Oreste S. Bursi

Benchmarks for finite element modelling of bolted steel connections

Abstract This paper presents part of the results of a study devoted to the analysis of bolted steel connections by means of finite elements. In detail, the paper introduces elementary tee stub connections which are endowed with different plastic failure mechanisms and can be adopted as benchmarks in the validation process of finite element software packages. Moreover, the simulations of these benchmarks performed by means of bricks as well as contact elements allow the properties and results of these elements to be commented upon. Finally, the comparison between computed and measured values permits the effectiveness and degree of accuracy of the proposed finite element models to be mirrored.

Basic issues in the finite element simulation of extended end plate connections

Abstract Numerical simulations of steel bolted connections performed with finite element models depend heavily upon constitutive relationships, step size, number of integration points, kinematic descriptions, element types and discretizations. The aforementioned items combined with complex non-linear phenomena which are commonly observed in connections render the finite element technique not attractive for this class of problems. In this paper these issues are scrutinized and both a legitimate methodology suitable to the analysis of extended end plate moment resisting connections and proper three-dimensional finite element models are established. These models are provided first for non-preloaded and preloaded bolted tee stubs which are proposed as benchmarks. Next, both a solid model and an assemblage of three-dimensional beam finite elements, viz. the spin , are proposed to model the bolt behaviour either in a rigorous or simplified fashion, respectively. Lastly, a three-dimensional non-linear finite element model suitable for the analysis of isolated extended end plate connections is proposed and validated.

Calibration of a finite element model for isolated bolted end-plate steel connections

Abstract This paper presents parts of results of a study devoted to the analysis of bolted steel connections by means of finite elements. Initially, the paper deals with the calibration of finite elements of the code ABAQUS on test data as well as on simulations of elementary tee stub connections engendered with the LAGAMINE software package. These connections were proposed as benchmarks in a previous companion paper and simulated to the ultimate limit state. Next, an assemblage of three-dimensional beam finite elements is proposed to model the bolt behaviour in a simplified fashion. Lastly, a three-dimensional finite element model is set with the ABAQUS code in order to simulate the stiffness and strength behaviour of isolated extended end-plate steel connections. The comparison between computed and measured values in each phase highlights the effectiveness and degree of accuracy of the proposed finite element models.

EVALUATION OF SOME IMPLICIT TIME-STEPPING ALGORITHMS FOR PSEUDODYNAMIC TESTS

Two types of implicit time-stepping algorithms have been proposed recently for pseudodynamic tests. The first type consists of an algorithm which relies on Newton iterations to satisfy the equations of motion. The second type consists of an algorithm which is based on the Operator-Splitting technique and does not require any numerical iteration. While one or the other has been preferred by some researchers, these time-stepping algorithms have not been analysed and compared under a uniform setting. In this paper, a concise summary of these schemes is presented, and they are evaluated in a consistent manner in terms of numerical dissipation, frequency distortion and experimental errors. The analytical results are validated by numerical simulations as well as experimental results. It is shown that the algorithm based on Newton iterations can control experimental error effects effectively by means of an error-correction procedure. The algorithm based on the Operator-Splitting technique demonstrates similar performance provided the I-Modification is adopted.

Behaviour of composite substructures with full and partial shear connection under quasi-static cyclic and pseudo-dynamic displacements

Six full-scale steel-concrete composite substructures with full and partial shear connection representing half bay within a moment-resisting frame were built and tested both in a, quasi-static cyclic and pseudo-dynamic regime. The specimens embodied two composite beams with full shear connection and four companion beams with two different degrees of partial shear connection all with exterior rigid joints.Tests were conducted in a set-up purposely designed to impose to specimens reversed horizontal displacements in a low-cycle high amplitude regime. The characteristics of the test apparatus ready for different structural members subjected to horizontal loading are illustrated. Moreover, the seismic performances of the specimens in terms of yielding and of maximum strength capacity as well as of displacement ductility are assessed. Finally, the accuracy of a European code calibrated upon monotonic loading is provided and other local characteristics of the composite substructure behaviour with low partial shear connection are commented upon.RésuméSix poutres mixtes béton-acier à échelle réelle ayant des connections au cisaillement complètes et partielles, représentant une démi-travée, dans le cadre d’une structure qui résiste aux moments, ont été construites et testées aussi bien dans un régime cyclique quasi-statique que dans un régime pseudo-dynamique. Les spécimens sont constitués de deux poutres composites ayant des connections au cisaillement, complètes et quatre poutres, de même dimension ayant deux différents degrés de connections au cisaillement partielles, toutes ayant des jointures extérieures et rigides.Les essais ont été faits selon une configuration étudiée intentionnellement pour imposer aux spécimens des déplacements horizontaux et opposés dans un régime à bas cycle et à haute amplitude. On expose les caractéristiques de l’appareillage destiné aux essais des différents membres structuraux soumis aux charges horizontales. En outre, les performances sismiques des spécimens ont été évaluées aussi bien du point de vue de l’éervement, et de la capacité maximale de résistance que de la ductilité du déplacement. Enfin, une comparaison d’un code européen calibré sur une charge monotone est vérifiée et d’autres caractéristiques locales de la conduite de la substructure mixte ayant un degré bas des connections au cisaillement, sont commentées.

