Slender Masonry Towers Research Articles

Influence of soil-structure interaction on the site-specific seismic demand to masonry towers

Joint analysis of hazard and fragility is becoming a widespread and unavoidable tool to estimate losses caused by earthquakes. The application of such analysis to buildings on soft soil is improved when the dynamic soil - foundation - structure interaction is considered, since both the reference hazard on site and the structural performance are modified by soil compliance. This study investigates and compares the site-specific seismic demand required to squat or slender masonry towers settled on stiff or soft soil. To this aim, 96 non-linear dynamic analyses were performed on 3D models, including soil, foundation and structure and excited by fourteen unscaled records of real earthquakes. Distributions of the equivalent bending rotation of structure and of peak and residual rotations of foundation were calibrated on numerical results and convoluted with the hazard curves of three Italian cities, to compute the mean annual rate of exceeding different values of structural and foundation demand. The resulting curves highlight that soil deformability enhances the bending demand and produces a not negligible permanent tilt in towers.

On the role played by the openings on the first frequency of historic masonry towers

The manuscript provides a wide database for historic masonry towers collecting their modal, mechanical and geometrical features. This large amount of data was collected according to a literature review, then summing up as many as 56 different case studies. The collected data was then used to identify the main physical parameters influencing the modal behaviour of slender masonry towers, including the openings on the facades. After a critical discussion of the data reported in the database, the existing empirical or semi-empirical formulations available for the estimation of the first natural frequency of such structural typology are first evaluated. Subsequently the effects of the openings, as revealed through the analysis of the experimental results reported in the database, are discussed by comparison with a simple but effective numerical model. Despite the difficulties to quantify the effect of the openings along the height of the tower on the main frequency due to a cross-contribution of mass and stiffness, a simple but effective formulation is proposed which is able to account for this parameter.

Failure analysis and performance of compact and slender carved stone walls under compression and seismic loading by the FEM approach

Abstract Most of existing constructions were built of unreinforced masonry. The behavior of this material is governed by the physical and mechanical characteristics of the composite, self-weight and earthquake loading. The heterogeneity of masonry is also reflected in the anisotropic behavior of this material with different performance and failure under seismic forces. The capability of the applied model to simulate the nonlinear behavior of masonry and collapse modes on compact walls is validated through numerical examples under uniaxial compression, seismic loading and experimental results. The compact walls with solid section presented a poor performance with brittle failure. Conversely, the compact walls with window presented a more ductile performance by the redistribution of stresses. This combined failure by bending and shear stresses is also observed in two slender masonry towers with solid section and with one large window at belfry. Both towers did not present masonry crushing at ultimate conditions and it is not observed the failure by shear stresses at belfry because only one window is included in the FEM model of the tower. Other reported works on the same tower are used to compare the results by including more windows at belfry to induce a brittle failure.

Modelling and analysis of South Indian temple structures under earthquake loading

The gopuram (multi-tiered entrance gateway) and the mandapam (pillared multi-purpose hall) are two representative structural forms of South Indian temples. Modelling and seismic analysis of a typical 9-tier gopuram and, 4- and 16-pillared mandapam of the 16th century AD Ekambareswar Temple in Kancheepuram, South India, are discussed. The seismic input is based on a probabilistic seismic hazard analysis of the archaeological site. Two modelling strategies, namely lumped plasticity and distributed plasticity modelling, and three analysis approaches, namely linear dynamic, non-linear, static and dynamic analyses were adopted for the seismic assessment of the gopuram. Unlike slender masonry towers, the vulnerable part of the gopuram could be at the upper levels, which is attributable to higher mode effects, and reduction in cross section and axial stresses. Finite element and limit analysis approaches were adopted for the assessment of the mandapam. Potential collapse mechanisms were identified, and the governing collapse of lateral load, calculated based on limit theory, was compared with the seismic demand as a safety check. Simple relations, as a means of rapid preliminary seismic assessment, are proposed for the mandapam.

Epistemic Uncertainties in Structural Modeling: A Blind Benchmark for Seismic Assessment of Slender Masonry Towers

AbstractThe paper reports the results of a blind benchmark developed as a part of the preliminary activity of the research project RiSEM (Italian acronym for Seismic Risk on Monumental Buildings). ...

Time-history analysis of slender masonry towers: a parametric study on the reliability of a simplified Bouc and Wen approach

The assessment of existing masonry structures under seismic loading requires reliable and expedite numerical modelling approaches. These approaches should take into account both the specific non-linear behaviour of the material (f.i. the small tensile strength) and, in case of time-history analysis, the hereditary nature of the restoring forces that describe the masonry mechanical behaviour. The paper, considering the need of simplified but effective methods to assess the seismic response of masonry towers, proposes an expeditious approach based on an equivalent Bouc and Wen model. The model, that has been extensively employed to describe a wide range of hysteretic behaviours like degradation of stiffness and strength, has the advantage of the computational simplicity since only one auxiliary non-linear differential equation is needed to describe the hysteretic behaviour. As a prototype of masonry towers, a cantilever masonry beam is analysed and the non-linear Bouc and Wen model is employed to reproduce the system hysteretic response assuming that the first mode shape governs the dynamic behaviour. A two-steps identification procedure is proposed. Static non-linear analyses are employed to assess a few of the Bouc and Wen model parameters; remaining ones are assessed in order to minimize the error between the estimated displacement and the one obtained in a reference finite element model of the structure. Within the paper, the identification of the parameters needed to build the single-degree-of-freedom oscillator is analysed in depth analysing the effects of four different seismic natural records. The results of the identification procedure show a general trend concerning the values to be selected for the Bouc and Wen parameters.

