1,720,995 research outputs found
Flexural and Shear Resistance of High Strength Concrete Beams
Full text linkIn the present paper, an analytical model is proposed that is able to determine the shear resistance of high strength
reinforced concrete beams with longitudinal bars, in the presence of transverse stirrups. The model is based on the evaluation of the
resistance contribution due to beam and arch actions. For the resistance contribution of the main bars in tension the residual bond
adherence of steel bars and the crack spacing of R.C. beams are considered. The compressive strength of the compressed arch is also
verified by taking into account of the biaxial state of stresses.
The model was verified on the basis of experimental data available in the literature and it is able to include the following
variables in the resistance provision: - geometrical percentage of steel bars; - depth-to-shear span ratio; - resistance of materials; -
crack spacing; - tensile stress in main bars; - residual bond resistance;- size effects. Finally, some of the more recent analytical
expressions able to predict the shear and the flexural resistance of concrete beams are mentioned and a comparison is made with
experimental data
CRITERI E TECNICHE DI VALUTAZIONE E RIDUZIONE DELLA VULNERABILITÀ SISMICA DEL CENTRO STORICO
No full textUna valutazione della vulnerabilità sismica, sia attraverso approcci fenomenologici che attraverso più accurati modelli meccanici non può prescindere dalla conoscenza (il più possibile accurata) di tali caratteristiche del costruito, che può essere acquisita spesso soltanto attraverso campagne di rilievo e di indagini sul costruito. In questo contesto, vengono inizialmente descritte le caratteristiche salienti del centro storico di Modica, per poi passare in rassegna i metodi di valutazione della vulnerabilità sismica a
scala territoriale; infine verranno presentate alcune tecniche di mitigazione della vulnerabilità sismica, e presidi antisismici da mettere in atto per evitare che trasformazioni del costruito richieste per una più idonea fruizione del bene possano risultare nocive alla sicurezza sismic
Flexural behaviour of calcarenite masonry walls reinforced with FRP sheets
No full textThe use of fiber-reinforced polymers (FRP) for structural strengthening has become increasingly popular in recent years. Several applications of FRP have been proposed and applied, depending on the target of the technique, kind and/or material of the structural member. In particular, because of their great tensile strength, FRP materials are commonly used to enhance the out-of-plane behaviour of masonry walls, allowing to increase their strength, ductility and improving safety against overturning. For these reasons, FRP laminates are often applied in vulnerable ancient buildings in seismic areas to reinforce façades and walls with poor structural features.
However, some issues arise when adopting composites in historical constructions, the most related to the aesthetical impact of laminates and compatibility between FRP and masonry. Consequently, a correct evaluation of the reinforcement percentages for strength and ductility purposes is crucial, as well as the effective increase of structural performances.
This paper presents a numerical-analytical approach able to reproduce the flexural behaviour of out-of-plane loaded masonry walls. The model is based on a simplified representation of the member, the latter modeled as a cantilever beam. Mechanical non-linearity is introduced by means of moment-curvature relationships, deduced with proper constitutive laws of masonry and by taking into account the ultimate debonding strain of FRP. Second order effects are considered by adopting an iterative step-by-step procedure. Comparisons are made in terms of moment-curvature and load-displacement curves with experimental data available in the literature and with non-linear finite element analyses, showing both good agreement. Finally, parametric considerations on the reinforcement percentages are made in terms of strength and ductility
Effect of the different data survey scale on assessment of seismic exposure and vulnerability of the historic center of Caltabellotta
Full text linkThe results of the prediction of exposure and seismic vulnerability for the buildings of the historic center of
Caltabellotta, obtained with databases of different levels of accuracy, are compared. In particular, the results obtained
on the basis of the estimation of the characteristics and of the distribution of the typologies derived from the filling
in of the CARTIS sheets on a sector scale are compared with those obtained through a survey from the outside to a
building scale. In this latter area, indicators contained in the CARTIS are suitably supplemented with those available
in the literature, partly modified to adapt them to the local reality. The vulnerability is evaluated on the basis of the
RISK-UE method, using suitably adapted values of the vulnerability modifiers. In the application of the procedure,
the difficulties emerged in the recognition and attribution of the typology of masonry in the presence of plastered
buildings are highlighted. In this context, a typological investigation is developed which, starting from the survey
and the material classification of the buildings with exposed faces, and retracing the possible transformation processes
that the structural housing units have completed, formulating two simplified criteria for the attribution of material
properties. to the buildings plastered according to the plano-altimetric characteristics and the elevation of the
buildings. The outcomes prove the accuracy of the procedure based on survey at the sector scale
Shear Design of High Strength Concrete Beams in MRFs
