•Load distribution in hollow-core floors is modelled through a general approach.•Model schematizes floor units as Saint-Venant beams and joints as rotational hinges.•The solving system is expressed ...only as a function of the shear forces in joints.•Obtained results are in good agreement with experimental data from the literature.•Model is applied to construction of design charts to be used in current practice.
A general design method is provided to predict the load distribution at serviceability condition in hollow-core floors formed by precast units linked together through cast in place reinforced concrete joints. Each panel forming the floor is schematized as a Saint-Venant beam connected to the others by means of rotational hinges. In this way, the only unknowns of the solving system, characterized by an exponential dichotomy, are represented by shear forces transmitted along joints. The model is first validated through comparisons with significant experimental results available in the literature, and subsequently applied to the construction of design charts to be used in current practice. These latter are also compared with the provisions on load distribution effects suggested by European Standard UNI EN 1168, pointing out some limitations of current design procedures and suggesting possible improvements.
This work focuses on the mechanical characterization of the inorganic matrix used for Fiber-Reinforced Cementitious Matrix (FRCM) composites, nowadays widely used to retrofit existing reinforced ...concrete and masonry structures. While several works in technical literature investigate the experimental behavior of the whole FRCM composite, few information are available on the mechanical characterization of the mortar, which contains polymers and synthetic fibers in its admixture. However, the knowledge of its behavior in tension, especially after crack formation, is an important feature for the calibration of constitutive models to be adopted in the study of structural elements strengthened with FRCM. To this aim, an experimental program was performed on mortar specimens characterized by different shapes and dimensions, tested under direct tension or three-point-bending. From the performed tests, it was possible to characterize inorganic matrix behavior both in the uncracked stage, through the determination of the elastic parameters (elastic modulus and Poissons coefficient), and in the cracked stage. The use of digital image correlation (DIC) technique also allowed the study of the evolution of crack propagation in the specimens. Lastly, a correlation factor between axial and flexural tensile strength is proposed, for both design and numerical modelling purposes.
This work focuses on the mechanical characterization of the inorganic matrix used for Fiber-Reinforced Cementitious Matrix (FRCM) composites, nowadays widely used to retrofit existing reinforced ...concrete and masonry structures. While several works in technical literature investigate the experimental behavior of the whole FRCM composite, few information are available on the mechanical characterization of the mortar, which contains polymers and synthetic fibers in its admixture. However, the knowledge of its behavior in tension, especially after crack formation, is an important feature for the calibration of constitutive models to be adopted in the study of structural elements strengthened with FRCM. To this aim, an experimental program was performed on mortar specimens characterized by different shapes and dimensions, tested under direct tension or three-point-bending. From the performed tests, it was possible to characterize inorganic matrix behavior both in the uncracked stage, through the determination of the elastic parameters (elastic modulus and Poisson’s coefficient), and in the cracked stage. The use of digital image correlation (DIC) technique also allowed the study of the evolution of crack propagation in the specimens. Lastly, a correlation factor between axial and flexural tensile strength is proposed, for both design and numerical modelling purposes.
Shrinkage effects on short-term behavior of reinforced concrete elements are often neglected both in design code provisions and in numerical simulations. However, it is known that their influence on ...serviceability performance can be significant, especially in case of lightly-reinforced beams. As a matter of fact, the restraint provided by the reinforcement on concrete determines a reduction of the cracking load of the structural element, as well as an increase of its deflection. This paper deals with the modeling of early-age shrinkage effects in the field of smeared crack approaches. To this aim, an existing non-linear constitutive relation for cracked reinforced concrete elements is extended herein to include early-age concrete shrinkage. Careful verifications of the model are carried out by comparing numerical results with significant experimental data reported in technical literature, providing a good agreement both in terms of global and local behavior.
In this work, a consistent formulation for the representation of concrete behavior before and after cracking has been implemented into a non-linear model for the analysis of reinforced concrete ...structures, named 2D-PARC. Several researches have indeed pointed out that the adoption of an effective modeling for concrete, combined with an accurate failure criterion, is crucial for the correct prediction of the structural behavior, not only in terms of failure load, but also with reference to a realistic representation of crack initiation and development. This last aspect is particularly relevant at serviceability conditions in order to verify the fulfillment of structural requirements provided by Design Codes, which limit the maximum crack width due to appearance and durability issues. In more details, a constitutive model originally proposed by Ottosen and based on non-linear elasticity has been here incorporated into 2D-PARC in order to improve the numerical efficiency of the adopted algorithm, providing at the same time an accurate prediction of the structural response. The effectiveness of this procedure has been verified against significant experimental results available in the technical literature and relative to reinforced concrete beams without stirrups failing in shear, which represent a problem of great theoretical and practical importance in the field of structural engineering. Numerical results have been compared to experimental evidences not only in terms of global structural response (i.e. applied load vs. midspan deflection), but also in terms of crack pattern evolution and maximum crack widths.
