Gianmarco De Felice

Out-of-Plane Seismic Capacity of Masonry Depending on Wall Section Morphology

To what extent does a wall subjected to out-of-plane seismic action behave monolithically and fail by overturning or, conversely, split into separate leaves? How much does the workmanship—the set of construction specifications that historical treatises collect under the definition of “rule of art”—influence the structural behaviour of the wall? These research topics have proved highly significant in the recent seismic events, but yet remain insufficiently known and handled without the appropriate analysis tools. In this article, the dependence of the out-of-plane seismic capacity of masonry walls on the morphology of the wall section is investigated starting from real masonry sections, surveyed from historic buildings, which are modelled using the distinct element method. The seismic capacity is estimated by pushover analyses with uniform increasing horizontal forces and dynamic analyses under acceleration pulses. The results highlight the effective reduction in strength and displacement capacity of masonry sections depending on the transverse bond provided by stones.To what extent does a wall subjected to out-of-plane seismic action behave monolithically and fail by overturning or, conversely, split into separate leaves? How much does the workmanship—the set of construction specifications that historical treatises collect under the definition of “rule of art”—influence the structural behaviour of the wall? These research topics have proved highly significant in the recent seismic events, but yet remain insufficiently known and handled without the appropriate analysis tools. In this article, the dependence of the out-of-plane seismic capacity of masonry walls on the morphology of the wall section is investigated starting from real masonry sections, surveyed from historic buildings, which are modelled using the distinct element method. The seismic capacity is estimated by pushover analyses with uniform increasing horizontal forces and dynamic analyses under acceleration pulses. The results highlight the effective reduction in strength and displacement capacity of mason...

Out-of-plane seismic resistance of masonry walls

Seismic vulnerability of unreinforced masonry buildings is studied by means of simplified out-of-plane collapse mechanisms that take into account connections with transversal walls. According to experimental evidence, the analysis assumes that failure is reached with a rigid body motion of a part of the facade that falls down. Two classes of mechanism are examined: the overturning of the facade due either to a vertical crack at the connection or a diagonal crack on the transversal wall, both defined resorting to a simple model of masonry fabric, viewed as a regular assembly of rigid blocks and elastic plastic joints with friction but no cohesion. The use of simplified mechanisms give rise to an explicit evaluation of the seismic resistance to changes in the geometry and in the masonry fabrics, that could be used by practising engineers. This formulation is developed for both static horizontal actions and ground velocity peak, in the belief that the latter probably gives a better approximation of seismic action, while also providing, by comparison with the results of static forces, an estimate of the behaviour factor for unreinforced masonry. Eventually, the analytical forecasts are compared with numerical results obtained by means of the distinct element method.

Review of Out-of-Plane Seismic Assessment Techniques Applied To Existing Masonry Buildings

ABSTRACT Observations after strong earthquakes show that out-of-plane failure of unreinforced masonry elements probably constitutes the most serious life-safety hazard for this type of construction. Existing unreinforced masonry buildings tend to be more vulnerable than new buildings, not only because they have been designed to little or no seismic loading requirements, but also because connections among load-bearing walls and with horizontal structures are not always adequate. Consequently, several types of mechanisms can be activated due to separation from the rest of the construction. Even when connections are effective, out-of-plane failure can be induced by excessive vertical and/or horizontal slenderness of walls (length/thickness ratio). The awareness of such vulnerability has encouraged research in the field, which is summarized in this article. An outline of past research on force-based and displacement-based assessment is given and their translation into international codes is summarized. Strong and weak points of codified assessment procedures are presented through a comparison with parametric nonlinear dynamic analyses of three recurring out-of-plane mechanisms. The assessment strategies are marked by substantial scatter, which can be reduced through an energy-based assessment.

A review of experimental investigations and assessment methods for masonry arch bridges

Abstract Masonry arch bridges constitute a significant proportion of European road and rail infrastructures. Most of them are well over 100 years old and are supporting traffic loads many times above those originally envisaged. The inherent variation in their constituent materials, the traditional design criteria and methods used for their construction, their deterioration over time caused by weathering processes and the development of other defects, significantly influence the mechanical response of these historic structures. A deep understanding on the numerous factors that affect the structural behaviour of masonry arch bridges and on the analysis methods to assess the life expectancy of such bridges and inform maintenance and strengthening strategies is essential. This paper provides a critical review of the experimental studies that have been carried out and of the assessment approaches that have been developed in the last three decades to these aims. The current knowledge is established and areas of possible future research work are identified, with the aim of providing students and researchers, asset managers and bridge owners, and practitioners with a guidance for research activities and maintenace strategies.

An Efficient Approach for Seismic Fragility Assessment with Application to Old Reinforced Concrete Bridges

A procedure for seismic fragility assessment, suitable for application to non ductile RC structures is presented, which is based on the estimate of a response surface that gives the probability of failure of the structure as a function of the random variables that affect the response. The seismic fragility or risk is then evaluated through numerical integration. The method considers different sources of uncertainty: (i) in the seismic input, through the use of different accelerograms for the dynamic analysis; (ii) in the structural response, through the use of a refined nonlinear finite element model; and (iii) in the ultimate state capacity, taking into account the different modes of failure which may occur, for which a random mechanical capacity model is available. Aiming at reducing the number of simulation analyses, the uncertainties on the seismic input and on the mechanical parameters governing the response are treated according to the response surface methodology, while the limit-state randomness is treated explicitly during the simulations. Using the proposed procedure, the seismic safety of two reinforced concrete bridges from Italian highway network, with simply supported deck and either single stem or frame piers, is evaluated. The results are expressed in terms of fragility curves as function of spectral acceleration. The obtained results highlight the influence of material randomness on reliability and the relative importance of seismic input with respect to mechanical and epistemic uncertainty.

