Project

STAND4HERITAGE (S4H) - ERC Project - NEW STANDARDS FOR SEISMIC ASSESSMENT OF BUILT CULTURAL HERITAGE

Goal: Built historic masonry structures are important cultural assets in Europe, playing a key role in the economy, through tourism. Their correct maintenance/assessment is thus unavoidable, while they are very sensitive to out-of-plane loading through earthquake motions.
The present project aims at defining new standards for the out-of-plane performance assessment of masonry structures. It follows a very complete process, from the study of the seismic input, to the seismic capacity of masonry structures and the occurence of specific damage limit state.
1) Sampling of realistic earthquake motions generated from real earthquakes, parameter representative variation and Monte-Carlo simulations
2) Extensive shaking-table testing of masonry specimens (plastered, mortared, dry-stack, rocking blocks) under various input signals. Use of state-of-art Non-Damaging-Testing methods (DIC, sonic tests, infrare thermography, ...)
3) Development and validation of intermediate numerical approaches (Rocking dynamics, Macro-element models) against the extensive experimental dataset in a probabilistic way. Incremental Dynamic Analysis used to build up the response statistics.
4) Definition of specific limit state for built heritage (e.g associated to the safeguard of mural paintings) in terms of out-of-plane displacement. Extraction of guidelines for performance assessment of heritage buildings.

