1,721,092 research outputs found
Seismic risk assessment of residential buildings by the Heuristic vulnerability model: influence of fragility curve models and inventory scale
Full text linkTypological-observational methods still constitute one of the most commonly applied tools for evaluation of the seismic risk and vulnerability of the existing building stock. Their efficiency is mainly related to the effectiveness of the procedure for deriving fragility curves, and the reliability and completeness of the database that describes the building stock. This paper presents a comparison between the vulnerability and damage distribution assessment provided by fragility curves used in the Macroseismic and Heuristic methods, and a comparison of exposure evaluation methodologies according to two different approaches, namely a compartment- and a building-scale survey. An application to the case study of the residential building stock in the historic center of Alcamo, a town of 45,000 inhabitants in Western Sicily (Italy), shows the major reduction in fragility provided by recalibration of the masonry buildings’ ductility values that characterize the Heuristic method. Moreover, the efficiency of the compartment scale survey approach, based on the CARTIS typological-structural characterization method of ordinary buildings in urban areas, is underlined
Friction-based beam-to-column connection for low-damage RC frames with hybrid trussed beams
No full textHybrid Steel-Trussed Concrete Beam (HSTCB) is structural typology suitable for light industrialization. HSTCBs usually cover long span with small depths, which lead to significant amount of longitudinal rebars. The latter make beam-column joints more prone to damage due to earthquake-induced cyclic actions. This phenomenon can be avoided using friction-based BCCs. Friction devices at Beam-to-Column Connections (BCCs) have become promising solutions to reduce the damage experienced by structural members during severe earthquakes. Few solutions have been developed for cast-in-place Reinforced Concrete (RC) and steel-concrete composite Moment Resisting Frames (MRFs), because of the difficulty of designing cost-effective damage-proof connections. This paper proposes a friction-based BCC for RC MRFs made with HSTCBs. Firstly, the proposed connection is described, and its innovative characteristics are emphasized. Secondly, the design method of the connection is outlined. A detailed 3D FE model representative of a beam-column joint fitted with the proposed connection is developed. Several monotonic and cyclic analyses are performed, investigating different design moment values. Lastly, the numerical results are discussed, which demonstrate the efficiency of the proposed solution in preventing damage to RC members, and in ensuring satisfactory dissipative capacity
Numerical analysis of the effects of PBO-FRCM confinement on RC columns
No full textThis paper presents a finite element (FE) analysis on the behavior of reinforced concrete (RC) squared and rectangular columns strengthened by PBO-FRCM, under axial force and bending moment. The modeling technique adopted for the compressive behavior of confined concrete is previously validated developing FE models for specimens of plain concrete wrapped by PBO-FRCM and comparing the numerical results with those obtained by experimental tests on squared and rectangular confined columns. Then, the model of the RC element is developed reproducing the load condition of columns in a MRF loaded by horizontal forces with constant axial load applied to the pillar during the analysis. The numerical model is validated against experimental results obtained by the authors in a previous study
Caratteristiche tipologico-strutturali per la valutazione della vulnerabilità sismica nel centro storico di Caltabellotta tra persistenze e trasformazioni
No full textThe research carried outin this paper aims at the knowledge of the typological and constructive characteristics of the building in Caltabellotta, in order to think about the seismic vulnerability. To achieve this goal, sheets were drawn up on the building types found and on the construction elements, looking for a method to overcome the difficulty of knowing the masonry due to the presence of plaster
Influence of the effectiveness factors in assessing the shear capacity of RC beams strengthened with FRP
No full textShear failure of RC beams strengthened with composite textiles is often affected by the different failure modes characterizing the FRP reinforcement. The most relevant analytical models for evaluating the shear capacity of RC beams strengthened with FRP take into account these failure modes by introducing an effectiveness factor “R”, which reduces the ultimate FRP tensile stress. Moreover, the interaction between stirrups and FRP reinforcement leads to a reduced efficiency of the transverse steel reinforcement due to the brittle failure of composite textile which hinders the yielding of all the stirrups involved by critical crack. In this regard, some analytical models introduce an effectiveness factor “r”, aiming at reducing the yielding stress of stirrups. The procedures to calculate the above two parameters represent the main differences characterizing most of analytical models, significantly influencing their results. For this reason, the present paper focuses on the comparison of the different procedures to assess the effectiveness factors, proposing a new procedure for each effectiveness factor by modification of already existing formulations. Influence of the arrangement of composite reinforcement on the efficacy of stirrups, affected by brittle failure of FRP, is considered by means of the ratio between effective strain of composite to yielding strain of steel. The proposed procedures are employed in a design-oriented analytical model able to calculate the shear strength of RC beams retrofitted with FRP reinforcement arranged in any direction. The model is formulated aiming at representing an extension of EN1992 shear model to beams strengthened with FRP. The efficacy of the proposed procedures is assessed by comparing the experimental results against the predictions obtained via the design-oriented model and the above-mentioned analytical models
Comparative analysis of shear resisting models for hybrid steel trussed concrete beams
No full textThe hybrid steel trussed concrete beams represent a structural solution widely adopted in the industrial constructions thanks to the numerous advantages due to their use, such as economic convenience, high performances and constructional speed de-riving from the partial prefabrication process and from the self load-carrying capacity of the beam in the first operative phase, prior to the in-site casting of concrete. The hybrid steel trussed concrete beams examined in the present study are constituted by two prin-cipal components, i.e. a steel joist with inclined rebars, realized in industry, which is welded to a smooth steel plate and then embed-ded within the concrete material cast in situ. The proposed study concerns the modeling of the shear behavior of these beams provid-ing a synthesis of the most relevant scientific contributions currently available in the technical literature regarding both analytical and numerical models for the prediction of the shear resistance of the beam
