in the seismic analyses for the design/assessment of masonry buildings. In this article, an investigation on in-plane lateral strength of URM piers has been proposed thorough a comparison bet ...

Modelling the mechanical response of adobe components under uniaxial loading

Conference paper - T. li Piani, T. li Piani, T. li Piani, J. Weerheijm, J. Weerheijm, L Koene, Lambertus J. Sluys

This paper presents a constitutive relationship to describe the uniaxial response in statics of brick and mortar samples of Adobe, a traditional masonry whose components are made of sundried soil mixture reinforced with fibres. Only recently Adobe has been attracting scientific attention, primarily as a consequence of the dramatic failures these structures have suffered in regions prone to earthquakes. Furthermore, it possesses eco-friendly material properties which are attractive features for western countries forced to reduce the environmental impact of modern building industry. Nevertheless, the mechanical properties of Adobe are still largely neglected, especially with regards to the influence of soil mixture components. The study of the structural performance of masonry starts from the assessment of the material performance of its components. Thus, an extensive characterization campaign was performed by Delft University of Technology and the Military Engineering Laboratory of the Netherlands. Three types of bricks and one type of mortar with different mixture components proportions, were subjected to granulometry, moisture content, density tests and uniaxial compressive and three point bending tests. Predictive formulations for compressive and tensile strength and deformation values have been proposed by the authors. These relations include the dependency of mixture components and moisture content. In this paper, constitutive laws are developed for Adobe in pure compression and tension validated by experimental results. In compression, the force-displacement curves were interpolated according to several existing constitutive laws and the model originally developed by Priestley for concrete masonry elements was finally selected as best fitting. Despite the differences in terms of mechanical parameters, the analytical assessment revealed that the experimental force-displacement graphs of all the different types of bricks could be interpolated using the same model with the same calibrating values. Furthermore, the uniaxial response in tension was derived according to an inverse approach. A numerical model recently developed by the authors and calibrated with respect to the compressive and bending tests was used to simulate uniaxial tensile tests. Also in tension, a common trend among types was observed. The results of the constitutive modelling frames components of Adobe within the class of quasi brittle (geo)materials, with particular reference to concrete. This paper presents the experimental results of the tested samples and the related analytical and numerical modelling.@en

Contributed

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High-dimensional numerical optimization of fiber reinforced polymers with variational autoencoders and Bayesian optimization

Master thesis - J. Storm, Lambertus J. Sluys, I.B.C.M. Rocha, T. li Piani, G.N.J.C. Bierkens

Designing engineering structures relies on accurate numerical simulations to predict the behaviour of a structure before its realization. In the design process, many variables influence the final structure. There is an incentive for optimizing the design based on the desire for cheaper structures and less material usage. Although a wide variety of optimization techniques exist, in practice many structures are not fully optimized and could fulfill their purpose with less material usage. This partly results from optimization techniques generally requiring many simulations for problems with a high number of variables. In creating increasingly complex models, simulating its performance can take up to days or weeks to compute, incentivizing the development of optimization methods that use as little simulations as possible. The goal of this thesis is to provide a method of optimization which significantly reduces the required number of simulations to be performed, aiming to overcome the issue of required computational effort. The optimization problem used in this thesis is the geometric optimization of a fiber reinforced polymer (FRP) microstructure. Each evaluation requires a Finite Element analysis, and many parameters are required to describe the geometry. The goal is to find the maximum stress at perfect plasticity during uniaxial tension, interpreted as a measure of strength. While generally only fibers with a circular cross-section are used, here a morphing parameter is introduced that changes this shape between being circular and square. Furthermore, fibers are allowed to overlap, effectively creating a single fiber with a complex shape. This geometry optimization provides a challenging problem for which different optimization techniques can be compared. The approach taken in attempting to minimize the number of function evaluations is a combination of several machine learning methods. Based on a limited number of initial samples, Bayesian optimization (BO) is applied. In BO a prediction model in the form of a Bayesian Neural Network (BNN) is created and used to inform further sampling. This prediction model provides a mean and a standard deviation in its prediction, both of which are used to find the best point to sample next. The number of initial samples required to create an accurate prediction model increases exponentially with the number of parameters. It is therefore opted to first use a variational autoencoder (VAE) to reduce the number of parameters in which BO is performed, by encoding the parameters in a lower dimensional representation. The variational autoencoder does this without requiring any function evaluation. Results show that when encoding the original parameters using the VAE, the encoded representation is unable to recreate all possible configurations of the original parameters. Furthermore, by transforming to a lower dimensional representation, within this representation the complexity of a function increases compared to the original function, generally leading to many local optima. This complexity proves difficult for the BNN to accurately predict based on a limited number of samples. As a result, BO does optimize the result, but does not reliably find the global optimum of the reduced parameter space. No clear conclusion can be made on the overall performance of the method compared to alternative optimization methods. Recommendations are made for what additional studies could be performed. Further recommendations are given for solving issues limiting the current performance as well as possible additions to the framework. The fiber geometry optimization serves as a good case to compare different optimization methods. It is shown that the geometry has a significant influence on the mechanical performance of a FRP microstructure, and optimization is therefore beneficial. The load case considered is however too specific for the optimized result to have direct practical use. Still, it does demonstrate that the results of an optimization study can be generalized. As the optimization framework is data driven, the optimization objective could easily be extended to study more realistic problems.