Paulo Vila Real

A component model for the behaviour of steel joints at elevated temperatures

Abstract Recent experimental evidence has shown that steel joints exhibit a distinct change in their moment–rotation response under increasing temperature. In terms of cold design, the component method is currently the widely accepted procedure for the evaluation of the various design values. It is the purpose of the present paper to extend the component method to the prediction of the response of steel joints under fire loading. Using typical mechanical models consisting of extensional springs and rigid links, whereby the springs exhibit a non-linear force deformation response (here taken as a bi-linear approximation), an analytical procedure is proposed capable of predicting the moment–rotation response under fire conditions that incorporates the variation of yield stress and Young’s modulus of the various components as the temperature increases. An application to a cruciform flush end-plate beam-to-column steel joint is presented and compared to the experimental results obtained under various loading conditions.

Numerical Modeling of Lateral-Torsional Buckling of Steel I-Beams under Fire Conditions—Comparison with Eurocode 3

A geometrically and materially non-linear finite e lement program, i.e., a general model, has been used to determine the lateral-torsional resistance of steel I-beams under fire conditions, according to the same material properties o f Eurocode 3, Part 1-2. Two yield strengths, one cross section, one type of load and four different time exposures to the ISO 834 standard fire have been considered. The numerical results have been compared to the results o f the simple model presented in Eurocode 3, Part 1-2. When compared with the general model, this simple model leads to a safety level that depends on the slenderness of the beam, being unsafe for intermediate non-dimensional slenderness. A new proposal has been made for a s imple model that ensures a conservative result when compared to the general model.

Axially Loaded Stainless Steel Columns in Case of Fire

The simple model of Eurocode 3, for the fire resistance evaluation of stainless steel members, are based on the procedures used for carbon steel structural elements. However, due to the existing differences in the constitutive laws of these two materials, it is expected that it would not be possible to use, in both materials, the same formulae for the member stability calculation, as proposed in Eurocode 3. This paper aims at increasing the knowledge on the behaviour of stainless steel axially loaded columns at elevated temperatures. For this purpose, a geometrical and material non linear computer code has been used to determine the buckling load of these elements. The Eurocode formulae are evaluated and a new proposal, that ensures accurate and conservative results when compared with the numerical simulations, is presented.

Preliminary Design of a Composite Material Flywheel

Flywheel rotor performance monitoring and damage detection are increasingly gaining the interest of manufacturers of aircraft engines. This is primary due to the fact that there is a necessity for improving safety during operation as well as a need for lower maintenance costs. Applied techniques for damage detection and health monitoring of rotors are essential for engine safety, reliability and life prediction. Preliminary design of such a flywheel studied here is based on a simple model of annular rotating disk with stress-free boundary conditions. In addition to the critical rotational speed, the paper analyses the influence of the leading design parameter - material plastic anisotropy - on the development of plastic zone and stress/strain distributions.

Behaviour and resistance of cold-formed steel beams with lipped channel sections under fire conditions

Purpose Steel beams composed of cold-formed sections are common in buildings because of their lightness and ability to support large spans. However, the instability phenomena associated to these members are not completely understood in fire situation. Thus, the purpose of this study is to analyse the behaviour of beams composed of cold-formed lipped channel sections at elevated temperatures. Design/methodology/approach A numerical analysis is made, applying the finite element program SAFIR, on the behaviour of simply supported cold formed steel beams at elevated temperatures. A parametric study, considering several cross-sections with different slenderness’s values, steel grades and bending diagrams, is presented. The obtained numerical results are compared with the design bending resistances determined from Eurocode 3 Part 1-2 and its French National Annex (FN Annex). Findings The current design expressions revealed to be too conservative when compared with the obtained numerical results. It was possible to observe that the FN Annex is less conservative than the Annex E, the first having a better agreement with the numerical results. Originality/value Following the previous comparisons, new fire design formulae are tested. This new methodology, which introduces minimum changes in the existing formulae, provides safety and accuracy at the same time when compared to the numerical results, considering the occurrence of local, distortional and lateral torsional buckling phenomena in these members at elevated temperatures.