Date: 1 September 2019

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Project log

Marco Francesco Funari
added a research item
This paper proposes a general equation to assess the crack inclination upper threshold when non-periodic textures characterise masonry walls. The proposed formulation introduces the computation of the frictional resistance at the macro-block interface by evaluating two masonry quality indexes, i.e., vertical and horizontal lines of trace. The proposed equation is adopted in conjunction with a macro-block limit analysis formulation in which the failure mechanism is parametrised and formulated according to the upper bound limit analysis theorem, coupled with a heuristic solver that is able to minimise the load multiplier and identify the geometry of the associated macro-block. The proposed analytical model is verified in a number of case studies by comparing advanced DEM simulations and numerical results arising from the literature.
Carla Colombo
added a research item
The present work aims to expand the knowledge of the behaviour of masonry corners, which are capital to obtain an integral seismic response in masonry buildings. In particular, the influence of the seismic load orientation (from π/4 to π/2) is investigated experimentally, numerically and analytically. Both units and interfaces have been subjected to a material characterisation process, following which pseudo-static 1:4 scaled experiments on a tilting table have been conducted on a symmetric dry-joint masonry corner. The experimental results have also been simulated using a discrete element model. Finally, a new analytical limit analysis model has been developed, which considers both experimental and numerical observations and accounts for rocking-sliding and flexural mechanisms. In general, a good agreement is found between the three approaches, both in terms of collapse mechanism and load multiplier.
Nathanaël Savalle
added 2 research items
Dry-stone retaining walls can be found worldwide and constitute critical assets of the built heritage for many sloped territories, holding cultural and economic value. Their design currently follows empirical rules, though the first steps towards a static safety assessment have recently been proposed in the scientific and engineering literature. However, the seismic design of these structures still lacks research studies. Therefore, this work conducts discrete element simulations to assess their dynamic behaviour. First, the approach is validated through existing scaled-down shaking table experiments, and it is found that the numerical simulations are conservative (i.e., on the safe side). Next, full-scale dry-stone retaining walls are subjected to harmonic excitations as an idealisation of earthquakes. Finally, based on a simplified limit-equilibrium analytical tool, their seismic behaviour factor is estimated for the first time in the literature, which falls within the proposed values of the European standards (Eurocode 8). This will allow engineers to adopt a validated behaviour factor in practice to assess and design dry-stone retaining walls with a pseudo-static approach.
Nathanaël Savalle
added a research item
Heritage masonry structures are often modelled as dry-jointed structures. On the one hand, it may correspond to the reality where the initial mortar was weak, missing, or has disappeared through time because of erosion and lixiviation. On the other hand, this modelling approach reduces complexity to the studied problem, both from an experimental and theoretical/numerical point of views, while being conservative. Still, for modelling purposes, in addition to the joint friction, numerical approaches require a specific elastic parameter, the dry-joint stiffness, which is often hard to estimate experimentally. This work numerically investigates the effect of the joint stiffness on the collapse of scaled-down tilting test experiments carried out on perforated dry-joint masonry shear walls. It is found that geometrical imperfections of bricks and the absence of vertical precompression load can lead to very low equivalent dry-joint stiffness, which strongly affects the results, both in terms of collapse and damage limit state (DLS) loads, with practical implications for the engineering practice.
Marco Francesco Funari
added a research item
This paper presents numerical investigations using the mesoscale approach coupled with the discrete macro-element approach for masonry structures, i.e., each macro-element represents a single unit stone. At first, parametric analyses are performed on a U-shape masonry prototype made with stone. Nonlinear static analyses are performed to investigate parameters that affect the results when a mesoscale masonry pattern representation is adopted. Results demonstrate how mesoscale representation is a powerful alternative to model unreinforced masonry structures within a discrete macro-element approach (particularly if compared with classic homogeneous FE methodologies). However, one of the main challenges in using the mesoscale approach for the structural assessment of masonry buildings, made with stones having different dimensions, is the unit by unit description. The complexity of the problem, and the amount of information needed, usually preclude the study of these structures deterministically. To this end, a digital tool to generate randomised masonry patterns using a few input parameters is proposed. A box structure is adopted as parent geometry, and ten masonry patterns with different degrees of randomness are investigated by performing nonlinear static and dynamic simulations. The outcomes focus on the influence of masonry patterns and demonstrate how irregularity of units can affect the structural response leading to a reduction in terms of strength and ductility if compared to regular distribution of masonry units.
Marco Francesco Funari
added a research item
A digital tool is presented and made available for the rapid structural assessment of historic masonry domes. It is especially suited for masonry domes that present long meridian cracks; ergo partitioned slices governed by a pushing failure mode. The proposed procedure considers a Heyman’s no-tension mechanical model that has been implemented within a user-friendly visual programming environment. The numerical approach includes parametric modelling of the failure mechanism that allows exploring the domain of solutions using the kinematic theorem of limit analysis. A heuristic search method is subsequently adopted to refine the geometry of the collapse mechanism and to compute the value of the horizontal trust. Validation of the results has been achieved considering St. Peter’s dome. As reported in the literature, the behaviour of this dome shifted from a rigid shell-type — stiffened by hoop stresses — towards a pushing type of dome partitioned by long meridian cracks. Unlike time-consuming and advanced methods of analysis, the present procedure allows the users to perform a structural assessment of a historic masonry dome in a few seconds and offers the possibility of including: (i) the dome’s drum in the analysis, if applicable; and (ii) rings as strengthening measure, whose number, position (dome or drum) and material (capacity) are user-defined. The goal is to make the tool easily and freely available at the disposal of students, researchers, and structural engineers.
Nathanaël Savalle
added a research item
A two-step strategy for the mechanical analysis of unreinforced masonry (URM) structures, either subjected to in- and out-of-plane loading, is presented. At a first step, a semi-automatic digital tool allows the parametric modeling of the structure that, together with an Upper bound limit analysis tool and a heuristic optimization solver, enables tracking the most prone failure mechanism. At a second step, a coupled concurrent FE model with micro- and macro-scales is assumed. A micro-modeling description of the masonry is allocated to regions within the failure mechanism found in the former step. In converse, the other domain regions are modeled via a macro-approach, whose constitutive response is elastic and orthotropic and formulated through closed-form homogenized-based solutions. The application of the framework is based on non-linear static (pushover) analysis and conducted on three benchmarks: (i) an in-plane loaded URM shear wall; (ii) a U-shaped URM structure; and (iii) a URM church. Results are given in terms of load capacity curves, total displacement fields, and computational running time; and compared against those found with a FE microscopic model and with a limit analysis tool. Lastly, conclusions on the potential of the framework and future research streams are addressed. Keywords: Masonry, Micro-modeling, Macro-modeling, two-step approach, Homogenization, URM Applications, Concurrent FE model
Georgios Vlachakis
added 2 research items
Masonry structures have been observed to display a high vulnerability to failure under seismic action. This stems from the fact that their structural configurations usually lack adequate connections among the distinct elements, resulting in the formation of local mechanisms experiencing Out-Of-Plane (OOP) collapse. In this context, rocking dynamics has proven to be a valuable methodology for the analysis of masonry walls. Classical rocking theory can provide a fast solution to the dynamic phenomena taking place if simple configurations are examined. Nevertheless, as the degrees of freedom and the boundary conditions increase, the complexity increases, and thus the classical rocking theory becomes impractical. In the meantime , recent developments in computational modelling of masonry structures are gaining significant attraction. This includes block-based models which inherently consider the complexity of the problem and enable the solution to be obtained easily in the discretised spatial and time domains. However, despite their widespread use, applications of such models usually lack a reliable treatment of damping. The present work attempts to bridge the gap between the well-established energy loss of the classical rocking theory and the treatment of damping of block-based computational models. To do so, the dynamics of the problem are reviewed and an equivalent viscous damping model is proposed. A unilateral dashpot formulation allows the replication of the impulsive nature of the energy loss at impact. Afterwards, a calibration methodology is adopted for the practical range of the problem's parameters and a ready-to-use equation is provided, which respects energy equivalence. The performance of the proposed damping model is also evaluated through comparisons with experimental results.
Unreinforced masonry structures, particularly façade walls, are seismically vulnerable due to their weak connections with adjacent walls, floors, and/or roofs. During an earthquake, such walls formulate local mechanisms prone to out-of-plane collapse. This behavior has been largely investigated using classical rocking theory, which assumes the structure responds as a rigid body undergoing rocking motion, with energy dissipation at impact. Due to the complexity of the problem, however, e.g., number of degrees of freedom or boundary conditions, numerical block-based modeling is gaining momentum. However, numerical models lack a consistent and reliable treatment of the energy loss at impact. This paper bridges the gap between the well-established energy loss of classical rocking theory and the treatment of damping in numerical modeling. Specifically, it proposes an equivalent viscous damping model through novel ready-to-use predictive equations that capture the dissipative phenomena during both one-sided and two-sided planar rocking motion. The results reveal a satisfactory performance of the proposed model through comparisons with experimental results from literature and highlight its universality and robustness through applications of the model in fundamentally different block-based numerical modeling software.
Nathanaël Savalle
added a research item
The observation of damages caused by past seismic events demonstrated the high vulnerability of masonry systems, which represent intrinsically diverse and complex structures with resistance to horizontal forces highly dependent on the capacity of ensuring a monolithic behaviour. In this framework, tilting tests represent a low-cost and effective strategy to obtain the ultimate shear and out-of-plane capacities of masonry structures. In this work, the design of a large tilting table facility is introduced. Moreover, a Finite Element micro-model numerical simulation is presented, which constitutes a preliminary validation of the modeling methodology adopted. With this aim, the methodology has been validated on experimental data from the literature. Failure mechanisms and collapse load factors are compared after performing a non-linear static analysis, being a suitable tool to simulate the progressive tilting process. Lastly, a sensitivity study is conducted with the aim to investigate and identify the parameters that influence the future tilting tests.
Nathanaël Savalle
added a research item
Modelling masonry bond pattern is still challenging for the scientific community. Though advanced Laser Scanning methods are available and allow to extract blocks sizes and shapes of actual masonry structures, they are up to now very time-consuming and complex to set up. Therefore, modelling masonry as an ideal and regular assemblage of regular units is still very common in the scientific field. This paper presents a generative algorithm for masonry specimens built with a single-leaf cond pattern. It is based on C# programming under the environment offered by Rhinoceros (+ Grasshopper). Five components have been constructed (wall, corner, T and cross-connections, and opening). They can be assembled, up to infinity, to build complex masonry specimens. Moreover, they are all parametrised to account for every wish of the modeller. The global methodology is found highly time-efficient, with the creation of an initial geometry composed of 5-10 components requiring around 10 minutes and, while the update due to a parameter variation is done in less than one second. The paper finally discusses the next developments of the promising generative algorithm.
Anjali Mehrotra
added a research item
This paper presents a user-friendly, CAD-interfaced methodology for the rapid seismic assessment of historic masonry structures. The proposed multi-level procedure consists of a two-step analysis that combines upper bound limit analysis with non-linear dynamic (rocking) analysis to solve for seismic collapse in a computationally-efficient manner. In the first step, the failure mechanisms are defined by means of parameterization of the failure surfaces. Hence, the upper bound limit theorem of the limit analysis, coupled with a heuristic solver, is subsequently adopted to search for the load multiplier’s minimum value and the macro-block geometry. In the second step, the kinematic constants defining the rocking equation of motion are automatically computed for the refined macro-block model, which can be solved for representative time-histories. The proposed methodology has been entirely integrated in the user-friendly visual programming environment offered by Rhinoceros3D + Grasshopper, allowing it to be used by students, researchers and practicing structural engineers. Unlike time-consuming advanced methods of analysis, the proposed method allows users to perform a seismic assessment of masonry buildings in a rapid and computationally-efficient manner. Such an approach is particularly useful for territorial scale vulnerability analysis (e.g., for risk assessment and mitigation historic city centres) or as post-seismic event response (when the safety and stability of a large number of buildings need to be assessed with limited resources). The capabilities of the tool are demonstrated by comparing its predictions with those arising from the literature as well as from code-based assessment methods for three case studies.
Nathanaël Savalle
added an update
Free access to the publication "Learning from failure: Damage and failure of masonry structures, after the 2017 Lesvos earthquake (Greece)"
Note that the link is accessible only until October the 6th
 
