Periodic Reporting for period 3 - STAND4HERITAGE (New STANDards for seismic assessment of built cultural HERITAGE)
Periodo di rendicontazione: 2022-09-01 al 2024-02-29
STAND4HERITAGE (S4H in short) ambitiously engages in introducing new standards for safeguarding built cultural heritage for the next generations, which is a major societal demand. Due to its large diversity, the accurate description of the structural behaviour and safety of heritage buildings is still an open issue, particularly when subjected to earthquake ground motions. Among the most frequently observed seismic damage mechanisms in these buildings, the out-of-plane of masonry walls is acknowledged as the main cause for building loss and injuries to people. There are many unresolved challenges to effectively assess the out-of-plane seismic behaviour of masonry structures. First, it is necessary to understand less well-known phenomena in masonry dynamics, which largely influence the out-of-plane behaviour and the capacity of heritage buildings. A recent blind test to predict the capacity of benchmark masonry structures to resist dynamic excitations demonstrated that, although advanced simulation tools are available, leading international researchers are still unable to consistently provide a collapse estimate. S4H addresses the aspects for successful development of approaches for seismic response prediction of masonry structures, integrating the necessary stages for out-of-plane assessment. Specifically, it aims to generate novel: integrated stochastic-based models to consider the seismic signal in the dynamic response and capacity; datasets of the dynamic response evaluated after an extensive shaking table testing program; numerical approaches for simulation of the out-of-plane seismic behaviour; an integrated analytical approach for out-of-plane seismic assessment of heritage buildings. S4H objectives are in line with the UN 2030 agenda for sustainable cities and communities. The project is founded on the experience of the PI in the topic, and on the interdisciplinary expertise of his team in facing the challenges to provide optimal intervention solutions for heritage buildings.
The S4H team designed and installed tilting and settlement tables. Experiments on masonry corners have already been conducted on the tilting table, highlighting the effect of loading orientation on their collapse. The shaking table and the new 6-cameras DIC system have also been successfully installed at UMinho, and an extensive experimental programme involving free- and forced-rocking of free-standing single-blocks has been completed. A large campaign encompassing vertical spanning strip walls on the shaking table was finished on April 2024. A large campaign on U-shaped masonry structures is now being initiated.
The S4H team has investigated the dry-joint interface stiffness and damping parameters of block-based structures. A new experimental procedure based on vibration tests has been proposed to identify such properties. A novel methodology to correlate the numerical viscous damping with the analytical coefficient of restitution for the dynamic analysis of rocking structures based on extensive numerical simulations was developed. It also revealed the conditions under which rocking motion terminates even when the structure is still subjected to ground motion. The team demonstrated the great impact of low dry-joint stiffness on the seismic capacity of masonry structures, underlining that current design recommendations are not appropriate for these structures. An extensive experimental campaign has been carried out to characterise the mechanics of dry-joint interfaces. Based on such outcomes, numerical models were constructed, and interface stiffness and damping were quantified.
In addition to the real catalogue, a homogeneous simulated dataset covering a wide range of earthquake magnitude, distance and soil categories has been developed through the stochastic source-based approach. A novel stochastic site-based simulation methodology has also been proposed to simulate the low-frequency portion of records accurately. Machine-learning-based ground motion models have been developed to be integrated with the site-based approach for the simulation of scenario events in the next stages. The outcomes of these simulations are being used to understand the effect of signal characteristics on the response of masonry and rocking structures. For instance, the team investigated the seismic response of rocking structures through machine-learning algorithms. Additionally, the suitability of simulated datasets has been numerically tested for alternative masonry prototypes in assessing their seismic response in parallel to code-based ground motion selection and scaling. The team is also investigating the optimal intensity measures for probabilistic seismic assessment of masonry buildings considering both in-plane and out-of-plane responses to define suitable rules for selecting and scaling the ground motions.
Various engineering tools have been developed. A comprehensive limit analysis model for the failure of masonry corners has been developed based on the outcomes of tilting tests. A rapid tool for the seismic assessment of masonry structures, capable of combining limit analysis and rocking dynamics, has been proposed. The team has also provided a graphic tool capable of quickly generating masonry structures with various masonry patterns.
Finally, novel time-based vulnerability curves for the out-of-plane seismic safety assessment have been developed, providing the capacity for different out-of-plane geometric indexes and their seismic response for a wide range of seismicity levels in Europe. Additionally, numerical fragility curves have been derived through a probabilistic performance-based seismic framework and supported by stochastic seismic signals to evaluate the expected damage in regions with limited recorded seismic activity.
