Analytical models to determine in-plane damage initiation and force capacity of masonry walls with openings

Masonry panels consisting of piers and spandrels in buildings are vulnerable to in-plane actions caused by seismicity and soil subsidence. Tectonic seismicity is a safety hazard for masonry structures, whereas low-magnitude induced seismicity can be detrimental to their durability due to the accumulation of light damage. This is particularly true in the case of unreinforced masonry. Therefore, the development of models for the accurate prediction of both damage initiation and force capacity for masonry elements and structures is necessary. In this study, a method was developed based on analytical modeling for the prediction of the damage initiation mode and capacity of stand-alone masonry piers; the model was then expanded through a modular approach to masonry walls with asymmetric openings. The models account for all potential damage and failure modes for in-plane loaded walls. The stand-alone piers model is applicable to all types of masonry construction. The model for walls with openings can be applied as is to simple buildings but can also be extended to more complex structures with simple modifications. Model results were compared with numerous experimental cases and exhibited very good accuracy.Peer ReviewedPostprint (author's final draft

Seismic vulnerability of different in geometry historic masonry towers

In the present paper, a simple predictive approach for the seismic vulnerability of existing masonry towers is proposed evaluating it on a series of “idealized” benchmark cases using different simplified approaches, namely the procedure proposed by the Italian code and pushover conducted with two commercial codes (UDEC and Tremuri). In UDEC the geometry is intentionally idealized into quadrilateral elements with different thickness, in order to properly reproduce the hollow square cross-section. The utilization of a 2D approach drasti-cally reduces the computational effort required in carrying out medium scale systematic com-putations. In Tremuri macro-elements are used, providing very fast predictions as well. Within such simplified frameworks, 16 different cases that can be encountered in practice are critically analyzed, changing two key parameters that proved to be important for the vulnerability determination, namely slenderness and transversal shear cross area. The simplifications introduced in the modelling phase allow for fast sensitivity analyses in the inelastic range and an estimation of the acceleration factor in that range of slenderness that is useful for practical purposes. Simplified formulas fairly representing the obtained seismic vulnerability are also reported and put at disposal to any practitioner interested in a prelimi-nary estimation of the behavior of the towers before doing any calculation. For validation purposes, the results obtained previously by one of the authors by means of refined full 3D Abaqus discretizations on 25 existing towers located in the Northern Italy are also reported. Good agreement between the predictions provided by the simplified method here proposed and previously presented reference data is obtained

On the mechanical behavior of masonry

In this chapter, a review on the mechanical behaviour of masonry is presented. The aim is to establish a base of knowledge and understanding of masonry that will underpin its mechanical characteristics and will inform the decisions towards the selection of the computational tool used which are going to be described in the following chapters. Initially, a brief description of the factors that influence the mechanical response of masonry and the variation of the material properties are discussed. The review then considers the possible causes of cracking in masonry and the different failure modes that may occur during loading. Principal findings from the review are summarised at the end of the chapter

Quantification of damage evolution in masonry walls subjected to induced seismicity

This paper aims to quantify the evolution of damage in masonry walls under induced seismicity. A damage index equation, which is a function of the evolution of shear slippage and opening of the mortar joints, as well as of the drift ratio of masonry walls, was proposed herein. Initially, a dataset of experimental tests from in-plane quasi-static and cyclic tests on masonry walls was considered. The experimentally obtained crack patterns were investigated and their correlation with damage propagation was studied. Using a software based on the Distinct Element Method, a numerical model was developed and validated against full-scale experimental tests obtained from the literature. Wall panels representing common typologies of house façades of unreinforced masonry buildings in Northern Europe i.e. near the Groningen gas field in the Netherlands, were numerically investigated. The accumulated damage within the seismic response of the masonry walls was investigated by means of representative harmonic load excitations and an incremental dynamic analysis based on induced seismicity records from Groningen region. The ability of this index to capture different damage situations is demonstrated. The proposed methodology could also be applied to quantify damage and accumulation in masonry during strong earthquakes and aftershocks too.The work presented in this paper is supported by the – Seismic Monitoring, Design and Strengthening For thE GrOningen Region, Project number: RAAK.MKB09.021.Peer ReviewedPostprint (published version

