1,054 research outputs found
Structural Behavior of Telescopic Steel Pipe for a Full-Scale 60 kW Wind Turbine Tower
No full textA simple analytical model, including local effects due to buckling and shear to moment interaction, was developed to pre-dict the load-carrying capacity of CHS tubes under flexure and shear. A finite-element analysis with ABAQUS Code was also conducted for validation of the proposed model. By properly modeling the imperfection effects due to the ovalization of steel tube, a good correlation of the structural response and failure mode was also achieved, and a good correlation with the analytical model was also achieved. Numerical and analytical results were compared with experimental results recently obtained by the author with good agreement. Experimental tests refer to full-scale static test to failure were conducted on 6 m length of steel pipe constituting a segment of a telescopic wind tower with a 60-kW wind turbine. The diameter of the circular cross-section of steel pipes was 900 mm and the nominal thickness 10 mm. Steel grade was S355 J2, according to Eurocode 3. Although local buckling caused slight strength degradation, the reduction due to shear to moment interaction was very significant, while the recorded response showed a good amount of post-buckling ductility although the ovalization of cross-sections
Flexural response of rc beams failing in shear
No full textIn this paper, an analytical model to determine the flexural response of simply supported RC beams under four-point bending tests
failing in flexure and shear is presented. The model is able to provide load-deflection curves, including also the shear contributions, which are
determined assuming a kinematic rigid plastic model able to consider different strength contributions such as the concrete, the dowel action,
and transverse reinforcement with progressive yielding. For each contribution, a physical explanation is provided to link the strength evaluation
with a specific kinematic evolution for the determination of the overall response of RC beams under combined shear and flexural loads.
An extensive comparison with the experimental data available in the literature is made to check the reliability of the simplified proposed
model to predict also the complete flexural response of beams including postpeak resistance when shear failure is attained. The comparisons
revealed good agreement between the experimental and analytical results. The proposed model can be simply used for manual calculations of
the flexural response of RC beams that fail in flexure or shear
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)
A new dynamic identification technique: Application to the evaluation of the equivalent strut for infilled frames
No full textA new time domain identification technique for systems under Gaussian white noise input is presented, requiring for its application the measurement of the system response but no information about input intensity. The technique proposed is based on the statistic moment equations derived by using a special class of mathematical models named "potential models". These models allow one to determine fundamental properties of the response statistics, making it possible to identify stiffness and dissipation features of a structural system, and also to determine the excitation input. The technique proposed is here applied to the identification of the strut equivalent to the infill of a single story-single bay frame subjected to lateral loads, showing a reduced effort compared to any procedure based on static experimental tests and a higher reliability of the results compared to identification procedures for the strut based only on mathematical assumptions. © 2003 Elsevier Science Ltd. All rights reserved
An output-only stochastic parametric approach for the identification of linear and nonlinear structures under random base excitations: Advances and comparisons
No full textIn this paper a time domain output-only Dynamic Identification approach for Civil Structures (DICS) first formulated some years ago is reviewed and presented in a more generalized form. The approach in question, suitable for multi- and single-degrees-of-freedom systems, is based on the statistical moments and on the correlation functions of the response to base random excitations. The solving equations are obtained by applying the Itô differential stochastic calculus to some functions of the response. In the previous version ([21] Cavaleri, 2006; [22] Benfratello et al., 2009), the DICS method was based on the use of two classes of models (Restricted Potential Models and Linear Mass Proportional Damping Models) while its generalization for use with different models from the ones mentioned above is discussed. In the paper the new class of models to which the DICS method is applicable are described. Further, the advantages and disadvantages of the approach in question are examined, also by a comparison with some techniques available in the literature. © 2013 Elsevier Ltd
Dimensionless analysis of RC rectangular sections under axial load and biaxial bending
