Salvatore Caddemi

Detecting Multiple Open Cracks in Elastic Beams by Static Tests

This paper concerns with the identification of multiple open cracks in a beam by measurements of the damage-induced variations in the static deflection of the beam under a prescribed load condition. Each crack is simulated by an equivalent linear spring connecting the two adjacent segments of beam. Sufficient conditions on the static measurements which allow for the unique identification of the damage are presented and discussed for nonuniform beams under some ideal boundary conditions. The inverse analysis is based on an explicit expression of the crack-induced variation in the deflection of the beam under a given load distribution and it provides exact closed-form expressions of position and severity of the cracks in terms of the measured data. The theoretical results are confirmed by a comparison with static tests carried out on a steel beam with localized damages.

Detecting Damage in a Beam by Static Tests

This paper presents a constructive procedure for the identification of a single crack in a beam based on the knowledge of the damage-induced variations in the static deflection of the beam. The crack is simulated by an equivalent rotational spring connecting the two adjacent segments of the beam. The analysis is based on an explicit expression of the crack-induced variation in the deflection of the beam under a given load distribution. The theoretical results are confirmed by a comparison with static measurements on steel beams with a crack.

Advances in dynamic instability: can a beam-column undergo tensile flutter?:

Tensile instability in beam-like structures has been highlighted in very few papers; the studies reported in the specific literature are limited to beam-columns characterised either by high shear deformation or by the presence of a single structural junction allowing a transversal displacement discontinuity. Moreover, to the authors’ knowledge, the flutter instability associated to tensile axial load has not yet been disclosed. This work aims to offer further contribution to the knowledge of tensile instability of beam-columns by considering the dynamic instability of an Euler Bernoulli beam in presence of an arbitrary number of internal sliders endowed with translational elastic springs. The use of the generalised functions allows an exact evaluation of the eigensolution, provided in closed form, both for conservative and nonconservative axial load. In particular, the following relevant question is posed: Can a beam-column undergo tensile flutter instability? A comprehensive parametric analysis conducted in this work gives an affirmative answer to the asked question.

New Frontiers on Seismic Modeling of Masonry Structures

An accurate evaluation of the nonlinear behaviour of masonry structural elements in existing buildings still represents a complex issue that rigorously requires nonlinear finite element strategies difficult to apply to real large structures. Nevertheless, for the static and seismic assessment of existing structures, involving the contribution of masonry materials, engineers need reliable and efficient numerical tools, whose complexity and computational demand should be suitable for practical purposes. For these reasons the formulation and the validation of simplified numerical strategies represents a very important issue in masonry computational research. In this paper an innovative macro-element approach, developed by the authors in the last decade, is presented. The proposed macro-element formulation is based on different, plane and spatial, macro-elements for the simulation of both the in-plane and out-of-plane behaviour of masonry structures also in presence of masonry elements with curved geometry. The mechanical response of the adopted macro-element is governed by nonlinear zero-thickness interfaces, whose calibration follows a straightforward fibre discretization, and the nonlinear internal shear deformability is ruled by equivalence with a corresponding geometrically consistent homogenized medium. The approach can be considered as ‘parsimonious’ since the kinematics of the adopted elements is controlled by very few degrees of freedom, if compared to a corresponding discretization performed by using nonlinear FEM strategies. This innovative discrete-element strategy has been implemented in two user-oriented software codes 3DMacro and HiStrA (Historical Structures Analysis), which simplifies the modelling of buildings and historical structures by means of several wizard generation tools and input/output facilities. The proposed approach, that represents a powerful tool for the structural assessment of structures in which the masonry plays a key role, is here validated against experimental results involving typical masonry monumental sub-structural elements and numerical results involving real-scale structures.

A NEW DISCRETE MACRO-NODE ELEMENT FOR THE SEISMIC BEHAVIOUR MODELLING OF REINFORCED CONCRETE FRAMES

Abstract. Recent earthquakes have demonstrated that the seismic behaviour of existing reinforced concrete buildings, not designed to resist to earthquake loadings, is strongly affected by the local collapses of the beam-to-column joints that can be subjected to shear collapse of the central region or bond-slip of the longitudinal steel bars. In this paper a new macro-node element able to account for the nonlinear behaviour of the beam-to-column joints is presented. The model can be represented by a simple mechanical scheme constituted by an articulated quadrilateral whose rigid edges connect beams and columns through nonlinear discrete interfaces and whose internal deformability is related to a single degree of freedom only. The model is able to account for the shear failure of the joint region as well as the flexural and shear plastic deformations at the contact edges of the connected elements allowing the nonlinear modeling of a frame structure through an assemblage of non-linear macro-nodes connected by means of elastic frame elements.

Seismic Vulnerability of the Concordia Temple

This work focuses on the seismic risk evaluation of the Concordia temple, situated in the Valley of the Temples in Agrigento (Italy). In the paper a general methodology to assess the seismic vulnerability, to be applied also to any kind of structures composed of stone blocks, is proposed. The vulnerability assessment has been conducted by means of equivalent nonlinear static analyses along the principal directions of the structure and the subsequent identification of equivalent single degree of freedom systems. Furthermore, the seismic vulnerability has been expressed both in a deterministic and a probabilistic context by evaluating the severe damage probability.

Closed Form Buckling Solutions of Euler-Bernoulli Columns With Multiple Singularities

In this paper the Euler-Bernoulli column in presence of multiple concentrated open cracks and for general boundary conditions is studied. The request of an integration procedure able to lead to exact closed form buckling solutions for any number, position and intensity of the cracks is satisfied. A model of concentrated crack based on the adoption of the distributions (generalized functions) is presented. In particular, the exact buckling mode solution and the corresponding exact buckling load equation is obtained. A parametric study for different boundary conditions is presented.Copyright

Generalised Functions for Modelling Singularities: Direct and Inverse Problems

The possibility of utilising the generalised functions (distributions) and the related theory to model singularities showing a strongly local effect is explored in this work. In particular, singularities due to concentrated damages, to the presence of internal or external constraints or to abrupt changes of physical or geometrical properties, will be considered along the span of straight beams and modelled by means of Dirac’s deltas or Heaviside functions. New developments of the distribution theory can be efficaciously adopted to provide closed form solutions, both in static and dynamic regime, in the case of damaged beams regardless of the number, position and intensity of the concentrated damages without the request of any additional computational work. Furthermore, the explicit expressions obtained in terms of eigenmodes are efficaciously adopted to address the identification problem of multiple damages by dynamic tests.