Vibration based damage identification of masonry structures

In the process of preservation of ancient masonry structures, damage evaluation and monitoring procedures are particularly attractive, due to the modern context of minimum repair and observational methods, with iterative and step-by-step approaches. High-priority research issues related to damage assessment and monitoring are global non-contact inspection techniques, sensor technology, data management, diagnostics (decision making and simulation), dynamic (modal) analysis, self-diagnosing / self-healing materials, and prediction of early degradation. On these concerns, the present paper aims to assess damage in masonry structures at an early stage. Replicates of historical constructions were built in virgin state. Afterwards, progressive damage was applied and modal identification analysis was performed at each damage stage, aiming at finding adequate correspondence between dynamic behavior and internal crack growth. Accelerations and dynamic strains were recorded in many points of the replicates. Comparisons between different techniques based on vibrations measurements are made to evaluate different damage identification methods

Global damage identification based on vibration signatures applied to masonry structures

The present paper aims at damage assessment of masonry structures in an early stage. Two replicates of historical constructions were built in virgin state, one arch with 1.5 m span and one shear wall of 1 m2. Afterwards, progressive damage was applied and sequential mo-dal identification analysis was performed in each damage stage, aiming at finding adequate relations between changes in dynamical behaviour and internal crack growth. During the dynamic tests, accelerations and strains were recorded in many points of the replicates. Comparisons between different techniques based on vibrations measurements were made to evaluate which methods are the most suitable for identifying damage in masonry con-structions

Damage identification based on vibration measurements applied to masonry structures

The present paper aims to explore damage assessment in the masonry structures at an early stage by vibration measurements. Two replicates of historical constructions were built in virgin state: one arch with 1.5 m span and one shear wall with 1.0 m2. Afterwards, progressive damage was applied and sequential modal identification analysis was performed at each damage stage, aiming to find adequate correspondence between dynamic behavior and internal crack growth. Accelerations and strains in many points were record in the replicates. Eigen frequencies, mode shapes and modal strains were derived from the dynamic measurements. Environmental effects of the temperature and relative humidity on the dynamic response were studied. A first updating process was performed on the results of the undamaged arch to tune a finite element model. Moreover, the tests were repeated with added masses to scale the mode shapes. Finally, a brief analysis of the results of the several damage scenarios are presented in the paperThe authors would like to express their gratitude for the Fundacao para a Ciencia e Tecnologia, from Portugal, for providing a doctoral scholarship to the first Author, Contract SFRH/BD/24688/2005

Vibration signatures to identify damage in historical constructions

The paper aims at exploring damage assessment in masonry structures at an early stage by vibration measurements. One arch replicate of historical constructions was built as reference, undamaged, state. Afterwards, progressive damage was induced and sequential modal identification analysis was performed at each damage stage, aiming to find adequate correspondence between dynamic behaviour and internal crack growth

Damage identification in masonry structures with vibration measurements

The paper aims at exploring damage assessment in masonry structures at an early stage by vibration measurements. For this purpose, one approach is proposed combining global and local ND methods. To further evaluate the approach, one masonry tower in Portugal was studied together with one wall model in the laboratory. The model was built as reference, undamaged, state. Afterwards, progressive damage was induced and sequential modal identification analysis was performed at each damage stage, aiming to find adequate correspondence between dynamic behavior and internal crack growth. The paper presents all the analyses carried out with the aim to detect and locate the damage by means of vibrations measurements

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A spectrum-driven damage Identification technique: application and validation through the numerical simulation of the Z24 Bridge

