EXPERIMENTAL VALIDATION OF IN-PLANE FRICTIONAL RESISTANCES IN DRY BLOCK MASONRY WALLS

This paper presents the experimental and analytical validation of the lateral strength of dry block masonry walls under in-plane loading. The analytical evaluation of the in-plane frictional resistances activated at the onset of the rocking-sliding mechanisms is revisited in order to account for the different contributions of the self weight of the wall and additional loads. It is assumed that the wall is arranged in a running bond pattern, with rigid blocks and dry contact interfaces governed by cohesionless Coulomb failure criterion. The accuracy and robustness of the analytical results are assessed by experimentally testing both the resultant frictional resistances and their applications points. Both pure sliding and rocking-sliding failure modes are simulated with a testing device designed and realized ad hoc (no standard equipments and procedures were found in the literature). A good agreement between the analytical and experimental results is shown for the selected cases

Pushover analysis of rocking façades in masonry churches:the role of friction and geometry in identifying homogeneous classes of vulnerability

The out-of-plane failure of façades is one of the most typical local mechanisms in masonry churches recognizable in the aftermath of a seismic event. The analysis of such a failure is addressed in this paper with reference to a small sample of existing masonry churches hit by the seismic event of 21st August 2017 in the Ischia Island (Italy). The main aim is to assess the influence of the geometric parameters of the façades and of the interlocked sidewalls on the vulnerability of the façades to out-of-plane mechanisms, using nonlinear static analysis. According to the displacement-based approach, the pushover analysis is carried out considering the geometric nonlinearity, namely by evaluating the static multiplier for varied kinematic configurations, and by means of a macro-block model involving the stabilising contribution of frictional resistances exerted by the sidewalls of the churches. In order to develop seismic assessments, the seismic demand is represented by ADRS (acceleration-displacement response spectra) for different limit states, obtained according to the Italian seismic code. Then, the capacity is compared with the seismic demand in terms of both forces and displacements and the relevant influence of the frictional resistances and of some geometric parameters on the response are highlighted. Finally, the capacity curves are critically discussed in order to identify ‘a posteriori' homogeneous classes of façades within the examined sample in terms of vulnerability and to develop future statistical analyses and fragility curves for the individuated homogeneous classes.</p

Literature Review of the In-Plane Behavior of Masonry Walls: Theoretical vs. Experimental Results

In-plane strength of masonry walls is affected by the resistant mechanisms activated in the walls, i.e., related to flexural or shear behavior. The latter one can occur in the walls according to different failure modes depending on both mortar and unit strengths and on the type of assembling, i.e., ‘regular’ or ‘irregular’ texture. In this paper, a critical review of the existing design formulations for the in-plane strength of masonry walls is firstly presented, with important information on the achievable failure modes depending on the geometrical and mechanical features of the masonry fabric. Then, experimental tests are collected from the literature and a comparison between theoretical and experimental results is carried out. The presented analyses are aimed to highlight the differences between the existing formulations and to identify the most suitable ones

Formulating the in-plane frictional resistances and collapse mechanisms for multi-storey masonry block walls

In this paper a macro-block model accounting for frictional resistances is presented to assess the lateral strength of a multi-storey masonry block wall. The kinematic approach of limit analysis is used to define the load factor causing the onset of rocking-sliding mechanism under in-plane horizontal loading. A dry frictional contact condition is assumed at the rigid block interfaces, according to the Coulomb's law with non-associated flow rule. The key aspect of the proposed approach is the introduction of a criterion to evaluate the contribution of the actual frictional resistances depending on the inclination angle of the crack line. An accurate assessment of the frictional resistances is also obtained by distinguishing two different contributions (the wall own weight and additional vertical loads) and their application points. Hence, a sensitivity analysis is performed with respect to the overloading condition, the friction coefficient, and geometrical parameters such as the shape ratios of the wall and the unit block and the number of rows.&nbsp; The analytical results of the proposed model are also validated against results from other existing macro and micro-block modelling approaches in terms of load factor. The comparison confirms the reliability of the proposed model that allows, with similar results, great simplification of the computational effort with respect to micro-block models

infrared thermography for the characterization of painted vaults of historic masonry buildings

The infrared thermography is a type of non-destructive investigation which can find interesting application in acquiring information about the structural features of ancient masonry buildings. In this case, in fact, the needs of preservation of the historical values have to be compound with the needs of achieving a proper level of knowledge of the parameters influencing the structural behaviour in order to perform a reliable evaluation of their seismic safety. A recent application of the infrared thermography was proposed in the framework of the Project on the seismic evaluation of the Museum of Capodimonte in Naples (Italy). The objective was to clarify if the painted vaults covering some rooms could have structural function and to identify their constructive typology. In this circumstance, an interesting methodological approach, with more general validity, has been developed by integrating the instrumental investigations with different sources of information, such as historical documents and hypotheses of critical interpretation

Management of multi-source information to identify the typology of the horizontal structures in historical masonry buildings: the case study of the Museum of Capodimonte in Naples (Italy)

