1,721,085 research outputs found
Plastic waste as a concrete mix component
No full textIn the last decades, several strategies have been employed to improve the characteristics of concrete in terms of mechanical strength, ductility, durability, lightness, workability, ability to prevent the oxidation of steel reinforcement, etc. In this study a new point of view is faced, that is the possibility to use concrete as a container of waste without worsening, or containing the worsening, of the properties mentioned before. In detail, it is investigated the possibility of recycling plastic waste in different forms, by using it as aggregate in the production of concrete.
The exploitation of waste, or byproducts, as alternative aggregate in concrete, and in detail is not new and results in a reduction in the exploitation of scarce natural resources. Productive use of waste leads to a reduction in the landfilling of waste through the transformation of waste into a resource. Here, plastic is not properly considered as a resource while concrete is considered a resource to limit the introduction of plastic waste in the environment.
The introduction of plastic waste in the concrete is not new [1-12] but in many cases, the waste is transformed before its use. Introducing not transformed plastic waste into ordinary concrete mixes is a challenge because, in connection with the characteristics of the plastic waste, the risk of a loss of performance is not so low.
To prove the possibility of reaching this objective with an acceptable loss of performance, the mechanical characteristics of concrete mixed with additional alternative plastic aggregates classified as waste are investigated and discussed in this paper. The experimental program includes the inclusion of different types of plastic wastes (different refers to the chemical composition and to the shape of the plastic aggregate) in the concrete. Different mixes with different percentages of waste are investigated to identify possible fields of application. The experimental results indicate that the use of plastic waste is possible within significant percentage ranges
Plastic Waste for Concrete Mixture: Advanced Strategies and Solutions
No full textIn recent years, various waste recycling strategies have emerged emphasizing the utilization of plastic waste in concrete mixtures. This practice offers a dual advantage by decreasing the demand for traditional aggregates, like sand and gravel, or lightweight aggregates while mitigating plastic accumulation in landfills and oceans, promoting a circular economy. Although high plastic content may worsen mechanical characteristics, proper mix designs can optimize concrete containing plastic aggregates to be lighter and beneficial for weight-sensitive applications. This study investigates the influence of plastic waste on concrete mechanical characteristics, incorporating different types of plastic waste in varying percentages to identify potential applications. Experimental results indicate that incorporating plastic waste does not significantly compromise concrete strength. Despite promising findings, challenges associated with using plastic waste in concrete must be addressed to optimize this practice and overcome drawbacks. These efforts align with sustainable waste management and eco-friendly construction practices, underscoring the importance of refining the use of plastic waste in concrete
Simplified analytical model for flexural response of external R.C. frames with smooth rebars
No full textIn this paper an analytical model in a closed form able to reproduce the monotonic flexural response of external RC beam-column joints with smooth rebars is presented. The column is subjected to a constant vertical load and the beam to a monotonically increasing lateral force applied at the tip. The model is based on the flexural behavior of the beam and the column determined adopting a concentrated plasticity hinge model including slippage of the main reinforcing bars of the beam. A simplified bilinear moment-axial force domain is assumed to derive the ultimate moment associated with the design axial force. For the joint, a simple truss model is adopted to predict shear strength and panel distortion. Experimental data recently given in the literature referring to the load-deflection response of external RC joints with smooth rebars are utilized to validate the model, showing good agreement. Finally, the proposed model can be considered a useful instrument for preliminary static verification of existing external RC beam-column joints with smooth rebars for both strength and ductility verification
Seismic vulnerability of structures and infrastructures: Strategies for assessment and mitigation
No full textSeismic engineering is constantly looking for new strategies and methods that provide designers with the opportunity to get more and more efficient solutions both from the performance and from the economic point of view. In this context, the scientific community is called not to miss its support and to face the new challenges coming from the observation of the damage caused by the recent earthquakes. This Special Issue of “Ingegneria Sismica” collects some works focusing the theme of the seismic vulnerability, some of them specifically refer to mitigation strategies while others address modeling strategies. Obviously, for the multiplicity of aspects involving the theme of "seismic vulnerability", only a few issues have been discussed. In particular, some works deal with the theme of base isolation from the point of view of design and seismic reliability, others are focused on the theme of structural robustness considered as a further goal of seismic design. Further papers are deepening the problems of interaction between frames and masonry infills, providing