Nonlinear Structural Performance of a Historical Brick Masonry Inverted Dome

ABSTRACT

Traditional domes are obtained by double curvature shells, which can be rotationally formed by any curved geometrical plane figure rotating about a central vertical axis. They are self-supported and stabilized by the force of gravity acting on their weight to hold them in compression. However, the behavior of inverted domes is different since the dome is downward and masonry inverted domes and their structural behaviors in the literature received limited attention. This article presents a nonlinear finite element analysis of historical brick masonry inverted domes under static and seismic loads. The brick masonry inverted dome in the tomb of scholar Ahmed-El Cezeri, town of Cizre, Turkey, constructed in 1508 is selected as an application. First, a detailed literature review on the masonry domes is given and the selected inverted dome is described briefly. 3D solid and continuum finite element models of the inverted masonry dome are obtained from the surveys. An isotropic Concrete Damage Plasticity (CDP) material model adjusted to masonry structures with the same tensile strength assumed along the parallel and meridian directions of the inverted dome is considered. The nonlinear static analyses and a parametric study by changing the mechanical properties of the brick unit of the inverted masonry dome are performed under gravity loads. The acceleration records of vertical and horizontal components of May 1, 2003 Bingöl earthquake (Mw = 6.4), Turkey, occurred near the region, are chosen for the nonlinear seismic analyses. Nonlinear step by step seismic analyses of the inverted dome are implemented under the vertical and horizontal components of the earthquake, separately. Static modal and seismic responses of the inverted masonry dome are evaluated using mode shapes, minimum and maximum principal strains and stresses, and damage propagations.     

Earthquakes and Tie-Rods: Assessment,Design, and Ductility Issues

The effectiveness of tie-rods is widely stressed in past earthquakes and they are still used today as reinforcement intervention, given that their use is a low-invasive and low-expensive technique. However, the earthquake design of these devices is not so simple since the main feature of a tie-rod derives from its ductility and that should be preserved as was done in the past. In this article, some considerations about static and seismic design of tie-rods are made, highlighting the main failure modes of the system. To assess seismic vulnerability of I-mode mechanism, displacement-based methods are usually used, requiring high elongation capability of the tie-rods. For this reason, an experimental campaign was carried out to define clearly the maximum elongation of tie-rods and to investigate the influence of bar length on ductility. The results have shown a good displacement capacity that decreases with the increase of steel strength. A simplified formulation, obtained from nonlinear kinematic analysis, is derived to evaluate quickly the seismic vulnerability of I-mode mechanism with tie-rods and to design this common retrofitting intervention in existing buildings.     

Analysis of the collapse mechanisms of medieval churches struck by the 2016 Umbrian earthquake

The 2016 Umbrian earthquake caused the collapse of several medieval churches, while it was noted that ordinary buildings only reported moderate or little damage. Researchers and technicians are looking to these religious constructions with the aim of understanding their structural behavior under seismic action. Depending on the direction of the seismic action, the typical collapse mode was the overturning of the side walls or of the church façade. This often produced the collapse of the roof structure. In many situations, the overturning was facilitated by a weak connection between the load-bearing walls. In this article, the collapse modes of three mediaeval churches are investigated. The article goes into some detail about what considerations are relevant when analyzing a historic masonry construction. The churches object of this study are located in Campi, a hamlet of Norcia, Italy. Between 2000 and 2004, a research team from the Technical University of Milan in collaboration with the Italian Ministry of Culture carried out an extensive investigation on the historic buildings of Campi, providing interesting data about the maintenance level and a summary of the structural state of the churches. These data were used in this article for a critical analysis of the causes of collapse, performed in combination with numerical simulations of the global behavior and local instability.     

Characterization of timber masonry walls with dynamic tests

Timber-framed wall buildings are seen all over Europe, especially in seismic regions, given its adequacy to resist earthquakes. The “Pombalino” buildings, developed after the great 1755 earthquake that destroyed Lisbon, constitute one of the best examples of historic seismic-resistant structures based on timber-framed masonry walls. The research presented in this article aimed at experimentally evaluating the seismic behavior of the “Pombalino” buildings. The experimental program was based on extensive dynamic testing on sub-structures of typical “Frontal” walls (the timber masonry walls), carried out at the LNEC (the Portuguese National Laboratory of Civil Engineering) shaking table. The tests comprised (a) seismic tests, in which the seismic action was applied with increasing amplitude in one direction; and (b) dynamic identification tests, aiming at evaluating the dynamic properties of the sub-structures and their evolution with damage accumulation.     