The evaluation of the seismic safety of ancient masonry buildings usually requires compounding the need of preservation of the historical values with the need of achieving a proper level of knowledge of the parameters influencing their structural behaviour. To this aim, non-destructive techniques of instrumental investigation have lately attracted increasing attention, although the provided data are frequently not exhaustive and require to be integrated with different sources of information, such as historical documents and hypotheses of critical interpretation. Therefore, the management of this multi-source information is a crucial aspect in defining a methodological approach to the structural evaluation of the cultural heritage. This paper describes an integrated approach developed in the framework of the Project on the seismic evaluation of the Museum of Capodimonte in Naples (Italy) with reference to the typological identification of the horizontal structures at the first level of the building. The management of the data derived from the application of the infrared thermography, integrated with the information from the visual inspections, the architectural survey and the historic analysis, has allowed obtaining a complete characterization of the structures under study

NON-LINEAR KINEMATIC ANALYSIS OF MASONRY WALLS OUT-OF-PLANE LOADED. THE COMPARATIVE ROLE OF FRICTION BETWEEN INTERLOCKED WALLS

In this paper the limit analysis of a simple out-of-plane failure mechanism of a laterally weakly connected masonry wall involving frictional resistances is developed according to the displacement-based approach. The pushover analysis is made considering geometric nonlinearity, i.e. by evaluating the static multiplier for varied kinematic configurations, as a function of the displacement of a control point. The effect of the interlocking between the front wall and the sidewalls gradually decreases after a certain displacement, due to the progressive detachment of the front wall and the variation of the frictional resistances can be represented by a non-linear function of the decreasing number of involved rows. The stabilizing role of friction between interlocked walls is compared to another system of strength in masonry buildings, i.e. the effect of tie-rods, with and without the detrimental effect of the static thrust of masonry vaults. The sensitivity of the load multiplier to these strength parameters is investigated with reference to different combinations of loading conditions. Comparative results and pushover curves are developed to evaluate the displacement capacities for each case analyzed

NON-LINEAR KINEMATIC ANALYSIS OF MASONRY WALLS OUT-OF-PLANE LOADED. THE COMPARATIVE ROLE OF FRICTION BETWEEN INTERLOCKED WALLS

In this paper the limit analysis of a simple out-of-plane failure mechanism of a laterally weakly connected masonry wall involving frictional resistances is developed according to the displacement-based approach. The pushover analysis is made considering geometric nonlinearity, i.e. by evaluating the static multiplier for varied kinematic configurations, as a function of the displacement of a control point. The effect of the interlocking between the front wall and the sidewalls gradually decreases after a certain displacement, due to the progressive detachment of the front wall and the variation of the frictional resistances can be represented by a non-linear function of the decreasing number of involved rows. The stabilizing role of friction between interlocked walls is compared to another system of strength in masonry buildings, i.e. the effect of tie-rods, with and without the detrimental effect of the static thrust of masonry vaults. The sensitivity of the load multiplier to these strength parameters is investigated with reference to different combinations of loading conditions. Comparative results and pushover curves are developed to evaluate the displacement capacities for each case analyzed

Performance-based Seismic Analysis of Rocking Masonry Façades Using Non-linear Kinematics with Frictional Resistances: A Case Study

In this paper the seismic assessment of rocking masonry walls is evaluated through the displacement-based approach. In particular, a case study is selected to analyse the rocking failure mechanism of the façade of an ancient masonry church, damaged during the 2016-17 Central Italy seismic sequence. For this purpose, a non-linear kinematic analysis is developed to define the load factor at the activation of the failure mechanism and its evolution until collapse, at large displacements. An advanced macro-block model is adopted to take into account the stabilising contribution of frictional resistances exerted by the interlocked walls. The seismic input is described through acceleration-displacement response spectra (ADRS), provided both by seismic codes and selected real accelerograms, and the seismic analysis is addressed according to the capacity spectrum method (CSM), in the form incorporated into the latest Commentary to the Italian technical standard for construction (CNTC19). The capacity is compared with the seismic demand through safety indexes, in terms of both forces and displacements, and the relevant influence of the frictional resistances on increasing the capacity is discussed. Incremental static analysis (ISA) curves are presented as another approach useful to highlight the relation between the peak ground acceleration (PGA) and the displacement demand

Seismic analysis of an existing masonry building according to the multi-level approach of the italian guidelines on cultural heritage

In this paper a multi-level approach proposed by the Italian Guidelines on Cultural Heritage was adopted to assess the seismic safety of an unreinforced masonry building located in Naples (Italy). In particular, the simplified model of the global seismic response at the territorial scale was used for the first level (LV1), while the nonlinear static (pushover) analysis and the equivalent frame modelling with nonlinear structural-elements were adopted for the more accurate global assessment level (LV3). Different evaluations of the safety indexes are compared in the framework of the LV1 level, with particular attention to their reliability in representing the main aspects of the seismic capacity of the building, in terms of the prevailing failure mechanism and the detection of the weaker direction. The achieved results were compared with those obtained by LV3 assessment level