Lucrezia Cascini

Contact Dynamics of Masonry Block Structures Using Mathematical Programming

A simple variational formulation for contact dynamics is adopted to investigate the dynamic behavior of planar masonry block structures subjected to seismic events. The numerical model is a two-dimensional assemblage of rigid blocks interacting at potential contact points located at the vertices of the interfaces. A no-tension and associative frictional behavior with infinite compressive strength is considered for joints. The dynamic contact problem is formulated as a quadratic programming problem (QP) and an iterative procedure is implemented for time integration. Applications to analytical and numerical case studies are presented for validation. Comparisons with the experimental results of a masonry wall under free rocking motion and of a small scale panel with opening subjected to in-plane loads are also carried out to evaluate the accuracy and the computational efficiency of the formulation adopted.

An Integrated Approach to Durability Design of Steel Structures Against Atmospheric Corrosion

To develop a durability design procedure based on lifetime safety factor method, different dose-response functions based on both ISO standards and the literature are presented for the prediction of the thickness loss due to atmospheric corrosion in metal structures. Finally, serviceability and ultimate limit states are defined for the durability design against corrosion.

3D rigid block micro-modelling of a full-scale unreinforced brick masonry building using mathematical programming

In this paper, we present a three-dimensional limit equilibrium analysis of an unreinforced brick masonry building. The structure under investigation is a one-room one-floor building that has been selected from a full-scale test carried out within the framework of a joint USA-Pakistan research project. The structural model of the building is an assemblage of rigid blocks, which interact through no-tension contact surfaces with Coulomb friction. A micro-modelling approach is adopted where each masonry unit is modelled as a rigid body. The underlying limit analysis formulation is based on the concave contact model, with contact forces located at the vertices of the interfaces. Iterative calculations are carried out to deal with the non-associative friction behaviour. The numerical analysis is carried out with the aid of a computer program that provides as output the failure load and the collapse mechanism. The comparison with experimental outcomes shows that the adopted formulation is capable to predict the actual behaviour of 3D masonry structures with a reasonable computational effort.

Probabilistic time variant assessment of thin-walled steel members under atmospheric corrosion attack

AbstractAtmospheric corrosion is a relevant problem for steel structures and components exposed in aggressive environment in case of poor and/or unfeasible maintenance and inspection during service life. As for thin-walled members, the corrosion hazard can be exacerbated due to the thin thickness of components and the coupled effect between corrosion and buckling can significantly reduce the structural capacity of such structures. Following these considerations, this paper presents a study on the reliability of a thin-walled steel section subjected to the damage induced by atmospheric corrosion in outdoor environments, combining predictive corrosion models for metals with structural reliability applications. A general procedure for the evaluation of the time variant capacity is proposed and discussed in detail. Finally, an application to a C-lipped cold formed section is presented and a reliability analysis of the deteriorating section is carried out to evaluate the coupled effect of corrosion and bucklin...

LiABlock_3D: A Software Tool for Collapse Mechanism Analysis of Historic Masonry Structures

ABSTRACT A rigid block model is proposed for collapse mechanism analysis of three-dimensional historic masonry structures subjected to point live loads, seismic-induced lateral loads and settlements. The model is made of polyhedral rigid blocks interacting at no-tension, frictional contact interfaces and can be used to represent complex assemblages and bond patterns. The formulation and the solution procedure of the underlying limit equilibrium analysis problem were implemented in LiABlock_3D, a MATLAB based tool with Graphical User Interface (GUI). The software was designed to import the geometric model from commercial Computer Aided Design (CAD) tools, thus allowing high flexibility of structural configurations and masonry patterns. The graphical interface is also used to define material properties as well as boundary and loading conditions. Numerical and experimental case studies from the literature were analyzed to show the ability of the model developed in predicting the collapse behavior of a variety of structural typologies. Those include arches, vaults, and domes under vertical and horizontal live loads and spreading supports. A two-story masonry building with a barrel vault at first level is also analyzed under variable lateral loads and support movement. Potentialities and limitations of the proposed formulation and tool are discussed on the basis of the results obtained and also in terms of computational efficiency.

NON-SMOOTH CONTACT DYNAMICS OF PLANAR MASONRY STRUCTURES USING MATHEMATICAL PROGRAMMING

In this paper an incremental formulation for contact dynamic analysis of masonry block structures is presented. The model is composed of rigid bodies interacting at potential contact points located at the vertexes of the block interfaces. A no-tension behavior with finite friction and infinite compressive strength is assumed at contact interfaces. The contact dynamic problem is governed by equilibrium equations, which relate external, inertial and contact forces, and by kinematic equations, which ensure compatibility between contact displacement rates and block degrees of freedom. Quadratic programming is used to solve the optimization problem arising from the formulation of the variational problem associated to dynamics of the block assemblages. To evaluate the accuracy and computational efficiency of the implemented formulation, applications to case studies from the literature are presented. 2902 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2902-2909

ON THE USE OF POINT CONTACT MODELS FOR COLLAPSE MECHANISM AND DYNAMIC ANALYSIS OF MASONRY STRUCTURES

Abstract. In this paper, we discuss the main issues concerning the use of point-based models to represent contact interactions in computational limit analysis and non-smooth contact dynamics of masonry structures. To investigate the response of masonry structures, numerical models composed of rigid blocks interacting at contact points located at the vertexes of the interfaces are used. A no-tension behavior with finite friction and infinite compressive strength is assumed at contact interfaces. The limit analysis problem and the contact dynamic problem are formulated in terms of equilibrium equations, which relate external and contact forces, kinematic equations, which ensure compatibility between contact displacement rates and block degrees of freedom, and additional relationships to model the behavior of contacts. Mathematical programming is used to solve the optimization problems arising from both limit analysis and the dynamic of the block assemblages. The accuracy and computational efficiency of the implemented formulations are discussed with reference to case studies selected from the literature.

Assessment of masonry structures under lateral loads via 3D rigid block limit analysis

This paper presents an improved computational model for the analysis of masonry structures based on continuum mechanics finite element approaches. The proposed numerical technique uses a cracktracking algorithm to model the formation of strain localization bands within the discretization domain. This strategy results in two major benefits. First, the representation of the discrete cracks experienced by masonry structural elements is more accurate and consistent with limit analysis, which in turn leads to the realistic prediction of the collapse mechanisms. Second, the numerical solution is mesh-bias independent ensuring the objectivity of the simulation to the direction of the utilized mesh. The efficiency of the proposed algorithm is illustrated through the numerical simulation of a selected experimental test on a masonry pier-spandrel system.

Rocking response of masonry block structures using mathematical programming

Abstract. In this paper a variational formulation for dynamic analysis is adopted to investigate rocking behaviour of masonry block structures under lateral loads. The model is composed of rigid bodies interacting at potential contact points located at the vertexes of the bock interfaces. A no-tension and associative frictional behaviour with infinite compressive strength is assumed at contact interfaces. The contact dynamic problem is governed by equilibrium equations, which relate external, inertial and contact forces, and by kinematic equations, which ensure compatibility between contact displacement rates and block degrees of freedom. Mathematical programming is used to solve the optimization problem arising from the formulation of the variational problem associated to dynamics of the block assemblages. To evaluate the accuracy and computational efficiency of the implemented formulation, a validation study is presented for rigid blocks subjected to rocking behaviour under different acceleration pulse types and for an in-plane wall panel problem from the literature. A good agreement in terms of failure mechanism and response time histories was observed. The computational efficiency and the stability of the implemented procedure were found to be encouraging, thus suggesting that the proposed model may be used to model dynamic behaviour of masonry block assemblages with a large number of rigid bodies.