Effect of ground-motion sequences on a unreinforced masonry wall restrained by an elasto-plastic tie-rod

This work investigates the effect of international ground-motion sequences on the out-of-plane response of an ordinary-building façade. The following assumptions are made on the wall boundary conditions: the wall is resting on a foundation, it is adjacent to transverse walls and restrained by elasto-plastic tie rods with finite elongation capacity. Four walls are considered of different aspect ratio and size; two types of masonry are assumed, and the tie is designed following a force-based procedure according to the Commentary to the Italian Building Code. The walls are modelled as rigid blocks of finite thickness and free to rotate on one side only. The rocking response of the walls, excited in the out-of-plane direction under 56 sequences of records, is evaluated. The effect of sequences is estimated by the comparison of the response experienced during the sequence and under a single record, strongest in terms of either peak ground acceleration or velocity. Finally, in order to reduce the vulnerability originated by a seismic sequence, a proposal of a reduced behaviour factor to be adopted in the design of tie rods is formulated

Out-of-Plane Seismic Response of Unreinforced Masonry Walls: Conceptual Discussion, Research Needs, and Modeling Issues

Modeling unreinforced masonry walls, subjected to seismic loads applied normal to their plane, has received much attention in the past. Yet, there is a general lack of conformance with regard to what aspects of seismic response a computational model should reflect. Boundary conditions are certainly an important aspect, as the response can involve two-way bending or just one-way bending and, in the second case, along vertical or horizontal directions. In this respect, flexural restraint of wall intersections can be significant in addition to size and placement of openings. Moreover, in-plane damage can modify the boundary conditions and the overall out-of-plane performance. Proper modeling of actions is also relevant, as they can be a result of distortions imposed upon wall elements and/or inertial forces along the span of a wall. Axial forces can markedly affect the out-of-plane response of the wall, particularly vertical compressive forces, which can enhance out-of-plane strength. The outcome of static verifications can be more conservative than that of dynamic analyses, but the latter are much more complex to carry out. These topics are discussed with reference to previous research, observations in the field and in the laboratory, as well as numerical analyses on three-dimensional models.info:eu-repo/semantics/publishedVersio

Shake‑table testing of a stone masonry building aggregate: overview of blind prediction study

City centres of Europe are often composed of unreinforced masonry structural aggregates, whose seismic response is challenging to predict. To advance the state of the art on the seismic response of these aggregates, the Adjacent Interacting Masonry Structures (AIMS) subproject from Horizon 2020 project Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) provides shake-table test data of a two-unit, double-leaf stone masonry aggregate subjected to two horizontal components of dynamic excitation. A blind prediction was organized with participants from academia and industry to test modelling approaches and assumptions and to learn about the extent of uncertainty in modelling for such masonry aggregates. The participants were provided with the full set of material and geometrical data, construction details and original seismic input and asked to predict prior to the test the expected seismic response in terms of damage mechanisms, base-shear forces, and roof displacements. The modelling approaches used differ significantly in the level of detail and the modelling assumptions. This paper provides an overview of the adopted modelling approaches and their subsequent predictions. It further discusses the range of assumptions made when modelling masonry walls, floors and connections, and aims at discovering how the common solutions regarding modelling masonry in general, and masonry aggregates in particular, affect the results. The results are evaluated both in terms of damage mechanisms, base shear forces, displacements and interface openings in both directions, and then compared with the experimental results. The modelling approaches featuring Discrete Element Method (DEM) led to the best predictions in terms of displacements, while a submission using rigid block limit analysis led to the best prediction in terms of damage mechanisms. Large coefficients of variation of predicted displacements and general underestimation of displacements in comparison with experimental results, except for DEM models, highlight the need for further consensus building on suitable modelling assumptions for such masonry aggregates

Comparison of the effects of traditional and innovative tie-rods in reducing the seismic vulnerability of church façades: the case of San Francesco in Mirandola

This contribution discusses the effect of steel tie-rods installed in a church façade subjected to 60 recorded earthquakes. The church façade is firstly analysed as a two-sided and a one-sided rocking SDOF system. For the one-sided rocking, sidewalls are modelled through either elastic or rigid contact to compare the two modelling techniques. Secondly, two configurations of tie-rods are investigated: (i) traditional tie-rods with a specific elasto-plastic constitutive law and (ii) innovative tie-rods with a dissipative component. The chosen case study is the San Francesco Church located in Mirandola, hit by the 2012 Emilia Romagna earthquake. The results of nonlinear dynamic analyses are presented in terms of median and standard deviation of maximum normalised displacements for each of the 60 seismic inputs. The results show the great benefit introduced by both traditional and dissipative tie-rods, with remarkable reductions of maximum rotations up to an order of magnitude with respect to the unrestrained façade. Moreover, the increment of damping coefficient is associated to a reduction of the standard deviation of the amplitude peaks, which is a positive aspect for the reliability of the response of the damped wall. Finally, the two models, rigid and elastic contact, of sidewalls provide results in excellent agreement in terms of median and standard deviation of the maximum normalised rotations

