1,721,029 research outputs found
Numerical prediction of the shear response of semi-prefabricated steel-concrete trussed beams
No full textIn this study, the shear behavior of hybrid steel-trussed-concrete beams (HSTCBs) realized with prefabricated steel trusses embedded into a concrete core cast in situ, is investigated by means of Finite Element (FE) numerical simulations. HSTCBs do not behave as classical RC elements nor composite beams. Up to now, there are not specific design criteria in the building codes and the calculation of this type of beams is conducted by means of design-by-testing procedures. The knowledge of the material behavior as well as the understanding of the interaction between materials in contact is the first requirement for the definition of proper design procedures and calculation methods for practitioners to be inserted in the international building codes. In the present study, the numerical simulation of the global beam behavior through the modeling of the local material response and contact properties, allow a detailed knowledge of the shear resisting mechanism aimed at the definition of simplified calculation formula. The accuracy of the numerical prediction is validated against the results of a reference experimental campaign of three-point bending tests with shear failure carried out by the author in a previous work. A first analytical approach for the interpretation of the FE results is conducted applying the variable strut inclination method currently prescribed in Eurocode 2 for classical RC beams. Conversely, in the paper it is shown how all information coming from the FE analysis are of paramount importance for the possible development of more proper simplified calculation methods of the shear capacity of this particular beam typology
Experimental analysis, numerical and analytical modeling of shear strength mechanisms in Hybrid Steel Trussed Concrete Beams
Full text linkThe purpose of the present dissertation is the study of the shear behavior of the so-called, in the recent scientific literature, Hybrid Steel Trussed Concrete Beams (HSTCBs). Such beams represent a structural typology which usually consists of a steel truss embedded into a concrete core so that, after curing and maturation, the two materials behave as a unique structural system, the steel members working as the reinforcement of the beam itself.
Since the Seventies, the HSTCBs are widely employed in civil constructions because they allow to industrialize the building process, avoiding substantial alterations in the construction processes and organizational protocols of the industries.
With regard to the introduction of this beam typology within seismic framed structures, it is necessary to develop specific design criteria based on the capacity design approach, ensuring both an adequate shear resistance in order to prevent brittle failure modes and a cyclic dissipative behavior of beam-to-column joints.
While the issues concerning the flexural behavior has been widely investigated in the literature, particularly focusing on the connection deformability and strength, the problems related to the shear behavior still represent an open issue. Within this framework, the present thesis aims at investigating the shear response of HSTCBs and the stress transfer mechanism between the steel members and the surrounding concrete.
With reference to the stress transfer mechanisms, theoretical analyses with the aim of interpreting the experimental results of push-out tests on pieces of HSTCBs are developed. Such models for the prediction of the maximum slip force refer both to the classical truss models with variable inclination of the compressed concrete strut, typically adopted for the classical Reinforced Concrete (R.C.) structures, and models with a failure mechanism governed by the dowel effect, generally used for composite structures. The application of these models, according to their original formulation, generally leads to an underestimation of the maximum load experimentally obtained by various authors from the push-out tests. For this reason, the formulation of further strut and tie models, on one hand, and dowel-mechanism models, on the other hand, has been developed. In those models proper changes have been introduced in order to take into account the geometrical and mechanical characteristics of the beam object of study.
Besides the analytical interpretation of the maximum load obtained in the push-out tests, a two-dimensional (2D) non-linear finite element (FE) model is also developed with the aim to simulate, under few simplified hypotheses, the mechanical response of the beam identifying the stresses transfer mechanisms. The result of the 2D modeling highlights the difficulty of grasping, with an extremely simplified model, the large variety of parameters on which the transferring of the stresses and the failure modes depend. Among these parameters, the ones playing a preeminent role are the three-dimensional (3D) geometry and the actual bond between the surfaces of the steel bars (smooth or ribbed) and the concrete in which they are embedded.
