Beatrice Belletti

Development of guidelines for nonlinear finite element analyses of existing reinforced and pre-stressed beams

ABSTRACT The Dutch Ministry of Infrastructure and the Environment initiated a project to reevaluate the carrying capacity of existing bridges and viaducts through the use of nonlinear finite element analyses (NLFEA) which are more and more becoming an usual instrument of calculation in the daily design procedures. Numerical simulations of several case studies taken from experimental programs have therefore been performed in order to assess and criticize the finite element approaches. In this paper guidelines for nonlinear finite element analyses are proposed to optimize the results obtained from numerical simulations of reinforced and pre-stressed beams in order to reduce model and users factor. The numerical results are also compared with analytical procedures proposed by the new Model Code 2010 which proposes different numerical and analytical procedures to evaluate the carrying capacity of existing structures based on the definition of different safety levels.

Shear Capacity of Normal, Lightweight, and High-Strength Concrete Beams according to Model Code 2010. II: Experimental Results versus Nonlinear Finite Element Program Results

AbstractNonlinear finite element analysis (NLFEA) is a useful tool for the assessment and design of structures if the reliability of the prediction is known in advance. Therefore, it makes sense to tailor finite element programs to specific types of structural members by calibrating them against test results obtained on similar types of specimens. By increasing the accuracy of prediction for such specified types of structural members, assessment and design are possible with higher reliability than can be obtained with analytical models. This strategy is illustrated for the case of shear-reinforced flanged beams using the constitutive model PARC_CL implemented into ABAQUS code. A comparison with analytical models shows the power of tailored FEM calculations in combination with reliability considerations.

Behavior of Prestressed Steel Beams

This paper reports on the behavior of simply supported (I-shaped cross section) steel beams prestressed by tendons. It is well known that this typology of beams has successfully been used mainly in the past. Prestressed steel beams are lighter than traditional ones that have the same length and vertical load capacity; this aspect could make them economically advantageous and a viable solution in many practical situations. This paper analyzes prestressed steel beams having a medium span ranging from 35 to 45 m and which are to be used as roof structural elements. This study focuses on two parameters that are considered two of the fundamental items for the design: the number of deviators and the value of the prestressing force. This study has been carried out with nonlinear finite-element analyses that take into account both mechanical and geometrical nonlinearities. In particular, the behavior of these beams has been investigated up to failure during tensioning and during loading (after tensioning). The effect on the structural response of bracing, which can be only at the top flange of the beams or at the top and bottom flanges of the beams, also has been considered.

Numerical prediction of the response of a squat shear wall subjected to monotonic loading

In this paper, the behaviour of a squat shear wall is investigated. The study fits into the experimental programme driven by CEOS.fr on modelling of the behaviour of reinforced concrete (RC) structures subjected to monotonic and cyclic loading. The shear wall has been analysed through non-linear finite element (NLFE) analyses and analytical procedures, and the results obtained were compared with the experimental results. The design shear resistance of the wall has been evaluated with analytical and numerical procedures following the prescriptions of the new Model Code 2010, according to which the resistance of RC structures can be assessed through standard analytical procedures and from the results obtained with NLFE analyses applying three different safety format methods. In order to validate the structural assessment obtained with numerical procedures, the analyses have been carried out using two different finite element codes: the total strain crack model implemented in the finite element code DIANA and the constitutive model Physical Approach for Reinforced-Concrete under Cyclic Loading implemented in a user subroutine in ABAQUS code.

Shear Capacity of Normal, Lightweight, and High-Strength Concrete Beams according to Model Code 2010. I: Experimental Results versus Analytical Model Results

Many models to determine the shear capacity of shear reinforced beams are based on the truss analogy. Various proposals have been formulated in recent years, all of which differ with regard to the limits of strut inclination. Remarkably, those limits do not depend on the type of concrete, which could be expected to be critical for the shear friction capacity of the cracks, which is supposed to be a major influencing factor with regard to the limit of strut rotation. Tests on beams with I-shaped cross sections have been carried out on beams made of normal, lightweight, and high-strength concrete. The experimental results are compared, in Part I of this paper, with those obtained by analytical models and, in Part II, with those obtained by nonlinear finite element programs tailored to this specific application. The result is that the type of concrete does not lead to significant changes in strut rotation capacity, so that the strut rotation limit values have general validity. The level of approximation approach, as presented in the Federation Internationale du Beton/International Federation for Structural Concrete (fib) Model Code of Concrete Structures 2010 is justified: more sophisticated calculation models lead indeed to more accuracy in the determination of the shear capacity.

