1,720,999 research outputs found
Comparative experimental analysis on the compressive behaviour of masonry columns strengthened by FRP, BFRCM or steel wires
No full textIn the last decade, several studies have investigated the application of Fibre Reinforced Polymer (FRP) wraps to masonry piers in order to provide a confinement effect and enhance compressive strength and ductility. Although this technique has proved to be quite effective, various drawbacks arise when organic resins are used to bind fibres. To solve these problems, different techniques have been developed to be used as alternative methods for enhancing the structural performances of weak masonry columns. Among these, the use of Basalt Fibre Reinforced Cementitious Matrix (BFRCM) wrapping, or the application of steel wires at mortar joints. This paper presents the results of an experimental study on the compressive behaviour of clay brick masonry columns reinforced with FRP wraps, Basalt Fibre Reinforced Cementitious Matrix (BFRCM) or with steel wires. Uniaxial compressive tests were performed on twelve retrofitted columns and four control specimens up to failure. Two masonry grades were considered varying the mix used for the mortar. The results are presented and discussed in terms of axial stress-strain curves, failure modes and crack patterns of tested specimens. Comparisons with unreinforced columns show the capabilities of these techniques in increasing the structural efficiency with reduced aesthetical impact
Flexural behaviour of glulam timber beams reinforced with FRP cords
No full textGlued laminated timber (glulam) is widely used as a construction material to make up lightweight and large span structures. The basic principle of this material consists in bonding together a number of layers of dimensioned timber with structural adhesives, in order to increase strength and stiffness of the member, and allowing to make up sustainable structures with great visual impact. Recent applications showed the effectiveness of fibre-reinforced polymer (FRP) composites in enhancing the structural performances of glulam beams, with particular reference on their flexural and shear strength. In fact FRP reinforcements could be used to strengthen existing structures or to reduce the dimensions of new structures to be designed. Considering the importance of the latter application, the present work shows the results of four-point bending tests on fifteen small scale glulam specimens, reinforced with glass (GFRP) or carbon (CFRP) cords, varying the kind of adhesive (epoxy resin or melamine glue). Eight further large-scale beams were tested in order to evaluate the role of the scale effect. Finally, an analytical model was developed, able to predict the behaviour of multilayer heterogeneous wood sections and which takes into account the effect of the reinforcements
Effects of confinement level, cross-section shape and corner radius on the cyclic behavior of CFRCM confined concrete columns
No full textThe main results of an experimental research aiming to investigate the behavior of medium-size low-strength concrete columns wrapped with Carbon Fiber Reinforced Cementitious Matrix (CFRCM) under monotonic and cyclic compressive axial loads are presented. Thirty columns with circular, square and rectangular cross-sections were tested under monotonic and cyclic axial loads to investigate the effect of the confinement level, the cross-section shape and the corner radius on the stiffness, strength, and ductility of CFRCM confined concrete columns under cyclic loads. The results prove that CFRCM confining jackets provide substantial gain in compressive strength, deformability and absorbed energy
Analytical prediction of ultimate moment and curvature of RC rectangular sections in compression
No full textThis paper presents closed form expressions linking the ultimate bearing capacity to the ultimate curvature of rectangular RC sections subjected to axial load and bending moment acting in one of the two symmetry planes of the section. With respect to possible simplified formulations the following effects are also considered: confinement of the concrete, hardening of the longitudinal reinforcement, and presence of reinforcing bars distributed orthogonally to the neutral axis. The formulation is proposed in dimensional terms after a preliminary definition of the geometrical and mechanical parameters governing the structural response of the class of sections considered. The analytical expressions derived using the proposed approach also allow one to determine the compression level that makes the ultimate bending moment maximum as well as to evaluate the curvature corresponding to the first yielding of the principal reinforcement in tension. Comparing this value of curvature with the ultimate one, an approximate estimation of the available ductility of curvature of the section can be made. The analytical procedure is validated by comparing the results with those obtained using a typical numerical approach. Some experimental results are also considered. © 2013 Springer Science+Business Media Dordrecht
Effect of steel collars on the seismic behaviour of axially-cracked historical stone columns
No full textGranite and heavy stone circular columns could often be found in the cultural heritage among ancient churches and historical buildings in all the Mediterranean area. Their good strength properties allow them to carry big load values, while their bright colours and aesthetical characteristics were used by a lot of architects in the past to achieve structural solutions with great visual impact.Though such materials have great compressive strength values, environmental effects, especially long term effects, can damage the structural members, by cracking them. In this way the slenderness of the column increases, and the presence of an imposed ground motion can be very dangerous, since the column will be more vulnerable to rocking motion, which in critical cases could lead to overturning or material crushing due to stress concentration.This paper focuses on the behaviour of cracked granite and heavy stone columns subjected to rocking motion due to pulse type ground shaking. In this field, the effect of the presence of circular collars is analysed and discussed. The overturning spectra are determined, including the presence of the collars, showing their effectiveness in reducing the overturning risk. Comparisons are shown with numerical analyses and a simplified analytical procedure is proposed. © 2013 Elsevier Ltd
Stability analysis of clay brick masonry columns: numerical aspects and modelling strategies
