Rita Bento

A hysteretic model for “frontal” walls in Pombalino buildings

The heritage value of the mixed wood-masonry 18th century Pombalino buildings of downtown Lisbon is recognized both nationally and internationally. These buildings have a three-dimensional timber structure composed of wooden floors, stairs and walls intended to provide better seismic resistance and are enclosed by masonry walls. These interior wooden walls are called “frontal” walls and their behaviour under cyclic loading has scarcely been studied. This report describes an experimental programme to determine the hysteretic behaviour of these “frontal” walls, using static cyclic shear testing with imposed displacements. Two tests were conducted on two identical real-size walls. A new hysteretic model for the cyclic behaviour of these “frontal” walls in Pombalino buildings is presented and calibrated based on the experimental results. The hysteresis model was developed based on a minimum number of path following rules that can reproduce the response of the wall tested under general monotonic or cyclic loading. The model is constructed using a series of exponential functions and linear functions. The nine parameters in this model capture the nonlinear hysteretic response of the wall. The hysteretic behaviour of such walls subjected to cyclic loading exhibit high nonlinear force-displacement responses and high ductility.

The Extended Adaptive Capacity Spectrum Method for the Seismic Assessment of Plan-Asymmetric Buildings

The use of nonlinear static procedures (NSPs) on the seismic assessment of real existing plan-irregular structures has so far been studied by a limited number of authors. This fact limits the application of such methods to assess current existing structures, the majority of which are irregular in plan. An extended version of the adaptive capacity spectrum method (ACSM) for the seismic assessment of plan-irregular buildings is presented in this paper. The novelty of this proposal is to comprise the most accurate features of commonly used NSPs in order to overcome the problems that subsist in three-dimensional pushover analyses. The accuracy of the procedure is tested in three plan-irregular real buildings. The results are compared with the capacity spectrum method (CSM) with the features proposed in FEMA 440, with the extended N2 method for plan-asymmetric structures, with the adaptive capacity spectrum method (ACSM) and with the most exact nonlinear dynamic analyses. Several seismic intensities are tested, in order to evaluate the performance of the procedure in different stages of structural inelasticity.

Comparison of Nonlinear Static Methods for the Seismic Assessment of Plan Irregular Frame Buildings with Non Seismic Details

The use of Nonlinear Static Procedures (NSPs) for the seismic assessment of plan irregular buildings is challenging. The most common pushover-based approaches have led to adequate results in regular buildings, and hence, there is a need to verify the validity of such methods on the assessment of irregular structures. In this article, four commonly used nonlinear static procedures (CSM, N2, MPA, ACSM) are applied on the assessment of two existing five- and eight-story plan-asymmetric buildings in Turkey. The accuracy of the different NSPs is evaluated through comparisons with the results derived from nonlinear dynamic analyses. The results are presented in terms of interstory drifts, normalized top displacements, lateral displacement profiles, chord rotations, base shear, and top displacement ratios. The performance of such procedures in evaluating the damage limitation according to the Eurocode8 is also verified. Special attention is given to the ACSM (Adaptive Capacity Spectrum Method) whose performance in 3D plan irregular buildings has recently been tested. Conclusions about the performance of each NSP are outlined at the end of the article.

Fragility curves for old masonry building types in Lisbon

AbstractImproving the seismic resistance of traditional buildings is essential for preserving cultural heritage and increasing their safety. This is especially important for old masonry buildings in Lisbon (“Pombalino”, “Gaioleiro” and “Placa”), which are still used for housing and services. Taking this into account, this paper is focused on the seismic assessment of these three types of buildings. The buildings were modelled based on the equivalent frame model approach, their dynamic characteristics were determined and non-linear static (pushover) analyses were performed. Furthermore, for the seismic demand of Lisbon, the seismic performance of such building classes was defined and compared. Finally, with the aim of supporting seismic risk and loss estimation studies, a probabilistic assessment was carried out and the fragility curves for each building type derived.

Seismic performance of irregular bridges – comparison of different nonlinear static procedures

The adequate seismic performance of transportation infrastructures is important for the functioning of the economy and society. This paper focuses on the seismic assessment and analysis of one of the most important components of these infrastructures, the bridges. In this field, nonlinear static procedures (NSPs) have gained significant attention, resulting in different proposals to improve the accuracy of the procedures while keeping their simplicity. The main goal of this study is focused on the evaluation of the applicability of NSPs for irregular reinforced concrete viaducts. A comparative approach is pursued by resorting to (1) the analyses of the performance of three well-known NSPs (N2 method, modal pushover analysis and adaptive capacity spectrum method) and (2) the extension of the scope of previous studies in this field to a more recent method, the extended N2. As such, a set of bridges with different levels of irregularity, configurations and lengths is investigated. The accuracy of different NSPs is evaluated by comparing the results of NSPs with the ones obtained by means of nonlinear dynamic analyses. The comparison of results confirms the acceptable performance of the multi-modal NSPs and highlights the effectiveness of extended N2 method with respect to its simplicity.

