1,720,994 research outputs found
Closed-form expressions for the macroscopic elastic constants of Flemish bond masonry walls
No full textThe problem of obtaining reliable closed-form expressions for the macroscopic elastic coefficients of Flemish bond brickwork according to the mechanical properties and the geometry of joints and units is dealt with. Unlike most similar existing works, which are limited to single-wythe walls, here the coexistence of headers and stretchers is taken into account, together with the presence of collar joints. Similarly to the so-called Method of Cells for fiber-reinforced composites, any Representative Volume Element (RVE) of the wall is divided into sub-cells. A piecewise-differentiable 3D strain-periodic displacement field, depending on a limited number of degrees of freedom (d.o.f.s), is formulated over the RVE. Suitable boundary conditions are prescribed at the interfaces between the sub-cells, thus reducing the number of independent d.o.f.s. The remaining d.o.f.s can be related to the macroscopic strains of the RVE. Upon integration of the microscopic stress and strain fields, the homogenized elasticity matrix can be obtained. The accuracy of the theoretical predictions is assessed by comparison with the results of Finite Element analyses of the RVE subjected to elementary macroscopic stresses, and with other benchmarks available in the literature
Optimal fiber-reinforcement of no-tension masonry walls through a stress-based formulation
No full textA topology optimization problem is dealt with, which aims at distributing a prescribed amount of fiber-reinforcement over any masonry wall, so as to maximize the overall stiffness of the strengthened element. A no-tension (NT) model is adopted to account for the negligible tensile strength of brickwork. The equilibrium of the NT body is enforced through an energy-based method, which replaces brickwork by an equivalent orthotropic medium with constraints on the stress state. The inability if the reinforcement to carry compressive stresses is also taken into account in a similar way. The stress analysis of the reinforced NT body can be straightforwardly embedded within the topology optimization formulation, with no need for demanding incremental approaches. Both the regions to be strengthened and the local orien-tation of the optimal FRP strips are identified. To improve accuracy in the enforcement of the stress constraints, an efficient formulation that uses stresses as main variables of the elastic problem is implemented. Also, the structural compliance is computed through the evaluation of the complementary strain energy. A preliminary numerical example is shown, to assess the capabilities of the proposed procedure
An innovative approach for the finite element modelling of masonry cracking
No full textThe performance of masonry structures under seismic conditions is strongly influenced
by cracking phenomena that have to be taken into account to obtain a reliable evaluation
of mechanical resources. An innovative finite element procedure is presented to simulate
initiation and propagation of in-plane tensile crack in masonry material. The material is studied
at the macro-level and modelled as a homogenous continuum by means of triangular shell
elements. The cracks are considered as localized inelastic deformations in the frame of the
classical theory of plasticity. Control of tensile stress is formulated and implemented along
possible cracking lines, corresponding to the mesh edges, in terms of generalized forces at the
nodes. When the limit tension is reached at one node and the crack starts to open, the activated
inelastic constitutive law is taken as a single-branch softening curve. A Parametric Linear
Complementarity Problem is solved to evaluate the cracking evolution of the structure until
collapse. Some numerical examples are presented to validate the formulation
Fragility analysis of masonry structural units by Response Surface method
No full textStructural masonry aggregates include a set of inhomogeneous structural units that
can interact under seismic action; therefore the seismic analysis cannot ignore the inevitable
interactions resulting from structural contiguity between adjacent buildings [1,2]. The study
of a masonry aggregate cannot neglect the unavoidable uncertainties related to geometries
and material characteristics of their components. In this work the first results of a research
focused on the fragility analysis of masonry structural units by statistical procedures are presented.
In order to take the structural and geometrical variabilities and uncertainties involved
in the problem into account, the Response Surface (RS) statistical method is used, where the
expected value of a response parameter (for instance the acceleration corresponding to the
attainment of a prescribed limit state of the building) is approximated through a polynomial
function of a set of selected variables [3]. The RS model is calibrated through numerical data
obtained by non-linear static analysis, with reference to a masonry building (structural unit)
whose geometrical and mechanical properties are varied in prescribed ranges. The number of
simulations and the values of the variables to be used to obtain the data for the RS calibration
are defined by applying the Design of Experiments Theory [3]. Finally, fragility curves are
evaluated through the RS obtained from the numerical simulation data.