Georgios Vlachakis
added a research item
On the 12th of June 2017 an earthquake of Mw=6.3 struck SSE of Lesvos Island, causing one human fatality and severe damage to the built environment. The traditional settlement of Vrissa was the most affected area, having masonry structures as the majority of its building stock. The objective of the present study is two-fold: to present the structural damage and failure patterns induced by the Lesvos earthquake to masonry structures; to highlight the causes and weaknesses that led to damage, or the factors that prevented it. Particular attention is paid to traditional construction techniques and architectural features that contributed to the seismic response of the structures, either having beneficial or detrimental effect. To this end, a field reconnaissance has been conducted and meaningful technical conclusions are drawn by the observations. Structural systems of both unreinforced and timber-reinforced masonry are inspected. Besides the identification of frequent cases of local, out-of-plane and in-plane mechanisms, combined global mechanisms are also pointed out. Finally, insight of the performance of past interventions is also given, assisting the challenging task of engineering practice.
Anjali Mehrotra
added an update
The Historical and Masonry Structures (HMS) group of the Institute for Sustainability and Innovation in Structural Engineering (ISISE), University of Minho, Portugal, plans to open soon a position for a junior or experienced researcher already with a PhD (duration of the contract may be up to 4 years) to join the STAND4HERITAGE project, which is funded by a European Research Council Advanced Grant.
The position will focus on the stochastic analysis of the seismic signal with the aim to generate a representative variation of ground motion records (both source and structure-sensitive), and to examine the influence of the signal on the dynamic (seismic) behaviour of masonry structures.
Necessary qualifications: PhD in Civil Engineering or Earthquake Engineering with a strong background in stochastic analysis and geophysics, or similar qualifications.
If interested, please send your résumé to Dr Anastasios Giouvanidis (agiouvanidis@civil.uminho.pt) until Sunday, August 23rd (23:59 GMT).
 
