Rafael Ramirez
@isise.net
Researcher
Institute for Sustainability and Innovation in Structural Engineering (ISISE)
RESEARCH, TEACHING, or OTHER INTERESTS
Civil and Structural Engineering, Building and Construction, Mechanics of Materials, Modeling and Simulation
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Arezu Feizolahbeigi, Rafael Ramirez, and Paulo B. Lourenço
Elsevier BV
Rafael Ramirez, Bahman Ghiassi, Paloma Pineda, and Paulo B. Lourenço
MDPI AG
Masonry walls comprise an important part of the building envelope and, thus, are exposed to environmental effects such as temperature and moisture variations. However, structural assessment usually neglects the influence of these hygro-thermal loads and assumes ideal conditions. This paper presents a hygro-thermo-mechanical model and its application to simulate the impact of temperature- and moisture-related phenomena on the structural behavior of masonry walls. A fully coupled heat and mass transfer model is presented and a 2D finite element model is prepared to simulate the behavior of a brick masonry wall under various hygro-thermal scenarios. Two different mortars are considered: namely, cement mortar and natural hydraulic lime mortar. The results are evaluated in terms of temperature and moisture content distribution across the wall thickness. The hygro-thermal model is further extended to incorporate mechanical effects through the total strain additive decomposition principle. It is shown that the hygro-thermo-mechanical response of the brick masonry wall is a complex 2D phenomenon. Moreover, the environmental loads change the natural stress distribution caused by gravitational loads alone. Finally, the wall with cement mortar develops higher levels of stress when compared to the one with lime mortar, due to the dissimilar hygro-thermal behavior between the constituent materials.
Rafael Ramirez, Rosana Muñoz, and Paulo B. Lourenço
MDPI AG
The repair and strengthening of historical masonry buildings is a fundamental aspect in the conservation of the built cultural heritage. Temporary shoring or strengthening are often used and, usually, involve the introduction of new metallic elements. The connection between the original substrate and the new elements must be analyzed carefully to prevent further damage to the building. This paper presents a study on the mechanical behavior of metal anchors applied to brick masonry walls. An experimental campaign is developed, and a series of pull-out tests are carried out on masonry walls built in a laboratory with natural hydraulic lime mortar and low mechanical strength bricks. Two groups of tests are conducted, namely, with the actuator in the direction of the anchor axis and with the actuator inclined with respect to the fastener axis. Moreover, two types of anchoring systems are used, namely, adhesive (chemical and cementitious grout) and mechanical anchors. The experimental results are compared to predictive analytical formulas available in the literature for estimation of the ultimate load capacity, according to the type of failure. From the comparison between experimental and analytical values, it is proven that the analytical formulation originally developed for concrete substrates cannot be directly extrapolated to brick masonry cases, and specific predictive formulas should be developed. The presented research can be used to select the most efficient anchoring system for strengthening and retrofitting of historical brick masonry structures.
R. Ramirez, B. Ghiassi, P. Pineda, and P.B. Lourenço
Elsevier BV
I. Tomić, A. Penna, M. DeJong, C. Butenweg, A. A. Correia, P. X. Candeias, I. Senaldi, G. Guerrini, D. Malomo, B. Wilding,et al.
Springer Science and Business Media LLC
AbstractCity centres of Europe are often composed of unreinforced masonry structural aggregates, whose seismic response is challenging to predict. To advance the state of the art on the seismic response of these aggregates, the Adjacent Interacting Masonry Structures (AIMS) subproject from Horizon 2020 project Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) provides shake-table test data of a two-unit, double-leaf stone masonry aggregate subjected to two horizontal components of dynamic excitation. A blind prediction was organized with participants from academia and industry to test modelling approaches and assumptions and to learn about the extent of uncertainty in modelling for such masonry aggregates. The participants were provided with the full set of material and geometrical data, construction details and original seismic input and asked to predict prior to the test the expected seismic response in terms of damage mechanisms, base-shear forces, and roof displacements. The modelling approaches used differ significantly in the level of detail and the modelling assumptions. This paper provides an overview of the adopted modelling approaches and their subsequent predictions. It further discusses the range of assumptions made when modelling masonry walls, floors and connections, and aims at discovering how the common solutions regarding modelling masonry in general, and masonry aggregates in particular, affect the results. The results are evaluated both in terms of damage mechanisms, base shear forces, displacements and interface openings in both directions, and then compared with the experimental results. The modelling approaches featuring Discrete Element Method (DEM) led to the best predictions in terms of displacements, while a submission using rigid block limit analysis led to the best prediction in terms of damage mechanisms. Large coefficients of variation of predicted displacements and general underestimation of displacements in comparison with experimental results, except for DEM models, highlight the need for further consensus building on suitable modelling assumptions for such masonry aggregates.
Abide Aşıkoğlu, Jennifer D’Anna, Rafael Ramirez, Fabio Solarino, Antonio Romanazzi, Maria Pia Ciocci, and Nicoletta Bianchini
Springer Science and Business Media LLC
AbstractMasonry buildings of historical centres are usually organized within aggregates, whose structural performance against seismic actions is challenging to predict and constitutes still an open issue. The SERA—AIMS (Seismic Testing of Adjacent Interacting Masonry Structures) project was developed to provide additional experimental data by testing a half-scale, two-unit stone masonry aggregate subjected to two horizontal components of dynamic excitation. In this context, this paper investigates the reliability of the modelling approach and the assumptions adopted to generate a three-dimensional continuum finite element model. The work involves two stages, namely a blind pre-diction and a post-diction phase, and proposes a series of simulation analyses including a strategy to shorten the actual records and save computation costs. The study was performed to investigate the extent of uncertainty in modelling for such masonry aggregates in relation to the experimental outcomes. Pre-diction results were proven to be not accurate in terms of predicted displacements and damage patterns. The upgrades introduced for the post-diction analyses, including the calibration of the elastic modulus and the introduction of a non-linear interface between the two units, allowed to improve the outcomes, with reasonable results in terms of predicted base shear force, displacements along Y-direction and damage pattern for the non-linear stage. The overall approach showed to be appropriate for the structural analysis of existing masonry aggregates, but the accurate modelling of this type of structure remains challenging due to the high level of uncertainties.