Failure of masonry infill walls under out-of-plane loads

The failure of infills, which may develop both in-plane and/or out-of-plane, causes casualty risk and heavy socio-economic consequences. In addition, the total or partial collapse of an infill may lead to unfavourable conditions affecting the overall structural response, such as the formation of an open storey. The collapse of infill walls, especially in the out-of-plane direction, may occur even for moderate intensity of the ground motion. For these reasons, the interest in the out-of-plane behaviour of masonry walls has been growing in the last years. Previous studies have shown that the height/thickness ratio, the height/length ratio and the boundary conditions are key parameters affecting the out-of-plane behaviour of infills. Moreover, the presence of an opening in the infill may also influence the out-of-plane response. In this regard, the few studies available in the literature up to now present contradictory results. In this paper, the out-of-plane resistance of infill walls is investigated by means of non-linear monotonic (push-over) finite element analyses, where masonry is modelled with a smeared-crack approach and contact interfaces are used to model the interaction between the masonry panel and the surrounding frame. The influence of different factors on the out-of-plane resistance is investigated, namely the height/thickness and height/length ratios of the infill, the masonry compressive strength and presence of a central opening

Numerical evaluation of masonry infill walls behaviour under out-of-plane loads

Observation of damage in seismic events has highlighted that collapse of infill walls in the out-of-plane direction may occur even for moderate intensity of ground motion. Different analytical models have been proposed in the last decades for the assessment of the out-of-plane response of infills and their applicability under different conditions has been checked also with experimental tests. In this paper, a numerical solution is adopted by using a smeared crack approach, in which the masonry panel is modelled as a a non-linear continuum and contact surfaces are located only at the interface between masonry and frame elements; horizontal out-of-plane loads are applied monotonically as body forces. Height/thickness ratio, height/length ratio, masonry compressive strength and stiffness of frame elements are varied to investigate their influence on the out-of-plane resistance. Results confirm previous experimental evidence, such as the inverse proportionality of the strength with respect to the span length, the strength reduction with varying height/length ratio slightly affected by masonry compressive strength and thickness. Comparisons of the results with analytical models show that, in general, the latter give a conservative estimate of the strength, but the degree of approximation of the considered equations is strongly affected by the height/thickness of the infill, and, to a much lesser extent, by the infill height/length ratio, whereas it is not influenced by the masonry compressive strength. It is found that each equation is suitable in a different range of height/thickness ratios

Static penetration test for historical masonry mortar

The penetration test for historical masonry mortar presented in this study is based on the principle of "static" penetration. A pin is driven at constant velocity by a stepper motor controlled by a computer. The test result is the penetration load as a function of the penetration depth. The penetrometer has been tested on masonry walls consisting of decayed mortar. The objective of the test is to provide information about the mechanical characteristics of mortar (friction coefficient, cohesion). To this end, the results are compared with those from direct shear tests on mortar samples and with those from a previous percussion penetration test. (C) 2016 Elsevier Ltd. All rights reserved

Low-impact techniques for seismic strengthening fair faced masonry walls

Two techniques for the seismic strengthening of fair faced rubble masonry walls are proposed and tested on a shake table. The first solution entails the use of carbon fibre reinforced polymer connectors installed from outside through the natural stone units, without perforating the entire wall thickness, thus leaving the internal wall surface undisturbed. In the second solution, stainless-steel cords are embedded in repointed mortar joints of the fair face and connected, by means of stainless-steel bars, to a thermo-insulating composite reinforced mortar applied to the internal side. Shake table tests were performed under natural accelerograms on real scale multi-leaf rubble masonry walls, built with the stone units retrieved from the debris of a hamlet heavily damaged in the 2016 Central Italy earthquakes. Both strengthening solutions proved effective in enhancing the seismic capacity by preventing leaf separation and masonry disintegration, and in limiting damage development under earthquake excitation. Thanks to the compatibility with original materials and the preservation of the fair face, they are suitable for mitigating the seismic vulnerability of architectural heritage

CHARACTERIZATION OF HISTORICAL MASONRY MORTAR FROM SITES DAMAGED DURING THE CENTRAL ITALY 2016-2017 SEISMIC SEQUENCE: THE CASE STUDY OF ARQUATA DEL TRONTO

Mortar quality is a fundamental parameter to take into account when studying the structural behavior of masonry, especially under seismic actions. Separation between the leaves of rubble masonry can occur, inducing the partial or total collapse of the construction. A good quality mortar is essential to delay/prevent the separation of leaves, but often, especially in ancient building with a cultural value, mortars have low binder capabilities. The paper presents an experimental investigation on mortar specimens taken from buildings of a little municipality in Marche region, Arquata del Tronto, heavily damaged by recent earthquakes in Central Italy (2016-2017). Both diagnostic techniques as X-Ray diffraction, Fourier-Transform infrared spectroscopy and calcimetry, and mechanical test as compression tests were carried out in order to correlate the obtained values with the performance of the original masonry