Seismic performance evaluation of slender masonry towers: a case study

Summary Historical structures and preserving their cultural values are crucial issues for humanity, not only because of their link to important certain periods in the past, but also their unique architectural features. Although many historical structures continue to offer services while keeping their historical values, some of them are at high risk in seismic prone regions. Therefore, the understanding of their structural performance under strong ground motions has been of significant importance to the civil societies as well as engineering community. The structural systems of historical buildings, generally, consist of masonry walls or piers. The behavior of such walls is controlled by either deformation or force. Seismic performance evaluation of historical structures can be carried out within the framework of performance-based evaluation principles. This paper mainly discusses the basic principles to be considered in performance-based seismic evaluation of historical structures. Proposed seismic hazard levels, evaluation of existing seismic hazard, selection of earthquake ground motions as well as site geology, geological and tectonic settings of the area, seismic activity of the region and local soil conditions are needed for a thorough performance evaluation. Seismic performance evaluation of a clock tower located in eastern Turkey was accomplished based on the proposed principles. Copyright © 2015 John Wiley & Sons, Ltd.

Effectiveness of nonlinear static procedures for slender masonry towers

This paper investigates the accuracy of pushover-based methods in predicting the seismic response of slender masonry towers, through comparison with the results from a large number of nonlinear time-history dynamic analyses. In particular, conventional pushover analyses, in both their force- and displacement-based variants, are considered, and seismic assessment through the well-established N2 method is also addressed. The study is conducted by applying a simple non-linear elastic model recently developed and implemented in the computational code MADY to represent slender masonry structures. The model enables both pushover analyses and non-linear dynamic analyses to be performed with a minimum of effort. A multi-record incremental dynamic analysis carried out for a quite large number of structural cases, each of which is subjected to a comprehensive set of dynamic nonlinear analyses, is used to evaluate the accuracy of pushover methods in predicting the global structural response, as represented by the usual capacity curve together with a damage curve, both of which are compared with dynamic envelopes. Local responses, in terms of lateral displacements and the distribution of damage along the tower height are also compared. The results reveal that the key issue in the accuracy of pushover methods is the nature of the lateral load applied, that is, whether it is a force or a displacement. Different ranges of expected deformation are suggested for adopting each type of lateral load to better represent the actual behaviour of masonry towers and their damage under seismic events through pushover methods.

Seismic improvement of slender masonry tower by using hysteretic devices and partial prestressing technique

An innovative system for seismic improvement of slender masonry towers by using hysteretic devices and partial prestressing technique was developed and applied to a case study. The proposed technique consists in a low level of prestressing of the upper part of the tower in order to localize in the un-prestressed lower part of the tower, i.e. a limited zone near the basement, the vertical displacements due to the cracking of masonry under seismic action. The positioning of dissipative devices, such as the Buckling-Restrained Axial Dampers, across the localization zone allows a significant contribution in terms of damping for hysteretic dissipation. The main effect of such an intervention is the reduction of the seismic demand to the tower and consequently the reduction of the top displacement as well as of the level of damage of the masonry. Both numerical analyses and experimental tests on a scale model of a Venetian bell tower were carried out showing the efficiency and reliability of the proposed technique.

SIGNIFICANT GROUND MOTION PARAMETERS FOR EVALUATION OF THE SEISMIC PERFORMANCE OF SLENDER MASONRY TOWERS

The evaluation of seismic risk of masonry monuments requires to study the combination of vulnerability and hazard. In the present work, the global seismic response of slender masonry towers has been studied by means of a specific 3-D fibre model. Accounting for the particular behaviour of such structures, the hazard should also be described by a suitable measure of intensity of the seismic action. A variety of different parameters relating with the ground acceleration recordings have been investigated for what regards their correlation with the damage indicators of the model. The combination of the peak ground velocity of the horizontal component and of the significant duration is an effective measure of intensity. This measure can be improved by considering the accord of the frequency content of the ground motion with the dynamical characteristics of the tower. Since in some cases the effect of the vertical component proved to be important, a further improvement can be obtained by taking into account also the vertical ground motion intensity.

A THREE-DIMENSIONAL MODEL FOR VULNERABILITY ANALYSIS OF SLENDER MEDIEVAL MASONRY TOWERS

A fibre model to describe the global dynamic response of slender masonry towers is presented for use in deterministic vulnerability analysis. The main stresses are axial in this type of structure, and coupling between flexural and axial modes in the inelastic region may be critical. The model accounts for the three-dimensional response of the structure and the relations between coupling effects and masonry characteristics. An exhaustive parametric study revealed that compression strength and height are the most important parameters determining global response to seismic excitation, and that the response is often very sensitive to the vertical component of the ground motion. The combination of flexural and axial vibrations can induce serious additional damage that should be considered in seismic risk analysis.