The present paper focuses on a damage identification method based on the use of the second order spectral properties of the nodal response processes. The explicit dependence on the frequency content of the outputs power spectral densities makes them suitable for damage detection and localization. The well-known case study of the Z24 Bridge in Switzerland is chosen to apply and further investigate this technique with the aim of validating its reliability. Numerical simulations of the dynamic response of the structure subjected to different types of excitation are carried out to assess the variability of the spectrum-driven method with respect to both type and position of the excitation sources. The simulated data obtained from random vibrations, impulse, ramp and shaking forces, allowed to build the power spectrum matrix from which the main eigenparameters of reference and damage scenarios are extracted. Afterwards, complex eigenvectors and real eigenvalues are properly weighed and combined and a damage index based on the difference between spectral modes is computed to pinpoint the damage. Finally, a group of vibration-based damage identification methods are selected from the literature to compare the results obtained and to evaluate the performance of the spectral index.The authors would like to express their sincere gratitude to Prof. Dr. Guido De Roeck for sharing his information about the Z24 Bridge. The first author would also like to acknowledge the Italian Ministry of Education, Universities and Research (MIUR) for the Ph.D. scholarship provided

Monitoring of historical masonry structures with operational modal analysis: Two case studies

Two monuments in Portugal are being monitoring by the University of Minho: the Clock Tower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. Vibration sensors and temperature and relative air humidity sensors are installed in the two monuments. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response. The aim is to explore damage assessment in masonry structures at an early stage by vibration signatures as a part of a heath monitoring process to preserve the historical constructions. The paper presents all the preceding dynamic analysis steps before the monitoring task, which includes the installation of the monitoring system, the system identification and subsequent FE model updating analysis, the automatic modal identification and the investigation of the influence of the environment on the identified modal parameters.(undefined

2,4,5-Triaminopyrimidines as blue fluorescent probes for cell viability monitoring: synthesis, photophysical properties, and microscopy applications

Monitoring cell viability is critical in cell biology, pathology, and drug discovery. Most cell viability assays are cell-destructive, time-consuming, expensive, and/or hazardous. Herein, we present a series of newly synthesized 2,4,5-triaminopyrimidine derivatives able to discriminate between live and dead cells. To our knowledge, these compounds are the first fluorescent nucleobase analogues (FNAs) with cell viability monitoring potential. These new fluorescent molecules are synthesized using highly efficient and cost- effective methods and feature unprecedented photophysical properties (longer absorption and emission wavelengths, environment-sensitive emission, and unprecedented brightness within FNAs). Using a live– dead Saccharomyces cerevisiae cell and theoretical assays, the fluorescent 2,4,5-triaminopyrimidine derivatives were found to specifically accumulate inside dead cells by interacting with dsDNA grooves, thus paving the way for the emergence of novel and safe fluorescent cell viability markers emitting in the blue region. As the majority of commercially available viability dyes emit in the green to red region of the visible spectrum, these novel markers might be useful to meet the needs of blue markers for co-staining combinations

Predicting olive phenology in Portugal in a warming climate

Prediction of flowering of olive trees should account for chilling requirements, using an appropriate chilling unit for the accounting of chilling accumulation. After chilling requirements are satisfied, dormancy break takes place. Thereafter, the trees enter the forcing phase, in which the thermal time approach is used, but an appropriate base temperature must be determined. Such a model was developed, calibrated and validated for many olive cultivars (De Melo-Abreu et al., 2004). After flowering, the occurrence of developmental stages may be predicted using a thermal time approach, but for warm regions a saw-tooth model, which is a model that reduces the effect of supra-optimal temperatures, is mandatory (Garcia-Huidobro et al., :1.982). According to the simulations of the model HadCM3, developed by the Hadley Centre, global climate warming will result in average temperature anomalies in winter, in Continental Portugal, of about 2°C, in SRES scenarios 81 and 82, 3°C in scenario A2, and 4 °C in scenario A:tFI, by the end of XXI century. (Miranda et al., 2006). In this study, we discuss the prediction of flowering and subsequent phenological stages and calculate and map the times of occurrence of flowering under three warming scenarios. No flowering or abnormal flowering events are also predicted.Portuguese Foundation for Science and Technology (FCT) under Project Futurolive (PTDC/AGR-AAM/:1.04562/2008)