The S4H team has investigated the dry-joint interface stiffness and damping parameters of block-based structures. A new experimental procedure based on vibration tests has been proposed to identify such properties. A novel methodology to correlate the numerical viscous damping with the analytical coefficient of restitution for the dynamic analysis of rocking structures based on extensive numerical simulations was developed. It also revealed the conditions under which rocking motion terminates even when the structure is still subjected to ground motion. The team demonstrated the great impact of low dry-joint stiffness on the seismic capacity of masonry structures, underlining that current design recommendations are not appropriate for these structures. An extensive experimental campaign has been carried out to characterise the mechanics of dry-joint interfaces. Based on such outcomes, numerical models were constructed, and interface stiffness and damping were quantified.
In addition to the real catalogue, a homogeneous simulated dataset covering a wide range of earthquake magnitude, distance and soil categories has been developed through the stochastic source-based approach. A novel stochastic site-based simulation methodology has also been proposed to simulate the low-frequency portion of records accurately. Machine-learning-based ground motion models have been developed to be integrated with the site-based approach for the simulation of scenario events in the next stages. The outcomes of these simulations are being used to understand the effect of signal characteristics on the response of masonry and rocking structures. For instance, the team investigated the seismic response of rocking structures through machine-learning algorithms. Additionally, the suitability of simulated datasets has been numerically tested for alternative masonry prototypes in assessing their seismic response in parallel to code-based ground motion selection and scaling. The team is also investigating the optimal intensity measures for probabilistic seismic assessment of masonry buildings considering both in-plane and out-of-plane responses to define suitable rules for selecting and scaling the ground motions.
Various engineering tools have been developed. A comprehensive limit analysis model for the failure of masonry corners has been developed based on the outcomes of tilting tests. A rapid tool for the seismic assessment of masonry structures, capable of combining limit analysis and rocking dynamics, has been proposed. The team has also provided a graphic tool capable of quickly generating masonry structures with various masonry patterns.
Finally, novel time-based vulnerability curves for the out-of-plane seismic safety assessment have been developed, providing the capacity for different out-of-plane geometric indexes and their seismic response for a wide range of seismicity levels in Europe. Additionally, numerical fragility curves have been derived through a probabilistic performance-based seismic framework and supported by stochastic seismic signals to evaluate the expected damage in regions with limited recorded seismic activity.
At the end of the project, the S4H project will provide an extensive experimental dataset of (i) static tilting tests, helpful to demonstrate the adequacy of different materials to be used on repeated masonry testing, (ii) free and forced rocking tests to validate rocking modelling approaches, and (iii) dynamic tests on masonry structures to understand the seismic behaviour of heritage buildings.
The team will develop a novel broadband stochastic ground motion simulation framework. A homogeneous ground motion dataset will be generated through simulations of scenario earthquakes accounting for the stochastic behaviour of input parameters. The dynamic signals used in the experimental campaign will come from a massive dataset of simulated seismic signals generated by the project, based on stochastic analysis of the most important seismic features of real accelerograms recorded during earthquakes. Both seismic input signals datasets and experimental shaking table results will be shared with the broadest community.
S4H will develop fast numerical and analytical tools for the seismic analysis of masonry structures. At the end of the project, numerous analytical rocking simulations would have been conducted to prove their efficiency in predicting the response of masonry specimens under stochastic loading and, therefore, to be used in practice as a simplified analysis tool. Similarly, an all-integrated macro-block approach will be validated to facilitate rapid assessments of masonry structures. This model will also include an automated generation of the geometry for faster and easier practical use.
The team will develop a novel broadband stochastic ground motion simulation framework. A homogeneous ground motion dataset will be generated through simulations of scenario earthquakes accounting for the stochastic behaviour of input parameters. The dynamic signals used in the experimental campaign will come from a massive dataset of simulated seismic signals generated by the project, based on stochastic analysis of the most important seismic features of real accelerograms recorded during earthquakes. Both seismic input signals datasets and experimental shaking table results will be shared with the broadest community.
S4H will develop fast numerical and analytical tools for the seismic analysis of masonry structures. At the end of the project, numerous analytical rocking simulations would have been conducted to prove their efficiency in predicting the response of masonry specimens under stochastic loading and, therefore, to be used in practice as a simplified analysis tool. Similarly, an all-integrated macro-block approach will be validated to facilitate rapid assessments of masonry structures. This model will also include an automated generation of the geometry for faster and easier practical use.