No full textStability analysis of masonry piers and columns is one of the most frequently treated subjects in the field of structural engineering. This attention is probably due to the challenge to solving the problem including different effects, which play an important role in evaluating the response of eccentrically-loaded columns. In this connection, accurate stability analysis of masonry piers and columns has to take into account the non-linear stress–strain law of masonry in compression, the limited tensile strength, the induced slenderness due to crack formation and geometrical non-linearity. Different theoretical models and numerical approaches were developed in the past to analyze the combined effect of buckling and strength in such structural members. In this paper a numerical method is derived and particularized for the case of clay brick masonry members. After a review of the most widely used analytical models for the compressive behaviour of masonry, the effects of a non-linear constitutive law in compression and cracking were taken into account with suitable moment–curvature curves. The latter were implemented in a simple numerical procedure, and made it possible to calculate the force–displacement curves and safety domains, which account for both strength and stability. The method was finally verified with results derived from non-linear finite element analyses, making it possible to make considerations about the suitability of the method and the related computational effort
Infilled frames: Developments in the evaluation of cyclic behaviour under lateral loads
No full textIn order to consider the modified seismic response of framed structures in the presence of masonry infills, proper models have to be formulated. Because of the complexity of the problem, a careful definition of an equivalent diagonal pin-jointed strut, able to represent the horizontal force-interstorey displacement cyclic law of the actual infill, may be a solution. In this connection the present paper, continuing a previous work in which a generalised criterion for the determination of the ideal cross-section of the equivalent strut was formulated, analizes some models known in literature for the prediction of the lateral cyclic behaviour discussing their field of validity. As a support of the discussion, the results of an experimental investigation involving single story-single bay infilled reinforced concrete. Frames under vertical and lateral loads with different kind of infill (actually not yet so much investigated) are presented. Finally, an improvement of a model known in the literature is proposed, taking the results of the experimental tests before mentioned into account
Strengthening of Masonry Columns with BFRCM or with Steel Wires: An Experimental Study
Full text linkNowadays, innovative materials are more frequently adopted for strengthening historical constructions and masonry structures. The target of these techniques is to improve the structural efficiency with retrofitting methods having reduced aesthetical impact. In particular, the use of basalt fiber togherer with a cementitious matrix emerges as a new technique. This kind of fiber is obtained by basalt rock without other components, and consequently it could be considered a natural material, compatible with masonry. Another innovative technique for strengthening masonry columns consists in applying steel wires in correspondence of mortar joints. Both techniques have been recently proposed and some aspects on their structural performaces are still open. This paper presents the results of an experimental study on the compressive behavior of clay brick masonry columns reinforced either with Basalt Fiber Reinforced Cementitious Matrix (BFRCM) or with steel wire collaring. Uniaxial compressive tests were performed on eight retrofitted columns and four control specimens up to failure. Two masonry grades were considered by varying the mix used for the mortar. Results are presented and discussed in terms of axial stress-strain curves, failure modes and crack patterns of tested specimens. Comparisons with unreinforced columns show the capability of these techniques in increasing ductility with limited strength enhancements
An innovative shear-tension angle bracket for Cross-Laminated Timber structures: Experimental tests and numerical modelling
No full textAn experimental testing programme on an innovative metal angle bracket for Cross-Laminated Timber structures is presented in this paper. The main novelty of the angle bracket is the use of fully-threaded screws to improve mechanical properties in tension direction. Monotonic tests to evaluate mechanical properties of the wall-to-floor connection in tension and shear directions are presented and discussed. A detailed three-dimensional finite element model, implemented in ABAQUS, which considers the typical non-linear behaviour of fasteners in timber element, is presented and used to reproduce the experimental results. The group effect and strength domain of the fasteners are also analysed. The finite element model can predict experimental results when the group effect and strength domain of the fasteners are taken into account. Finally, the finite element model was used to numerically analyse the effect of inclined loads and evaluate the strength domain of the innovative angle bracket. © 201
Dynamic behaviour of cracked granite and marble columns retrofitted with steel collars
No full textMarble and heavy stone columns are widely diffused in ancient churches and historical buildings in all the Mediterranean area. Their good mechanical properties allowed carrying great load values, while their bright colours and aesthetical characteristics have been used by a lot of ancient architects to achieve structural solutions with great visual impact. Despite their good compressive strength, marble columns could be damaged from environmental effects (e.g. longterm effects or thermal loads), which could crack the structural members. In this way, the slenderness of the column increases drastically and the presence of an imposed ground shaking could be critical, since the column will be more vulnerable to rocking motion and to overturning risk. This paper focuses on the rocking behaviour of cracked granite and marble columns subjected to a pulse type ground shaking. The effect of the presence of circular collars is analysed by means of a mechanical model. The overturning spectra are determined including the presence of the collars, showing their efficiency in reducing the overturning risk. Comparisons are shown with numerical analyses and a simplified design method is proposed
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