Linda Giresini

MECHANICAL CHARACTERIZATION OF MASONRY WALLS WITH CHAOTIC TEXTURE: PROCEDURES AND RESULTS OF IN-SITU TESTS

An in-situ experimental testing campaign on stone masonry walls performed in the Volterra (Pisa, Italy) hospital complex is described herein. The test-site is a disused building, dated back to the early 1930s, which offered the opportunity to perform destructive and non-destructive tests with multiple purposes: the masonry mechanical characterization of a wide group of nearby similar buildings, the comparison of several testing methods applied on masonry with chaotic texture and the development of the innovative twin panel test procedure. In this context, the failure mode for panels under shear and compression forces was interpreted and, through the results obtained from different techniques (flat-jack test, drilling test, diagonal compression test and shear compression test), a safety domain shear vs. compression for the rubble masonry type was also drawn up. The cross validation of several testing methods can suggest strategies to determine shear strength, deformation properties and ductility capacity of stone masonry walls with highly irregular texture.

Horizontally restrained rocking blocks: evaluation of the role of boundary conditions with static and dynamic approaches

The paper deals with the behavior of restrained rocking blocks under seismic actions. Structural or non-structural masonry or r.c. elements, such as building façades or pre-cast panels subjected to out-of-plane modes, may be assimilated to rocking blocks restrained by horizontal springs. Horizontal restraints can represent flexible floors or steel anchorages or any anti-seismic device designed to impede overturning probability. Their effect could improve, in most cases, the dynamic response of blocks in terms of reduction of rotation amplitude. Nevertheless, this effectiveness could vanish or, surprisingly, affect the response in negative way, resulting in overturning when low values of stiffness or one-sided motion in particular conditions are assumed. Two cases of horizontal restraints are analyzed: (1) concentrated restraint as single spring and (2) smeared restraint as spring bed with constant or linearly variable stiffness. The single stabilizing or destabilizing terms of the formulation are here analyzed and commented, providing practical evaluations to obtain enhancement of response in static and dynamic perspective. A numerical example of a masonry façade with non-linear boundary conditions has been provided highlighting how the choice of stiffness values affects the oscillatory motion and rebound effects. Finally, unit stiffness for masonry/concrete walls and retrofitting techniques, such as steel tie-rods, has been calculated.

Structural damage in the cities of Reggiolo and Carpi after the earthquake on May 2012 in Emilia Romagna

This paper addresses the structural damage to the main buildings of the cities of Reggiolo and Carpi after the primary earthquake shocks on May 20th and 29th, 2012, in Emilia Romagna. The damage survey, performed via form-based methods, highlights the different seismic behaviour of several types of buildings, especially those having historical features, and the consequences of the damage in terms of costs. Moreover, an analysis of some failure mechanisms activated in Reggiolo enables the evaluation of the local peak ground acceleration, due to the soil amplification.

Energy-based method for identifying vulnerable macro-elements in historic masonry churches

Seismic vulnerability of historic churches is a well known issue in earthquake engineering. The need of preserving these buildings encourages the development of reliable numerical methods to assess their seismic behavior. In this paper a new approach is presented, based on evaluating damage pattern obtained by non-linear dynamic analysis and the energy dissipated by each macro-element during earthquakes. A “hierarchy of dissipated energy” concept emerges to give a scale of vulnerability of the parts that compose a church. By modifying masonry mechanical parameters or geometric features, the crack pattern and amount of energy dissipation density of each element is varied and calibrated to achieve the desired hierarchy. The structural designer can therefore estimate the effectiveness of strengthening devices by checking reduction and possibly migration of dissipated energy density from weaker structural elements to more resistant ones, together with a preferable damage pattern. The proposed strategy is applied to a single nave church, hit by the Emilia Romagna earthquake (Italy, 2012), first defining a scale of vulnerability of the macro-elements and then proposing a rehabilitation strategy, which improves the seismic response in terms of damages and dissipated energy. The strong vulnerability of the main dome vault is shown, due to the combination of its high dissipated energy density with its intrinsic weakness. Strengthening techniques are aimed to reduce the amount of dissipated energy of vulnerable macro-elements and to attenuate out-of-plane mechanisms.

