Abstract

Complex masonry monuments represent an important part of the built cultural heritage and most of them are vulnerable to seismic actions. Their large scale, irregularity, and heterogeneity makes it challenging to characterize their structural behaviour. This work addresses the state of conservation as well as the structural behaviour and seismic vulnerability of the most ancient body of the National Palace of Sintra, Portugal: the Bonet building. This body was built on top of Arabic foundations during the reign of King Dinis, around the year 1281, and since then few alterations were made to the building. In order to minimize the multiple uncertainties usually existing in complex masonry buildings, whether related to geometry or masonry mechanical properties, a detailed structural survey was conducted together with different in-situ experimental tests. All the tests performed were important to the adequate characterization of the building and the calibration of the numerical models. The final values adopted for the mechanical properties of the rubble stone masonry are presented and can be used as a reference for future works in ancient Portuguese monuments of the same period. Afterwards, nonlinear static analyses were performed in two different software (3MURI and ABAQUS). Comparisons and discussion of the results are made. The differences in modelling strategies and characterization of materials between the two software are considered with regard to their realism, computational effort, data availability and applicability to large scale structures. Efforts to calibrate and obtain the same behaviour of the building for the different software were made, involving geometry, boundary conditions and characterization of the material constitutive laws.

Abstract

The Bibi-Khanum Mosque was originally built in 1399-1405 and was one of the largest and most magnificent mosques in the Islamic world during the 15th century. In recent years, the monument underwent several complex reconstructions. Among many other major restoration activities, the inner arch of the portal that collapsed in the 1897 earthquake was restored. The monument has been restored to be one of the best shapes in its history, thus it has become essential to conduct continuous structural health monitoring (SHM) of it to ensure its preservation for humanity. The SHM became the main objective of an ongoing extensive project, some results of which are presented herein. The structural health monitoring consisted of three major phases. The first phase includes a real-time monitoring of the monument by seismometers, which are permanently installed throughout the monument. They are used to monitor the effects of large and small earthquakes and ambient vibrations on the resonant frequencies of all major structures of the monument. By utilizing a system identification approach, the possibility of a structural anomaly development can be detected from the change in its resonance frequency. The second phase consists of subsequent laser scanning that is deployed to monitor anomalies of the monument’s geometry in 3D. The monument’s geometry is captured as a collection of points, which is called a “point cloud”. Laser scanning is planned to be conducted several times a year to capture global movements of the monument due to changes in the elevation of the underground water table in rainy and dry seasons. The third phase focuses on a development of a finite-element (FE) model based on the as-found geometry of the point clouds. It is calibrated based on the collected data to ensure acceptable correlations with the results of the measurements. The FE model is generated for use in future restoration efforts to evaluate the performance and efficiency (if any) of the proposed restoration measures. Based on the results of numerical simulations and structural health monitoring, preventive measures will be developed. In addition, recommendations for further preservation of the historic monument will be developed. This paper describes the preliminary results of the first phase and current results of the second phase of this multiphase project.

Abstract

In the last two decades, the province of Groningen, located in the North-East of the Netherlands, has been subjected to an increasing number of earthquakes induced by gas extractions. The existing building stock is mainly composed by unreinforced masonry (URM) buildings not conceived to resist seismic loads. The need of reducing the vulnerability of these buildings by means of retrofit interventions, led to the development and adoption of a new guideline (NPR9998:2018). As regards the seismic assessment of URM buildings using nonlinear static analysis, the guideline includes significant differences with respect to Eurocode 8, which is adopted in other European countries. The more significant differences lay in the description of failure mechanisms and constitutive laws of piers and spandrels, inthe identification of limit states and in the calculation of seismic demand. In the last years, the assessment and retrofit in the region has been carried out using software based on an equivalent-frame strategy: among these, the 3Muri software has been widely adopted. The solver of this program is the research software TREMURI. In this work, a new version of the solver adopted by the software 3Muri, complying with the requirements of the new Dutch guideline, was developed; the tool was then validated with simple examples. To illustrate the specificities of the new guideline, the seismic assessment of a building representative of one of the most widely diffused URM building typologies in the area was performed.

Abstract

Earthquakes are some of the most serious causes of degradation and destruction of the heritage buildings. The earthquake can cause different damages, directly and indirectly to the historical buildings and their elements. The biggest part of the heritage buildings was built essentially following empirical rules, refining the proportions of structural elements by an intuitive perception of the structural behaviour. In most cases, this trial took only static actions into consideration, so, since seismic horizontal actions modify the behaviour in a significant way, an earthquake may frequently produce cracks and local collapses. Seismic assessment of heritage buildings is relevant for any preservation project. Using specific investigations and checks, the best retrofit method can be chosen. Based on different case studies, the aim of the paper is to recommend useful framework and easy applicable assumptions for practicing engineers to evaluate the vulnerability of the historic structures and the possibilities of further steps in their development. Seismic assessment of historic buildings remains a challenging task. There is a high level of complexity compared with the assessment of standard buildings. The assessment and the diagnosis of heritage buildings in seismic areas require an extensive knowledge on the structural typologies and behaviour of heritage buildings. The investigation on previous damages from earthquakes is very important. Adequate and realistic computer modelling of complicated historic structures requires significant designers’ expertise. It is probably best to start with the simplest realistic model and then, if necessary, develop a model that reflects more structural features and complexity. The presented paper investigates the challenges posed by, and solutions needed, to ensure the structural longevity of historic structures. Finding the potential for future development of heritage buildings is an important task of the contemporary construction sector. The paper presents only 3 specific case studies but based on the results it is possible to produce some more general recommendations concerning the seismic assessment, the possibility to identify the vulnerability of historic structures and to give the recommendations for extending the service life of Heritage buildings.