1,721,094 research outputs found
The Role of the Adhesive on the Bond Behavior of SRPs Applied on Masonry Supports: Experimental and Numerical Study
No full textSteel Reinforced Polymers (SRP) have been recently introduced and adopted as strengthening systems for existing constructions. Although the interest for this kind of strengthening materials is increasing also for masonry structures, in particular for historic constructions, only few studies specifically pertained to masonry elements strengthened with SRPs are available in the literature. In this context, a twofold purpose is at the basis of the present paper. The first one consists of experimentally investigating the bond behavior of masonry elements strengthened with SRPs using different types of adhesives and strips density. The second purpose aims at developing simple formulations for evaluating the bond resistance of masonry elements strengthened with SRPs applied with different types of adhesive systems
Proposal of a scissor-based model for the non-linear analysis of RC beam-column joints strengthened by FRP
No full textThe paper presents a new simple modeling approach for studying the monotonic response of RC beam-column joints externally strengthened by Fiber Reinforced Polymer (FRP) materials. The approach assumes a parallel combination of the behavior of the joint in the unstrengthened configuration and the contribution of strengthening system. To achieve this, the common scissor model, where the behavior of joint shear panel is modeled through a rotational spring, is here modified by introducing an additional spring, arranged parallel to the concrete spring, to account for the contribution of strengthening system. Regarding the behavior of the additional spring, the authors proposed a multilinear simplified constitutive law by appropriately combining analytical models available from the literature with specific guidelines provided by Italian technical standards. The proposed model, implemented in the computer code OpenSees and validated against experimental case studies from the literature, demonstrates its strong capability to capture the contribution of the strengthening system on both the strength and ductility of joints
Modeling and numerical analysis of the bond behavior of masonry elements strengthened with SRP/SRG
No full textThe nonlinear structural analysis represents a powerful tool for the study of the seismic response of new
and existing constructions. In particular, nonlinear static analysis, also denoted as pushover analysis, is
widely used for RC and steel structures and, recently, new seismic codes extended the use of this type
of analysis to the case of masonry structures. The reliability of the results deduced from nonlinear analyses
is not always ensured since the numerical results can depend on the modeling strategy and on the
adopted solution techniques. Moreover, in the case of masonry structures strengthened with fiber reinforced
polymers (FRP), particular regards has to be addressed not only to the masonry material model but
also to the modeling of FRP-system, taking into account the complex phenomena characterizing the interaction
between the FRP and the masonry supports. Aim of the present paper is to discuss some strategies,
in the framework of the nonlinear finite element analysis, regarding the elements choice and the models
to adopt for reliable nonlinear analyses of masonry structures reinforced with FRP strips. Specific structural
problems are described and solved, discussing the role and the reliability of the adopted strategies.
Finally, the seismic analysis of a masonry façade and the design of suitable FRP strengthening systems are
performed
Numerical investigation on the bond behavior of FRCM strengthening systems
No full textRecent experimental studies involving Fabric Reinforced Cementitious Matrix (FRCM) strengthening systems externally applied to structural supports have underlined important aspects characterizing their response. In particular, failure mechanisms quite different from the ones emerged in case of traditional Fiber Reinforced Polymers (FRP) have been observed. These mechanisms particularly underline the role of additional phenomena to necessarily consider for the study and the development of theoretical models/design formulas specific for FRCMs. Aim of the present paper is to analyze the role of different aspects characterizing the behavior of FRCM strengthening systems externally applied on structural supports. Among these, it is mainly considered the role of the upper mortar layer, and, in particular, the influence of its possible damage state during the interaction mechanism between the reinforcement and the matrix. With this aim, a simple theoretical model is here presented. It accounts for the interaction between the reinforcement and the mortar matrix at the level of interface, by considering both the de-bonding and the tensile failure of mortar phenomena, which generally affect the resistant mechanism of FRCMs. The results presented in the paper underline the role of the different components of the strengthening system and their influence both in terms of local and global response
Monotonic Modeling of Exterior RC Beam-Column Joints with Substandard Construction Details Strengthened by FRP
No full textI danni riscontrati negli edifici in c.a. progettati prima dell’introduzione delle recenti normative hanno evidenziato l’elevata vulnerabilità dei nodi trave-pilastro nei riguardi delle azioni sismiche.
Oggetto della presente memoria è la simulazione numerica del comportamento ciclico di nodi esterni in c.a. effettuata mediante l’implementazione di un macro-modello del nodo nel quale il comportamento a taglio dello stesso e l’aderenza delle barre longitudinali in acciaio all’interfaccia nodo-trave sono riprodotti mediante il “modello a forbice”. Il modello, implementato in OpenSees, è dapprima impiegato per simulare il comportamento di nodi in c.a. collezionati all’interno di un database sperimentale.