Influence of height on Tsunami fragility of masonry buildings resulting from Monte Carlo analysis
No full textThe interest in building vulnerability to tsunamis has gained increasing attention within the scientific community. The destructive events in the last decades and the correlated losses in terms of human lives and things have been crucial in this growing interest. The issue of how constructions can contrast the tsunami waves or what influences their collapse has been different times faced when distinguishing between different building typologies. Here the parameter “building height” and its effect on the tsunami fragility of buildings are studied. Monte Carlo simulations are carried out for this purpose considering a range of tsunami scenarios and a set of buildings with random characteristics. Masonry buildings in the Mediterranean area are referred to whose diffusion overcomes any other structural typology. A simplified procedure is used for the assessment of buildings, based on the analyses of impacted walls at the ground floor in substitution of the analysis of the entire structure. This approach guarantees a reduced computational effort in favor of the possibility of managing a high number of cases (large-scale assessment) and obtaining of results statistically significant. This study wants to contribute to the enhancement of coastal resilience strategies by providing information about the relationship between masonry structure height and fragility under tsunami actions and providing valuable information to guide engineering practices, improve building codes and enhance the resilience of masonry structures against future tsunami events
Shear Capacity Model with Variable Orientation of Concrete Stress Field for RC Beams Strengthened by FRP with Different Inclinations
Full text linkA design-oriented analytical model able to evaluate the shear capacity of reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) sheets or strips oriented in any direction is proposed. The formulation of the model is based on the variable-inclination stress-field approach, aiming to extend the provisions of current European standards to beams strengthened in shear using FRP. The main novelty of the model lies in taking into account the possible different inclination of steel stirrup and FRP reinforcement in determining the orientation of a compressed concrete stress field, and in shear strength evaluation, overcoming the approximation of the known models with variable inclination of the concrete strut in the assessment of concrete strut capacity, in which the value that has to be assigned to the shear reinforcement direction is not defined, that is, either that of the steel stirrup or the external FRP reinforcement. The proposed model is able to take into account different steel stirrup and external FRP shear reinforcement orientation in assessing the reduction of the steel transverse reinforcement efficiency due to the brittle failure of the composite and also as a function of the effective composite to yielding steel strain ratio. Moreover, regarding the former aspect, a simplified approximate procedure is proposed for solving the drawbacks related to verifying compressed concrete strength in the suggested method of application of code models for RC beams strengthened by means of FRP reinforcement inclined with a different slope from the pre-existing steel stirrup. Complete and U-shaped schemes are considered. The effectiveness of the proposed model adopting different relations for assessment of the FRP effective strains proposed in the literature is investigated, differentiating them by shape of the cross section and by the possible presence of fiber-anchoring devices. The shear capacity predicted by the model and those obtained using international codes and literature models are compared against the experimental results, proving that the proposed model is the most effective in predicting the shear strength when considering specimens having steel stirrups and FRP shear reinforcement arranged with different inclinations
ANALISI SPERIMENTALE DEL COMPORTAMENTO CICLICO DI NODI DI TRAVI SER E PILASTRI IN C.A
No full textResults of experimental investigation on cyclic behavior of beam-column joints made up of hybrid steel trussed concrete beams connected to reinforced concrete columns are presented. Specimens are representative of joints in framed structures subjected to seismic actions designed according to current Italian technical standard codes. The aim of the experimental testing was to verify strength capacity and ductility of the connection, focusing both the global behavior and the force transmission mechanisms between steel truss and concrete in the region close to the beam-column joint
EXPERIMENTAL AND FINITE ELEMENT ANALYSIS OF THE CYCLIC BEHAVIOUR OF LINEAR DISSIPATIVE DEVICES
No full textIn the past years, low-damage design of structures is becoming an efficient approach by engineers and researchers in order to mitigate the structural damage to buildings during a seismic event. To this aim, one of the most popular strategies is to endow framed structures with either viscous, hysteretic metallic, or viscoelastic devices. As an alternative to these systems, friction devices have been also studied, proving to be an effective solution. Steel braces endowed with linear dissipative devices based on friction can be used effectively both in the case of new and existing structures. Studies conducted on these devices stressed that their behaviour is mainly influenced by type of friction materials, loss of bolt preload and effect of disc springs. An experimental campaign has been performed at the Materials and Structures Laboratory of the University of Palermo on linear dissipative devices with different types of friction materials i.e., steel, thermal sprayed aluminium, and brass, to check their effectiveness. Finite element analysis using ABAQUS has been done to design, check the functionality, and get insight into the experimental results of the linear dissipative devices. An investigation has been done on the effectiveness of disc springs to limit the bolt preload variation in the device and the effect of thicknesses of plates on the functionality of linear friction dissipative device. The results showed that thermal sprayed aluminium, coupled with structural steel, is a good friction material as it provides stable hysteresis loops and high friction coefficient as compared to brass, and appropriately designed disc springs are able to limit bolt preload variation. The experimental results showed that the thermal sprayed aluminium provides a friction coefficient between 0.57 and 0.6 without significant variation even for a large number of cycles, while for the brass the friction coefficient at the beginning of the test was 0.25 and then it increased to 0.45 at the end of test, exhibiting large variation due to stick and slip phenomenon. The FEM analysis proved that the disc springs are able to minimize the variation of the contact pressure due to the Poisson effect and proper thickness of friction plates are important for the performance of friction device
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