Full text linkThis paper presents the criteria for the shear design of high strength concrete (HSC) beams in moment resisting frames (MRFs). The formulation of an analytical model is provided for the case of beams with longitudinal reinforcement in the presence of transverse stirrups. The model is of additive type, in the meaning that the shear resistance of the beam is evaluated as the sum of several contributions. In particular, the contribution of concrete, longitudinal rebars, and transversal reinforcement are taken into account. Furthermore, for assessing the concrete contribution, a classical approach is followed, according to which two effects arise in the shear mechanism: the arc and the beam effect. The features of these two resisting mechanisms are particularized to the case of HSC in steel reinforced beams and the maximum concrete contribution is limited to the maximum compressive strength of the concrete strut in biaxial state of stress. Moreover, for the evaluation of the resistance contribution of the longitudinal steel rebars in tension, the model takes into account the residual bond adherence between HSC and steel reinforcement and the spacing between subsequent cracks. The results are compared with the prescriptions currently provided in the main building codes and with different analytical models existing in the literature. For the comparison, the analytical expressions are applied to a set of experimental data available in the literature and design observations are made on the geometrical percentage of steel bars, the resistance of materials, the residual bond stress and the depth-to-shear span ratio
Effect of FRP strengthening on the flexural behaviour of calcarenite masonry walls
No full textThe use of fiber-reinforced polymers (FRP) for structural strengthening has become increasingly popular in recent years. Several applications of FRP have been proposed and applied, depending on the target of the technique, kind and/or material of the structural member. In particular, because of their great tensile strength, FRP materials are commonly used to enhance the out-of-plane behaviour of masonry walls, allowing to increase their strength, ductility and improving safety against overturning. For these reasons, FRP laminates are often applied in vulnerable ancient buildings in seismic areas to reinforce façades and walls with poor structural features. However, some issues arise when adopting composites in historical constructions, the most related to the aesthetical impact of laminates and compatibility between FRP and masonry. Consequently, a correct evaluation of the reinforcement percentages for strength and ductility purposes is crucial, as well as the effective increase of structural performances. This paper presents a numerical-analytical approach able to reproduce the flexural behaviour of out-of-plane loaded masonry walls. The model is based on a simplified representation of the member, the latter modeled as a cantilever beam. Mechanical non-linearity is introduced by means of momentâcurvature relationships, deduced with proper constitutive laws of masonry and by taking into account the ultimate debonding strain of FRP. Second order effects are considered by adopting an iterative step-by-step procedure. Comparisons are made in terms of momentâcurvature and loadâdisplacement curves with experimental data available in the literature and with non-linear finite element analyses, showing both good agreement. Finally, parametric considerations on the reinforcement percentages are made in terms of strength and ductility
Analytical stress-strain law of FRP confined masonry in compression: Literature review and design provisions
No full textThe use of Fibre Reinforced Polymer (FRP) wraps has become common in practical applications to retrofit existing columns with poor structural features. Wrapping the member with one or more FRP sheets makes it possible to induce confinement action and enhance strength and ductility. This application has been widely studied and adopted in reinforced concrete members for about twenty years, while its suitability to masonry columns and piers has been investigated during the last decade. The results of several studies were summarized in different design expressions for calculating effective confinement pressure, ultimate compressive stress and strain, and the overall trend of the stress-strain curve. Despite this huge amount of research, some results seem actually to be in contrast with the experimental results available in the literature, due to the different key variables arising in this application. This paper presents a comparative analysis of the main existing theoretical models to predict the stress-strain curve of FRP confined masonry in compression. Clay brick masonry is studied and criteria to obtain the strength increase are initially analyzed and compared with experimental results, evaluating the reliability of each expression. In the second part, models to calculate the overall constitutive law in compression are examined and the average error and coefficient of variation are calculated for each model
Finite element analysis of the out-of-plane behavior of FRP strengthened masonry panels
No full textIn the present study a numerical model is proposed for the response of out-of-plane loaded calcarenite masonry walls strengthened with vertical CFRP strips applied on the substrate by means of epoxy resin. A simplified structural scheme is considered consisting in a beam fixed at one end, subjected to constant axial load and out-of-plane lateral force monotonically increasing. Two different constraint conditions are taken into account: in the first one, the panel is assumed free to rotate at the top end while, in the second one, the rotation is restrained. Three-dimensional finite elements are used for the calcarenite parts and an equivalent constitutive law available in the literature is considered for the compressive behavior of the system ashlar-mortar. Conversely, shell elements are used for modeling the CFRP strips and linear elastic behavior is assumed for the composite while cohesive contact properties are introduced at the FRP-calcarenite interface. The model is validated using both experimental results available in the literature and simplified analytical formulations recently presented by the authors in a previous paper
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
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