Aníbal Costa

Analysis of the Out-Of-Plane Seismic Behavior of Unreinforced Masonry: A Literature Review

Although the issue of the out-of-plane response of unreinforced masonry structures under earthquake excitation is well known with consensus among the research community, this issue is simultaneously one of the more complex and most neglected areas on the seismic assessment of existing buildings. Nonetheless, its characterization should be found on the solid knowledge of the phenomenon and on the complete understanding of methodologies currently used to describe it. Based on this assumption, this article presents a general framework on the issue of the out-of-plane performance of unreinforced masonry structures, beginning with a brief introduction to the topic, followed by a compact state of art in which the principal methodologies proposed to assess the out-of-plane behavior of unreinforced masonry structures are presented. Different analytical approaches are presented, namely force and displacement-based, complemented with the presentation of existing numerical tools for the purpose presented above. Moreover, the most relevant experimental campaigns carried out in order to reproduce the phenomenon are reviewed and briefly discussed.

Experimental testing, numerical modelling and seismic strengthening of traditional stone masonry: comprehensive study of a real Azorian pier

Stone masonry is one of the oldest building techniques used worldwide and it is known to exhibit poor behaviour under seismic excitations. In this context, this work aims at assessing the in-plane behaviour of an existing double-leaf stone masonry pier by experimental testing. Additionally, a detailed 3D finite element numerical analysis based on micro-modelling of the original pier is presented (fully describing the geometry and division of each individual elements, namely infill, blocks and joints) aiming at simulating the experimental test results. This numerical strategy can be seen as an alternative way of analysing this type of constructions, particularly useful for laboratory studies, and suitable for the calibration of simplified numerical models. As part of a wider research activity, this work is further complemented with the presentation of an effective retrofit/strengthening technique (reinforced connected plaster) to achieve a significant improvement of its in-plane cyclic response which is experimentally verified in the results presented herein.

Out-of-plane behaviour of existing stone masonry buildings: experimental evaluation

Masonry structures can be considered as the simplest type of structures concerning its assemblage but, at the same time, it is one of the most complex construction materials in terms of mechanical properties and correct behaviour assessment. In this context, the work herein presented aims at describing an experimental testing campaign recently carried out in order to characterize the out-of-plane behaviour of traditional masonry constructions. Taking advantage of the existence of a traditional two-storey masonry building abandoned after the 1998 Azores earthquake, several in-situ tests were defined and performed with the application of quasi-static cyclic loads at the building top level in the out-of-plane direction. In addition, the efficiency of retrofitting and/or strengthening techniques applied during the 1998 Azores reconstruction process was also experimentally evaluated. Finally, an overall discussion of these techniques is presented, resorting also to previous tests’ results carried out by the same authors, aiming at inferring and suggesting quantifications of strengthening techniques’ contributions for future interventions on existing buildings. For this purpose, simple analytical mechanical approaches were adopted in order to provide numerical estimates of strength that were found in good agreement with the experimental results.

Structural Behaviour and Retrofitting of Adobe Masonry Buildings

Earth is one of the most widely used building materials in the World. Different types of adobe dwellings are made to assure protection and wellbeing of the population according to the diverse zones needs. Therefore, it is important to study the structural behaviour of the adobe masonry constructions, analysing their seismic vulnerability, which may help in preventing social, cultural and economic losses. In the present chapter, an explanation of the seismic behaviour of adobe buildings, a summary of recent research outputs from experimental tests conducted on adobe masonry components and from numerical modelling of full-scale representative adobe constructions are reported. In addition, different rehabilitation and strengthening solutions are presented and results from the testing of retrofitted adobe constructions and components are discussed.

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.