N. Bianchini, M. P. Ciocci, F. Solarino, A. Romanazzi, R. Ramirez, J. D’Anna, and A. Aşıkoğlu
Springer Science and Business Media LLC
AbstractThis paper presents numerical simulations within the frame of the project SERA—AIMS (Seismic Testing of Adjacent Interacting Masonry Structures). The study includes blind pre-diction and post-diction stages. The former was developed before performing the shaking table tests at the laboratory facilities of LNEC (Lisbon), while the latter was carried out once the test results were known. For both, three-dimensional finite element models were prepared following a macro-modelling approach. The structure consisted of a half-scaled masonry aggregate composed by two units with different floor levels. Material properties used for the pre-diction model were based on preliminary tests previously provided to the participants. The masonry constitutive model used for the pre-diction study reproduced classical stress–strain envelope, whereas a more refined model was adopted for the post-diction. After eigenvalue analysis, incremental nonlinear time history analysis was performed under a unique sequence based on the given load protocol to account for damage accumulation. In the post-diction, the numerical model was calibrated on the data recorded during the shaking table tests and nonlinear dynamic analysis repeated under the recorded accelerogram sequence. The interaction between the two units was simulated through interface elements. Moreover, the timber floors were accounted following different strategies: not modelling or considering nonlinear wall-to-floor connections. Advantages and disadvantages are then analysed, comparing the pre-diction and post-diction results with the experimental data. Numerical results differ from the experimental outcomes regarding displacements and interface pounding, although a clear improvement is visible in the post-diction model.
Rafael Ramirez, Bahaman Ghiassi, Daniel V. Oliveira, and Paulo B. Lourenço
Trans Tech Publications, Ltd.
Fiber reinforced polymers (FRP) have been widely used for strengthening and repair of masonry structures since the 1990s. Although the short-term performance of such systems has been extensively studied, their durability and long-term behavior are still scarcely known. Therefore, a better understanding of the corresponding degradation mechanisms and durability issues is of major interest, especially in cases of externally bonded systems where the materials are prone to undergo a more severe decay. Different accelerated aging tests have been developed in order to simulate weathering conditions in a shorter time: water immersion, freeze-thaw, hygrothermal cycles, salt crystallization, UV radiation, etc. Nonetheless, accelerated aging data cannot be used to make reliable service life estimations without a clear correlation with real environmental processes. In this study, we present the preliminary results (3/12 years) of a real exposure experimental campaign devoted to analyzing the natural aging of masonry components reinforced with externally bonded glass fibers (GFRP). The aging conditions consist of: (a) direct outdoor exposure, i.e. outdoor hygrothermal variation + sun and rain; (b) indirect outdoor exposure, i.e. outdoor hygrothermal variation + sheltered from sun and rain; (c) laboratory conditions as control group. The specimens consist of solid extruded fired-clay bricks strengthened with unidirectional GFRP sheets following the wet lay-up procedure. The aging effects on bond performance are studied by means of single-lap shear tests. Finally, the effect of brick surface treatment and the application of an external render on bond durability is investigated.
R. Ramirez, B. Ghiassi, P. Pineda, and P.B. Lourenço
Elsevier BV
Rafael Ramirez, Hamid Maljaee, Bahman Ghiassi, Paulo B. Lourenço, and Daniel V. Oliveira
Informa UK Limited
Abstract Application of Fibre Reinforced Polymers (FRPs) as external reinforcement for masonry structures has been found to be a promising technique, but the long-term behavior of such systems still needs attention. This study presents an overview of the experimental activities followed by the authors on durability of externally bonded FRP-masonry components subjected to water immersion and accelerated hygrothermal exposure. Both moist and hygrothermal environments were found to be extremely deteriorating in the studied materials and led to significant degradation of mechanical properties and loss in bond strength. The effect of mechanical surface treatment on the bond durability performance was also investigated.
Rafael Ramírez, Nuno Mendes, and Paulo B. Lourenço
MDPI AG
The Benedictine Monastery of São Miguel de Refojos, located in Cabeceiras de Basto (Portugal), is a monumental complex and a distinctive example of the 18th century Portuguese Baroque architecture. This study addresses the state of conservation of the church as well as the evaluation of its structural behavior and seismic performance. An initial inspection and diagnosis campaign revealed that the structure presents low to moderate damage and other non-structural issues generally associated with high levels of moisture and water infiltration. In order to study the structural performance, a three-dimensional (3D) numerical model was prepared based on the finite element method. This model was calibrated with respect to dynamic identification tests and nonlinear static analyses were then performed to evaluate the seismic behavior. Capacity curves, deformations, crack patterns, and failure mechanisms were used to characterize the structural response. Additionally, the safety evaluation for horizontal actions was verified by means of limit analysis. An overall good agreement was found between the results of the pushover and the limit analyses. To conclude, the present work provides a comprehensive evaluation of the state of conservation of the church and verifies the safety condition of the structure for seismic actions.