André Furtado

Seismic performance of the infill masonry walls and ambient vibration tests after the Ghorka 2015, Nepal earthquake

Recent earthquakes have demonstrated a significant contribution of the masonry infill walls in the structural response of the reinforced concrete (RC) buildings. Field observations after the 25th April’s earthquake in Nepal reinforce the conclusion regarding the influence of the infill walls increasing significantly the structural stiffness, which has a direct impact on the natural frequencies of the structure and of structural elements. Firstly the manuscript focuses on the performance of the infilled RC structures, describing common Nepalese architectural configurations and the major damages observed in infilled RC buildings. Secondly, it shows results from data collected on ambient vibration tests performed in seven infill panels with different characteristics, such as geometric dimensions, openings and levels of damage. These results are used to study the influence of each parameter in the out-of-plane frequency of the wall panels. The present studies along the manuscript are followed by a presentation of the study cases (buildings and the walls), test setups, main results and conclusions.

Behavior of Rectangular Reinforced-Concrete Columns under Biaxial Cyclic Loading and Variable Axial Loads

AbstractThe behavior of reinforced-concrete (RC) elements subjected to axial loading variation in conjunction with cyclic biaxial bending is recognized as a very important research topic with a reduced number of experimental results available. Six full-scale RC rectangular columns were tested and analyzed to study the effects of variable axial load on the hysteretic behavior of RC building columns under biaxial horizontal loading. The experimental results are presented and discussed in terms of damage evolution, global hysteretic behavior, stiffness degradation, columns’ capacity, and energy dissipation. The global findings revealed the significant effects of the axial load variation on the hysteretic behavior of RC columns.

Geometric characterisation of Portuguese RC buildings with masonry infill walls

Recent earthquakes showed that the vulnerability of some RC buildings with masonry infill walls is high when subjected to seismic actions. During the design practice, the infills are commonly treated as non-structural elements, despite their recognised contribution to the structural response of the buildings. The safety assessment of this type of buildings is important and any detailed information is essential, since such information is needed for estimation of the losses that future earthquakes are likely to induce. The present study focuses on the observation and analysis of architectural and structural design drawings of 80 buildings that represent common RC buildings with masonry infill walls located in Portugal. The data were analysed with the purpose of estimating geometric properties of the masonry infill panels confined by RC frames. Fourteen-hundred masonry infill walls were observed and were divided in to different types according to the different dispositions of the openings. Several measurements were performed in order to have deeper knowledge about the percentage of openings that exist in masonry infill walls and consequently in the building’s façade. Infill panels’ dimensions were also determined and other parameters related to the general characteristics of the buildings and the structural elements were also analysed. Parameters such as beams’ and columns’ dimensions and reinforcement details or slab thickness were also analysed. The collected data are utilized to derive probabilistic distributions, whose goodness-of-fit are partially verified with a statistical test. The results from this study can be used in structural modelling development of nonlinear models for masonry infill panels or computation of fragility models. In addition, the statistical parameters such as mean values, standard deviations, probability density functions and their goodness-of-fit have also been investigated for all the entire parameters.

Evaluation of different strengthening techniques’ efficiency for a soft storey building

The assessment of seismic vulnerability and strengthening of existing buildings is a topic of relevant importance and priority, as evidenced in recent earthquakes around the world, particularly in Southern European countries. Some architectural solutions adopted in the decade of 1970, combined with the common design and construction practices at that time, particularly in what regards to the seismic design, influences the seismic vulnerability of these structures. The objective of the present work is to study, based on numerical analyses, different strengthening techniques to adopt into an existing building with the behaviour potentially governed by soft storey mechanism when subjected to seismic actions. The influence of the masonry infill panels will be studied and the seismic safety of the building will be assessed. Also, different strengthening techniques will be tested to fix/eliminate the soft storey like response, namely: RC columns jacketing, addition of steel bracings with and without shear link and addition of RC shear walls. The strengthened buildings results will be compared with the results of the original structure, deducting about the structural efficiency by each type of strengthening technique adopted. The costs associated to each solution will be determined and compared with the market value of the building.

Double-Leaf Infill Masonry Walls Cyclic In-Plane Behaviour: Experimental and Numerical Investigation

Received: November 08, 2017 Revised: January 05, 2018 Accepted: January 23, 2018 Abstract: Background: The infill masonry walls are widely used in the construction of reinforced concrete buildings for different reasons (partition, thermal and acoustic demands). Since the ‘60s decade, one of the most common typology in the southern Europe was the double-leaf infill walls. Recent earthquake events proved that this specific typology have an important role in the seismic response of reinforced concrete structures in terms of stiffness, strength and failure mechanisms. However, modelling approaches of these specific infill panels cannot be found over the literature.