simplified modeling strategies, suggesting criteria to reduce interaction effects, but above all by providing methods for the analysis of combined in-plane / out-of-plane behavior. The themes related to modeling are also addressed with particular care. Other papers in fact face the issues of model uncertainty and of the reliability of constitutive laws for normal and high strength confined concrete, being the latter of fundamental importance for the assessment of the rotational capacity of reinforced concrete structural elements under seismic actions. Moreover, the problem of the reliability of seismic vulnerability assessment methods is also discussed, with particular reference to multimodal "pushover" analysis. This Special Issues is composed of 10 paper produced by 29 authors, to whom we would like to address a special thank for the effort made during the editorial phases. Finally, the Guest Editors, Paolo Castaldo, Liborio Cavaleri e Fabio Di Trapani, wish to thank Prof. Gianmario Benzoni and Prof. Rosario Montuori for this opportunity and for their assistance
FE modeling of Partially Steel-Jacketed (PSJ) RC columns using CDP model
No full textThis paper deepens the finite element modeling (FEM) method to reproduce the compressive behavior of partially steel-jacketed (PSJ) RC columns by means of the Concrete Damaged Plasticity (CDP) Model available in ABAQUS software. Although the efficiency of the CDP model is widely proven for reinforced concrete columns at low confining pressure, when the confinement level becomes high the standard plasticity parameters may not be suitable to obtain reliable results. This paper deals with these limitations and presents an analytically based strategy to fix the parameters of the Concrete Damaged Plasticity (CDP) model. Focusing on a realistic prediction of load-bearing capacity of PSJ RC columns subjected to monotonic compressive loads, a new strain hardening/softening function is developed for confined concrete coupled with the evaluation of the dilation angle including effects of confinement. Moreover, a simplified efficient modeling approach is proposed to take into account also the response of the steel angle in compression. The prediction accuracy from the current model is compared with that of existing experimental data obtained from a wide range of mechanical confinement rati
Response spectrum analysis of frame structures: reliability-based comparison between complete quadratic combination and damping-adjusted combination
No full textIn the framework of seismic design of structures, response spectrum analysis (RSA) is the
most commonly used approach in practice. The most popular combination rule is the complete
quadratic combination (CQC) which is also prescribed by the most of seismic design
codes and is based on the assumptions that the seismic acceleration is a white noise process
and the peak factor ratios associated to the total and modal responses are unitary. Recently,
the damping adjusted combination (DAC) rule has been developed for base-isolated structures
to overcome the aforementioned simplified assumptions. Although it has been proved
that the simplifications about peak factors lead to noticeable errors in the case of baseisolated
structures, the accuracy gain of DAC with respect to CQC in the case of fixed-base
structures is still unknown. Therefore, the paper presents an in-depth study on the RSA of
three-dimensional frame structures, aimed to evaluate the accuracy of the above methods.
Two reference classes of frame structures having different degree of complexity are considered.
Average interstorey drift and floor torsion responses, obtained from a set of Time
History Analyses are compared with those of the modal combination rules. Lognormal
joint probability density functions of the predictive errors from CQC and DAC are finally
evaluated for a reliability assessment of the two combination rules under bidirectional seismic
excitations
Flexural behavior of hybrid glass beams with rectangular cross-sections
No full textAn experimental investigation regarding the flexural and the shear behavior of glass beams with length 900, 1300, 1700 mm and rectangular cross-section is presented and discussed. Rectangular cross-sections were obtained by assembling three float glass panels of depth 200 mm and thickness 6 mm through an acrylic adhesive with an effective depth of 19.52 mm (6 + 0.76 + 6 + 0.76 + 6 mm). Some specimens were also reinforced internally with steel plates of thickness 6 mm and depth 25 mm and thickness 6 mm and plates of thickness 6 mm and depth 50 mm placed at the bottom portion of the beams for the entire length of the beams themselves. Three specimens for each investigated series were tested in flexure focusing on the flexural and shear response through the determination of the load-deflection curves, and the crack patterns at rupture. The shear span to depth ratios a/d were 2, 3 and 4, respectively. In the paper an analytical model is also presented for a preliminary design of composite glass beams able to predict the ultimate load including limit states due to glass cracking, flexural failure with glass crushing or plates yielding, shear compression and diagonal tension failure. This model can be useful to perform simulations in order to investigate the structural resistance of hybrid glass beams to the varying of the geometrical characteristics of beam, of the reinforcement area and on the type of reinforcements
Seismic analysis and risk mitigation of existing constructions
Full text linkFollowing a thorough and lengthy procedure, we would like to thank all contributors for their highest calibre papers,
which comprise the Special Issue on “Seismic analysis and risk mitigation of existing constructions” of the Open
Construction and Building Technology Journal.