Therefore, after the developing of the simplified modeling, a detailed 3D FE model containing solid elements is realized by means of the software Abaqus 6.10. The model was developed in collaboration with the research group of Prof. Gianvittorio Rizzano of the Department of Civil Engineering, University of Salerno. Particularly, the developed models are representative, on one hand, of cases in which the diagonals of the steel truss are ribbed and, on the other hand, cases in which they are made up of smooth steel. The simulation concern cases in which the hypothesis of perfect bond between the surfaces is assumed or, similarly, cases in which there is no bond between the steel and the concrete as well as the more realistic case in which a specific bond stress-slip relationship at the interface is introduced. Besides the modeling of the experimental tests, also a parametric numerical analysis is provided with the aim of evaluating the influence of the geometrical and mechanical features of the various components of the HSTCB, such as the deformability of the bottom steel plate, the type of steel constituting the diagonal web bars (smooth or ribbed) as well as the mechanical characteristics of the materials.
In addition to the study of the local problems of stresses transfer, some theoretical and experimental studies are carried out in order to investigate the global behavior of the structural elements. In particular, an experimental campaign is performed on simply supported HSTCB specimens loaded with a concentrated force in the midspan and designed to exhibit a shear failure. For the execution of the tests, a particular type of steel truss produced by the industry Sicilferro Torrenovese Torrenova (ME) is employed. Six specimens have been manufactured and classified into two series, "A" and "B". Particularly, the specimens of series "A" have been tested inducing a positive bending moment; on the contrary, the specimens of series "B" have been tested so that a negative bending moment arises. Before the concrete casting, electric strain gauges have been placed on the specimens in correspondence of the tensile and compressed diagonal bars (in the section near the welding to the inferior plate) and in the bar of the upper chord in correspondence with the central mesh of the truss in the shear span. After casting and curing of the concrete, strain gauges were placed even on the bottom steel plate. The obtained experimental results are compared with the detailed numerical FE model representative of the abovementioned tests, showing a good agreement in terms of load-displacement curve as well as crack pattern evolution.
The numerical analysis is followed by the analytical interpretation for the assessment of the shear strength of the beams. In the first instance, the prediction models existing in the literature and typically employed for the classic R.C. structures have been applied. They can be mainly classified into "additive models" and "strut and tie models". In the additive models the value of shear strength is calculated as the sum of the contribution due to the concrete and the additional contribution provided by the shear reinforcement. The strut and tie models, instead, are primarily truss models in which the hypothesis of the variable inclination or 45° inclination of the compressed concrete strut is assumed. In addition to these classical formulations, also other computational models recently developed by some authors for the HSTCBs are taken into account. Successively, also a specific model able to interpret the shear strength mechanism in the tested beam typology is proposed.
Considering the three-point bending tests performed on the HSTCBs, a further 3D model, realized with the software Abaqus 6.11, is developed in a simplified way, with the aim of managing a model sufficiently accurate in the estimation of the maximum load that, in the same time, would allow computational efforts appropriate for the generation of a certain number of different cases for the study of the size effect on beams with similar geometry. The model has been developed under the guide of Professors Roberto Ballarini and Jialiang Le of the Department of Civil Engineering, University of Minnesota. Starting from specific scaling criteria, three different sizes of beams are considered and the numerical load-displacement curve is obtained also interpreting the failure mechanisms and the evolution of the cracks. The numerical analyses have been developed with the aid of computers and software provided by the Minnesota Supercomputing Institute
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
The structural behaviour of hybrid steel-trussed concrete beams: A literature review of experimental tests and theoretical models
Full text linkHybrid Steel-Trussed Concrete Beams (HSTCBs), introduced in civil construction around the 70s, combine a steel truss within an in-situ cast concrete core, often with a steel or concrete bottom plate. Initially favoured in industrial buildings for their semi-prefabricated construction and ability to span large distances with contained depths, HSTCBs have subsequently attracted scientific interest in residential construction, focusing on static and seismic response. The technical literature on this topic highlights that HSTCBs do not follow the same mechanical rules of RC or steel-concrete composite beams, necessitating specific insights into their behaviour under flexure, shear, and seismic conditions. This review aims to collect the major scientific results obtained in the last twenty-five years by several researchers in Italy and abroad, beside the outcomes of some relevant earlier studies. The reviewed papers encompass findings from experimental campaigns on weldings, push-out test specimens, simply supported beams and beam-to-column joints. Some of these studies also incorporate proposals for analytical formulations aimed at offering design-oriented and code-compliant prediction models, alongside finite element simulations to replicate the strengthening mechanisms. Following a thorough synthesis of the primary findings to date, the literature review underscores notable gaps in knowledge and still open issues, particularly concerning long-term performance and size-effect laws
Shear strength of High-strength concrete beams: modeling and design recommendations
No full textIn the present paper, the flexural and the shear resistance of high strength reinforced concrete (HSC) beams with longitudinal bars, in the presence of transverse stirrups is analyzed both theoretically and experimentally. The experimental researches here presented are parts of previous researches carried out by the author. Researches refer to HSC beams with high percentages of steel bars failing in shear and in flexure. From the analytical point of view, a model based on the evaluation of the resistance contribution due to beam and arch actions including bond splitting and concrete crushing failure modes is developed and presented. The model was verified against available experimental results and those recently obtained by the author. Some of the more recent analytical expressions able to predict the shear and the flexural resistance of concrete beams were mentioned and design considerations are made referring to a ductile design of HSC beams. Finally, design recommendations were deri..