Simple and complex modelling of timber-framed masonry walls in Pombalino buildings

Timber-framed (TF) masonry has been developed as an effective lateral-load resisting system in regions of high seismicity such as Southern Europe. A salient feature of the ‘last generation’ of TF buildings is the presence of diagonal members that may consist of two diagonal braces. The present study focusses on alternative modelling procedures, ranging from simple to rather complex, for this interesting type of traditional structure. All models are applied to study the behaviour of full-scale specimens of diagonally-braced TF panels. The complex model is based on plasticity with contact surfaces for the connection between timber diagonals and masonry infills. A parametric analysis using this model shows that masonry infills affect only slightly the lateral force carried by this TF panel configuration. Furthermore, two simple modelling techniques are put forward for application in the analysis of large, realistic structures incorporating TF walls. The first one is directly connected to the complex modelling and is based on substructuring. A nine-step procedure is developed and is found to properly reproduce the response of the test specimens. The second simple model is a phenomenological one, developed on the basis of observed behaviour during tests and is a complete hysteretic model; however, for comparison purposes, all models are evaluated here with respect to the prediction of the envelope (pushover) curve for the walls tested under lateral loads.

Methods and Approaches for Blind Test Predictions of Out-of-Plane Behavior of Masonry Walls: A Numerical Comparative Study

ABSTRACT Earthquakes cause severe damage to masonry structures due to inertial forces acting in the normal direction to the plane of the walls. The out-of-plane behavior of masonry walls is complex and depends on several parameters, such as material and geometric properties of walls, connections between structural elements, the characteristics of the input motions, among others. Different analytical methods and advanced numerical modeling are usually used for evaluating the out-of-plane behavior of masonry structures. Furthermore, different types of structural analysis can be adopted for this complex behavior, such as limit analysis, pushover, or nonlinear dynamic analysis. Aiming to evaluate the capabilities of different approaches to similar problems, blind predictions were made using different approaches. For this purpose, two idealized structures were tested on a shaking table and several experts on masonry structures were invited to present blind predictions on the response of the structures, aiming at evaluating the available tools for the out-of-plane assessment of masonry structures. This article presents the results of the blind test predictions and the comparison with the experimental results, namely in terms of formed collapsed mechanisms and control outputs (PGA or maximum displacements), taking into account the selected tools to perform the analysis.

Mechanical Characterization of Masonry Walls With Flat-Jack Tests

The results from an experimental campaign on old masonry buildings from Lisbon are presented and discussed. The tests aim at the evaluation of the masonry deformability properties in compression and the shear strength parameters based on flat-jack testing technique. Tests were carried out in both internal brick masonry walls and external rubble limestone masonry walls. The evaluation of the shear parameters was done according to a new testing technique—shear tests onmasonry walls with flat-jacks—involvingmore than one masonry unit. One of the goals is the calibration and development of this testing technique and to show its first application to the test of rubble stone masonry walls. For that, the experimental technique is fully explained in this paper, and the results of some in situ tests are used to discuss the calibration procedure. Because of the characteristics of the walls, in particular, the great heterogeneity and thickness of the external masonry walls, the application of the flat-jack testing technique involved some uncertainties that are described and debated in this work.

Architectural and Structural Characteristics of Masonry Buildings between the 19th and 20th Centuries in Lisbon, Portugal

ABSTRACT The masonry buildings constructed between the 19th and 20th centuries in Lisbon are commonly recognized for their eclectic style and structural vulnerability. This article presents the main characteristics of these buildings in the aim of preserving their cultural value. The socio-economic conditions on what they were constructed are identified. This includes the possible reasons for the negative impression attributed to the buildings, which end up to be known as “gaioleiro” (meaning bird cage). The architectural features are described in terms of urban plan and aesthetics, configuration of the buildings and layout of the flats. The structural system and materials are characterized. In addition, an estimation of the mechanical properties of the materials is presented based on the Bayesian approach. The main weaknesses and alterations implemented are also identified, putting in evidence the possible consequences for the structure and seismic performance.

Pombalino Constructions: Description and Seismic Assessment

This chapter describes the Pombalino building structures built in Lisbon downtown and other parts of Portugal during the reconstruction after the 1755 earthquake, as well as their earthquake resistant features. In particular the importance of the Gaiola Pombalina, a tridimensional wood truss characteristic of those constructions, in the potential seismic resistance of these buildings is discussed. The effects in their seismic resistance of the architectural and structural changes to which these buildings have been submitted since the original construction, usually with negative consequences,, is also discussed. Some strengthening and advanced analytical modelling strategies for these buildings are also mentioned. Finally, the socio-economic feasibility of strengthening this construction is briefly discussed, as well as the importance of their preservation. To be noticed that the reconstruction of Lisbon is the first time in the history of mankind that a large town was built providing widespread seismic resistance to its buildings aiming at avoiding future tragedies of the same type.