The topic of the Special Issue encompasses a large number of issues spanning the design of special interventions for
the reduction of the effects of earthquakes on civil structures and infrastructures, to the structural identification and
assessment issues.
The field of seismic engineering is continuously looking for new strategies and methods, which empower the
designers and make them able to obtain more accurate response predictions. Researchers are involved in this process
and are called to successfully encounter new challenges emerging from the increasing need for the assessment of
existing constructions, especially when assuming strategic roles.
As is also reflected by the papers presented in the Special Issue, the continuous advances of the research in this field
moves across two basic directions. On the one hand, there is the direction of the robustness and the reliability of the
recent nonlinear seismic assessment methods (static, dynamic, incremental dynamic). Several approaches can be
followed to predict the response of structures to strong ground motions; however the results coming from each of them
are in some cases conflicting and not always amenable to easy interpretation.
On the other hand, the reliability of structural models still remains a major task of structural engineering and of
seismic engineering in particular. Mathematical models have to reproduce the physics of structures and its evolution
during complex damaging processes. Global and local models tend to reflect this by minimizing the loss of information.
In the Special Issue, we are proud to present state-of-the-art research findings described in detail in 9 papers
authored by 27 researchers of different universities in Italy, California (USA), Greece and United Kingdom. The papers
deal with the seismic analysis and risk mitigation aiming to address different purposes by proposing numerical,
analytical approaches and experimental tests
Experimental determination of viscous damper parameters in low velocity ranges
No full textIn the last decades many strategies for seismic vulnerability mitigation of structures have been developed through analytical studies and experimental tests. Among these, energy dissipation by external devices assumes a great relevance for the relative design simplicity, even if applied to complex structures, and the effectiveness in reducing seismic demand. In particular, the use of fluid viscous dampers represents a very attractive solution because of their velocity-dependent behaviour and relatively low costs. The application on structures requires specific study under seismic excitation and a particular care of structural details. In this context the use of proper constitutive models for the dampers assumes a fundamental role. Seismic codes, as well as literature models generally provide a velocity-dependent relationship with two characteristic constants defining the shape of the force-displacement curve. In this paper an experimental campaign aimed at the determination of the damper constants in the range of low velocities is presented. A fluid viscous damper is tested with different ramp velocity functions. Results show that the assumption of velocity independence of the damper constants fails for the case of low velocity, giving rise to new issues about the limit of validity of the constitutive models generally adopted for viscous dampers
A new hybrid procedure for the definition of seismic vulnerability in Mediterranean cross-border urban areas
No full textAssessment of seismic vulnerability of urban areas provides fundamental information for activities of planning and management of emergencies. The main difficulty encountered when extending vulnerability evaluations to urban contexts is the definition of a framework of assessment appropriate for the specific characteristics of the site and providing reliable results with a reasonable duration of surveys and post-processing of data. The paper proposes a new procedure merging different typologies of information recognized on the territories investigated and for this reason called “hybrid.” Knowledge of historical events influencing urban evolution and analysis of recurrent building technologies are used to evaluate the vulnerability indexes of buildings and building stocks. On the other hand, a vulnerability model is calibrated by means of experimental and numerical investigations on prototype buildings representative of the most recurrent typologies. In the final framework, the vulnerability index, calculated through simplified assessment forms, is linked to the seismic intensity expressed by the peak ground acceleration and associated with an index of damage expressing the economical loss. The procedure has been tested on the urban center of Lampedusa island (Italy) providing as the output vulnerability index maps, vulnerability curves, critical PGA maps, and estimation of the economical damage associated with different earthquake scenarios. The application of the procedure can be suitably repeated for medium-to-small urban areas, typically recurring in the Mediterranean by carrying out each time a recalibration of the vulnerability model
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