Indagini teoriche e sperimentali su dissipatori ad attrito per edifici in acciaio in zona sismica
No full textThe present paper presents the results of experimental analyses carried out to study the behaviour of slotted bolted connections (SBC) as friction steel dampers. The devices consist of bolted joints with slotted holes, which can be used in both steel and RC framed structures or, alternatively, into beam-column and column-foundation joints.
The most suitable configurations to increase friction are investigated utilizing steel S355J0 plates and class 10.9HV high-strength bolts, under controlled pre-load and considering different types of surface treatment.
Experimental tests are carried out making use of a universal testing machine, which allows mak-ing displacement-controlled tests. Once the pre-load frictional force is reached, the plates begin to slide each other through the hollow holes, dissipating energy through friction.
The paper shows the results obtained during the tests in terms of frictional force vs. displacement, friction coefficient values and variation pre-load in bolts. The results are compared with the theo-retical values derived from the calculation
Experimental Investigation of the Shear Response of Precast Steel-Concrete Trussed Beams
No full textThe results of an experimental campaign of three-point bending tests on precast composite beams, named hybrid steel-trussed concrete beams (HSTCBs), are provided. HSTCBs are typically constituted by a precast steel truss embedded in a block of concrete cast in place. Two series of specimens were manufactured, designed such that shear failure would occur, and tested under positive and negative bending moment. The experimental results obtained showed that fragile shear failure occurred in almost all cases, evidencing the crisis of the compressed concrete strut involved in the collapse mechanism. Yielding of the steel members provided ductility to the system, especially in those cases in which the mechanical properties of the concrete were adequate and allowed the failure of the strut to be delayed. Some of the more accredited expressions for prediction of shear resistance available in the literature were used to assess the shear capacity and compared against those experimentally obtained for all specimens. The existing formulas mainly refer to classical reinforced concrete (RC) beams, but analytical models recently developed for HSTCBs were considered for interpreting the test results. On the basis of the experimental outcomes and the results obtained from their analytical interpretation, comments and design considerations on the main parameters ruling the resisting mechanism occurring in the tested beam typology are provided
Stress transfer mechanism investigation in hybrid steel trussed-concrete beams by push-out tests
No full textResults of push-out tests carried out on Hybrid Steel Trussed–Concrete Beams (HSTCBs) before and after the concrete
casting are presented and interpreted. Firstly, in order to check the ability ofweldings before casting, tensile
tests were performed on specimens reproducing different types of welded joints. Simplified design formulae
were used to predict their ultimate strength. Secondly, results obtained by push-out tests on specimen representative
of the beambefore and after the concrete casting are presented and discussed. Finally, simplified analytical
models proposed by the current European building codewere adapted to the specific typology to roughly predict
the ultimate strength obtained by push-out tests on specimens complete with concrete casting
Simplified analytical model for moment–axial force domain in the presence of shear in R.C. members externally strengthened with steel cages
No full textEquations for a hand calculation of moment–axial force domain in the presence of shear for R.C. beam/column externally strengthened with steel angles and strips are developed. The analytical derivation is made assuming, for axial load and flexure, the equivalent stress-block parameters for internal forces, considering the confinement effects induced in the concrete core by external cages both in the cases of strips or angles yielding. Limit states due to bond failure, concrete crushing and yielding of steel angles and strips in flexure and in shear, including moment-to-shear interaction, are considered. The proposed model gives results in a good agreement with available experimental data and it allows a hand control of the influence of the main parameters governing the problem (angle and strip geometry and mechanical properties of constituent materials)
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