Non-linear analysis of the low-cycle fracture behaviour of isolated Tee stub connections

Abstract The present work deals with the numerical analysis of the low-cycle fracture behaviour of isolated Tee stub connections with partial fillet welds. The overall objective of the research is to assess the seismic performance of bolted partial strength beam-to-column joints under seismic loading; but first, the complexity of these joints is approached after understanding the behaviour of more simple geometries which govern the response. In fact, the study focuses on the low-cycle fracture behaviour of Tee stub connections that are elemental components of extended end plate connections with partial fillet welds. First, the general experimental program dealing with bolted end plate joints and component parts is presented. The program comprises sets of constant and variable displacement amplitude cyclic tests both on complete specimens and on components. Test results have shown good performance of bolted extended end plate moment joints under cyclic loading as well as that of fillet welds that represent an economic solution for thin and moderate extended end plates. Then, the connection material is characterized from a microstructural and fracture mechanics standpoint. Successively, detailed three-dimensional non-linear finite element analyses are carried out in order to tune model material parameters; whilst two-dimensional inelastic analyses are performed in a monotonic and cyclic loading regime to validate connection finite element models. Lastly, a parametric study is conducted in order to define details able to reduce loading-induced toughness demands. Analyses have inferred that fracture driving force demands, quantified in terms of crack tip opening displacements, are reduced by using fillet welds matching the end plate material, by limiting welding-induced residual stresses and by increasing the yield-to-ultimate strength ratio compatibly with plastic analysis requirements.

Pseudodynamic tests of a concentrically braced frame using substructuring techniques

Abstract The bottom story of a half-scale model of a three-story concentrically braced steel frame, designed in accordance with the seismic provisions recently proposed by AISC Specification Task Committee 113, has been tested by means of the pseudodynamic method incorporated with analytical substructuring techniques. It has been shown that the use of an unconditionally stable implicit time integration scheme allows one to adopt a simple substructuring method, by which all degrees of freedom of a discrete-parameter structural model can be retained and those associated with zero mass in the experimental substructure can be conveniently ignored in testing. The experimental results are consistent with numerical results obtained with an analytical model that accounts for the linear and nonlinear behavior of bracing connections. The frame specimen exhibited a satisfactory performance under the maximum expected seismic loads.

Identification, Model Updating, and Validation of a Steel Twin Deck Curved Cable-Stayed Footbridge

To perform a realistic reliability analysis of a complex cable-stayed steel footbridge subject to natural hazard and corrosion, this article addresses a rational process of modeling and simulation based on identification, model updating, and validation. In particular, the object of this study is the Ponte del Mare footbridge located in Pescara, Italy; this bridge was selected as being a complex twin deck curved footbridge because it is prone to corrosion by the aggressive marine environment. With the modeling and simulation objectives in mind, a preliminary finite element (FE) model was realized using the ANSYS software. However, uncertainties in FE modeling and changes during its construction suggested the use of experimental system identification. As a result, the sensor location was supported by a preliminary FE model of the footbridge, although to discriminate close modes of the footbridge and locate identification sensor layouts, Auto Modal Assurance Criterion (AutoMAC) values and stabilization diagram techniques were adopted. Modal characteristics of the footbridge were extracted from signals produced by ambient vibration via the stochastic subspace identification (SSI) algorithm, although similar quantities were identified with free-decay signals produced by impulse excitation using the ERA algorithm. All these procedures were implemented in the Structural Dynamic Identification Toolbox (SDIT) code developed in a MATLAB environment. The discrepancies between analytical and experimental frequencies led to a first update of the FE model based on Powells dog-leg method that relied on a trust-region approach. As a result, the identified FE model was capable of reproducing the response of the footbridge subject to realistic gravity and wind load conditions. Finally, the FE was further updated in the modal domain, by changing both the stationary aerodynamic coefficients and the flutter derivatives of deck sections to take into account the effects of the curved deck layout

EXPLICIT PREDICTOR–MULTICORRECTOR TIME DISCONTINUOUS GALERKIN METHODS FOR LINEAR DYNAMICS

Abstract This paper focuses on the formulation and implementation of explicit predictor– multicorrector Time Discontinuous Galerkin methods for linear structural dynamics. The formulation of the schemes is based on piecewise linear functions in time that approximate displacements and momenta. Both the predictors and correctors are designed to inherit third order accuracy from the exact parent implicit Time Discontinuous Galerkin method. Moreover, they are endowed with large stability limits and controllable numerical dissipation by means of an algorithmic parameter. Thereby, the resulting algorithms appear to be competitive with standard explicit algorithms for structural dynamics. Representative numerical simulations are presented illustrating the performance of the proposed numerical schemes and confirming the analytical results.

Capabilities of a Fiber Bragg Grating Sensor System to Monitor the Inelastic Response of Concrete Sections in New Tunnel Linings Subjected to Earthquake Loading

In a comprehensive experimental campaign, we investigated the capabilities of Fiber Bragg Grating (FBG) sensors in monitoring the inelastic response of new circular concrete tunnel linings, subjected to seismic events. The FBG sensors measured the strains of steel reinforcement to be treated by a decision support system (DSS). First, a set of four-point bending tests was performed on tunnel substructures, with the aim of characterizing the cross-section under cyclic loading and of designing an FBG sensor package for use in a unique full-scale test on a structure, which represented a complete circular section of the tunnel lining. Several types of FBG packages, to be embedded in and applied externally to the tunnel section, were tested to find the best solution. For comparison purposes, some standard devices were also used. The results of the experimental campaign are presented in detail, highlighting the performance of FBG sensors in reliable inelastic strain measurement of ductile concrete sections in seismic zones. Finally, the use of these data by a DSS allowed for the estimate of current structural conditions and damage at the monitored sections.