Comparative analysis of the cyclic behaviour of beam-column joints with plain and deformed reinforcing bars

Damage reports after recent earthquakes proves that slippage between steel reinforcing bars and the surrounding concrete is one the common causes of damage and collapse of existing RC building structures. The bond-slip mechanism assumes particular importance in RC building structures built until the 70’s, with plain reinforcing bars, previously to the enforcement of modern seismic codes. This type of structures is usually characterized by poor reinforcement detailing, poor bond properties and inadequate concrete confinement. In RC buildings subjected to cyclic loads, as the induced by earthquakes, high stress concentration occurs at the beam-column joints, making this regions prone to the occurrence of severe damage. Beam-column joints are particularly sensitive to the bond-slip mechanism due to the stress concentration, but also due to the fact that anchorage of beam and column longitudinal reinforcing bars is typically made in the joint vicinity. In this paper are presented the main results of the cyclic tests performed on two full-scale beam-column joints with the same geometry and reinforcement detailing, representative of interior joints in RC building structures built until the mid-70’s, without adequate seismic detailing. One specimen was built with plain reinforcing bars (poor bond properties) and the other with deformed bars (good bond properties). For a better comprehension of the bond properties influence on the cyclic behavior of the beam-column joints, a comparison is established between the main experimental results obtained for the two specimens. The comparative analysis shows that the bond-slip mechanism has a strong influence in the cyclic response of RC structural elements.

In situ Out-of-Plane Cyclic Testing of Original and Strengthened Traditional Stone Masonry Walls Using Airbags

This article presents a field experimental campaign carried out on an existing one-story stone masonry building, aiming at characterizing the out-of-plane behavior of its walls. A bidirectional test set-up based on a self-equilibrated airbag system was developed and used on three similar masonry walls under distinct conditions: original, retrofitted, and strengthened. The results obtained and the main advantages and shortcomings found in the test set-up are discussed. Finally, some of the most popular retrofitting and/or strengthening techniques applied during the 1998 Azores reconstruction process are critically analyzed, aiming at suggesting quantifications for future interventions on existing unreinforced masonry buildings.

Statistical Characterization of Structural Demand under Earthquake Loading. Part 2: Robust Estimation of the Dispersion of the Data

Performance-based earthquake engineering methodologies often require a probabilistic model of structural demand. Since observations masking the probability distribution of the majority of the data are frequently found, robust estimation methods are proposed to estimate the probabilistic model parameters (i.e., central value and dispersion). The performance of thirty-three robust dispersion estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, combinations involving dispersion and central value (defined in a companion article) estimators are proposed.

Adobe and Modernism in Ílhavo, Portugal

The debate on the rehabilitation of adobe buildings and their heritage value leads to the inadequacies that still exist in the architectural characterization and conservation status of these buildings, especially outside large urban centers. This study seeks to contribute to this debate by focusing on adobe construction techniques in Ílhavo, Portugal, during the transition phase between vernacular and the architecture of the Modern Movement. The study also seeks to contribute to developing knowledge of the evolutionary process of adobe construction, associated with the appropriation and application of the new architectural language, by focusing on the period from the 1940s to the 1960s. Identified are the major defects associated with changes in construction methods. The data are intended to support the protection of this heritage. In Portugal, increasing importance is currently attributed to modernist buildings because they are focal points for the characterization of the countrys architectural history. The preservation efforts for these buildings have encountered obstacles in terms of maintaining identity, given the recent interventions that were implemented. This conflict is seen, in a comprehensive manner, in the vernacular construction of adobe. However, knowledge of historical and cultural issues could even support projects in the tourism industry by valuing and preserving heritage.

Seismic Vulnerability and Risk Assessment of Historic Masonry Buildings

Seismic risk evaluation of built-up areas involves analysis of the level of earthquake hazard of the region, building vulnerability and exposure. Within this approach that defines seismic risk, building vulnerability assessment assumes great importance, not only because of the obvious physical consequences in the eventual occurrence of a seismic event, but also because it is the one of the few potential aspects in which engineering research can intervene. In fact, rigorous vulnerability assessment of existing buildings and the implementation of appropriate retrofitting solutions can help to reduce the levels of physical damage, loss of life and the economic impact of future seismic events. Vulnerability studies of urban centres should be developed with the aim of identifying building fragilities and reducing seismic risk. As part of the rehabilitation of the historic city centre of Coimbra, a complete identification and inspection survey of old masonry buildings has been carried out. The main purpose of this research is to discuss vulnerability assessment methodologies, particularly those of the first level, through the proposal and development of a method previously used to determine the level of vulnerability, in the assessment of physical damage and its relationship with seismic intensity.