A finite element model, where a non-conforming quadrilateral element is utilized, capable of analyzing the dynamic nonlinear behavior in a biaxial stress field of unreinforced masonry panels is ...presented. For the material, the linear elastic-plastic constitutive law is adopted. The formulation for the linear element and the extension for the linear elastic-plastic element are proposed. The solution is carried out by a direct step by step integration procedure in time domain, based on the Newmark method of the equilibrium equations, inclusive of inertial and damping actions, the latter evaluated using the Rayleigh hypothesis. The procedure was implemented in a computer program and verified by the analysis of an unreinforced masonry shear panel, the dynamic behavior of which was analyzed experimentally 1, 2. The comparisons between the numeric results and laboratory test measurements show good agreement, proving the good performance of the non-conforming quadrilateral element also for time-dependent and markedly nonlinear analyses. In addition, the case of Parma Cathedral Bell-Tower subjected to a dynamic excitation available in literature, was analyzed using the proposed model. The same case was approached by a reliable finite element code 3, using quadratic serendipity elements and a more dense mesh than in the previous analysis. The results, in terms of kinematic parameters, stress and strain fields, etc. obtained by the two models, agree, proving that the use of a non-conforming quadrilateral element leads to analyses which are computationally economical and simple to use in input.
A nonlinear analysis of reinforced concrete foundation plates resting upon ground, based on a finite element model, capable of simulating the evolutive behavior up to rupture of the soil and/or of ...the RC plate, as well as of evaluating both the serviceability and the ultimate loads, is proposed. The contact problem between an RC plate and soil is solved by a unilateral elastic-plastic Winkler type model, where the plate-soil bonds have tensile strength equal to zero and compressive behavior described by a nonlinear curve, which is a function of geomechanical properties, capable of simulating phenomena such as the softening after the pressure has reached the maximum strength, as well as the residual strength. Moreover, the model also takes into account friction forces which arise on the contact surface between plate and soil. The RC plate is modeled by materially nonlinear layered finite elements where an orthotropic incrementally linear relationship and equivalent uniaxial concept are used to represent the behavior of concrete under biaxial stresses, while a uniaxial bilinear elasto-plastic model with hardening is employed for rebar. After cracking, the smeared orthogonal coaxial rotating crack model is adopted and tension stiffening, reduction in compressive strength and stiffness along the crack direction, and strain softening in compression are accounted for. The fundamental equations of the plate upon unilateral Winkler type ground are reviewed and generalized. The problem is solved by adopting an incremental approach, and the modified Newton-Raphson iteration method is employed to ensure convergency of nonlinear solution. The proposed finite element model was tested by comparisons with another analytical model available in literature, showing a good agreement. Furthermore, parametric analysis was conducted in order to investigate the influence of reinforced concrete nonlinear behavior of friction forces between plate and soil, and of relative density or consolidation index of the soil, on the nonlinear response of foundation plates.
In the last years, the industries are applying automation techniques with the aim to increase their efficiency to remain competitive. Due to this fact, there is an intensive search for techniques and ...methods applied to manufacturing systems for improvements, whether in quality, service deadlines and / or increased production. Several studies and practical applications have indicated that the Automated Guided Vehicles (AGVs) are efficient for transport task in industries and warehouses. The management of these AGVs is the key to a transportation system that ensures the improvements envisioned by industries. One of the main problems encountered in the management of AGVs is the decision to dispatch. Some authors suggest that a weak point of dispatching rules, even the multi-attributes, is to consider only the values of variables in current time for decision-making. This paper proposes a prediction model in which one achieves an improvement in the optimization objective by reading from specific states of the factory in the near future. The proposal is based on the use of cover ability tree from modelling in Petri nets with ability to provide important data for AGVs dispatch system. From these data, the dispatch system can take more assertive decisions to optimize the performance of Flexible Manufacturing Systems (FMS). The tests are performed using the software CPNtools, to model Petri nets, and Simio software to build the virtual environment, thereby having two different levels of abstraction. The validation is done through the analysis of scenarios that can happen in a production system, and with the use of the proposal of prediction is verified that in these scenarios is possible to extract important information.
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