The results have highlighted the importance of the probabilistic procedures as methods able
to consider the variabilities and the uncertainties involved in the problem of the fragility of
masonry structures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Increase in seismic resistance for a dry joint masonry arch subjected to hinge control
Get PDFDamages to vaulted masonry and their vulnerability to seismic activities are continuously ob-served with each new earthquake. The behaviour of these systems is becoming well understood, and reinforcement strategies and techniques are continually advancing. It is often the case however that the application of reinforcement is done in such a manner that the failure of the system is transformed directly from one of stability to strength. This direct transformation over-looks the intermittent stages that exist between stability and strength, and thus provides an in-complete picture to the potential behaviours of the system. With the objective of maintaining the four-hinged mechanization failure, this work experimentally examines the increase in resistance that occurs through controlling the available positions for hinge development of a dry-stack masonry arch subjected to constant horizontal accelerations. From this experimentation, it is observed that controlling the hinge locations can increase the resistance of the arch while also providing a defined failure mechanism
Damage control, preservation procedures and durability studies: an investigation approach through the Milan Duomo Cathedral archives
No full textSince the long collaboration between Veneranda Fabbrica del Duomo and Politecnico di Mi-lano (VFD) was renewed, the Duomo Cathedral has been investigated from different points of view in order to enhance the continuous care procedures, which can be understood in the theo-retical frame of preventive and planned conservation [1].
Among the different study approaches, the collaboration with the historical archive of the VFD showed the potentialities for recording the main pathologies afflicting the building during dif-ferent periods and for classifying the intervention criteria set for facing specific problems affect-ing the main loadbearing structures and their materials.
The archive documents provided precious indications concerning the restoration works and strategical measures adopted for the common decay problems presented by the building mate-rials [2], [3]. A turning point in the intervention philosophy, observed in the archives docu-ments, occurred in the beginning of the 1960s, when the Cathedral was concluded, and the VFD had to move from construction and maintenance activities to the conservation issues [4]. On behalf of the large amount of interventions that became a constant care for the building, from the second half of the last century, the VFD promoted interesting efforts in the mainte-nance policy by experimenting new technological solutions [5]. With the aim to protect the dif-ferent features of the Cathedral, new special mixtures were introduced in the common interven-tion criteria, experimenting on site new resins for repairing. At an impressive extension, these practices produced new systems made up of different materials, namely marble and stones, iron, mortars and resins, whose compatibility on the long run is still to be evaluated. This work fo-cuses on the consequences observed after the development of a clear common practice for the care requested by such a complex building
Cost-benefit analysis for the retrofit of masonry buildings through performance-based seismic assessment
No full textSeismic assessment and retrofit of unreinforced masonry (URM) structures is a relevant topic nowadays, especially in countries where the majority of the buildings were built before the introduction of seismic design codes. Recent earthquakes have demonstrated that the structural weakness of URMs is responsible of fatalities, injuries and large economical losses in terms of reconstruction costs and business interruption. Due to the complex seismic response of URM and to the lack of exhaustive guidelines, engineers and practitioners experience difficulties when involved in rehabilitation design projects of masonry. Uncertainties in the analysis procedures are hardly quantified, resulting in conservative structural assessment and expensive retrofits. In this paper, a possible retrofitting cost optimization process is discussed adopting the PEER Performance Based Earthquake Engineering (PEER-PBEE) methodology. Particularly, thanks to a schematic step-by-step procedure (i.e. hazard, structural, damage and loss analyses) the performance of the URM building is expressed in the form of potential earthquake induced economic losses. In this sense, the effectiveness of different retrofitting design scenarios is assessed on an analytical bases taking into account the initial costs (retrofit) and the related benefits (reduction of monetary losses)
Influence Of FRCM Retrofitting Systems On The Shear Behaviour Of Pre-Damaged Masonry Panels
No full textIn recent years, the Italian territory has been stroke by seismic phenomena of high intensity, which caused great damages, especially in old masonry constructions. Therefore, restoring damaged buildings, with the aim to recover or improve their structural capacity, is a key aspect in the post-seismic interventions. Fiber reinforced composite materials could be used to this purpose. One aspect which is worth to investigate is the application of these rein-forcement typologies on damaged structural elements. Even though many experimental cam-paigns are available concerning the mechanical improvement given by composite materials applied on undamaged structural elements, only few can be found considering strengthening of already damaged elements. The scope of this work is to evaluate the shear response of damaged masonry walls reinforced with Fiber Reinforced Cementitious Matrix (FRCM). In particular, diagonal compression tests were performed on two unreinforced masonry walls realized with clay bricks and lime-based mortar, producing an extended state of damage. Afterwards, the same walls were strengthened with FRCM and subjected again to diagonal compression test. Comparisons between the results of the unreinforced samples and the damaged strengthened ones, in terms of shear strength and post-peak behavior, will be presented
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