Stress Distributions in an Annular Disk Possessing Stress Induced Material Anisotropy

A semi-analytical stress solution is obtained for a rotating anisotropic disk of constant thickness and density. The solution proceeds along the classical line by dividing the disk into elastic and plastic zones, and then solving for the axially-symmetric stress distributions in each zone, matching subsequently stresses at the elastic-plastic border. The edges of the disk are supposed to be stress free and no kinematics boundary conditions are involved in the analysis. The principal axes of anisotropy coincide with the in-plane radial and circumferential directions. Comparison with an isotropic material modeling suggests an improvement in a preliminary engineering design when plastic orthotropy is accounted for.

Effect of Plastic Anisotropy on the Size of Elastic-Plastic Boundary in a Rotating Disk Problem

The problem of dependence of stress distribution and size of elastic-plastic boundary on the angular velocity, material anisotropy, boundary conditions and geometric parameters in rotating disks is of great importance due to a large number of applications. In particular, all of these parameters can have a significant effect on the development of plastic zones in such disks. The elastic stress distribution in rotating anisotropic disks with constant and variable thickness is well known. However, there are only a few studies incorporating plastic stress analysis for anisotropic materials. Considering the case of a single elastic perfectly-plastic annular rotating disk, subjected to typical stress boundary conditions, the influence of the leading design parameters - material anisotropy coefficients - on the size of elastic-plastic boundary arising due to the action of centrifugal forces is investigated. An axisymmetric problem is formulated assuming that the principal axes of anisotropy coincide with the radial and tangential directions in the plane of the disk. The Hill’s quadratic yield criterion is adopted in the plastic zone, and material properties in the elastic zone are considered to be isotropic obeying the general Hooke’s law. All stresses are assumed to be continuous across the elastic-plastic boundary. Three different characteristic values of rotational speed are chosen in numerical calculations. It is demonstrated that the size of the plastic zone is very sensitive both to the change in material anisotropy coefficients and the magnitude of angular velocity.

Numerical Behaviour of a Steel Sub-frame System in Fire

Steel framed buildings are generally designed with “simple” shear-resisting connections, and lateral forces are resisted by vertical bracing and shear walls. However, when a beam form part of a complete structure, its behaviour is complex and very much dependant on the restraint at the member ends. In order to capture the beam behaviour during a fire, it is therefore required to take a wonder view and examine the behaviour of a representative sub-structure [1]. Using the data and results from the few available sub-structure fire tests, numerical models were developed and validated to try to explain and predict the behaviour of such systems.

Residual Strength of a Steel-Concrete Composite Structure Subjected to a Design Seismic Event Followed by Fire

Summary This paper presents a numerical investigation of the residual strength of a typical PR moment-resistant multi-storey steel framed structure, subjected to a design seismic event followed by fire. In order to allow a calibration with some real results from fire tests on a natural scale, the architectural and structural definitions of the eight-storey steel Cardington building were chosen as the reference case, adapted to deal with basic seismic requirements. The seismic action was simulated with an artificial accelerogram with PGA of 0.6g, chosen to achieve significant energy dissipation in the joints. The adopted fire event is limited to an isolated compartment and it is defined as the natural fire observed during a full-scale fire test carried out at the BRE. Finally, the results are discussed in terms of robustness requirements for extreme events. Keywords : Earthquake, Fire, Connections, Steel structures, Extreme events, Buildings. 1. Introduction The possibility of fire following an earthquake is a major threat in seismic regions, as was observed on several historical great earthquakes: Lisbon 1755 (Fig. 1), San Francisco 1906 and 1989, Tokyo 1923 and Kobe 1995. Della Corte

Application of the Component Method to Steel Joints under Fire Loading

Recent research [1] on the behaviour of steel structures under fire loading highlighted the influence of joint behaviour on the overall response of the structure. The lack of experimental results on the response of steel joints under fire conditions and the use of numerical models relying on empirical relations established from tests either at room temperature, or for a limited range of (low) temperatures, has led to a simplistic specification from the current codes of practice. In fact, according to Eurocode 3, Part 1.2 [2] and Annex J [3], the concentration of mass within the joint area, when compared to the connecting members, delays its temperature increase, therefore suggesting that joints could be disregarded under fire conditions. However, in contrast to the EC3 specification, recent experimental results [4,5] have highlighted the need to evaluate the behaviour of steel joints at elevated temperatures, since they exhibit a pronounced reduction of strength and stiffness that clearly affect the global response of the structure.