Structural Analysis and Consolidation Strategy of the Historic Mediceo Aqueduct in Pisa (Italy)

The present work assesses the state of conservation of the historical Mediceo Aqueduct in Pisa, with classification of architectural elements, decay of materials and failures in view of the restoration. The preview of collapses and the design of interventions in a significant part of the aqueduct are performed. New masonry buttresses for the entire path with optimal distribution are determined to ensure safety and integrity to the monument.

Temporary Preventive Seismic Reinforcements on Historic Churches: Numerical Modeling of San Frediano in Pisa

The idea to apply temporary and precautionary seismic reinforcements to protect artistic assets in historical buildings is hereby presented. The example of the San Frediano Church in Pisa is addressed to show the improvements in its seismic response due to steel wire ropes applied to arches and columns. Numerical analysis demonstrate the reduction of the shear force at the base of the stone columns. The proposed reinforcements are reversible, temporary and with low aesthetic impact: they can be quickly installed in the beginning of seismic events, as an evolution of the techniques adopted after the last Italian earthquakes (Abruzzo 2009 Emilia 2012).

Collapse of the Historic City Walls of Pistoia (Italy): Causes and Possible Interventions

In the paper are discussed the likely causes of the collapse and the temporary safety features adopted to secure a collapsed portion of the Historic Walls of the city of Pistoia (Italy). The walls of medieval origin, affected by various subsequent modifications and alterations, have been subjected to a sudden collapse, after a period of heavy rain, for a length of about 25 meters. Hereby are described the probable causes of the collapse, due to a poor quality of the walls (external façades with external layer made up of river pebbles and inner filling material in-coherent), height of building is not modest (approximately eleven meters), a significant differential in height between the two faces (about four meters) and a not unlikely rotation of the base. It is proposed a technique of temporary reinforcement with a system of steel tie-beams and braces with a view to the work of reconstruction of the partially collapsed and consolidation of the lateral parts of wall.

Tests Results and Simple Structural Analysis of the Main Lighthouse in the Harbor of Livorno (Italy)

The present work assesses the structural analysis of the main lighthouse of Livornos harbor. It is made by a r.c. framework, built in the 50s as reconstruction of medieval tower similar to it. The wind and seismic actions (with and without collaboration of the masonry infill and façade) are investigated, showing the fundamental contribution of the masonry layers for a satisfactory structural response.

Collapse of corrugated metal culvert in Northern Sardinia: analysis and numerical simulations

The paper illustrates the possible causes of collapse of a Corrugated Metal Culvert (CMC), occurred in Northern Sardinia after an extreme rainfall event in 2013. The possible causes of collapse are related to the conditions before and during the rainfall. Erosion and corrosion phenomena, which caused material decay and an improper water flow, have been discussed. Numerical analyses were performed to identify buckling multipliers with a finite element model simulating the effect of combined erosion and corrosion. The analysis showed a greater sensitivity in terms of buckling resistance when the soil erosion is concentrated in the lower portion of the culvert rather than in the lateral one.

A Proposal for the Consolidation of a R.C. Social Housing by Means of External Hybrid Steel-Glass Frameworks

A proposal for the seismic consolidation of an existing r. c. social housing complex is presented. The intervention is thought to concern just the external facades in order to minimize costs and discomfort of inhabitants. Two external hybrid steel-glass bracing frameworks have been designed, with the aim to reach both seismic and energetic advantages. The mechanics of the framework system takes advantages from the compressive strength of the glass panels and the tension strength of steel braces and columns. A hypothetical application on a typical r. c. building dating back to the ‘60s in the city of Leghorn (Italy) is illustrated.