53 research outputs found
Out-of-plane seismic response of masonry façades using discrete macro-element and rigid block models
This paper investigates the out-of-plane response of masonry façades under earthquakes by means of two different approaches. A discrete macro-element approach, based on modelling the structure by means of spatial deformable macro-elements interacting through nonlinear zero-thickness interfaces, and the classical approach in which the masonry façade is assumed as a rigid block subjected to earthquake loading. The latter method neglects the elasticity of the masonry element and contemplates the energy dissipation only at each impact by means of a coefficient of restitution. The results of dynamic non-linear analyses, performed with the two methods on a real case of a church façade, provide a first comparison between the two ap-proaches highlighting some limits of application of the simplified rigid block model
Numerical Modelling of Masonry Arches Strengthened with SFRM
The adoption of effective strengthening techniques of historical constructions is one of the most widely debated aspects in structural engineering. Within this topic, the application of steel fiber reinforced mortar (SFRM) has been recently proposed as a low invasive and effective way to obtain a considerable structural benefit in the safety of existing masonry structure. To this purpose, in this paper the experimental results obtained on a circular masonry arches are presented. The considered specimens, subjected to a vertical increasing static load, is tested in the unstrengthened and strengthened configurations, and is part of a wider experimental campaign. After presenting and discussing the experimental results, they are compared with those relative to numerical simulations conducted by means of a discrete macro-element (DME) strategy, based on a simple mechanical scheme, able to model the nonlinear behavior of masonry structures with a limited computational effort. Such an approach is here extended to model the SFRM strengthening technique accounting for the main failure mechanisms associated to the combined presence existing masonry and the additional strengthening layer applied at the intrados of the arch. Numerical and experimental results demonstrate the efficacy of the proposed retrofitting strategy both in terms of bearing capacity and increase of ductility
A Novel Methodology Using Simplified Approaches for Identification of Cracks in Beams
Abstract In this paper, natural frequency based forward and inverse methods are proposed for identifying multiple cracks in beams. Forward methods include simplified definition of the natural frequency drops caused by the cracks. The ratios between natural frequencies obtained from multi-cracked and un-cracked beams are determined by an approach that uses the local flexibility model of cracks. This approach does not consider nonlinear crack effects that can be easily neglected when the number of cracks is not excessive. In addition, an expression, which removes the necessity of repeating natural frequency analyses, is given for identifying the connection between the crack depths and natural frequency drops. These simplified approaches play crucial role in solving inverse problem using constituted crack detection methodology. Solution needs a number of measured modal frequency knowledge two times more than the number of cracks to be detected. Efficiencies of the methods are verified using the natural frequency ratios obtained by the finite element package. The crack detection methodology is also validated using some experimental natural frequency ratios given in current literature. Results show that the locations and depths ratios of cracks are successfully predicted by using the methods presented
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
A Procedure for Multiple Damage Identification in Elastic Beams
This paper concerns with the identification of multiple 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 elastic rotational
spring connecting the two adjacent segments of the beam. Sufficient conditions on the static measurements which allow for the
unique identification of the damage are presented and discussed for beams under various sets of boundary conditions. The analysis is
based on an explicit expression of the crack-induced variation in the static deflection of the beam. The present results are obtained by
non trivial extension of recent results given by the authors regarding the identification of a single crack in a beam by static tests
Multi-cracked Euler-Bernoulli beams: Mathematical modeling and exact solutions
Localized flexibility models of cracks enable one for simple and effective representation of the behavior of damaged beams and frames. Important applications, such as the determination of closed-form solutions
and the development of diagnostic methods of analysis have attracted the interest of many researchers in
recent years. Nevertheless, certain fundamental questions have not been completely clarified yet. One of
these issues concerns with the mechanical justification of the macroscopic model of rotational elastic
spring commonly used to describe the presence of an open crack in a beam under bending deformation.
Two main analytical formulations have been recently proposed to take into account the singularity generated by the crack. The crack is represented by suitable Dirac\u2019s delta functions either in the beam\u2019s flexural rigidity or in the beam\u2019s flexural flexibility. Both approaches require some caution due to
mathematical subtleties of the analysis. Motivated by these considerations, in this paper we propose a
justification of the rotational elastic spring model of an open crack in a beam in bending deformation.
We show that this localized flexibility model of a crack is the variational limit of a family of one-dimensional
beams when the flexural stiffness of these beams tends to zero in an interval centered at the
cracked cross-section and, simultaneously, the length of the interval vanishes in a suitable way. We also
show that the static and dynamic problem for the flexibility model of cracked beam can be formulated
within the classical context of the theory of distributions, avoiding the hindrances encountered in previous
approaches to the problem. In addition, the proposed treatment leads to a simple and efficient determination
of exact closed form solutions of both static and dynamic problems for beams with multiple
cracks
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
Crack detection in elastic beams by static measurements
This paper deals with 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 linear spring
connecting the two adjacent segments of the beam. Sufficient conditions on static measurements which allow for the unique
identification of the crack are presented and discussed. The inverse analysis provides exact closed-form expressions of position and severity of the crack as functions of deflection measurements for different boundary conditions. The theoretical results are confirmed by a comparison with static measurements on
steel beams with a crack. Extension of the presented analysis to multiple cracks is briefly discussed
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