Determination of Shear Strength of Masonry Panels Through Different Tests

This study addresses the problem of evaluation of strength of masonry walls. In-plane behavior of masonry panels has been studied under monotonic diagonal-compression and shear-compression loading in quasi-static test facility. The results of 35 laboratory and in situ tests are analyzed to show that in the case of the diagonal compression test results are lower than the strength of masonry walls evaluated trough the shear-compression test, highlighting the problem of choosing the test which best simulates to the real behavior of the masonry when stressed by lateral loads. A presentation is also given of the results of a F.E. investigation for shear strength evaluation of masonry walls. F.E. modeling non-linear procedure was used for the representation of masonry panels. The numerical simulations are compared with experimental results and the reliability of the different finite element models is discussed, thus confirming the different shear strength values measured in the experimental campaign.     

Minimum Thrust of Rounded Cross Vaults

This study analyzes the static behavior of the rounded cross vaults based on the limit analysis approach developed for masonry structures and adopts a rigid no-tension constitutive model with no sliding. The kinematic theorem of the limit analysis with a compatible tridimensional mechanism is applied on these structures with the aim of evaluating the minimum thrust. In this way it was possible to build some abaci in which the ratio between the minimum thrust and the weight is plotted versus the geometrical characteristics of the vaults. Finally, the proposed abaci are used to calculate the thrust of the main vault of the Diocletian Baths in Rome.     

Experimental Studies on Buried Barrel Vaults

The paper concerns an interaction problem between soil and masonry vaults in historic buildings. A particular emphasis was placed on the influence of finishing method of vaults extrados and fill material properties on the behavior of masonry vaults. The results of experimental studies on barrel vaults with and without backfill are presented. During the experiments three finishing methods of vaults extrados and three fill materials were investigated. The results of the experiments show that the presence of backfill and type of vaults extrados finish affect the behavior and load-carrying capacity of tested elements. Moreover, tests were performed on vaults without fill for comparative purposes. The comparison of experimental results obtained for specimens with and without fill shows that the presence of backfill in vault haunches modifies the failure mechanism and increases load capacity of the analysed models. The presented results confirm the importance of backfill as a structural element of vaulted structures.     

Structural Identification of a Masonry Tower Based on Operational Modal Analysis

A wide program of structural assessment has been carried out by Politecnico di Milano on the historic bell tower of the church Chiesa Collegiata in Arcisate (Varese, northern Italy). Within this context, the first part of the article summarizes the results obtained from the application of the stochastic subspace identification method to ambient response data collected in two dynamic tests, carried out in June 2007 and June 2008. Next presented is the vibration-based methodology developed for the calibration of a three-dimensional finite element model of the tower, consisting in the successive application of systematic manual tuning, sensitivity analysis, and simple system identification algorithm.     

Crack Patterns Induced by Foundation Settlements: Integrated Analysis on a Renaissance Masonry Palace in Italy

This study presents some numerical results related to the analysis of the structural damage of a historic masonry building, Palazzo Gulinelli, in Ferrara, Italy. A detailed analysis of the inhomogeneities of the facade, historic documentation, and recent restoration interventions carried out in an adjacent building, suggest that the Palace underwent various modifications both on the structural configuration and on the borne loads. Such modifications might be the main cause of some differential settlements and of the consequent significant crack pattern on the load-bearing walls. Therefore, in the present paper the occurrence of a crack pattern on the facade is simulated by carrying out standard linear and non-linear finite element (FE) homogenized models; differential settlements are applied in order to reproduce the structural changes occurred over time. Previous experiences of the authors (for example, Acito and Milani in 2012 and Mallardo et al. in 2008), the current crack pattern of the building (of its facade in particular) and the monitoring data referring to some of them are the main references for the analysis carried out. The structural survey, the numerical results, and the data monitoring suggest two main conclusions: 1) a good correlation between numerical results and monitoring data is assessed, therefore the cracks can be reasonably related to past differential settlements; and 2) the cracks/damage that occurred as a consequence of differential foundation settlements reduce the ability of the facade to resist seismic actions.     

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (I): Displacement-based Approach Using Simple Failure Mechanisms

ABSTRACT

A displacement-based (DB) assessment procedure was used to predict the results of shake table testing of two unreinforced masonry buildings, one made of clay bricks and the other of stone masonry. The simple buildings were subject to an acceleration history, with the maximum acceleration incrementally increased until a collapse mechanism formed. Using the test data, the accuracy and limitations of a displacement-based procedure to predict the maximum building displacements are studied. In particular, the displacement demand was calculated using the displacement response spectrum corresponding to the actual shake table earthquake motion that caused wall collapse (or near collapse). This approach was found to give displacements in reasonable agreement with the wall’s displacement capacity.