No full textThis paper proposes a numerical procedure able to provide ultimate curvature and moment domains of rectangular RC sections subjected to combined axial load and biaxial bending. The formulation is carried out in dimensionless terms in order to give results that are valid for classes of sections characterized by the same values of the geometric and mechanical parameters governing the section response. The role of some of these parameters is investigated here. The results show possible correlations linking the actual values of moment and curvature to the values corresponding to two cases of uniaxial bending to be considered separately. © 2012 Elsevier Ltd
Theoretical approaches for modelling buckling effects in rebars of RC members
No full textBuckling of longitudinal bars in reinforced concrete (RC) members is definitely a critical issue in framed structures subjected to seismic loads. Second order effects can affect the compressive stressâstrain law of steel bars, influencing ductility calculations of RC structures. Moreover, literature studies show that buckling can occur over a length wider than stirrupsâ pitch (global buckling mode), involving more stirrups and inducing large deflections in the bar. If the critical length is not carefully estimated, stirrupsâ failure can occur, causing also the sudden loss of confining effects in concrete. This paper presents the results of different approaches for calculating the critical conditions in longitudinal bars. A discrete mechanical model is proposed, based on the solution of a continuous beam with elastic supports, with deflections restrained in one side to simulate the presence of the concrete core. It allows describing the transition from local buckling (between the stirrups) and global buckling, on the basis of the relative stiffness stirrup-bar. Two other methods corresponding to different computational efforts are also adopted for the sake of comparison. In particular, non-linear finite element analyses are carried out including the effect of strain hardening in the constitutive law of steel and finally, comparisons are made with a simplified closed-form solution proposed in the literature. This last comparison allows to assess the reliability of these expressions and their applications for obtaining parametric considerations useful for design
A statistical moments based approach for the dynamic identification of civil structures
No full textIn recent years, interest in developing identification techniques that are valid in the case of unmeasured input has increased. In this field some interesting parametric approaches have been proposed. Nevertheless, the improvement of the available techniques or the formulation of new techniques is desirable. In this paper a time domain dynamic identification approach based on the statistical moments of the response of civil structures under base random excitations is discussed. Two types of models are used: the classically damped models characterized by mass proportional damping and the so-called “potential models” which are non linear in damping and stiffness. By applying the Itô differential stochastic calculus to some functions of the response, algebraic equations that depend on the above statistical moments can be obtained. These equations can be used for the dynamic identification of the mechanical parameters characterizing the structural model, in the case of unmeasured input as well, and the identification of the input itself. The above equations reveal the possibility of identifying the dissipation characteristics independently from the input characteristics
Concrete softening effects on the axial capacity of RC jacketed circular columns
No full textAmong the different strengthening techniques to repair RC structures, reinforced concrete (RC) jacketing is one of the most commonly adopted, especially for columns. Its wide application is due to its easy application and relatively reduced cost with respect to other methods (e.g. FRP wrapping, Shape Memory Alloy active confinement). The target of RC jacketing is to increase axial, flexural capacity and ductility of weak existing members by means of two main effects: confinement action provided by the jacket and composite action between external jacket and inner concrete. Different theoretical studies have been carried out to calculate the strength enhancement due to confinement action and most of these are based on the adaptation of classical models for confinement evaluation in RC members. However, experimental investigations on compressive behaviour of RC jacketed sections have shown that the actual axial capacity could be substantially lower than that analytically evaluated with classical confinement models. This fact could be explained by taking into account the presence of tensile stresses developing in the jacket, due to the different dilatation of the inner core and the external jacket. This phenomenon is relevant especially in members where the concrete properties of the jacket are different with respect to those of the core, causing the premature failure of the external layer. This paper presents a simplified approach able to evaluate these effects. In particular RC jacketed circular columns are analysed as case study and the member is studied by considering the different concrete properties of core, jacket and cover. Circumferential and radial stresses are firstly calculated under the assumption of linear elastic behaviour and plane strain state. The model is extended in the non-linear range by adopting a secant constitutive law. Finally, comparisons are made with experimental data available in the literature, showing good agreement and explaining some experimental results
- …