Effect of the Panel Width Support and Columns Axial Load on the Infill Masonry Walls Out-Of-Plane Behavior

ABSTRACT The aim of this research is to contribute to increase the understanding regarding the infill panels’ OOP behavior and evaluate the influence of different variables in the panel’ performance, such as: gravity load and panel support condition. For these experimental tests were carried composed by two full-scale infill panels subjected to uniform OOP pressure applied by airbags, subjected to gravity load applied in the top of the frame ‘columns and the other one was built partially supported in the bottom beam. The second goal of this work was to perform a comparative study between these two specimens with other three tests already tested.

Seismic Performance of Buildings in Nepal After the Gorkha Earthquake

Abstract Following the strong earthquake of Gorkha, Nepal, on April 25, 2015, and a strong aftershock on May 12, a field reconnaissance of structural damage and structural collapses was performed around the affected areas, particularly in the region around the capital Kathmandu. The main goal was to develop detailed descriptions of the seismic performance of the Nepalese building stock. To achieve this goal, the field reconnaissance survey was carried out after the two main seismic events. In this chapter, a summary of the survey is provided, focusing on both recent reinforced concrete (RC) buildings and older substandard constructions. In addition, detailed descriptions of the observed damage to urban masonry building stock and rural vernacular constructions are provided. This chapter presents evidence from the field that justifies the observed seismic performance and enables the depiction of damage modes, which could be insightful regarding future efforts to develop earthquake-resistant constructions and strategies to improve the seismic behavior around the world.

Calibration of a simplified macro-model for infilled frames with openings:

During the last years, some experimental efforts were conducted in order to evaluate the in-plane cyclic behaviour of infilled reinforced concrete frames considering and not openings. From the experiments, it was observed that the openings reduced infill panels’ stiffness, strength and energy dissipation capacity. In the literature, there are different numerical approaches to predict the infill panels expected behaviour with and/or without openings when subjected to in-plane demands. The experimental data are of full importance to calibrate the numerical models and evaluate their accuracy. A good calibration of the numerical models could result on a better and accurate safety assessment of the existing buildings and designing of the new ones. The main aim of this article is to evaluate the capacity of a simplified double strut model to represent the cyclic behaviour of infilled reinforced concrete frames with and without openings using the software OpenSees. The five infilled reinforced concrete frames tested by different authors and with different configurations will be simulated. Details from each specimen modelling will be provided along the article, and the accuracy of this numerical modelling approach will be evaluated in terms of force–displacement hysteretic curves. Additionally, a state-of-art review regarding the in-plane tests will be presented containing the main characteristics of the specimens and conclusions performed by each author.

Numerical modelling of RC strengthened columns under biaxial loading

During an earthquake, the reinforced concrete (RC) structures are subjected to deformations that may lead their structural elements to exceed the corresponding resistance limit state, forcing them to have nonlinear responses. The application of realistic numerical models that can represent the non-linearity of each structural element requires full examination and calibration. Furthermore, simplified numerical approaches that can represent the seismic behaviour of original and strengthened RC elements are of full importance. For this, the experimental tests are useful to calibrate the numerical models, and thus to capture as well as possible the real response of the elements. The main goal of this work is to evaluate the efficiency of a simplified numerical approach to represent strengthened RC columns with steel and CFRP jacketing, subjected to biaxial horizontal loading. The numerical modelling efficiency will be evaluated by comparing the numerical results with the experimental ones in terms of shear-drift hysteretic behaviour, initial stiffness and stiffness degradation, maximum strength and energy dissipation. The results shows a good performance of the numerical models, mainly for the RC columns strengthened with CFRP jacketing technique.

Seismic Vulnerability and Parametric Study on a Bare Frame Building in Nepal

Recent earthquakes have demonstrated a significant contribution of the masonry infill walls in the structural response of the reinforced concrete (RC) buildings. Field observations after the 25th April’s earthquake in Nepal reinforce the conclusion regarding the influence of the infill walls increasing significantly the structural stiffness, which has a direct impact on the natural frequencies of the structure and of structural elements. Firstly, the manuscript focuses on the performance of the infilled RC structures. Secondly, a bare frame existing building in Nepal was studied, modelled and calibrated with results from data collected on ambient vibration tests. The seismic vulnerability of the building and a parametric study was conducted to study the influence of each material properties in the structural response. The influence of the infill masonry walls presence was also evaluated.