Nathanaël Savalle
added an update
For researchers who are interested in the project and want to participate to it. Some National Funding Agency have concluded an agreement with the ERCEA that allocate grants for researchers to visit/work (for brief period) on ERC granted projects.
Please find more detailed information below, as well as conditions of applications that may be different depending on your country:
For EU researchers, the aim is to help potential applicants to build ERC project proposals.
Please note that it concerns only some national funding agencies.
In any case, you're kindly invited to contact us if you want to build such a proposal either directly or on our website (https://stand4heritage.org)
 
Nathanaël Savalle
added a project goal
Built historic masonry structures are important cultural assets in Europe, playing a key role in the economy, through tourism. Their correct maintenance/assessment is thus unavoidable, while they are very sensitive to out-of-plane loading through earthquake motions.
The present project aims at defining new standards for the out-of-plane performance assessment of masonry structures. It follows a very complete process, from the study of the seismic input, to the seismic capacity of masonry structures and the occurence of specific damage limit state.
1) Sampling of realistic earthquake motions generated from real earthquakes, parameter representative variation and Monte-Carlo simulations
2) Extensive shaking-table testing of masonry specimens (plastered, mortared, dry-stack, rocking blocks) under various input signals. Use of state-of-art Non-Damaging-Testing methods (DIC, sonic tests, infrare thermography, ...)
3) Development and validation of intermediate numerical approaches (Rocking dynamics, Macro-element models) against the extensive experimental dataset in a probabilistic way. Incremental Dynamic Analysis used to build up the response statistics.
4) Definition of specific limit state for built heritage (e.g associated to the safeguard of mural paintings) in terms of out-of-plane displacement. Extraction of guidelines for performance assessment of heritage buildings.