The behaviour of single span stone masonry skew arches

The work reported in this paper summarises the development and results obtained from a 3D computational model, using the distinct element software 3DEC, that was used to investigate the effect of the angle of skew on the load carrying capacity of sixteen different single span stone masonry arches. The variables investigated in the research were the arch span, the span : rise ratio and the skew angle. In order to gain an understanding of the behaviour of the arches, no attempts were made to model the effects of fill, spandrel walls or any other construction details. For each model, a full width vertical line load was applied incrementally to the extrados at quarter span until collapse. At each load increment the predicted crack development and vertical deflection profile was recorded. The results are compared with similar “square” (or regular) arches in order to identify the influence of skew on the behaviour of the arches

From model-driven to data-driven : a review of hysteresis modeling in structural and mechanical systems

Hysteresis is a natural phenomenon that widely exists in structural and mechanical systems. The characteristics of structural hysteretic behaviors are complicated. Therefore, numerous methods have been developed to describe hysteresis. In this paper, a review of the available hysteretic modeling methods is carried out. Such methods are divided into: a) model-driven and b) datadriven methods. The model-driven method uses parameter identification to determine parameters. Three types of parametric models are introduced including polynomial models, differential based models, and operator based models. Four algorithms as least mean square error algorithm, Kalman filter algorithm, metaheuristic algorithms, and Bayesian estimation are presented to realize parameter identification. The data-driven method utilizes universal mathematical models to describe hysteretic behavior. Regression model, artificial neural network, least square support vector machine, and deep learning are introduced in turn as the classical data-driven methods. Model-data driven hybrid methods are also discussed to make up for the shortcomings of the two methods. Based on a multi-dimensional evaluation, the existing problems and open challenges of different hysteresis modeling methods are discussed. Some possible research directions about hysteresis description are given in the final section

Thermal–mechanical modelling around the cavities of underground coal gasification

Underground coal gasification (UCG) is an efficient method for the conversion of the deep coal resources into energy. This paper is concerned with a feasibility study of the potential of deeply lying coal seams (>1200 m) for the application of UCG combined with subsequent storage of CO2 for a site located in Bulgaria. A thermal–mechanical coupled model was developed using the ABAQUS software package to predict the heat transfer, the stress distributions around the UCG and the consequent surface subsidence. Material properties of rocks and coal were obtained from existing literature and geomechanical tests which were carried out on samples derived from the demonstration site in Bulgaria. Three days of gasification has been simulated by assigning a moving heat flux on a cell of 2 m × 2 m × 2 m at a velocity of 2 m/day. Results of temperature and stress distribution showed that the developed numerical model was able to simulate the heat propagation and the stress distribution around cavities under a thermal–mechanical coupled loading during the UCG process. Also, the surface subsidence was found to be 0.08 mm after three days of gasification for the case studied. It is anticipated that the results of this paper can be used for the prediction and optimization of the UCG process in deep coal seams

Experimental, numerical and field study investigating a heritage structure collapse after the 2015 Gorkha earthquake

This paper presents an investigation of the collapse of a 325-year-old multi-tiered heritage temple during the 2015 Gorkha earthquake in Kathmandu, Nepal. The research comprises a reconnaissance survey followed by a geotechnical investigation and numerical back-analysis carried out to understand the potential causes of the collapse. The assessment of the structural configuration of the temple indicated seismic vulnerability in the design due to the presence of discontinuous columns over the height of the temple and age-weakened bonding in the masonry walls. The geotechnical investigation revealed the presence of competent soil strata at the location, assisting the survey which indicated no differential or excessive settlement in the foundation. A series of cyclic triaxial tests were conducted on samples recovered during the geotechnical investigation to determine dynamic behaviour of the soil. Further, dynamic analysis of the plinth of the temple under the recorded acceleration–time history indicated a maximum drift percentage of 1.4% and residual relative displacement of 32 mm suggesting the potential reason behind the collapse. The output of this research will support seismic rehabilitation of ancient structures within World Heritage sites across Nepal and effective action plans to safeguard them against future earthquake hazard