Successivamente, tale modello è opportunamente modificato per portare in conto la presenza di un rinforzo
esterno realizzato con impiego di materiali compositi (FRP/FRCM). A tal fine, sono stati selezionati dalla letteratura alcuni nodi rinforzati, ed il presente studio documenta i risultati delle prime simulazioni numeriche effettuate.Analysis of damage exhibited by RC buildings designed before the introduction of the modern seismic codes pointed
out the high vulnerability of beam-column joints toward seismic actions. This paper focuses on numerical simulating the behavior of
exterior RC joints under seismic loading based on a macro-modelling approach, which employs the “scissors model” to schematize
the shear behavior of the joint and the bond-slip of the longitudinal steel rebars at the beam-joint interface. The model, implemented
in the OpenSees computer code, is first applied to simulate the monotonic and cyclic behaviour of several deficient RC beam-columns
joints collected in experimental database compiled from the literature. Then, the model is modified to consider the presence of com-
posite materials (FRP/FRCM) in the external strengthening of RC joints. To this purpose, some representative strengthened specimens
found in the literature were selected, and the results of the first performed analyses are presented in the paper
A Nonlinear Macro-Model for the Analysis of Monotonic and Cyclic Behaviour of Exterior RC Beam-Column Joints
No full textThe study presents a numerical investigation on exterior reinforced concrete (RC) beam-column joints under seismic actions based on a macro-modelling approach proposed by the authors in a recent paper. The followed approach makes use of the well-known “scissors model” where two nonlinear rotational springs arranged in series were introduced to schematize the shear behavior of the joint panel and, moreover, the possible occurrence of the debonding of longitudinal steel rebars at the beam-joint interface. In this paper, the scissor model is employed in the context of a novel predictive approach with the twofold objective to: 1) develop a new model for the estimate of the maximum shear strength of RC joints by performing a multivariate linear regression analysis on a set of experimental tests and, 2) define a new
multilinear backbone joint shear stress-strain law to be assigned to one of the mentioned springs. In particular, the identification of the shear strain parameters is
obtained by performing a sensitivity analysis in which a number of monotonic load-drift numerical curves are derived by varying the strain values in ranges opportunely a-priori defined and compared with the experimental ones to investigate their accuracy. Finally, cyclic analyses on RC joints collected in the experimental database are carried out by considering the backbone joint shear stress-strain law identified in the calibration process. The analyses are performed by using the nonlinear open-source finite element platform, OpenSees, in which the “pinching4” uniaxial material model, available in the software library, is implemented to set the parameters governing the hysteresis rules and pinching effect. To this purpose, five literature proposals suggesting the values to use for such parameters are taken into account and their assessment is presented in the paper. The obtained outcomes have allowed, on the one hand, to identify the proposal providing the best numerical simulations of the experimental results and, on the other end, to draw useful indications on how to further improve the cyclic modelling by opportunely modifying the
setting of the “pinching4” material model parameters
An application of damage detection methods to a real world structure subjected to ground motion excitation
Get PDFThis paper aims at investigating the efficacy of different state-of-art damage detection methods when applied to real world structures subjected to ground motion excitations, for which the literature contributions are, at present, still not fully comprehensive. To this purpose the paper analyses two test structures: (1) a four-story scaled steel frame tested on a shake table in a controlled laboratory conditions, and (2) a seven-story reinforced concrete building monitored during the seismic excitations of the 1999 Chi-Chi (Taiwan) Earthquake main shock and numerous fore and aftershocks. Some model based damage approaches and statistics based damage indexes are reviewed. The different methodologies and indexes are, then, applied to the two test structures with the final aim of analysing their performance and validity within the case of a laboratory scaled model and a real world structure subjected to input ground motion
A macro-modelling approach for RC beam-column exterior joints: first results on monotonic behaviour
Get PDFThe present paper concerns the numerical study of the behavior of exterior RC beam–column joints under seismic actions by using a macro-modelling approach. The beam-column joint element is modelled through the well-known “scissors model” in which the two main mechanisms governing the overall behavior of the RC joints are considered by means of two nonlinear rotational springs in series. In particular, the first spring represents the shear deformation of the joint panel, while the second one represents the “fixed-end-rotation” of the beam due to the debonding of the longitudinal steel rebars at the beam-joint interface. In the model, the two springs are defined by proper moment-rotation constitutive laws selected from the literature. In particular, for the spring simulating the shear behavior of the joint panel, various combinations of some literature proposals are taken into account with the purpose to identify the laws better simulating the overall response of the RC joint.
The numerical simulations are performed by using the OpenSees software in which the ability of the considered constitutive laws to reproduce the monotonic behavior of RC beam-column joints is assessed by considering an experimental database of cyclic tests collected from the literature.
Finally, preliminary cyclic analyses are also carried out by considering the backbone envelopes of the best constitutive models previously identified in the calibration process.
It is worth highlighting that, with respect to other similar literature approaches − often validated on the basis of a few experimental tests performed by the same proposals’ developers − the model presented herein is characterized by the following twofold advantage: a) easy to implement but, at the same time, capable of simulating both monotonic and cyclic response of tests with appreciable accuracy and, b) more robust and powerful since it was calibrated by considering experimental test results made available from a variety of researchers on the same typology of RC joints investigated
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