Evaluation of the interaction effects in coupled thin walled prestressed concrete roof elements

ABSTRACT In this paper roof elements, representative of typical precast reinforced concrete one storey industrial buildings, will be analysed. In particular non linear finite element analyses will be carried out in order to investigate the interaction effects in coupled thin-walled prestressed concrete roof elements. Coupled roof elements are sometimes used to reduce deformations and stresses in lateral elements subjected both to longitudinal and transversal bending moments and to torsional moment due to un-symmetric vertical loads and wind action.

Compressive Membrane Action Effects on Punching Strength of Flat RC Slabs

The design of reinforced concrete flat slabs in practice can be governed at failure by punching shear close to concentrated loads or columns. Punching shear resistance formulations provided by codes are calibrated on the basis of experimental tests on isolated slabs supported on columns in axisymmetric conditions. Nevertheless, the behavior of flat slabs can be different than isolated specimens due to the potentially beneficial contributions of moment redistributions and compressive membrane actions. Accounting for the significance of these effects, nonlinear finite element analyses are performed with the crack model PARC_CL implemented in Abaqus. This paper aims to investigate a series of punching shear tests on slabs with and without shear reinforcement, different reinforcement ratios and loading conditions accounting for the potential contribution to the enhancement of the punching strength due to compressive membrane action (CMA). The numerical results with a multi – layered shell modeling are then post – processed adopting the failure criterion of the Critical Shear Crack Theory (CSCT). The results pointed out the significant outcomes and differences between standard specimens and actual members showing how the current codes of practice may underestimate the punching capacity.

Shear strength evaluation of RC bridge deck slabs according to CSCT with multi – layered shell elements and PARC_CL Crack Model

The shear resistance of RC slabs without shear reinforcement subjected to concentrated loads near linear support is usually calibrated on the base of tests on one – way slabs with rectangular cross section. However, the actual behavior of slabs subjected to concentrated loads is described properly by a two-way slab response. The aim of this paper consists in the evaluation of the shear resistance of bridge deck slabs using analytical formulations and Nonlinear Finite Element Analyses (NLFEA). The obtained numerical results are consequently compared with experimental observations from two test campaigns. The case studies were analysed by NLFE analyses carried out using the constitutive Crack Model PARC_CL (Physical Approach for Reinforced Concrete under Cycling Loading) implemented in the user subroutine UMAT.for in Abaqus Code. In order to predict properly global and local failure modes through a NLFE model, a multi – layered shell modelling has been used. As shell element modelling is not able to detect out – of – plane shear failures, the ultimate shear resistance of these slabs is evaluated by means of a post – processing method according to the Critical Shear Crack Theory (CSCT).

Capacity Design–Based Seismic Forces in Floor-to-Beam Connections of Precast Concrete Frames

AbstractThe stiffness and strength of roof units and their connections to supporting beams are fundamental parameters to define the diaphragm behavior of precast structures. In this paper, an analytical method for the calculation of actions in floor-to-beam connections of roof systems without topping slab and without floor-to-floor connections is presented. The proposed procedure can be applied to rectangular single-story precast concrete frames of industrial buildings. One-span, multi-bays regular frames, characterized by symmetry of stiffness and mass distributions are analyzed by assuming floor-to-beam connections with infinite stiffness and strength. The procedure is applied in the perspective of capacity design approach by providing practical formulations for the design and retrofitting of floor-to-beam connections. This approach aims at concentrating the critical regions, where energy dissipation of the structure occurs, at the base of columns designed to fail in bending. An over-resisting behavior ...

Shell Modelling of a 1/13 Scaled RC Containment Vessel under Cyclic Actions with PARC_CL Crack Model

The energetic resources exploitation became a big issue in present days. Globally 30 countries in the world are also exploiting Nuclear Power Plants (NPPs) for the generation of energy. In this case energy production issue is correlated to the requirements for population safeguard against radiation leakage and to safe nuclear waste storing. However, many of these NPPs, which are still producing a large amount of energy, need or will need in short times a renewal process. Reinforced concrete members are of strong importance for the safety and for the proper operation of NPPs. One of the most important structural elements is then the reinforced concrete containment vessel, RCCV, of the reactor. The correct prediction of the RCCV behaviour under sever action is essential for the assessment of existing structure safety and for the design of new ones. In the paper it is described the modelling of a 1/13 scaled reinforce concrete containment vessel tested at the National Center for Research on Earthquake Engineering of Taipei, Taiwan, under cyclic loading. The RCCV was analyzed by means of non linear finite elements analysis using multi layered shell elements. A secant total strain fixed crack model called PARC_CL, implemented at the University of Parma in the user subroutine UMAT.for in ABAQUS code, has been used to evaluate the mechanical non-linearity of RC elements. The multi layered shell elements approach with PARC_CL crack model provided good results in terms of local and global EDPs and it was able to give a good estimation of the post cracking behaviour until failure. Simulations results are provided in terms of displacements, strains and crack patterns. Although analyses provided good results, some issues like the modelling of the structure to foundation interface are still open.