Experimental and Numerical Response of Arch Bridge Historic Masonry Under Eccentric Loading

This study contributes to the knowledge of the compressive behavior of brickwork used in railway bridges and shows how to incorporate this information in structural modeling. An experimental investigation is carried out on brickwork specimens made with old clay bricks and lime mortar to reproduce the original components and the arrangement of masonry arch bridges built in Italy at the end of the nineteenth century. The specimens are subjected to monotonic and cyclic displacement-controlled compression tests, under centered and eccentric loading. Based on experimental results, a beam model with fiber cross-section is used to describe the macroscopic behavior of brickwork, where the fiber constitutive relationship is estimated according to the concentric tests. Eccentric tests are finally simulated and the comparison between theoretical predictions and experimental results reveals the capability of the model to reproduce the global force-displacement and bending moment-curvature experimental behavior and it...This study contributes to the knowledge of the compressive behavior of brickwork used in railway bridges and shows how to incorporate this information in structural modeling. An experimental investigation is carried out on brickwork specimens made with old clay bricks and lime mortar to reproduce the original components and the arrangement of masonry arch bridges built in Italy at the end of the nineteenth century. The specimens are subjected to monotonic and cyclic displacement-controlled compression tests, under centered and eccentric loading. Based on experimental results, a beam model with fiber cross-section is used to describe the macroscopic behavior of brickwork, where the fiber constitutive relationship is estimated according to the concentric tests. Eccentric tests are finally simulated and the comparison between theoretical predictions and experimental results reveals the capability of the model to reproduce the global force-displacement and bending moment-curvature experimental behavior and its suitability for the structural analysis of masonry arch bridges.

Overview of railway masonry bridges with a safety factor estimate

The European rail network includes a large number of masonry arch bridges for which the actual safety level is uncertain due to the rise in traffic demand and the material deterioration that have occurred since they have been built. For this study, a representative sample of 50 Italian large-span railway masonry arch bridges dating to the 19th and 20th centuries is selected. The sample includes single-span and multi-span bridges, shallow and deep arches, viaducts with slender and stocky piers, for which the geometric properties are taken from original design drawings and calculation reports. Despite such variability, the main structural characteristics and construction methods recur and comply with the design criteria suggested by historical treatises. The load-carrying capacity of the bridges and the corresponding safety factor with respect to rail traffic loads are assessed through a fiber beam based modeling approach. Safety levels are related to the shape of the arch, the height of the piers and the number of spans. Different constitutive assumptions are considered and the results of yield-design based methods are compared with those accounting for limited ductility of masonry in compression. The influence of uncertainties in the knowledge of geometric and mechanical parameters is also evaluated.The European rail network includes a large number of masonry arch bridges for which the actual safety level is uncertain due to the rise in traffic demand and the material deterioration that have occurred since they have been built. For this study, a representative sample of 50 Italian large-span railway masonry arch bridges dating to the 19th and 20th centuries is selected. The sample includes single-span and multi-span bridges, shallow and deep arches, viaducts with slender and stocky piers, for which the geometric properties are taken from original design drawings and calculation reports. Despite such variability, the main structural characteristics and construction methods recur and comply with the design criteria suggested by historical treatises. The load-carrying capacity of the bridges and the corresponding safety factor with respect to rail traffic loads are assessed through a fiber beam based modeling approach. Safety levels are related to the shape of the arch, the height of the piers and the n...

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.

Methods and Challenges for the Seismic Assessment of Historic Masonry Structures

ABSTRACT Despite the high vulnerability of historic structures to earthquakes, the approaches for evaluating seismic demand and capacity still appear inadequate and there is little consensus on the most appropriate assessment methods to use. To develop an improved knowledge on the seismic behavior of masonry structures and the reliability of analysis tools, two real-scale specimens were tested on a shake table, and several experts were invited to foresee failure mechanism and seismic capacity within a blind prediction test. Once unveiled, experimental results were simulated using multi-block dynamics, finite elements, or discrete elements. This article gathers the lessons learned and identifies issues requiring further attention. A combination of engineering judgment and numerical models may help to identify the collapse mechanism, which is as essential as it is challenging for the seismic assessment. To this purpose, discrete modeling approaches may lead to more reliable results than continuous ones. Even when the correct mechanism is identified, estimating the seismic capacity remains difficult, due to the complexity and randomness of the seismic response, and to the sensitivity of numerical tools to input variables. Simplified approaches based on rigid body dynamics, despite the considerable experience and engineering judgment required, provide as good results as do advanced simulations.

On Overturning of the Façade in Churches with Single Nave: Some Case Studies from L’Aquila, Italy, 2009 Earthquake

The recent earthquakes have shown the high vulnerability of the façades of churches, which detached from the longitudinal walls and failed by overturning. While being well known, this collapse mechanism is still under study as regards the contribution provided by the connections with longitudinal walls as well as the influence of masonry morphology. Three churches with single nave, which have suffered the abovementioned damage during the April 2009 earthquake in L’Aquila, Italy, are considered in the present paper. The seismic behavior of the churches is analyzed taking into account the effective morphology of masonry, by means of 2D Distinct Element analyses under both increasing static forces and dynamic acceleration pulses. The resulting capacity curve is then evaluated and compared to the case of a rigid body overturning showing to what extent the latter model provides a reliable estimate of the seismic behavior of the façade.